Zeitschriftenartikel: „AF magnetic order“

1

Syshchenko, O., T. Fujita, K. Prokeš, V. Sechovský und A. A. Menovsky. „Collapse of AF magnetic order in UNiAl under pressure“. Physica B: Condensed Matter 281-282 (Juni 2000): 208–9. http://dx.doi.org/10.1016/s0921-4526(99)00816-9.

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2

Tyulkina, Irina V., Denis S. Goldobin, Lyudmila S. Klimenko, Igor S. Poperechny und Yuriy L. Raikher. „Collective in-plane magnetization in a two-dimensional XY macrospin system within the framework of generalized Ott–Antonsen theory“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, Nr. 2171 (13.04.2020): 20190259. http://dx.doi.org/10.1098/rsta.2019.0259.

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The problem of magnetic transitions between the low-temperature (macrospin ordered) phases in two-dimensional XY arrays is addressed. The system is modelled as a plane structure of identical single-domain particles arranged in a square lattice and coupled by the magnetic dipole–dipole interaction; all the particles possess a strong easy-plane magnetic anisotropy. The basic state of the system in the considered temperature range is an antiferromagnetic (AF) stripe structure, where the macrospins (particle magnetic moments) are still involved in thermofluctuational motion: the superparamagnetic blocking T b temperature is lower than that ( T af ) of the AF transition. The description is based on the stochastic equations governing the dynamics of individual magnetic moments, where the interparticle interaction is added in the mean-field approximation. With the technique of a generalized Ott–Antonsen theory, the dynamics equations for the order parameters (including the macroscopic magnetization and the AF order parameter) and the partition function of the system are rigorously obtained and analysed. We show that inside the temperature interval of existence of the AF phase, a static external field tilted to the plane of the array is able to induce first-order phase transitions from AF to ferromagnetic state; the phase diagrams displaying stable and metastable regions of the system are presented. This article is part of the theme issue ‘Patterns in soft and biological matters’.

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Nocerino, Elisabetta, Ola K. Forslund, Chennan Wang, Hiroya Sakurai, Frank Elson, Rasmus Palm, Ugne Miniotaite et al. „Magnetic nature of wolframite MgReO₄“. Journal of Physics: Conference Series 2462, Nr. 1 (01.03.2023): 012037. http://dx.doi.org/10.1088/1742-6596/2462/1/012037.

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Abstract Rhenium oxides belonging to the family AReO4 where A is a metal cation, exhibit interesting electronic and magnetic properties. In this study we have utilized the muon spin rotation/relaxation (µ +SR) technique to study the magnetic properties of the MgReO4 compound. To the best of our knowledge, this is the first investigation reported on this interesting material, that is stabilized in a wolframite crystal structure using a special high-pressure synthesis technique. Bulk magnetic studies show the onset of an antiferromagnetic (AF) long range order, or a possible singlet spin state at T C1 ≈ 90 K, with a subtle second high-temperature transition at T C2 ≈ 280 K. Both transitions are also confirmed by heat capacity (Cp ) measurements. From our µ +SR measurements, it is clear that the sample enters an AF order below T C1 = T N ≈ 85 K. We find no evidence of magnetic signal above T N, which indicates that T C2 is likely linked to a structural transition. Further, via sensitive zero field (ZF) µ +SR measurements we find evidence of a spin reorientation at T Cant ≈ 65 K. This points towards a transition from a collinear AF into a canted AF order at low temperature, which is proposed to be driven by competing magnetic interactions.

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Chirkova, A. M., A. S. Volegov, D. S. Neznakhin, E. A. Stepanova und N. V. Baranov. „Pressure Induced AF - F - AF Magnetic Phase Transformations in Pd Substituted FeRh Compound“. Solid State Phenomena 190 (Juni 2012): 299–302. http://dx.doi.org/10.4028/www.scientific.net/ssp.190.299.

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At ambient pressure, the Fe0.49(Rh1-xPdx)0.51 alloys with the Pd concentration within 0 < x < 0.12 exhibit an antiferromagnetic (AF) state below the critical temperature Tt, while above x = 0.12 the alloys have a ferromagnetic (F) order up to the Curie temperature TC 650 K. The temperature and field dependences of the magnetization in the alloys with x = 0.08; 0.13 were investigated under hydrostatic pressure up to 10 kbar. The application of pressure of about 8.5 kbar is observed to induce the F-AF phase transition in the ferromagnetically ordered compound with x = 0.13. The AF-F-AF phase evolution was revealed with increasing pressure in the AF-ordered alloy with x = 0.08.

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TIWARI, RAJARSHI, und PINAKI MAJUMDAR. „NONCOLLINEAR MAGNETIC ORDER IN THE DOUBLE PEROVSKITES: DOUBLE EXCHANGE ON A GEOMETRICALLY FRUSTRATED LATTICE“. International Journal of Modern Physics B 27, Nr. 06 (05.02.2013): 1350018. http://dx.doi.org/10.1142/s0217979213500185.

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Double perovskites (DPs) of the form A 2 BB ′ O 6 usually involve a transition metal ion, B, with a large magnetic moment, and a nonmagnetic ion B ′. While many DPs are ferromagnetic, studies on the underlying model reveal the possibility of antiferromagnetic (AF) phases as well driven by electron delocalization. In this paper we present a comprehensive study of the magnetic ground state and Tc scales of the minimal DP model in three dimensions using a combination of spin-fermion Monte Carlo and variational calculations. The effective magnetic lattice in three dimensions is face centered cubic (FCC) and so geometrically frustrated. This promotes noncollinear spiral states and "flux" like phases in addition to collinear AF order. We map out the possible magnetic phases for varying electron density, "level separation" ϵB - ϵB', and the crucial B ′ B ′ (next neighbour) hopping t′.

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SPEZZANI, CARLO, PIERO TORELLI, MAURIZIO SACCHI, RENAUD DELAUNAY, CORYN F. HAGUE, ALESSANDRO MIRONE, FAHRAD SALMASSI, ERIC M. GULLIKSON und JAMES H. UNDERWOOD. „MAGNETIC COUPLING IN Co/Cu MULTILAYERS: FIELD-DEPENDENT ANTIFERROMAGNETIC ORDERING INVESTIGATED BY RESONANT X-RAY SCATTERING“. Surface Review and Letters 09, Nr. 02 (April 2002): 921–24. http://dx.doi.org/10.1142/s0218625x02003214.

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By simultaneous measurements of sample resistance and of X-ray resonant scattering, we tried to establish a direct correlation between magnetoresistance (MR) and antiferromagnetic (AF) order in a Co/Cu metallic multilayer. Field-dependent scattered intensity has been measured in a geometrical configuration corresponding to the Bragg peak coming from the AF coupling, at a photon energy close to the Co L 3 absorption edge (hν = 776.5 eV ). The comparison between measurements of the scattered intensity and of the resistance clearly shows a direct correlation between AF order and MR.

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Grimes, M., N. Gurung, H. Ueda, D. G. Porter, B. Pedrini, L. J. Heyderman, T. Thomson und V. Scagnoli. „X-ray investigation of long-range antiferromagnetic ordering in FeRh“. AIP Advances 12, Nr. 3 (01.03.2022): 035048. http://dx.doi.org/10.1063/9.0000320.

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We demonstrate a probe of long-range antiferromagnetic (AF) order in FeRh thin films using non-resonant magnetic x-ray scattering. In particular, x-rays at energies below the Fe K-edge have been used for the observation of magnetic Bragg peaks. Due to the low efficiency of the magnetic scattering, a grazing incidence geometry was used to optimise the diffracted intensity from the thin film samples. Based on Scherrer analysis, we estimate a coherence length similar to previous reports from x-ray magnetic linear dichroism (XMLD) experiments, indicating that domain sizes are limited to 40 nm which is consistent with the grain size. The temperature dependent behaviour of the AF order shows an inverse correlation with the emergence of the ferromagnetic (FM) moment, as expected from the phase diagram.

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Abulikemu, Aierxiding, Shenghan Gao, Toshiyuki Matsunaga, Hiroshi Takatsu, Cédric Tassel, Hiroshi Kageyama, Takashi Saito et al. „Partial cation disorder in Li₂MnO₃ obtained by high-pressure synthesis“. Applied Physics Letters 120, Nr. 18 (02.05.2022): 182404. http://dx.doi.org/10.1063/5.0088023.

