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Автор: Grafiati

Опубліковано: 14 березня 2023

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1

ICHINOSE, IKUO, and HISASHI YAMAMOTO. "FINITE TEMPERATURE NÉEL TRANSITION IN CPN−1 MODEL." Modern Physics Letters A 05, no. 17 (July 20, 1990): 1373–80. http://dx.doi.org/10.1142/s0217732390001566.

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Анотація:

We study in d space-dimensions the finite temperature Néel order transition in CPN−1 model as a low energy effective field theory of the antiferromagnetic Heisenberg model. For d=1 at any temperature and d=2 at any nonzero temperature, long range Néel order (LRNO) disappears, in agreement with the Mermin-Wagner-Coleman theorem. For d=3 in the weak coupling region, LRNO exists below the critical temperature T N (Néel temperature). T N decreases as the interlayer coupling becomes relatively weak compared with that within Cu-O layers.

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2

GARCÍA-CERVERA, CARLOS J. "One-dimensional magnetic domain walls." European Journal of Applied Mathematics 15, no. 4 (August 2004): 451–86. http://dx.doi.org/10.1017/s0956792504005595.

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Анотація:

Ferromagnetic materials may present a complicated domain structure, due in part to the nonlocal nature of the self interactions. In this article we present a detailed study of the structure of one-dimensional magnetic domain walls in uniaxial ferromagnetic materials, and in particular, of the Néel and Bloch walls. We analyze the logarithmic tail of the Néel wall, and identify the characteristic length scales in both the Néel and Bloch walls. This analysis is used to obtain the optimal energy scaling for the Néel and Bloch walls. Our results are illustrated with numerical simulations of one-dimensional walls. A new model for the study of ferromagnetic thin films is presented.

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3

SACHDEV, SUBIR, and R. JALABERT. "EFFECTIVE LATTICE MODELS FOR TWO-DIMENSIONAL QUANTUM ANTIFERROMAGNETS." Modern Physics Letters B 04, no. 16 (September 10, 1990): 1043–52. http://dx.doi.org/10.1142/s0217984990001318.

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Анотація:

We introduce a 2+1 dimensional lattice model, S0, of N complex scalars coupled to a compact U(1) gauge field as a description of quantum fluctuations in SU(N) antiferromagnets. Duality maps are used to obtain a single effective action for the Néel and spin-Peierls order parameters. We examine the phases of S0 as a function of N: the N→∞ limit can be deduced from previous work. At N=1, S0 describes monopoles and their Berry phases, spin-Peierls order, but not the Néel field: Monte-Carlo simulations show a second-order transition from a spin-Peierls phase to a Higgs phase which is the remnant of the Néel phase.

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4

Osaci, Mihaela, and Matteo Cacciola. "An adapted Coffey model for studying susceptibility losses in interacting magnetic nanoparticles." Beilstein Journal of Nanotechnology 6 (November 19, 2015): 2173–82. http://dx.doi.org/10.3762/bjnano.6.223.

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Анотація:

Background: Nanoparticles can be used in biomedical applications, such as contrast agents for magnetic resonance imaging, in tumor therapy or against cardiovascular diseases. Single-domain nanoparticles dissipate heat through susceptibility losses in two modes: Néel relaxation and Brownian relaxation. Results: Since a consistent theory for the Néel relaxation time that is applicable to systems of interacting nanoparticles has not yet been developed, we adapted the Coffey theoretical model for the Néel relaxation time in external magnetic fields in order to consider local dipolar magnetic fields. Then, we obtained the effective relaxation time. The effective relaxation time is further used for obtaining values of specific loss power (SLP) through linear response theory (LRT). A comparative analysis between our model and the discrete orientation model, more often used in literature, and a comparison with experimental data from literature have been carried out, in order to choose the optimal magnetic parameters of a nanoparticle system. Conclusion: In this way, we can study effects of the nanoparticle concentration on SLP in an acceptable range of frequencies and amplitudes of external magnetic fields for biomedical applications, especially for tumor therapy by magnetic hyperthermia.

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5

HONG, SEOK-IN. "PHASE STRUCTURES OF THE (2+1)-DIMENSIONAL INFINITE-NCPN−1 MODEL WITH TWISTED BOUNDARY CONDITIONS." Modern Physics Letters A 10, no. 15n16 (May 30, 1995): 1143–54. http://dx.doi.org/10.1142/s0217732395001265.

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Анотація:

We investigate the finite-temperature Néel transitions of the (2+1)-dimensional infinite-NCPN−1 model with a finite spatial dimension. We consider all possible boundary conditions containing the twisted (antiperiodic) one for the imaginary time (inverse temperature) and one finite space: periodic-antiperiodic, antiperiodic-periodic, and antiperiodic-antiperiodic. Simple analytic expressions for the long-range Néel order (LRNO) and the critical line are obtained. Phase diagrams have a region where LRNO appears. Our system can have LRNO even in the infinite-size limit if the imaginary-time axis has the antiperiodic boundary condition.

