Auswahl der wissenschaftlichen Literatur zum Thema „Field-dependent specific heat C(T,H)“

We review the results of specific-heat experiments on the S = 1 quasi-one-dimensional (quasi-1D) bond-alternating antiferromagnet Ni(C 9 H 24 N 4)( NO 2) ClO 4, alias NTENP. At low temperatures above the transition temperature of a field-induced long-range order, the magnetic specific heat (C mag ) of this compound becomes proportional to temperature (T), when a magnetic field along the spin chains exceeds the critical field H c at which the energy gap vanishes. The ratio C mag /T, which increases as the magnetic field approaches H c from above, is in good quantitative agreement with a prediction of conformal field theory combined with the field-dependent velocity of the excitations calculated by the Lanczos method. This result is the first conclusive evidence for a Tomonaga–Luttinger liquid in a gapped quasi-1D antiferromagnet.

Recently Takeuchi reported a weak, 'metamagnetic-like' increase in the magnetization around 42 T in single crystals of CeIrIn 5 for field in the c-direction. We report specific heat measurements on single crystal CeIrIn 5, H parallel c-axis, measured in the dc hybrid magnet at NHMFL in Tallahassee between 1.4 and 10 K. A clear anomaly in C/T in 35 T is observed to peak at 1.8 K, with an entropy of 6% of RIn2. This anomaly grows in size and shifts upwards in temperature (both monotonically) with increasing H until at 45 T T peak =4.1 K , with the entropy associated with the transition equal to 14% of RIn2. C/T data at 32 T show3 only the high temperature side of the peak occurring above 1.4 K, while C/T data at 28.5 T show no anomaly down to 1.4 K. This is consistent with our Tpeak vs H data, which imply T peak → 0 at 26 T.

Abstract We report anisotropy in the superconducting properties of FeTe0.55Se0.45 bulk single crystal synthesized via the self-flux method. We have performed magnetotransport, magnetic and heat capacity measurements on single crystals of same batch. The grown crystals have also been characterized by XRD, XPS and Raman measurements. The superconductivity at T C ∼ 14 K has been affirmed by the temperature-dependent resistivity, magnetic, and specific heat measurements. The anisotropy in the upper critical field (H C2), coherence length (ξ), and critical current density (J C) have been studied from the magnetotransport and magnetic measurements, respectively, under applied magnetic fields of 0–12 T along the ab-plane and c-axis. The critical current density has been estimated by Bean’s critical state model at different magnetic fields (J C(H)) and temperatures (J C(T)) measured for H‖ab-plane and H‖c axis. The anisotropic behaviour has also been observed for J C(H). The presence of ‘peak effect’ or fishtail characteristic has been noticed in M–H loops for H‖c only, which shows a shift towards the lower fields with increasing temperature. The nature of the pinning mechanisms in the sample has been determined by the normalized pinning force density using the Dew Hughes scaling rule, and the analysis of experimental data indicates the presence of δl-pinning in the sample. The temperature-dependent electronic specific heat has been fitted with the exponential law and the evaluated coupling constant 2Δ0/kBTc is ∼3.42 which is close to the universal BCS value of 3.53. The observed low value of residual Sommerfeld coefficient γ r e s ≈ 4.59 mJ mol−1 K2 indicates good quality of the grown single crystal.

In situ dilatometry experiments using high energy synchrotron X-ray diffraction in transmission mode were carried out at the high energy material science beamline P07@PETRAIII at DESY (Deutsches Elektronen Synchrotron) for the tempering steel AISI 4140 at defined mechanical loading. The focus of this study was on the initial tempering state ( f e r r i t e ) and the hardened state ( m a r t e n s i t e ). Lattice strains were calculated from the 2D diffraction data for different h k l planes and from those temperature-dependent lattice plane specific diffraction elastic constants ( D E C s ) were determined. The resulting coupling terms allow for precise stress analysis for typical hypoeutectoid steels using diffraction data during heat treatment processes, that is, for in situ diffraction studies during thermal exposure. In addition, by averaging h k l specific Y o u n g ′ s m o d u l i and P o i s s o n r a t i o s macroscopic temperature-dependent elastic constants were determined. In conclusion a novel approach for the determination of phase-specific temperature-dependent DECs was suggested using diffraction based dilatometry that provides more reliable data in comparison to conventional experimental procedures. Moreover, the averaging of lattice plane specific results from in situ diffraction analysis supply robust temperature-dependent macroscopic elastic constants for martensite and ferrite as input data for heat treatment process simulations.