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While atomic disorder has provided a paradigm shift in crystalline materials because of unusual atomic arrangements and functional response, “partial” disorder is scarcely reported until now. We discovered partial cation disorder in Li2MnO3 with fewer stacking faults, which was synthesized under high pressure. Mn and Li atoms in a Mn2/3Li1/3O2 layer disorder while Li atoms in a Li layer order. Magnetization and specific heat measurements indicate a long-range antiferromagnetic (AF) order below 35 K. The irreversibility observed in the magnetization data and the hump observed for the specific heat data suggest the coexistence of an AF order and a partial magnetic disorder. Neutron diffraction measurements reveal that the coexisted state is formed instead of the Néel AF state that has previously been reported for conventional Li2MnO3. These results indicate that high pressure makes a breakthrough to introduce partial disorder within crystals and designs not only a unique magnetic structure but also other physical properties.

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Chechenin, Nikolay G., Irina O. Dzhun, Georgy V. Babaytsev, Mikhail G. Kozin, Alexey V. Makunin und Irina L. Romashkina. „FMR Damping in Thin Films with Exchange Bias“. Magnetochemistry 7, Nr. 5 (17.05.2021): 70. http://dx.doi.org/10.3390/magnetochemistry7050070.

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Ferromagnetic resonance (FMR) linewidth (LW) is a tool for studying the high frequency properties of magnetic materials for their application in high-speed devices. Here, we investigate different mechanisms which determine FMR damping in bilayer ferromagnetic/antiferromagnetic (F/AF and AF/F) exchange bias systems. Variations of FMR LW with the thickness and deposition order of the F and AF layers were studied, as well as their correlation with the exchange bias field and roughness of the sample surface. We observed much larger LW in AF/F structures compared with F/AF samples. It was found that neither the exchange bias nor surface/interface roughness in the samples could explain the difference in LW for F/AF and AF/F samples. Instead, the different underlayer microstructure influenced the grainsize, leading to different angular dispersion of magnetization and different internal stray field in F-layers, promoting a different intensity of magnon scattering and FMR damping in F/AF and AF/F samples.

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Sera, Masafumi, und Shinichirou Kobayashi. „Magnetic Properties of the 4 Sublattice Model for the Antiferro (AF) Quadrupolar Order Dominated by the AF Octupolar and AF Exchange Interactions –A Simple Model for CeB6–“. Journal of the Physical Society of Japan 68, Nr. 5 (15.05.1999): 1664–78. http://dx.doi.org/10.1143/jpsj.68.1664.

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11

Arnhold, S., S. Glüer, K. Hartmann, O. Raabe, K. Addicks, S. Wenisch und M. Hoopmann. „Amniotic-Fluid Stem Cells: Growth Dynamics and Differentiation Potential after a CD-117-Based Selection Procedure“. Stem Cells International 2011 (2011): 1–12. http://dx.doi.org/10.4061/2011/715341.

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Amniotic fluid (AF) has become an interesting source of fetal stem cells. However, AF contains heterogeneous and multiple, partially differentiated cell types. After isolation from the amniotic fluid, cells were characterized regarding their morphology and growth dynamics. They were sorted by magnetic associated cell sorting using the surface marker CD 117. In order to show stem cell characteristics such as pluripotency and to evaluate a possible therapeutic application of these cells, AF fluid-derived stem cells were differentiated along the adipogenic, osteogenic, and chondrogenic as well as the neuronal lineage under hypoxic conditions. Our findings reveal that magnetic associated cell sorting (MACS) does not markedly influence growth characteristics as demonstrated by the generation doubling time. There was, however, an effect regarding an altered adipogenic, osteogenic, and chondrogenic differentiation capacity in the selected cell fraction. In contrast, in the unselected cell population neuronal differentiation is enhanced.

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Zhang, Lei, Tian Ai, Xiaoxi Tian, Chunmei Xu, Yonggui Wu, Zhongxu Yu und Shujuan Dai. „Microwave-assisted preparation of Ag/Fe magnetic biochar from clivia leaves for adsorbing daptomycin antibiotics“. Open Chemistry 20, Nr. 1 (01.01.2022): 388–400. http://dx.doi.org/10.1515/chem-2022-0156.

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Abstract Novel clivia biochar adsorbing daptomycin (DAP) was prepared by microwave digestion–anaerobic carbonization in this work. Fe/Ag submicron particles were introduced to the biochar surface based on the reducibility of biochar to enhance its adsorption capacity. Characterization confirmed that modified biochar (AF-biochar) had a higher particle size (126 μm), larger specific surface area (521.692 m2 g−1), richer pore structure, and higher thermal stability. The effects of the main variables (e.g., the solution pH, contact time, initial DAP concentration, and temperature) were investigated during adsorption. The results showed that AF-biochar could reach the adsorption equilibrium at pH 4.8 for 85 min. Besides, the adsorption capacity was 48.25 mg g−1, and the adsorption efficiency was 96.50% when the concentration of DAP was 25 mg L−1. The pseudo-second-order kinetics (R 2 = 0.9997), Langmuir equation (R 2 = 0.9999), and thermodynamics (R 2 = 0.9631) of AF-biochar fit well, indicating that the main adsorption process of AF-biochar was spontaneous, exothermic, and monolayer. Their adsorption was analyzed by physical and chemical adsorption. The main adsorption mechanisms included the electron donor–acceptor interaction, electrostatic force interaction, Lewis acid–base interaction, and H-bond interaction.

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Oltean-Péter, Balázs, Szilamér Korodi, István Benedek, Erzsébet Lázár, Johanna Kéri, Annamária Pakucs, István Kovács et al. „Imaging-derived Biomarkers Associated with Atrial FIBROsis, Structural Remodeling and the Risk of Cardioembolic Events in Patients with Atrial Fibrillation – the FIBROS Study“. Journal of Interdisciplinary Medicine 2, s4 (01.12.2017): 31–35. http://dx.doi.org/10.1515/jim-2017-0095.

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AbstractRecent studies demonstrated that despite restoration of the sinus rhythm, patients with a positive history of atrial fibrillation (AF) are still at risk of thromboembolic events. The primary objective of this study is to identify new imaging-derived biomarkers provided by modern imaging technologies, such as cardiac computed tomography angiography, delayed enhancement magnetic resonance imaging, or speckle tracking echocardiography, as well as hematological biomarkers, associated with the risk of intracavitary thrombosis in patients with AF, in order to identify the imaging-derived characteristics associated with an increased risk of cardioembolic events. Imaging data collected will be post-processed using advanced techniques of computational modeling, in order to fully characterize the degree of structural remodeling and the amount of atrial fibrosis. The primary endpoint of the study is represented by the rate of thromboembolic events. The rate of cardiovascular death, the rate of major adverse cardiovascular events, and the rate of AF recurrence will also be determined in relation to the degree of structural remodeling and atrial fibrosis.

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Uba, J. I., A. J. Ekpunobi und P. I. Ekwo. „A model of the response of GMR of metallic multilayers to external magnetic field“. Materials Science-Poland 33, Nr. 4 (01.12.2015): 835–40. http://dx.doi.org/10.1515/msp-2015-0099.

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AbstractIt has not been possible to transform resistivity models in terms of magnetic field in order to account for variation of giant magnetoresistance (GMR) with external magnetic field, which would have led to determination of material properties. This problem is approached mathematically via variation calculus to arrive at an exponential function that fits observed GMR values. Using this model in free electron approximation, the mean Fermi vector, susceptibility and total density of states of a number of metallic multilayers are determined from their reported GMR values. Susceptibility is found to depend on interface roughness and antiferromagnetic (AF) coupling; thus, it gives qualitative measure of interface quality and AF coupling. Comparison of susceptibilities and GMRs of electrodeposited and ion beam sputtered Co/Cu structures shows that a rough interface suppresses GMR in the former but enhances it in the latter.

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Nasser, J. A., und A. Bettachy. „Interpretation of the magnetic field dependence of the first-order AF-HX phase transition in NiBr2“. Journal of Physics: Condensed Matter 1, Nr. 48 (04.12.1989): 9561–70. http://dx.doi.org/10.1088/0953-8984/1/48/006.

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16

Hu, Xiao. „Magnetic-field-induced first-order N to AF transition: a prediction by the SO(5) theory“. Physica C: Superconductivity 341-348 (November 2000): 239–40. http://dx.doi.org/10.1016/s0921-4534(00)00459-7.