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6

Kong, Jian-Gang, Qing-Xu Li, Jian Li, Yu Liu, and Jia-Ji Zhu. "Self-Supervised Graph Neural Networks for Accurate Prediction of Néel Temperature." Chinese Physics Letters 39, no. 6 (June 1, 2022): 067503. http://dx.doi.org/10.1088/0256-307x/39/6/067503.

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Анотація:

Antiferromagnetic materials are exciting quantum materials with rich physics and great potential for applications. On the other hand, an accurate and efficient theoretical method is highly demanded for determining critical transition temperatures, Néel temperatures, of antiferromagnetic materials. The powerful graph neural networks (GNNs) that succeed in predicting material properties lose their advantage in predicting magnetic properties due to the small dataset of magnetic materials, while conventional machine learning models heavily depend on the quality of material descriptors. We propose a new strategy to extract high-level material representations by utilizing self-supervised training of GNNs on large-scale unlabeled datasets. According to the dimensional reduction analysis, we find that the learned knowledge about elements and magnetism transfers to the generated atomic vector representations. Compared with popular manually constructed descriptors and crystal graph convolutional neural networks, self-supervised material representations can help us to obtain a more accurate and efficient model for Néel temperatures, and the trained model can successfully predict high Néel temperature antiferromagnetic materials. Our self-supervised GNN may serve as a universal pre-training framework for various material properties.

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7

Capriotti, Luca, Adolfo E. Trumper, and Sandro Sorella. "Long-Range Néel Order in the Triangular Heisenberg Model." Physical Review Letters 82, no. 19 (May 10, 1999): 3899–902. http://dx.doi.org/10.1103/physrevlett.82.3899.

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8

Cai, Wupeng, Shinji Muraishi, Ji Shi, Yoshio Nakamura, Wei Liu, and Ronghai Yu. "Temperature-Driven Spin Reorientation Transition in CoPt/AlN Multilayer Films." Journal of Nanomaterials 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/814162.

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Анотація:

Spin reorientation transition phenomena from out-of-plane to in-plane direction with increasing temperature are observed for the 500°C annealed CoPt/AlN multilayer films with different CoPt layer thicknesses. CoPt-AlN interface and volume anisotropy contributions, favoring out-of-plane and in-plane magnetization, respectively, are separately determined at various temperatures. Interface anisotropy exhibits much stronger temperature dependence than volume contribution, hence the temperature-driven spin reorientation transition occurs. Interface anisotropy in this work consists of Néel interface anisotropy and magnetoelastic effect. Magnetoelastic effect degrades rapidly and changes its sign from positive to negative above 200°C, because of the involvement of stress state in CoPt films with temperature. By contrast, Néel interface anisotropy decays slowly, estimated from a Néel mean field model. Thus, the strong temperature dependence of CoPt-AlN interface anisotropy is dominated by the change of magnetoelastic effect.

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9

SONG, YUN, and HUAMING TANG. "THEORETICAL STUDY OF THE MAGNETIC EXCITATIONS IN COMPOUND Pr2BaNiO5." Modern Physics Letters B 16, no. 26 (November 10, 2002): 991–98. http://dx.doi.org/10.1142/s0217984902004743.

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Анотація:

A three-dimensional mixed-spin antiferromagnetic Heisenberg model is introduced to describe the interesting property of the coexistence of Haldane gap and antiferromagnetic long-range order in compound Pr 2 BaNiO 5. Within the Schwinger-boson mean-field theory, we investigate the temperature dependences of the Haldane gap and ordered parameters both below and above the Néel temperatures, and establish a theoretical explanation for the increase of the Haldane gap below the Néel temperature. Our results are in good agreement with neutron scattering experiments.

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10

YOU, WEN-LONG. "LONG-RANGE ORDER IN TWO-DIMENSIONAL XXZ MODEL." International Journal of Modern Physics B 23, no. 09 (April 10, 2009): 2195–201. http://dx.doi.org/10.1142/s0217979209052145.

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Анотація:

In the present paper, by applying the reflection positivity method due to Dyson, Lieb, and Simon, we rigorously establish the sufficient condition for existence of the Néel long-range order (NLRO) in two-dimensional spin-1/2 XXZ. Our result shows that if the anisotropic coupling Δ satisfies 0 ≤ Δ ≤ 0.30 or Δ ≥ 1.52, the existence of the NLRO along easy axis is proved.