The combining mechanism of the itinerant carrier pair and the local carrier pair (two-component model) is considered for doped fullerenes. The superconducting transition temperature T c , penetration depth λ, coherent length ξ, thermodynamic critical field H c and specific heat jump ΔC/T c are calculated and there is overall consistency between the calculations and the experiments for both alkali-metal-doped fullerenes ( Na 3 C 60, K 3 C 60, Rb 3 C 60 and RbCs 2 C 60) and alkaline-earth doped fullerenes ( Ba 6 C 60).

We develop a phenomenological model for high-T c superconductors. Some main features are emerging in copper oxides: characteristic quasi two-dimensional Cu-O planes, strong correlation of antiferromagnetism, existence of a vortex lattice structure, and observation of a small coherence length and a large penetration depth. These features indicate that the superconductive pair is reasonably constrained to a small volume in real space and may be conceived of as a string-carrying vortex, and therefore can be well simulated by the dual phenomenological local boson fields [Formula: see text] and Φ. The various mean-field ground states of the system are discussed. The field equations of motion are originally solved to get approximate analytical soliton solutions. The effective Hamiltonian is formulated by a variational method for finite temperatures. The model parameter behaviour described by the relationship of the variational parameters is investigated. We discuss the critical temperature T c , the specific heat cV and its jump Δc at T c , and the critical magnetic fields H c1 and H c2 . These results are in agreement with experimental observations, especially the critical behaviours and the zero temperature values. The model also allows interpretation of the variation of T c with oxygen vacancy x and that with doping fraction δ in Cu-O planes, as well as the dependence of γ (defined as the specific heat coefficient of the T-linear term) on δ.

Abstract Orthorhombic YAlGe-type TbAlGe is expected to have an interesting magnetic anisotropy due to zigzag chains of the Tb ions. We have grown the single crystal for the first time and measured the AC magnetic susceptibility and specific heat from 1.3 K to 60 K, and the vector magnetization for the b-plane up to 7 T at 4 K. The specific heat and AC magnetic susceptibility indicate that there are two antiferromagnetic transitions at T N1 = 38 K and TN2 = 7.6 K, where the transition at T N2 is first-order like. The magnetization curve at 4 K for the a-axis shows a large hysteresis, and metamagnetic transition appears at H 1 = 1.6 T in the field increasing process, and another metamagnetic transition at H2 = 3.5 T in addition to H 1 in the decreasing field process. The magnetization curves of the b- and c-axis are linear up to 7 T. The measurement of vector magnetization at 4 K reflects the hysteresis of the magnetization curve, and there is a large hysteresis. From this vector magnetization measurement, we have made the angular magnetic field phase diagram at 4 K for the b-plane. In this phase diagram, there are phase lines that cannot be obtained by ordinary magnetization measurement.

Terbium tritelluride, TbTe3, orders antiferromagnetically in three steps at TN1 = 6.7 K, TN2 = 5.7 K, and TN3 = 5.4 K, preceded by a correlation hump in magnetic susceptibility at T* ~8 K. Combining thermodynamic, i.e., specific heat Cp and magnetization M, and transport, i.e., resistance R, measurements we established the boundaries of two commensurate and one charge density wave modulated phases in a magnetic field oriented along principal crystallographic axes. Based on these measurements, the magnetic phase diagrams of TbTe3 at H‖a, H‖b and H‖c were constructed.

Abstract We have successfully trapped a field of 17.89 T at 6.5 K at the center of a compact coated-conductor (CC) stacks (13 × 12 × 11.7 mm3) within 75 min by suppressing flux jumps. The CC stack consists of 200 sheets of EuBa2Cu3O7 CCs with BaHfO3 nanorods to increase the critical current density at high fields and low temperatures. To enhance thermomagnetic stability, the central 50 CCs are coated with 1 µm thick Pb with large specific heat at low temperatures. Numerical calculations based on the actual J c–H characteristics reproduces the trapped field quantitatively. New directions for achieving even higher trapped field at higher temperatures and making use of the trapped field are discussed.