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17

CHEN, YAN, Z. D. WANG und C. S. TING. „NOVEL VORTEX STRIPE PHASE UNDER STRONG MAGNETIC FIELD IN HIGH TEMPERATURE SUPERCONDUCTORS“. International Journal of Modern Physics B 19, Nr. 01n03 (30.01.2005): 9–12. http://dx.doi.org/10.1142/s021797920502786x.

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The nature of vortex structure in the mixed state of high-temperature superconductors (HTS) is investigated by solving the Bogoliubov-de Gennes equations with consideration of competition between antiferromagnetic (AF) and d-wave superconductivity (DSC) orders. By varying the applied magnetic field and temperature, the geometry of vortex structure can take two different forms: conventional vortex lattice (triangular or square), or vortex stripe phases where all the order parameters including spin density wave, charge density wave and superconducting order exhibit stripe-like behavior. This novel vortex stripe phases may show up at low temperature and adjacent to upper critical field H c2 Phase diagram of temperature dependence of H c2 will be presented. Our results may shed light on the understanding of the low-temperature H c2 anomalies in some HTS. New experiments are proposed to test our predictions.

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Aidona, E., D. Kondopoulou, M. Alexandrou und N. Ioannidis. „ARCHAEOMAGNETIC STUDIES IN KILNS FROM N. GREECE“. Bulletin of the Geological Society of Greece 43, Nr. 4 (25.01.2017): 1888. http://dx.doi.org/10.12681/bgsg.11380.

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Archaeomagnetism combines the magnetic properties of baked materials with Archaeology. The archaeomagnetic method can be applied to any kind of permanent - in situ or displaced- burnt structures, such as kilns, ovens, hearths, burnt floors, tiles, bricks and pottery fragments, the latter for intensity measurements only. In this study we present the latest archaeomagnetic results from archaeological sites which are distributed in N. Greece (Polymylos, Sani, Thesssaloniki). The Natural Remanent Magnetization (NRM) and the magnetic susceptibility of the samples have been initially measured. The samples have been subjected to magnetic cleaning (AF and Thermal demagnetizations) and this procedure revealed the characteristic component of the ancient magnetic field. Rock magnetic experiments such as acquisition of the Isothermal Remanent Magnetization (IRM) and thermomagnetic analysis have been performed in pilot samples in order to identify the main magnetic carriers. Finally the secular variation curves for Greece and the SCHA.DIF.3K model were used in order to date these archaeological structures. This dating improved or modified the estimated archaeological ages.

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Li, Yanting, Bixia Gao, Qiyu Wang, Juan Zhang und Qiaoni Chen. „Coexistence of Charge Order and Antiferromagnetic Order in an Extended Periodic Anderson Model“. Chinese Physics Letters 38, Nr. 8 (01.09.2021): 087102. http://dx.doi.org/10.1088/0256-307x/38/8/087102.

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The competition between the RKKY interaction and the Kondo effect leads to a magnetic phase transition, which occurs ubiquitously in heavy fermion materials. However, there are more and more experimental evidences indicating that the valence fluctuation plays an essential role in the Ce- and Y-based compounds. We study an extended periodic Anderson model (EPAM) which includes the onsite Coulomb repulsion Ucf between the localized electrons and conduction electrons. By employing the density matrix embedding theory, we investigate the EPAM in the symmetric case at half filling. By fixing the onsite Coulomb repulsion U of the localized electrons to an intermediate value, the interplay between the RKKY interaction, the Kondo effect and the Coulomb repulsion Ucf brings rich physics. We find three different phases, the antiferromagnetic phase, the charge order phase and paramagnetic phase. When the hybridization strength V between the localized orbital and the conduction orbital is small, the Kondo effect is weak so that the AF phase and the CO phase are present. The phase transition between the two long-range ordered phase is of first order. We also find a coexistence region between the two phases. As V increases, the Kondo effect becomes stronger, and the paramagnetic phase appears between the other two phases.

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De Sensi, Francesco, Diego Penela, David Soto-Iglesias, Antonio Berruezo und Ugo Limbruno. „Imaging Techniques for the Study of Fibrosis in Atrial Fibrillation Ablation: From Molecular Mechanisms to Therapeutical Perspectives“. Journal of Clinical Medicine 10, Nr. 11 (24.05.2021): 2277. http://dx.doi.org/10.3390/jcm10112277.

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Atrial fibrillation (AF) is the most prevalent form of cardiac arrhythmia. It is often related to diverse pathological conditions affecting the atria and leading to remodeling processes including collagen accumulation, fatty infiltration, and amyloid deposition. All these events generate atrial fibrosis, which contribute to beget AF. In this scenario, cardiac imaging appears as a promising noninvasive tool for monitoring the presence and degree of LA fibrosis and remodeling. The aim of this review is to comprehensively examine the bench mechanisms of atrial fibrosis moving, then to describe the principal imaging techniques that characterize it, such as cardiac magnetic resonance (CMR) and multidetector cardiac computed tomography (MDCT), in order to tailor atrial fibrillation ablation to each individual.

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Murtazaev, A. K., A. B. Babaev und G. Y. Ataeva. „Critical properties of 2d disordered 3-state antiferromagnetic potts model ON TRIANGULAR LATTICE“. EPJ Web of Conferences 185 (2018): 11001. http://dx.doi.org/10.1051/epjconf/201818511001.

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By introducing a small amount of non-magnetic impurities into an antiferromagnetic (AF) two-dimensional (2D) Potts model on a triangular lattice it is that the impurities in spin systems described by this model result in the change of a first order to a second-order phase transition. The systems with linear sizes L × L = N, L = 9-144 are considered. Investigations are performed using the standard Metropolis algorithm along with Monte-Carlo single-cluster Wolff algorithm. On the basis of the theory of finite-size scaling, critical exponents (CE) are calculated: the heat capacity α, the susceptibility γ, the order parameter β, and the CE of the correlation radius ν.

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Perkins, Andy, Krishna Tunga und Suresh Sitaraman. „Acceleration Factor to relate Thermal Cycles to Power Cycles for Ceramic Ball Grid Area Array Packages“. Journal of Microelectronics and Electronic Packaging 3, Nr. 4 (01.10.2006): 177–93. http://dx.doi.org/10.4071/1551-4897-3.4.177.

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There is a need for a new Acceleration Factor (AF) that can relate Accelerated Thermal Cycle (ATC) fatigue life to Power Cycle (PC) fatigue life quickly and accurately in order to avoid over designing electronic packages for benign environments. An AF, such as the Norris-Landzberg AF, is only applicable when using it to predict fatigue life within the same environment, i.e. ATC to ATC or PC to PC. This work proposes an AF that takes into account the differences between ATC tests and PC tests for ceramic ball grid array (CBGA) packages by considering relevant design and environmental parameters. The new AF is based on relevant design parameters such as substrate size, substrate thermal conductivity, substrate thickness, coefficient of thermal (CTE) mismatch between the substrate and printed wiring board (PWB), PWB thickness, and environmental parameters such as temperature range (ΔT), frequency of cycles (f), and peak/junction temperature (Tj). Finite Element Models (FEM), experimental data, laser moiré interferometry, Design of Simulation (DOS), ANOVA, and regression analysis are used to develop the new AF. The new AF can be used to more accurately assess PC fatigue life from ATC tests so that expensive over-designing of electronic packages can be avoided for desktop/server/laptop applications.

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Maurya, Arun Kumar, Md Tahir Hossain Sarder und Amal Medhi. „Mott transition, magnetic and orbital orders in the ground state of the two-band Hubbard model using variational slave-spin mean field formalism“. Journal of Physics: Condensed Matter 34, Nr. 5 (16.11.2021): 055602. http://dx.doi.org/10.1088/1361-648x/ac3452.

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Abstract We study the ground state phase diagram of the degenerate two-band Hubbard model at integer fillings as a function of onsite Hubbard interaction U and Hund’s exchange coupling J. We use a variational slave-spin mean field method which allows symmetry broken states to be studied within the computationally less intensive slave-spin mean field formalism. The results show that at half-filling, the ground state at smaller U is a Slater antiferromagnet with substantial local charge fluctuations. As U is increased, the antiferromagnetic (AF) state develops a Heisenberg behavior, finally undergoing a first-order transition to a Mott insulating AF state at a critical interaction U c which is of the order of the bandwidth. Introducing the Hund’s coupling J correlates the system more and reduces U c drastically. At quarter-filling with one electron per site, the ground state at smaller U is paramagnetic metallic. At finite J, as interaction is increased beyond a lower critical value U c1, it goes to a fully spin polarized ferromagnetic state coexisting with an antiferro-orbital order. Further increase in U beyond a higher critical value U c2 results in the Mott insulating state where local charge fluctuation vanishes.