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11

Wernsdorfer, W., E. Bonet Orozco, K. Hasselbach, A. Benoit, B. Barbara, N. Demoncy, A. Loiseau, H. Pascard, and D. Mailly. "Experimental Evidence of the Néel-Brown Model of Magnetization Reversal." Physical Review Letters 78, no. 9 (March 3, 1997): 1791–94. http://dx.doi.org/10.1103/physrevlett.78.1791.

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12

Inaba, M., H. Matsukawa, M. Saitoh, and H. Fukuyama. "Néel and singlet RVB orders in the t-J model." Physica C: Superconductivity and its Applications 257, no. 3-4 (February 1996): 299–303. http://dx.doi.org/10.1016/0921-4534(95)00763-6.

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13

Zvyagin, A. A., and A. V. Makarova. "Néel temperature for undoped spin-Peierls quasi-one-dimensional model." Journal of Physics: Condensed Matter 16, no. 15 (April 2, 2004): 2673–80. http://dx.doi.org/10.1088/0953-8984/16/15/018.

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14

Nance, John, Kawsher A. Roxy, Sanjukta Bhanja, and Greg P. Carman. "Multiferroic antiferromagnetic artificial synapse." Journal of Applied Physics 132, no. 8 (August 28, 2022): 084102. http://dx.doi.org/10.1063/5.0084468.

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Анотація:

Artificial intelligence frameworks utilizing unsupervised learning techniques can avoid the bottleneck of labeled training data required in supervised machine learning systems, but the programming time of these systems is inherently limited by their hardware implementations. Here, a finite-element model coupling micromagnetics and dynamic strain is used to investigate a multiferroic antiferromagnet as a high-speed artificial synapse in artificial intelligence applications. The stability of strain-induced intermediate antiferromagnetic magnetization states (non-uniform magnetization states between a uniform 0 or 1), along with the minimum time scale at which these states can be programmed is investigated. Results show that due to the antiferromagnetic material's magnetocrystalline anisotropy, two intermediate states (Néel vector 1/3z, 2/3x, and Néel vector 2/3z, 1/3x) between fully x and fully z Néel vector orientations can be successfully programmed using 375 με strain pulses, and that the time associated with this programming is limited to ∼0.3 ns by the material's antiferromagnetic resonance frequency.

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15

Andreu, Irene, Ainhoa Urtizberea, and Eva Natividad. "Anisotropic self-assemblies of magnetic nanoparticles: experimental evidence of low-field deviation from the linear response theory and empirical model." Nanoscale 12, no. 2 (2020): 572–83. http://dx.doi.org/10.1039/c9nr05946f.

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Анотація:

Anisotropic assemblies of magnetic nanoparticles with a collective-interactive behavior that can be tuned by an alternating magnetic field amplitude display a cascade of unexpected physical effects and allow reformulation of Néel relaxation times.

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16

DANANI, ANDREA, and ALESSANDRO PELIZZOLA. "CLUSTER VARIATION APPROACH TO THE ANTIFERROMAGNETIC TRANSITION OF THE t-J MODEL." Modern Physics Letters B 07, no. 27 (November 20, 1993): 1761–71. http://dx.doi.org/10.1142/s021798499300179x.

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Анотація:

The antiferromagnetic phase transition associated with the breaking of the magnetic SU(2) symmetry of the t-J model is investigated by means of the cluster variation method in the pair approximation. The disordered and antiferromagnetic phases are characterized by means of their symmetry properties, and an analytical implicit expression is given for the Néel temperature.

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17

Muratov, Cyrill B., and Xiaodong Yan. "Uniqueness of one-dimensional Néel wall profiles." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, no. 2187 (March 2016): 20150762. http://dx.doi.org/10.1098/rspa.2015.0762.

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Анотація:

We study the domain wall structure in thin uniaxial ferromagnetic films in the presence of an in-plane applied external field in the direction normal to the easy axis. Using the reduced one-dimensional thin-film micromagnetic model, we analyse the critical points of the obtained non-local variational problem. We prove that the minimizer of the one-dimensional energy functional in the form of the Néel wall is the unique (up to translations) critical point of the energy among all monotone profiles with the same limiting behaviour at infinity. Thus, we establish uniqueness of the one-dimensional monotone Néel wall profile in the considered setting. We also obtain some uniform estimates for general one-dimensional domain wall profiles.

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18

SEMENOFF, GORDON W. "STRONG COUPLING QED BREAKS CHIRAL SYMMETRY." Modern Physics Letters A 07, no. 30 (September 28, 1992): 2811–18. http://dx.doi.org/10.1142/s0217732392004183.

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Анотація:

We show that the strong coupling limit of d-dimensional quantum electrodynamics with 2d/2[d/2] flavors of fermions can be mapped onto the s=1/2 quantum Heisenberg antiferromagnet in d–1 space dimensions. We use this mapping to prove that the strong coupling limit of QED breaks chiral symmetry. The staggered Néel order parameter of the antiferromagnet is the expectation value of a mass operator in QED and the spin-waves are pions. We speculate that the chiral symmetry breaking phase transition corresponds to a transition between the flux phase and the conventional Néel ordered phase of an antiferromagnetic t-J model.

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19

BARTKOWIAK, M. "HIGH-DENSITY EXPANSION FOR THE EXTENDED HUBBARD MODEL." International Journal of Modern Physics B 01, no. 05n06 (October 1987): 1277–310. http://dx.doi.org/10.1142/s0217979287001729.

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Анотація:

The Green’s-function diagrammatic high-density expansion technique for Hubbard’s operators is constructed and applied to the extended Hubbard model. The electron Green’s functions and the band structure of the ground state for arbitrary electron density are calculated in the zeroth-order in 1/z. The phase diagram, staggered magnetic susceptibility and the Néel temperature for the half-filled band case are derived in the first order of the high-density expansion. Connections of the high-density and linked cluster expansions are also discussed.

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20

Bisero, Diego. "A mathematical model for domain walls in ultrathin magnetic films with uniaxial anisotropy." Modern Physics Letters B 32, no. 09 (March 30, 2018): 1850097. http://dx.doi.org/10.1142/s0217984918500975.

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Анотація:

Domain walls are a basic ingredient of spintronic devices, nowadays. In this paper, a mathematical model for the solution of domain wall problems will be derived from a micromagnetic semiclassical approach. This model will prove to be suitable for the description of both Néel and Bloch walls, particularly in the case of magnetization uniformity distribution along the wall length of a uniaxial magnetic ultrathin film.

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21

Cazacu, Ana, Cristian Rotărescu, and Ilie Bodale. "The Relaxation Effects in the Preisach - Néel Model of Patterned Media." BULETINUL INSTITUTULUI POLITEHNIC DIN IAȘI. Secția Matematica. Mecanică Teoretică. Fizică 67, no. 2 (June 1, 2021): 9–18. http://dx.doi.org/10.2478/bipmf-2021-0006.

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Abstract In this paper, we present the calculation of thermal magnetic viscosity based on numerical simulations of relaxation isotherms curves for a Stoner–Wohlfarth ensemble. The Stoner–Wohlfarth particles is described by two equilibrium states and thermal activation is done by overcoming the energy barrier. For simulations we have used a new Preisach type model for Patterned Media, which takes into account the effects of time and temperature. The magnetization of the system is treated using the Preisach Model for Patterned Media with bimodal interactions field distributions. We have simulated relaxation curves starting from different points on the negative region of the descending branch of the major hysteresis loop and from the obtained data we evaluated the thermal fluctuation field. The results obtained for the linear energy barrier were compared with the non-linear energy barrier.

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22

Torres, T. E., E. Lima, A. Mayoral, A. Ibarra, C. Marquina, M. R. Ibarra, and G. F. Goya. "Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3−xO4nanoparticles." Journal of Applied Physics 118, no. 18 (November 14, 2015): 183902. http://dx.doi.org/10.1063/1.4935146.

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23

Hergt, Rudolf, Silvio Dutz, and Matthias Zeisberger. "Validity limits of the Néel relaxation model of magnetic nanoparticles for hyperthermia." Nanotechnology 21, no. 1 (November 30, 2009): 015706. http://dx.doi.org/10.1088/0957-4484/21/1/015706.

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24

Tournus, F., S. Rohart, and V. Dupuis. "Magnetic Anisotropy Dispersion in CoPt Nanoparticles: An Evaluation Using the NÉel Model." IEEE Transactions on Magnetics 44, no. 11 (November 2008): 3201–4. http://dx.doi.org/10.1109/tmag.2008.2002776.

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25

VUJINOVIĆ, M., M. PANTIĆ, D. KAPOR, and P. MALI. "THEORETICAL MODELS FOR MAGNETIC PROPERTIES OF IRON PNICTIDES." International Journal of Modern Physics B 27, no. 16 (June 7, 2013): 1350071. http://dx.doi.org/10.1142/s0217979213500719.

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Анотація:

We attempt to describe the magnetic properties of parent pnictide compounds by using both the J1–J2 Heisenberg model and its three-dimensional generalization, the J1–J2–Jc model. We also include spin anisotropy in the XY plane. In order to obtain the average magnetization and spin wave dispersion, we use the Green's functions method for spin operators in the random phase approximation. We obtain estimates for the model parameters by considering the low temperature experimental dispersion for the compounds CaFe 2 As 2 and BaFe 2 As 2 and conclude that theoretical dispersion can fit the experimental one if spatially anisotropic Hamiltonian is used. A good agreement between theory and experiment indicates that the Heisenberg model is applicable to parent pnictides at low temperatures. The applicability of the model for higher temperatures is checked by calculating the Néel temperature for both compounds. It turns out that the model overestimates the measured critical temperature. The Heisenberg model is not applicable to parent pnictides, for temperature comparable to Néel temperature. Our results thus confirm that all the magnetic properties of parent pnictides cannot be described with purely localized degrees of freedom, and that the itinerant magnetism should have an important role in these compounds. All results given in Sec. 3 are general and could be used in description of classes of compounds with spin stripe structure.