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Ortiz-Álvarez, Hugo Hernán, Francy Nelly Jiménez-García, Carolina Márquez-Narváez, José Dario Agudelo-Giraldo und Elisabeth Restrepo-Parra. „The Influence of Pressure on the Formation of FM/AF Configurations in LSMO Films: A Monte Carlo Approach“. Computation 8, Nr. 4 (06.11.2020): 93. http://dx.doi.org/10.3390/computation8040093.

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In this work, Monte Carlo simulations of magnetic properties of thin films, including the influence of an external pressure, are presented. These simulations were developed using a Hamiltonian composed by terms that represent the exchange interaction, dipolar interaction, Zeeman effect, monocrystalline anisotropy, and pressure influence. The term that represents the pressure influence on the magnetic properties was included, since for many applications, magnetic materials are a part of a multiferroic material together with a piezoelectric or a ferroelectric compound. Initially, the model was developed using generic parameters, in order to probe its suitable performance; after that, parameters were adjusted for simulating thin films of La0.67Sr0.33MnO3, a manganite with several technological applications because its Curie temperature is greater than room temperature. Including the pressure influence, it was observed the formation of several kind of FM/AF configurations as strip, labyrinth, and chess board forms. Furthermore, it was observed that, as the pressure increased, the critical temperature tended to decrease, and this result was in agreement with experimental reports.

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Matsuno, Shunichi, Hideki Ushio, Yuji Suwa und Hiroshi Kamimura. „V. Mechanism of Superconductivity“. International Journal of Modern Physics B 11, Nr. 32 (30.12.1997): 3815–31. http://dx.doi.org/10.1142/s0217979297001957.

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A possibility of phonon-mediated interaction as a mechanism of high- T c superconductivity is discussed. Because of different spatial distribution of Bloch wave function for up-spin particle and down-spin particle in the present model, the effective pair interaction which is derived from electron–phonon interaction is shown to have significant momentum- transfer dependence that is quite different from ordinary phonon-mediated interaction. This characteristic of pair interaction together with the geometric feature of Fermi-surface derived in a previous paper III leads to a dx2-y2 symmetric gap state which is consistent with experimental results. Since d-wave state has much smaller Coulomb repulsion term than s-wave state, strong electron-phonon coupling in the present model is expected to cause the occurrence of high-temperature superconductivity. However, in the present model, it is shown that a factor that reduces superconducting transition temperature appear as a result of a fluctuation effect of antiferromagnetic (AF) order of localized Cu spins. The factor λs which should be proportional to AF correlation length λ AF , determines the time scale τs which eliminates the contribution from the retarded effective pair interaction of time argument larger than τs. Existence of length scale λs explains why T c goes to zero as increasing hole carrier to some extent, and why non-magnetic impurity such as Pb reduces T c strongly. λs also explains the finite density of zero-gap states observed in overdoped regime or samples with non-magnetic impurities.

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PAOLONE, A., R. CANTELLI, F. CORDERO, M. CORTI, A. RIGAMONTI und M. FERRETTI. „ANELASTIC SPECTROSCOPY AND NQR RELAXATION IN Sr-DOPEN La2CuO4 AROUND THE AF PERCOLATION THRESHOLD“. International Journal of Modern Physics B 17, Nr. 04n06 (10.03.2003): 512–20. http://dx.doi.org/10.1142/s0217979203016169.

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Anelastic spectra and 139 La NQR relaxation measurements have been carried out in La 2 - x Sr x CuO 4 (LSCO) for x around the critical value xc = 0.02 separating the antiferromagnetic (AF) from the cluster spin glass (CSG) phase for T → 0. The anelastic spectra around 10 K show step-like features common to samples pertaining to both AF and CSG phases. In the light of recent neutron scattering measurements suggesting that the spin-glass phase of LSCO with x < xc corresponds to a microscopic phase separation between regions with x ~ 0 and x ~ 0.02, the rise of the elastic energy dissipation has been attributed to the movement of the domain walls within the x ≃ xc CSG regions. The spin dynamics driving the AF transition has been investigated by means of 139 La NQR relaxation rate. The in-plane magnetic correlation length ξ2D has been extracted. In spite of the vicinity to the percolation threshold, ξ2D(x = 0.016, T) follows the temperature behavior expected in the renormalized classical regime, with spin stiffness reduced to about 0.4 of the one in pure La 2 CuO 4. Still, the 3D transition occurs when ξ2D is of the order of about 150 lattice steps, as in pure La 2 CuO 4, possibly related to the presence of AF regions unaffected by the holes.

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Kohama, Yoshimitsu, Hajime Ishikawa, Akira Matsuo, Koichi Kindo, Nic Shannon und Zenji Hiroi. „Possible observation of quantum spin-nematic phase in a frustrated magnet“. Proceedings of the National Academy of Sciences 116, Nr. 22 (09.05.2019): 10686–90. http://dx.doi.org/10.1073/pnas.1821969116.

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Water freezes into ice in winter and evaporates into vapor in summer. Scientifically, the transformations between solid, liquid, and gas are called phase transitions and can be classified through the changes in symmetry which occur in each case. A fourth phase of matter was discovered late in the 19th century: the liquid crystal nematic, in which rod- or disk-shaped molecules align like the atoms in a solid, while continuing to flow like a liquid. Here we report thermodynamic evidence of a quantum analog of the classical nematic phase, the quantum spin nematic (SN). In an SN, the spins of a quantum magnet select a common axis, like a nematic liquid crystal, while escaping conventional magnetic order. Our state-of-the-art thermal measurements in high pulsed magnetic fields up to 33 T on the copper mineral volborthite with spin 1/2 on a frustrated lattice provide thermodynamic evidence for SN order, half a century after the theoretical proposal [Blume M, Hsieh YY (1969) J Appl Phys 40:1249; Andreev AF, Grishchuk IA (1984) J Exp Theor Phys 97:467–475].

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RADWAŃSKI, R. J., und J. J. M. FRANSE. „SPECIFIC HEAT OF UPd2Al3“. International Journal of Modern Physics B 07, Nr. 01n03 (Januar 1993): 38–41. http://dx.doi.org/10.1142/s021797929300010x.

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Particularities in the specific heat of UPd 2 Al 3, a λ-type of peak with a maximum at 14.5 K and a Schottky-type of peak with a broad maximum at 55 K, has been attributed to the 5f-subsystem of the U atoms. The U-5f contribution has been found to be described surprisingly well within a single-ion Hamiltonian that includes the charge multipolar (CMP) interactions and the antiferromagnetic (AF) exchange interaction between the U 3+ ions. The AF exchange parameter and the full set of the CMP parameters associated with the hexagonal symmetry have been evaluated. The energy-level scheme (ELS) of this Kramers ion is constructed. The ground-state function Γ8 of the 5f 3 electrons is highly anisotropic. This state results from higher-order charge multipolar interactions. Magnetic properties resulting from this scheme including the metamagnetic-like transition at 18 T, the strongly-reduced value for the U-ion moment and its field dependence are found to be in good agreement with experimental observations.

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Kamimura, Hiroshi, Masaaki Araidai, Kunio Ishida, Shunichi Matsuno, Hideaki Sakata, Kenji Sasaoka, Kenji Shiraishi, Osamu Sugino, Jaw-Shen Tsai und Kazuyoshi Yamada. „Elucidation of Spin-Correlations, Fermi Surface and Pseudogap in a Copper Oxide Superconductor“. Condensed Matter 8, Nr. 2 (04.04.2023): 33. http://dx.doi.org/10.3390/condmat8020033.