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26

Roy, Arnab, and P. S. Anil Kumar. "An extension of the Néel-Brown model for systems with multiple switching pathways." Journal of Magnetism and Magnetic Materials 424 (February 2017): 69–75. http://dx.doi.org/10.1016/j.jmmm.2016.09.070.

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27

Spinu, Leonard, and Alexandru Stancu. "Modelling magnetic relaxation phenomena in fine particles systems with a Preisach–Néel model." Journal of Magnetism and Magnetic Materials 189, no. 1 (October 1998): 106–14. http://dx.doi.org/10.1016/s0304-8853(98)00205-4.

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28

Kunyangyuen, Boonthum, Udomsilp Pinsook, and Salinporn Kittiwatanakul. "Ab-initio study and atomistic spin model simulations of Cr₂O₃ thin films." Journal of Physics: Conference Series 2431, no. 1 (January 1, 2023): 012042. http://dx.doi.org/10.1088/1742-6596/2431/1/012042.

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Анотація:

Abstract Magnetoelectric random access memory (MERAM) is the next generation technology of data storage with high-density and low power. Magnetoelectric material can be controlled by voltage such as an electric field to transform spin domain directions for storing data. One of the most promising materials that possess such properties near room temperature is Cr2O3. Although, the bulk has perfect properties for MERAM, it is necessary to fabricate thin films for applicable spintronic devices, i.e., reducing the required external control voltage; however, the film magnetic and physical properties might be different from bulk. In this work, we propose that the film properties might be induced by surface effects and are confirmed with Ab-initio calculation and atomistic spin simulation. The main simulation processes are the density functional theory (DFT) calculating, mapped with the classical Heisenberg model for exchange interaction constants up to the fifth nearest neighbour (J 1-J 5). The atomistic spin model was then used to approximate the Néel temperature (T N), comparing two methods i.e., Monte Carlo simulation and the Landau–Lifshitz–Gilbert (LLG) equation. The Néel temperatures of the film were found to be slightly lower than the bulk, which is in good agreement with previous experiments. Furthermore, the spin dynamic model gives more correct result comparing to the Monte Carlo method.

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29

CHANG, ZHE. "GREEN'S FUNCTION THEORY OF THE DOPED ANISOTROPIC ANTIFERROMAGNET." International Journal of Modern Physics B 14, no. 10 (April 20, 2000): 1037–57. http://dx.doi.org/10.1142/s0217979200001497.

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Анотація:

The Green's function theory of the t–J model is generalized to investigate phase diagram and magnetic properties of the doped anisotropic antiferromagnet, which is believed to describe the elementary properties of the high-temperature superconductors. Antiferromagnetic–metalic phase transition is shown. The explicit dependence of the Néel temperature and sublattice magnetization of the anisotropic doped antiferromagnets on anisotropic parameter ς, doping density δ and parameters of the t–J model are obtained for small doping concentration.

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30

Fabrykiewicz, P., M. Stękiel, I. Sosnowska та R. Przeniosło. "Deformations of the α-Fe2O3 rhombohedral lattice across the Néel temperature". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 73, № 1 (23 січня 2017): 27–32. http://dx.doi.org/10.1107/s2052520616017935.

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Анотація:

High-resolution synchrotron radiation powder diffraction patterns of α-Fe2O3 measured between room temperature and 1100 K, i.e. above the Néel temperature T N = 950 K, have been analyzed. The integral breadths of the Bragg peaks show a hkl-dependent anisotropy, both below and above T N. This anisotropy can be quantitatively described by using a statistical peak-broadening model [Stephens (1999). J. Appl. Cryst. 32, 281]. Model calculations show that the rhombohedral α-Fe2O3 lattice is deformed and the deformation leads to a monoclinic lattice with the unique monoclinic axis along the hexagonal [110] direction both below and above T N. The monoclinic symmetry of bulk α-Fe2O3 is compatible with α-Fe2O3 nanowire growth along the [110] direction reported in Fu et al. [Chem. Phys. Lett. (2001), 350, 491].

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31

SAKO, SANSHIRO, KAZUNARI OHSHIMA, MASAHIRO SAKAI, and SHUNJI BANDOW. "MAGNETIC PROPERTY OF CoO ULTRAFINE PARTICLE." Surface Review and Letters 03, no. 01 (February 1996): 109–13. http://dx.doi.org/10.1142/s0218625x96000231.

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Анотація:

The effect of the decrease in the coordination number of atoms in surface on the magnetic transition temperature was investigated experimentally and theoretically for CoO ultrafine particles. The decreasing tendency of the Néel temperature T N with decreasing average size was confirmed in the size range from 2.0 to 3.0 nm through the ESR measurement. The similar tendency of T N for size was gained through the calculation of T N in the mean-field theory using the prism model within the Ising thin-film model.

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32

SHAPIR, YONATHAN. "SUPPRESSION OF THE SUSCEPTIBILITY DIVERGENCE AT THE TRANSITION BETWEEN THE NÉEL AND THE RESONANTING VALENCE BOND PHASES OF THE HEISENBERG ANTIFERROMAGNET." Modern Physics Letters B 03, no. 09 (June 1989): 741–46. http://dx.doi.org/10.1142/s0217984989001163.

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Анотація:

The antiferromagnetic susceptibility is at most weakly divergent at an assumed Néel to resonanting valence bond (RVB) phase transition. This result, derived from the mapping onto a classical O(4) model in the “quenched approximation”, is argued to hold under the most general circumstances due to the constraints on the RVB states. It may provide an experimental distinction between the transition to an RVB and to a paramagnetic phase.

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33

LiMing, W., G. Misguich, P. Sindzingre, and C. Lhuillier. "From Néel long-range order to spin liquids in the multiple-spin exchange model." Physical Review B 62, no. 10 (September 2000): 6372–77. http://dx.doi.org/10.1103/physrevb.62.6372.

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34

Yuan, Qingshan. "The Néel order for a frustrated antiferromagnetic Heisenberg model: beyond linear spin-wave theory." Physics Letters A 275, no. 5-6 (October 2000): 481–85. http://dx.doi.org/10.1016/s0375-9601(00)00625-3.

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35

BISHOP, R. F., P. H. Y. LI, D. J. J. FARNELL, and C. E. CAMPBELL. "MAGNETIC ORDERING OF ANTIFERROMAGNETS ON A SPATIALLY ANISOTROPIC TRIANGULAR LATTICE." International Journal of Modern Physics B 24, no. 25n26 (October 20, 2010): 5011–26. http://dx.doi.org/10.1142/s021797921005716x.

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Анотація:

We study the spin-1/2 and spin-1 [Formula: see text] Heisenberg antiferromagnets (HAFs) on an infinite, anisotropic, two-dimensional triangular lattice, using the coupled cluster method. With respect to an underlying square-lattice geometry the model contains antiferromagnetic (J1 > 0) bonds between nearest neighbours and competing [Formula: see text] bonds between next-nearest-neighbours across only one of the diagonals of each square plaquette, the same diagonal in each square. In a topologically equivalent triangular-lattice geometry the model has two sorts of nearest-neighbour bonds, with [Formula: see text] bonds along parallel chains and with J1 bonds providing an interchain coupling. The model thus interpolates between an isotropic HAF on the square lattice at one extreme (κ = 0) and a set of decoupled chains at the other (κ → ∞), with the isotropic HAF on the triangular lattice in between at κ = 1. For the spin-1/2 [Formula: see text] model, we find a weakly first-order (or possibly second-order) quantum phase transition from a Néel-ordered state to a helical state at a first critical point at κc1 = 0.80 ± 0.01, and a second critical point at κc2 = 1.8 ± 0.4 where a first-order transition occurs between the helical state and a collinear stripe-ordered state. For the corresponding spin-1 model we find an analogous transition of the second-order type at κc1 = 0.62 ± 0.01 between states with Néel and helical ordering, but we find no evidence of a further transition in this case to a stripe-ordered phase.

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36

LIKHACHEV, D. V., and A. A. POVZNER. "WEAK ITINERANT ANTIFERROMAGNETISM: TWO-BAND NESTING MODEL AND EFFECT OF SPIN FLUCTUATIONS." International Journal of Modern Physics B 10, no. 10 (April 30, 1996): 1191–210. http://dx.doi.org/10.1142/s0217979296000441.

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Анотація:

In this work we calculate the effect of spin fluctuations on a weak itinerant antiferromagnetism of transition metals alloys described by a nesting model with the presence of both the nesting parts at the Fermi surface and the so-called “electron reservoir”. It is shown that the presence of “electron reservoir” with the large exchange enhancement factor of spin fluctuations leads to a decrease of the Néel temperature as compared to its value estimated in the mean-field approximation. A mechanism of magnetic order destruction, which is not associated with the scattering of the nesting parts electronic states on the “electron reservoir” spin fluctuations, is discussed. An extensive discussion of the thermophysical properties for this model, and of the physical and experimental implications of the results are presented.