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First-principles calculations for underdoped La2−xSrxCuO4 (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing a unique method of calculating the electronic-spin state of overdoped LSCO and by measurement of the spin-correlation length by neutron inelastic scattering, the origin of the phase-diagram, including the pseudogap phase in the high temperature superconductor, Sr-doped copper-oxide LSCO, has been elucidated. We have theoretically solved the long-term problem as to why the angle-resolved photoemission spectroscopy (ARPES) has not been able to observe Fermi pockets in the Fermi surface of LSCO. As a result, we show that the pseudogap region is bounded below the characteristic temperature T*(x) and above the superconducting transition temperature Tc(x) in the T vs. x phase diagram, where both the AF order and the KS particles in the Fermi pockets vanish at T*(x), whilst KS particles contribute to d-wave superconductivity below Tc. We also show that the relationship T*(xc) = Tc(xc) holds at xc = 0.30, which is consistent with ARPES experiments. At T*(x), a phase transition occurs from the pseudogap phase to an unusual metallic phase in which only the SS particles exist.

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Aidona, E., R. Scholger und H. J. Mauritsch. „NEW TECHNIQUES FOR SAMPLING AND CONSOLIDATION OF SEDIMENTS: APPLICATION TO BURNT SOILS FROM AN ARCHAEOLOGICAL SITE IN AUSTRIA“. Bulletin of the Geological Society of Greece 36, Nr. 3 (01.01.2004): 1129. http://dx.doi.org/10.12681/bgsg.16454.

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An archaeomagnetic study requires samples to be oriented very precisely prior to the removal from the site and to be transported safely since most of the times the collected samples are very soft and fragile. In this study we present new techniques for sampling and consolidation of sediments and unconsolidated soils, which are useful tools for palaeomagnetic and archaeomagnetic investigations. An application of the above techniques has been performed in burnt soils (roastbeds) in an archaeological site near Eisenerz (Austria), which used to be a cooper-smelting place in Bronze Age (around 1450 b.c.) Several roast beds have been collected and consolidated in order to investigate the distribution and the stability of the magnetization of these materials. We obtained around 350 samples and the natural remanent magnetization and the magnetic susceptibility of all these samples have been measured with a 2G squid cryogenetic magnetometer and a GEOFYSIKA KLY-2 susceptibility meter, respectively. Plots of the natural remanent magnetization and magnetic susceptibility versus depth indicate different layers of heating and give some first evidences for the use of these soils during the smelting procedure. Higher values of the intensity of the magnetization as well as of the magnetic susceptibility represent the more intense heating layer. Magnetic cleaning (thermal and Af demagnetization) of pilot samples revealed the presence of a stable component of magnetization. It seems, therefore, that these types of materials are suitable for an archaeomagnetic investigation, since they are able to record and preserve all the necessary magnetic information and provide important knowledge concerning the recent history of the Earth's magnetic field.

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Srinivasan, A., und Sidananda Sarma. „Co-Ni-Ga Alloys with Room Temperature Ferromagnetic Martensite Phase“. Advanced Materials Research 52 (Juni 2008): 95–101. http://dx.doi.org/10.4028/www.scientific.net/amr.52.95.

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Co-Ni-Ga and Co-Ni-Al alloys are expected to be good ferromagnetic shape memory alloys (FSMAs) owing to their higher ductility resulting from the presence of γ-phase precipitates and higher stability in preparation since they do not contain the highly volatile element Mn. Co-Ni- Ga alloys have a wide range of martensitic transformation and Curie temperatures. In order to explore the possibility of obtaining Co-Ni-Ga alloys with room temperature ferromagnetic martensitic phase, two series of compositions, viz., Co70-xNixGa30 (20 ≤ x ≤ 26) and CoxNi25Ga75-x (43 ≤ x ≤ 50) were taken up for investigation. Polycrystalline ingots of these alloys were prepared by arc melting followed by homogenization and quenching at ice water. Analysis of room temperature X-ray diffraction patterns revealed that most of these alloys had a single-phase (tetragonal) structure typical of a martensitic phase, while some of the alloys exhibited a two-phase (cubic and tetragonal) structure due to the presence of both martensite and austenite phases. All alloys having single martensite phase at room temperature showed martensitic transformation at elevated temperature as well as a linear change of the characteristic martensitic transformation temperatures (As, Af, Ms and Mf) with the number of valence electron to atom ratio (e/a). As, Af, Ms and Mf showed distinctive variations when aged in the martensite phase and austenite phase. All the alloys were ferromagnetic at room temperature and the Curie temperature was determined by high temperature ac magnetic susceptibility and magnetization measurements. The typical twin lamellar structure of martensite phase was observed by optical microscope and the development of the cubic γ-phase along with the parent β′-phase was investigated for different ageing temperatures and annealing temperatures. These studies provide useful information about the potential of these alloys for actuator applications.

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Dmour, Bianca-Ana, Radu-Stefan Miftode, Dan Iliescu Halitchi, Dana Teodora Anton-Paduraru, Codruta-Olimpiada Iliescu Halitchi, Ionela-Larisa Miftode, Ovidiu Mitu, Alexandru-Dan Costache, Celina-Silvia Stafie und Irina Iuliana Costache. „Latest Insights into Mechanisms behind Atrial Cardiomyopathy: It Is Not always about Ventricular Function“. Diagnostics 11, Nr. 3 (05.03.2021): 449. http://dx.doi.org/10.3390/diagnostics11030449.

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Atrial cardiomyopathy (ACM) represents a constantly evolving concept, with increasing importance in contemporary research and clinical practice. A better understanding of the mechanisms involved in atrial remodeling and its clinical correlations especially with atrial fibrillation (AF) and other cardiometabolic comorbidities may induce a significant impact on the diagnosis, prognosis, and therapeutic approach of ACM-related comorbidities. Although initially described several decades ago, investigators have only recently highlighted that several renal, metabolic, and cardiovascular diseases are determining factors for atrial remodeling and subsequent ACM. Based on data from multiple recent studies, our research emphasizes the correlations between ACM and other coexisting pathologies including cardiovascular, respiratory, or metabolic diseases, with fibrosis being the most incriminated pathophysiological mechanism. In addition to the usual tests, the paraclinical assessment of ACM is increasingly based on the use of various cardiac biomarkers, while the cardiac magnetic resonance (CMR) has become an increasingly tempting diagnostic too for describing morphofunctional aspects of the heart chambers, with the gadolinium contrast enhanced CMR (LGE-CMR) emerging as a commonly used technique aiming to identify and quantify the precise extent of atrial fibrosis. Further research should be conducted in order to clarify our knowledge regarding atrial remodeling and, therefore, to develop new and improved therapeutic approaches in these patients.

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Goetz, Christian, Patricia Martínez Díaz, Olaf Dössel, Axel Loewe, Jorge Sánchez, Amir Jadidi und Martin Eichenlaub. „Discrepancy Between LGE-MRI and Electro-Anatomical Mapping for Regional Detection of Pathological Atrial Substrate“. Current Directions in Biomedical Engineering 9, Nr. 1 (01.09.2023): 483–86. http://dx.doi.org/10.1515/cdbme-2023-1121.

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Abstract Atrial fibrillation (AF) is the most common sustained arrhythmia posing a significant burden to patients and leading to an increased risk of stroke and heart failure. Additional ablation of areas of arrhythmogenic substrate in the atrial body detected by either late gadolinium enhancement magnetic resonance imaging (LGE-MRI) or electroanatomical mapping (EAM) may increase the success rate of restoring and maintaining sinus rhythm compared to the standard treatment procedure of pulmonary vein isolation (PVI). To evaluate if LGE-MRI and EAM identify equivalent substrate as potential ablation targets, we divided the left atrium (LA) into six clinically important regions in ten patients. Then, we computed the correlation between both modalities by analyzing the regional extents of identified pathological tissue. In this regional analysis, we observed no correlation between late gadolinium enhancement (LGE) and low voltage areas (LVA), neither in any region nor with regard to the entire atrial surface (-0.3<r<0.3). Instead, the regional extents identified as pathological tissue varied significantly between both modalities. An increased extent of LVA compared to LGE was observed in the septal wall of the LA (asept.,LVA= 19.63% and asept.,LGE= 3.94%, with = median of the extent of pathological tissue in the corresponding region). In contrast, in the inferior and lateral wall, the extent of LGE was higher than the extent of LVA for most geometries (ainf.,LGE= 27.22% and alat.,LGE= 32.70% compared to ainf.,LVA= 9.21% and alat.,LVA= 6.69%). Since both modalities provided discrepant results regarding the detection of arrhythmogenic substrate using clinically established thresholds, further investigations regarding their constraints need to be performed in order to use these modalities for patient stratification and treatment planning.