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37

CAPRIOTTI, LUCA. "QUANTUM EFFECTS AND BROKEN SYMMETRIES IN FRUSTRATED ANTIFERROMAGNETS." International Journal of Modern Physics B 15, no. 12 (May 20, 2001): 1799–842. http://dx.doi.org/10.1142/s0217979201004605.

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We investigate the interplay between frustration and zero-point quantum fluctuations in the ground state of the triangular and J1–J2 Heisenberg antiferromagnets, using finite-size spin-wave theory, exact diagonalization, and quantum Monte Carlo methods. In the triangular Heisenberg antiferromagnet, by performing a systematic size-scaling analysis, we have obtained strong evidences for a gapless spectrum and a finite value of the thermodynamic order parameter, thus confirming the existence of long-range Néel order. The good agreement between the finite-size spin-wave results and the exact and quantum Monte Carlo data also supports the reliability of the spin-wave expansion to describe both the ground state and the low-energy spin excitations of the triangular Heisenberg antiferromagnet. In the J1–J2 Heisenberg model, our results indicate the opening of a finite gap in the thermodynamic excitation spectrum at J2/J1≃0.4, marking the melting of the antiferromagnetic Néel order and the onset of a non-magnetic ground state. In order to characterize the nature of the latter quantum-disordered phase we have computed the susceptibilities for the most important crystal symmetry breaking operators. In the ordered phase the effectiveness of the spin-wave theory in reproducing the low-energy excitation spectrum suggests that the uniform spin susceptibility of the model is very close to the linear spin-wave prediction.

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38

Thang, Nguyen Toan, and Pham Thi Thanh Nga. "Néel State in the Fermionized Spin 1/2 Heisenberg Antiferromagnet on Hypercubic and Triangular Lattices." Communications in Physics 22, no. 1 (May 7, 2012): 33–43. http://dx.doi.org/10.15625/0868-3166/22/1/631.

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Анотація:

We study the Néel state of the spin 1/2 Heisenberg antiferromagnet model on hypercubic and triangular lattices, employing an auxiliary fermion representation for spin operators with Popov-Fedotov trick. The unphysical states are eliminated on each site by introducing an imaginary chemical potential. Working in local coordinate systems we obtain the free energy and the sublattice magnetization for both lattices in an unified manner. We show that exact treatment of the single occupancy constraint gives a significant effect at finite temperatures.

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39

Lu, Kailiang, Dongping Chang, Tian Lu, Xiaobo Ji, Minjie Li, and Wencong Lu. "Machine Learning Model for High-Throughput Screening of Perovskite Manganites with the Highest Néel Temperature." Journal of Superconductivity and Novel Magnetism 34, no. 7 (April 22, 2021): 1961–69. http://dx.doi.org/10.1007/s10948-021-05857-3.

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40

Morinari, Takao. "Evolution of Néel order and localized spin moment in the doped two-dimensional Hubbard model." Journal of Magnetism and Magnetic Materials 281, no. 2-3 (October 2004): 188–94. http://dx.doi.org/10.1016/j.jmmm.2004.04.104.

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41

Lees, Benjamin. "Existence of Néel Order in the S=1 Bilinear-Biquadratic Heisenberg Model via Random Loops." Communications in Mathematical Physics 347, no. 1 (May 24, 2016): 83–101. http://dx.doi.org/10.1007/s00220-016-2656-1.

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42

Schindelin, C., D. Ihle, S. L. Drechsler, and H. Fehske. "Spin correlation functions and Néel order in the 2D Heisenberg model: effects of spatial anisotropy." Physica B: Condensed Matter 281-282 (June 2000): 819–20. http://dx.doi.org/10.1016/s0921-4526(99)01064-9.

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43

Sushkov, O. P. "t-J model. Dispersion relation and wave function of a hole on the Néel background." Solid State Communications 83, no. 4 (July 1992): 303–6. http://dx.doi.org/10.1016/0038-1098(92)90276-f.

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44

Moskvin, Alexander. "Structure–Property Relationships for Weak Ferromagnetic Perovskites." Magnetochemistry 7, no. 8 (August 3, 2021): 111. http://dx.doi.org/10.3390/magnetochemistry7080111.

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Анотація:

Despite several decades of active experimental and theoretical studies of rare-earth orthoferrites, the mechanism of the formation of their specific magnetic, magnetoelastic, optical, and magneto-optical properties remains a subject of discussion. This paper provides an overview of simple theoretical model approaches to quantitatively describing the structure–property relationships—in particular, the interplay between FeO6 octahedral deformations/rotations and the main magnetic and optic characteristics, such as Néel temperature, overt and hidden canting of magnetic sublattices, magnetic and magnetoelastic anisotropy, and optic and photoelastic anisotropy.

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45

CABRA, D. C., C. A. LAMAS, and H. D. ROSALES. "EVIDENCE OF A SPIN-LIQUID PHASE IN THE FRUSTRATED HONEYCOMB LATTICE." Modern Physics Letters B 25, no. 12n13 (May 30, 2011): 891–900. http://dx.doi.org/10.1142/s0217984911026590.