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Masunaga, Sueli H., Vagner B. Barbeta, Fábio Abud, Milton S. Torikachvili und Renato F. Jardim. „Phase Diagram Mapping out the Complex Magnetic Structure of Single Crystals of (Gd, Er)B4 Solid Solutions“. Magnetism 4, Nr. 1 (04.02.2024): 24–34. http://dx.doi.org/10.3390/magnetism4010002.

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Measurements of specific heat and magnetization in single crystals were used to map out the magnetic phase diagram of Gd1−xErxB4 (x = 0.2 and 0.4) solid solutions along the c-axis. While GdB4 orders antiferromagnetically (AF) at 41.7 K, with the easy plane of magnetization oriented perpendicularly to the c-axis, ErB4 displays AF ordering below 15.4 K, with the easy axis along c. Therefore, in solid solutions, the competition between the different spin anisotropies, as well as frustration, lead to a complex spin configuration. These measurements reveal that a 40% substitution of Er for Gd is sufficient for generating a phase diagram similar to the one for the ErB4 system, characterized by the occurrence of plateau phases and other exotic features attributed to the interplay of competing magnetic anisotropies.

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Pouget, Jean-Paul. „Spin-Peierls, Spin-Ladder and Kondo Coupling in Weakly Localized Quasi-1D Molecular Systems: An Overview“. Magnetochemistry 9, Nr. 2 (13.02.2023): 57. http://dx.doi.org/10.3390/magnetochemistry9020057.

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We review the magneto-structural properties of electron–electron correlated quasi-one- dimensional (1D) molecular organics. These weakly localized quarter-filled metallic-like systems with pronounced spin 1/2 antiferromagnetic (AF) interactions in stack direction exhibit a spin charge decoupling where magnetoelastic coupling picks up spin 1/2 to pair into S = 0 singlet dimers. This is well illustrated by the observation of a spin-Peierls (SP) instability in the (TMTTF)2X Fabre salts and related salts with the o-DMTTF donor. These instabilities are revealed by the formation of a pseudo-gap in the spin degrees of freedom triggered by the development of SP structural correlations. The divergence of these 1D fluctuations, together with the interchain coupling, drive a 3D-SP ground state. More surprisingly, we show that the Per2-M(mnt)2 system, undergoing a Kondo coupling between the metallic Per stack and the dithiolate stack of localized AF coupled spin ½ (for M = Pd, Ni, Pt), enhances the SP instability. Then, we consider the zig-zag spin ladder DTTTF2-M(mnt)2 system, where unusual singlet ground state properties are due to a combination of a 4kF charge localization effect in stack direction and a 2kF SP instability along the zig-zag ladder. Finally, we consider some specific features of correlated 1D systems concerning the coexistence of symmetrically different 4kF BOW and 4kF CDW orders in quarter-filled organics, and the nucleation of solitons in perturbed SP systems.

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Chen, Lebing, Xiaokun Teng, Ding Hu, Feng Ye, Garrett E. Granroth, Ming Yi, Jae-Ho Chung, Robert J. Birgeneau und Pengcheng Dai. „Thermal evolution of spin excitations in honeycomb Ising antiferromagnetic FePSe3“. npj Quantum Materials 9, Nr. 1 (13.05.2024). http://dx.doi.org/10.1038/s41535-024-00651-5.

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AbstractWe use elastic and inelastic neutron scattering (INS) to study the antiferromagnetic (AF) phase transitions and spin excitations in the two-dimensional (2D) zig-zag antiferromagnet FePSe3. By determining the magnetic order parameter across the AF phase transition, we conclude that the AF phase transition in FePSe3 is first-order in nature. In addition, our INS measurements reveal that the spin waves in the AF ordered state have a large easy-axis magnetic anisotropy gap, consistent with an Ising Hamiltonian, and possible biquadratic magnetic exchange interactions. On warming across TN, we find that dispersive spin excitations associated with three-fold rotational symmetric AF fluctuations change into FM spin fluctuations above TN. These results suggest that the first-order AF phase transition in FePSe3 may arise from the competition between C3 symmetric AF and C1 symmetric FM spin fluctuations around TN, in place of a conventional second-order AF phase transition.

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Houmes, Maurits J. A., Gabriele Baglioni, Makars Šiškins, Martin Lee, Dorye L. Esteras, Alberto M. Ruiz, Samuel Mañas-Valero et al. „Magnetic order in 2D antiferromagnets revealed by spontaneous anisotropic magnetostriction“. Nature Communications 14, Nr. 1 (21.12.2023). http://dx.doi.org/10.1038/s41467-023-44180-4.

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AbstractThe temperature dependent order parameter provides important information on the nature of magnetism. Using traditional methods to study this parameter in two-dimensional (2D) magnets remains difficult, however, particularly for insulating antiferromagnetic (AF) compounds. Here, we show that its temperature dependence in AF MPS3 (M(II) = Fe, Co, Ni) can be probed via the anisotropy in the resonance frequency of rectangular membranes, mediated by a combination of anisotropic magnetostriction and spontaneous staggered magnetization. Density functional calculations followed by a derived orbital-resolved magnetic exchange analysis confirm and unravel the microscopic origin of this magnetization-induced anisotropic strain. We further show that the temperature and thickness dependent order parameter allows to deduce the material’s critical exponents characterising magnetic order. Nanomechanical sensing of magnetic order thus provides a future platform to investigate 2D magnetism down to the single-layer limit.

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Postiglione, William M., Jierui Liang, Nileena Nandakumaran, Lucca Figari, Adam A. Aczel und Chris Leighton. „Direct neutron-diffraction-based measurement of magnetic order in brownmillerite SrCoO2.5 and La0.5Sr0.5CoO2.5 thin films“. APL Materials 12, Nr. 4 (01.04.2024). http://dx.doi.org/10.1063/5.0196646.

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Epitaxial cobaltites have emerged as exemplary materials for electrochemical gating, in large part due to their topotactic perovskite (P) ↔ brownmillerite (BM) transformations. SrCoO3−δ, for example, can be cycled between metallic ferromagnetic P SrCoO3 and insulating BM SrCoO2.5, realizing exceptional modulation of electronic, thermal, and optical properties. It is often presumed that such cycling also generates ferromagnetic–antiferromagnetic (F-AF) modulation due to the G-type AF order in bulk SrCoO2.5. Little is understood about magnetism in thin-film BM SrCoO2.5, however, meaning that the true magnetic property modulation is unclear. We address this here through a neutron diffraction study of BM La1−xSrxCoO2.5 films at x = 0.5 and 1.0. Lightly compressively strained SrCoO2.5 films are shown to retain G-type AF order, albeit with suppressed Néel temperature (∼340 K). Of high interest for AF spintronics, room-temperature F–AF cycling is thus possible across the SrCoO3-δ P ↔ BM transformation. At x = 0.5, however, BM La0.5Sr0.5CoO2.5 films are found to exhibit no detectable G-type AF order but instead weak F order (Curie temperature ∼115 K), unveiling a La0.5Sr0.5CoO3−δ phase diagram with two distinct F phases. These results thus uncover new, unanticipated magnetic phase behavior in these materials, in addition to being directly relevant to cobaltite-based magnetoionics.

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Nakagawa, Kurea, Tomoyuki Yokouchi und Yuki Shiomi. „Reconfigurable single-material Peltier effect using magnetic-phase junctions“. Scientific Reports 11, Nr. 1 (Dezember 2021). http://dx.doi.org/10.1038/s41598-021-03754-2.

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AbstractPeltier effects, which produce a heat flux at the junction of two different materials, have been an important technology for heating and cooling by electrical means. Whereas Peltier devices have advantages such as cleanliness, silence, compactness, flexibility, reliability, and efficiency, relatively complicated modular structures are unavoidable, leading to a higher cost than that of commonly used refrigeration technology. Here, we provide a concept of a Peltier device composed of a single magnetic material exhibiting a first-order magnetic transition. Our concept is based on a controllable junction structure consisting of two magnetic phases with opposite Peltier coefficients instead of a semiconductor junction. Using $${\mathrm{Mn}}_{1.96}{\mathrm{Cr}}_{0.04}\mathrm{Sb}$$ Mn 1.96 Cr 0.04 Sb samples with the first-order magnetic transition between ferrimagnetic (FI) and antiferromagnetic (AF) states, we successfully made a stable junction structure of AF/FI/AF by a pulse heating method and achieved a maximum Peltier coefficient of 0.58 mV. Our device concept was further verified by a numerical simulation based on a finite element method. The single-material Peltier effect reported here avoids a complex device design involving material junctions and is importantly reconfigurable.

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Liu, Panpan, Mason L. Klemm, Long Tian, Xingye Lu, Yu Song, David W. Tam, Karin Schmalzl et al. „In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFe2As2“. Nature Communications 11, Nr. 1 (12.11.2020). http://dx.doi.org/10.1038/s41467-020-19421-5.

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AbstractA small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe2As2, which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature Ts. Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature TN ( < Ts) and create in-plane resistivity anisotropy above Ts. Here we use neutron polarization analysis to show that such a strain on BaFe2As2 also induces a static or quasi-static out-of-plane (c-axis) AF order and its associated critical spin fluctuations near TN/Ts. Therefore, uniaxial pressure necessary to detwin single crystals of BaFe2As2 actually rotates the easy axis of the collinear AF order near TN/Ts, and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electronic/magnetic properties of the system.

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Joshi, Rajeev, Suman Karmakar, Kranti Kumar, Mukul Gupta und R. Rawat. „Room temperature giant magnetocaloric effect in Pd doped FeRh and the effect of martensitic transition“. Journal of Applied Physics 133, Nr. 17 (03.05.2023). http://dx.doi.org/10.1063/5.0135364.

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FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (Tt) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude.

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Cheng, Rui-Jin, Xiao-Xun Li, Qing Wang, De-Ji Liu, Zhuo-Ming Huang, Shuai-Yu Lv, Yuan-Zhi Zhou et al. „Suppression of stimulated Brillouin and Raman scattering using the alternately changing frequency laser and the transverse magnetic fields“. Chinese Physics B, 26.10.2023. http://dx.doi.org/10.1088/1674-1056/ad0716.

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Abstract A novel scheme to suppress both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) by combining an alternately changing frequency laser and a transverse magnetic field is proposed. The alternating frequency (AF) laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of laser frequency is less than the linear growth time of SBS. However, the AF laser is ineffective to suppress SRS that usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is also joined to suppress the SRS instability. The electrons trapped in the electron plasma waves (EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is also suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser and a transverse magnetic field with tens of tesla, and the total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference value for controlling SBS and SRS under the related parameters of inertial confinement fusion.

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Kawagoe, Takeshi, und Shigemasa Suga. „Antiferromagnetic domain formation and spin frustration induced by adjacent paired screw dislocations in 10 monolayer-thick Cr(001) films“. Japanese Journal of Applied Physics, 29.03.2023. http://dx.doi.org/10.35848/1347-4065/acc8aa.

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Abstract We investigated the growth and surface morphology of 10 monolayer (ML)-thick Cr(001) films on clean Au(001) surfaces. High-quality epitaxial Cr(001) films with large atomically flat terraces and distinct surface states were successfully fabricated through the growth at 300 K and subsequent post-annealing at 520 K. At 300 K, spin-polarized STM images of both the topological and magnetic structures of this Cr film were obtained. The magnetic images exhibited the following features: (1) the layered antiferromagnetic (AF) order appeared in adjacent terraces and one ML-depth shallow holes in the terraces, (2) significant spin frustrations induced by adjacent paired screw dislocations caused the AF domain formation with 90 degrees quantum axis rotation and large spin-frustration area, not always limited in the vicinity of screw dislocations. The feature (2) was qualitatively reproduced by the micromagnetic simulation. These findings may be essential for the further development of the spin-electronics utilizing thin AF films.

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Fukuzumi, Masafumi, Ryoichi Taniguchi, Seiji Komatsu, Fumihisa Ono und Akihiro Iwase. „Modification of lattice structure and magnetic properties of Fe-Rh alloys by energetic electron irradiation“. MRS Proceedings 792 (2003). http://dx.doi.org/10.1557/proc-792-r3.15.

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ABSTRACTIn order to modify the lattice structure and magnetic properties, we irradiate Fe-50at.%Rh alloys with 8 MeV electrons at room temperature. Effects of irradiation are investigated by using Superconducting QUantum Interference Device (SQUID) and X-Ray Diffractometer (XRD).Although the crystal structure is not changed by the irradiation and remains the B2 structure, the lattice parameter increases by about 0.1–0.3 % and the antiferromagnetic(AF)-ferromagnetic(FM) transition temperature decreases by 3–18 deg. with increasing the electron fluence. The present result shows that energetic electron irradiation can be used for the precise control of AF-FM transition temperature of Fe-50at.%Rh alloy.

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Guo, Dan, Luis M. Moreno-Ramírez, Carlos Romero-Muñiz, Yikun Zhang, Jia-Yan Law, Victorino Franco, Jiang Wang und Zhongming Ren. „First- and second-order phase transitions in RE6Co2Ga (RE = Ho, Dy or Gd) cryogenic magnetocaloric materials“. Science China Materials, 16.08.2021. http://dx.doi.org/10.1007/s40843-021-1711-5.

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AbstractRare-earth (RE) rich intermetallics crystallizing in orthorhombic Ho6Co2Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering, order of magnetic phase transition, and related magnetocaloric behavior. By tuning the type of RE element in RE6Co2Ga (RE = Ho, Dy or Gd) compounds, metamagnetic anti-to-paramagnetic (AF to PM) phase transitions could be tuned to ferro-to-paramagnetic (FM to PM) phase transitions. Furthermore, the FM ground state for Gd6Co2Ga is confirmed by density functional theory calculations in addition to experimental observations. The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho6Co2Ga and Dy6Co2Ga undergo a first-order phase transition in addition to a second-order phase transition, whereas only the latter is observed for Gd6Co2Ga. The two extreme alloys of the series, Ho6Co2Ga and Gd6Co2Ga, show maximum isothermal entropy change (∣ΔS iso max (5 T)∣) of 10.1 and 9.1 J kg−1K−1 at 26 and 75 K, close to H2 and N2 liquefaction, respectively. This outstanding magnetocaloric effect performance makes the RE6Co2Ga series of potential for cryogenic magnetic refrigeration applications.

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Masias Bruns, Mireia, Juan Pablo Ramirez-Mahaluf, Isabel Valli, María Ortuño, Daniel Ilzarbe, Elena de la Serna, Olga Puig Navarro et al. „Altered Temporal Dynamics of Resting-State Functional Magnetic Resonance Imaging in Adolescent-Onset First-Episode Psychosis“. Schizophrenia Bulletin, 22.08.2023. http://dx.doi.org/10.1093/schbul/sbad107.

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Abstract Background Dynamic functional connectivity (dFC) alterations have been reported in patients with adult-onset and chronic psychosis. We sought to examine whether such abnormalities were also observed in patients with first episode, adolescent-onset psychosis (AOP), in order to rule out potential effects of chronicity and protracted antipsychotic treatment exposure. AOP has been suggested to have less diagnostic specificity compared to psychosis with onset in adulthood and occurs during a period of neurodevelopmental changes in brain functional connections. Study Design Seventy-nine patients with first episode, AOP (36 patients with schizophrenia-spectrum disorder, SSD; and 43 with affective psychotic disorder, AF) and 54 healthy controls (HC), aged 10 to 17 years were included. Participants underwent clinical and cognitive assessments and resting-state functional magnetic resonance imaging. Graph-based measures were used to analyze temporal trajectories of dFC, which were compared between patients with SSD, AF, and HC. Within patients, we also tested associations between dFC parameters and clinical variables. Study Results Patients with SSD temporally visited the different connectivity states in a less efficient way (reduced global efficiency), visiting fewer nodes (larger temporal modularity, and increased immobility), with a reduction in the metabolic expenditure (cost and leap size), relative to AF and HC (effect sizes: Cohen’s D, ranging 0.54 to.91). In youth with AF, these parameters did not differ compared to HC. Connectivity measures were not associated with clinical severity, intelligence, cannabis use, or dose of antipsychotic medication. Conclusions dFC measures hold potential towards the development of brain-based biomarkers characterizing adolescent-onset SSD.

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Chernova, Natasha A., Miaomiao Ma, Jie Xiao, M. Stanley Whittingham, Jordi Cabana Jiménez und Clare P. Grey. „Magnetic Studies of Layered Cathode Materials for Lithium Ion Batteries“. MRS Proceedings 972 (2006). http://dx.doi.org/10.1557/proc-0972-aa06-10.