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Анотація:

In the present paper, we present some new data supporting the existence of a spin-disordered phase in the Heisenberg model on the honeycomb lattice with antiferromagnetic interactions up to third neighbors along the line J2 = J3, predicted in Ref. 1. We use the Schwinger boson technique followed by a mean field decoupling and exact diagonalization for small systems to show the existence of an intermediate phase with a spin gap and short range Néel correlations in the strong quantum limit [Formula: see text].

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46

POGORELOV, YURY G. "LONG–RANGE MAGNETIC ORDER IN La2NiO4+δ UNDER SMALL OXYGEN EXCESS". International Journal of Modern Physics B 07, № 01n03 (січень 1993): 178–81. http://dx.doi.org/10.1142/s0217979293000408.

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Within a continuum model based on the microscopic magnetic symmetry of Ni 2+ ion (spin S = 1) in the metal-oxide compound La 2 NiO 4+δ, a theoretical analysis is made of the stability of antiferromagnetic long-range order under the effect of oxygen interstitials at δ ≪ 1. It is shown that the Néel temperature dicreases significantly with growing δ though does not become zero, in contrast to that in the structurally isomorhic compound La 2 CuO 4+δ (but Cu 2+ spin S = 1/2).

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47

HUANG, HAI. "FIELD-THEORETICAL CALCULATIONS ON THE HALDANE GAP OF QUASI-ONE-DIMENSIONAL HEISENBERG ANTIFERROMAGNETS." International Journal of Modern Physics B 23, no. 31 (December 20, 2009): 5789–800. http://dx.doi.org/10.1142/s0217979209053898.

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One-dimensional Heisenberg antiferromagnets can be described by the O (3) nonlinear σ-model (NLσM). We give a review on zero temperature and finite temperature Haldane gaps obtained from this model. Based on the coupled-chain theory, we derive the finite temperature Haldane gap for triangular antiferromagnet RbNiCl 3. The Néel temperature is obtained as 11 K. In order to treat the anisotropy in crystal Ni ( C 2 H 8 N 2)2 NO 2( ClO 4), we relax the constraint of the NLσM and compute the finite temperature Haldane gap using a Ginzburg–Landau mean field approach. The comparison with the experimental data is discussed.

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48

Szytuła, Andrzej, Stanislav Baran, Bogusław Penc, Andreas Hoser, and Vladimir Dyakonov. "Magnetic Order in Quaternary NiMnGe:T (T = Cr, Ti) Compounds." Solid State Phenomena 289 (April 2019): 156–63. http://dx.doi.org/10.4028/www.scientific.net/ssp.289.156.

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Анотація:

The work reports the results of neutron diffraction measurements of NiMnGe:T systems where T is Cr or Ti. All investigated compounds have the helicoidal magnetic structure with the propagation vector k = (ka,0,0). The values of the ka component decrease with increasing Cr content and increase with increasing Ti content. For all compounds, except the sample with x = 0.18 in Cr-system, the helicoidal order is stable up to the Néel temperature. The obtained data are analysed based on simple model in which the magnetic interactions are described by two exchange integrals J1 > 0 for first and J2 < 0 for second neighbouring moments. This model clears up different dependence of ka component in different systems.

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49

Eshraghi, Mahin, and Parviz Kameli. "Structural and Magnetic Properties of Microwave Assisted Sol-Gel Synthesized La0.9Sr0.1MnO3 Manganite Nanoparticles." ISRN Nanotechnology 2014 (February 10, 2014): 1–6. http://dx.doi.org/10.1155/2014/867139.

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Анотація:

The structural and magnetic properties of nanoparticles of La0.9Sr0.1MnO3 (LSMO) were studied using powder X-ray diffraction (XRD), transmission electron microscope (TEM), and magnetic measurements. The XRD refinement result indicates that samples crystallize in the rhombohedral structure with R-3C space group. The dc magnetization measurements revealed that samples exhibit no hysteretic behavior at room temperature, symptomatic of the superparamagnetic (SPM) behavior. The results of ac magnetic susceptibility measurements show that the susceptibility data are not in accordance with the Néel-Brown model for SPM relaxation but fit well with conventional critical slowing down model which indicates that the dipole-dipole interactions are strong enough to cause superspin-glass-like phase in LSMO samples.

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50

Yokoyama, Hisatoshi, and Hiroyuki Shiba. "Hubbard Model in Strong Correlation Regime –Variational Monte-Carlo Studies on Singlet Liquid and Néel State–." Journal of the Physical Society of Japan 56, no. 10 (October 15, 1987): 3570–81. http://dx.doi.org/10.1143/jpsj.56.3570.

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