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AbstractThe magnetic properties of layered LiNi0.5Mn0.5O2 and NaNi0.5Mn0.5O2 cathode materials are studied using AC susceptibility and DC magnetization techniques in order to elucidate magnetic interactions within transition metal (TM) layers and between them in samples with various TM distributions. In NaNi0.5Mn0.5O2 antiferromagnetic (AF) ordering transition is found at 60 K and a spin-flop transition at high magnetic field. In LiNi0.5Mn0.5O2 obtained by ion exchange from NaNi0.5Mn0.5O2 ferrimagnetic ordering is found at around 100 K. The saturation magnetization and the hysteresis loop size of ion-exchanged compounds vary from sample to sample, which implies that the Ni2+ ions migrate upon ion exchange process. Magnetic properties of high-temperature and ion-exchanged LiNi0.5Mn0.5O2 are compared; magnetic ordering models for all compounds are proposed based on experimental results and Goodenough-Kanamori rules.

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Akroud, Karima, Mohamed Tahar Kadri, Hafid Belkhir und Kamel Zanat. „Study on the magnetic origin in p-type ferromagnetic semiconductor (Ga,Fe)Sb: ab initio calculations“. Physica Scripta, 12.08.2022. http://dx.doi.org/10.1088/1402-4896/ac8959.

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Abstract The electronic and magnetic properties of Ga1−xFexSb (x = 0.125, 0.25, 0.5) have been investigated using the first-principles calculations based on density functional theory (DFT) and DFT plus on-site repulsion scheme (DFT+U). We found that the Coulomb U parameter plays an important role in predicting the correct stable magnetic order. Using the DFT+U method, the ferromagnetic (FM) ordering is found to be the magnetic ground state for both concentrations 12.5% and 25%, where the DFT failed without on-site repulsion U-term correction. This failure of semi-local DFT functionals is the fingerprint of the correlated nature of Fe-3d electrons. This result is in good agreement with experiment. Increasing Fe concentration up to 50% changing the magnetic ground state from FM to antiferromagnetic (AF) phase. We have used the Heyd-Scuseria-Ernzerhof (HSE) method to calculate the unfolded band structure of supercell for Ga1−xFexSb for x = 0.125, in both FM and AF phases. The location of Fe-3d states in the calculation of the unfolded band structure showed a good accordance with recent resonance photoemission spectroscopy (RPES) experimental results. We have found that hole carriers have an important role at Fermi level E F . The rules of thumb to predict the stability of the ferromagnetism in Fe doped GaSb FMS have been discussed.

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Ernst, Sabine, Richard Underwood, Sonya Babu-Narayan und Simona Ben-Haim. „Abstract 18957: Modulation of Ganglionated Plexi as an Addition to Pv Isolation in Persistent Atrial Fibrillation Ablation“. Circulation 132, suppl_3 (10.11.2015). http://dx.doi.org/10.1161/circ.132.suppl_3.18957.

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Introduction: Catheter ablation of ganglionated plexi (GP) as an add on to pulmonary vein (PV) isolation has been reported to significantly improve outcome of atrial fibrillation (AF) ablation. In order to facilitate localization of these GPs, a novel imaging study is proposed that investigates the uptake of iodine-123 metaiodobenzylguanidine (mIBG, an analogon for norepinephrine) on the atrial level. This information is combined with 3D surface reconstruction from contrast computed tomography (cCT) or cardiac magnetic resonance (CMR). Methods: A total of 7 patients (5 male, mean age 64.3 yrs) with AF underwent mIBG nuclear studies using a dedicated solid state cardiac camera (D-SPECT, Spectrum Dynamics). Four patient had 4 persistent AF (3 prev. abl.) with less than 1 year of sustained AF, whereas 3 patient were in longstanding persistent AF (all prev. abl). The acquired data was merged with the 3D imaging and subsequently imported into the 3D electroanatomical mapping system (CARTO, Biosense Webster). During invasive AF ablations these sites were mapped to perform high frequency stimulation (HFS) to confirm GP locations. Results: In all pts, both the mIBG and CT scans were performed without any complications. Locations of high mIBG uptake corresponded to anatomical GP sites (LA & RA) in the majority of patients, but individual variations were observed. PV isolation was added in all but 1 pt (who had previous ablation) plus CFAE ablation if necessary. Follow-up of in median of 10.4 months demonstrated SR in all persistent AF patients (1 redo for atrial reentry). In patients with longstanding persistent AF: 2 pts are in SR (both AF at 1 week and 1 pt in AT at 6 weeks), while 1 pt remained in AF. Conclusion: The combination of mIBG and 3D imaging provides a novel type of “road map” for localizing GPs during AF ablation. As an add-on to PV (re-) isolation, this strategy was found to be beneficial for patients with persistent and longstanding persistent AF. Interestingly, pts with longstanding persistent AF (and multiple previous ablations) all recurred early in F/U but showed reversal to AT and finally SR at later stages. Further studies in larger patient cohorts need to confirm these initial observations.

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Alatic, J., D. Suran, M. Pirnat, D. Vokac und H. F. Naji. „Impact of restoration of sinus rhythm after catheter ablation of atrial fibrillation on reverse cardiac remodelling“. Europace 26, Supplement_1 (Mai 2024). http://dx.doi.org/10.1093/europace/euae102.176.

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Abstract Introduction Catheter ablation (CA) with pulmonary vein isolation (PVI) has become widely used for the treatment of atrial fibrillation (AF). Restoration of sinus rhythm in patients with AF is of vital importance, because AF induces the development of heart failure (HF) through various pathophysiological mechanisms, one of them is epicardial adipose tissue (EAT). EAT is a type of visceral adipose tissue that is in direct contact with the myocardium. Under pathological conditions it serves as a direct and indirect factor in pathogenesis of AF. It is also an established prognostic factor after CA of AF recurrence. Since cardiac magnetic resonance (CMR) represent the gold standard for the measurement of volume and muscle mass, it has been used more and more for the assessment of EAT volume lately. Purpose The aim of our study was to investigate the impact of restoration of sinus rhythm on EAT volume, and cardiac function and morphology evaluated by the CMR. Methods We prospectively included 17 patients with paroxysmal and persistent AF that were referred for CA. All patients underwent cardiac magnetic CMR prior to radiofrequency CA with PVI and 6 months thereafter in order to quantify periatrial EAT volumes and evaluate cardiac morphological and functional characteristics. AF recurrence rate was diagnosed by serial ECG recordings, Holter ECG monitoring and AF suggestive symptoms within 6 months of follow-up period. Results 17 patients, mainly male (76.5 %) with an average age of 62.35 ± 12.10 years were included in our study. The average body mass index (BMI) was 29.0 ± 4.71 kg/m2. Most patients had paroxysmal AF prior to CA (88.2 %). The recurrence rate of AF was 35.3 % after 6 months of follow-up. By performing CMR after 6 months of CA we observed lower median periatrial EAT volume (36.00 mL (IQR 38.25 mL) vs. 27.45 mL (IQR 30.94 mL); p= 0.004) and lower median left ventricular mass (LVM) (104.0 g/m2 (IQR 38 g/m2) vs. 100.0 g/m2 (IQR 42 g/m2); p= 0.019). Furthermore, when patients were stratified based on the AF status after the follow-up period, we observed that the patients who remained AF-free had significantly lower median periatrial EAT volumes (38.90 mL (IQR 43.84 mL) vs. 26.83 mL (IQR 33.25 mL); p= 0.003) and median LVM (96 g/m2 (IQR 35 g/m2) vs. 90 g/m2 (IQR 29.8 g/m2); p= 0.041) compared to the group of patients who relapsed where we did not observe a significant change in periatrial EAT volume (23.76 mL (IQR 26.84 mL) vs. 31.28 mL (IQR 27.84); p= 0.345) or LVM (117.5 g/m2 (IQR 34 g/m2) vs. 112 g/m2 (IQR 28.6 g/m2); p= 1.0). Significant correlation was observed between BMI and periatrial EAT volume (p= 0.029). Conclusions Restoration of sinus rhythm after CA of AF is associated to lower periatrial EAT volume and LVM. Patients who relapsed did not show reverse cardiac remodelling. Periatrial EAT volume significantly correlates with BMI.

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