The present paper presents the computational implementation of the industrial formulation of the thermodynamic properties of water at liquid and steam phases, proposed by the International Association for the Properties of Water and Steam, known as IAPWS-IF97. The validity field extends over to temperatures T between 0ºC and 800°C, for pressures p up to 100 MPa. Temperature T, specific volume v, specific enthalpy h, specific entropy s, specific heat at constant pressure cp and constant volume cv, besides saturation pressure ps, are calculated having a pair of known input values (p,T), (p,h) or (p,s). A comparative analysis between the IAPWS-IF97 routines and others, based on foregoing propositions, from an application on Rankine cycle, is made. IAPWS-IF97 has proved to be more precise, mainly because it accounts for the region of compressed liquid, besides requiring less processing time. The development is carried out as FORTRAN90 subroutines and functions and is available for public use according to a General Public License.

Dans la recherche de matériaux magnétoélectriques (ME) présentant des performances ME élevées, nous étudions dans cette thèse certains mécanismes fondamentaux qui conduit au renforcement du couplage magnéto-élastique dans les composites MEs. Notre étude porte sur les composites particulaires 0-3 composés de phase magnétostrictive (MS) de CFO imbibée dans des matrices ferroélectriques (FE) suivantes : à base de Pb PZT, PMNPT et leur alternative sans plomb KNN et BTO. Nous démontrons que la technique Laser Heated Pedestal Growth (LHPG) peut être utilisé pour synthétiser des échantillons massives avec une microstructure texturée prononcée entre les phases FE et MS. Scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) et X-ray diffraction (XRD) sont utilisés pour caractériser systématiquement l’orientation des grains, la taille des grains and la qualité d’interface entre les différentes phases citées ci-avant. Une étude systématique par le biais de la spectroscopie Raman, les mesures de magnétisation M (H,T) et de chaleur spécifique C(T,H) nous ont permis de sonder le couplage magnéto-élastique directement dans les échantillons MEs. En combinant les analyses des données structurales et thermodynamiques précédentes, cela montre que la structure avec une texture prononcée dans les échantillons synthétisés par LHPG conduit à une forte augmentation de la réponse magnéto-élastique. Nous soutenons que ce résultat est très prometteur pour la conception des matériaux ME. Enfin, nous suggérons que l'étude de la chaleur spécifique précédent offre une sonde sans contact pour étudier le couplage spin-réseau de manière intrinsèque dans une large gamme de matériaux ME y compris les multiférroiques
In the search for magnetoelectric (ME) materials with enhanced ME performances, in the present thesis we investigate some fundamental mechanisms leading to an enhanced magnetoelastic coupling in artificial ME composites. We focus on 0-3 particulate composites made of a magnetostrictive (MS) phase CFO embedded in the following ferroelectric (FE) matrices: Pb-based PZT, PMNPT and alternative lead-free KNN and BTO. We demonstrate that the laser heated pedestal growth (LHPG) technique can be successfully used to grow high-quality bulk samples exhibiting a pronounced textured microstructure between the FE and MS phases. Scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD) were used to characterise systematically grain orientation, grain size and quality of the interface between the FE and MS phases. A systematic study by means of Raman spectroscopy, magnetisation M(T,H) and field-dependent specific heat C(T,H) measurements enabled us to probe directly the magnetoelastic coupling in the ME samples. The combined analysis of the above structural and thermodynamic data consistently shows that the pronounced textured structure of the LHPG samples leads to an impressive enhancement of the magnetoelastic response. We argue that this result is very promising for ME material design. We finally propose that the above specific heat study offers a contactless probe to investigate the intrinsic spin-lattice coupling in a wide range of ME materials including multiferroics

Abstract Thermodynamics is based on impossible processes (adiabatic, reversible, isothermal) and nonexistent entities (perfect insulation, ideal gases) but must pass tests of consistency and agreement with experiment. ∂U/∂T defines a heat capacity C at constant volume or pressure per unit mass, volume, or mole number. C requires an equation of state U(p,V), either from microscopic theory or macroscopic measurements. A reversible adiabatic process (Q = 0) undergone by an ideal gas yields the Poisson relations between any two variables, for example, pressure and volume. pV is constant in isothermal processes, pVγ is constant in adiabatic processes, where γ=cp/cv. H=U+pV appears so often that it has acquired a name: enthalpy. Once called “heats” (of combustion, vaporization, etc.) are now more often called enthalpies. The stability of a fluid in a gravitational field g is determined by buoyancy. The boundary between atmospheric stability and instability is the dry, adiabatic lapse rate of temperature g/cp; “dry” means no change of phase

Abstract Human’s motion and its mechanisms had become interesting in the last years, where the medecine’s field search for rehabilitation methods for handicapped persons. Other fields, like sport sciences, professional or military world, search to distinguish profiles and ways to train them with specific purposes. Besides, recent findings in neuroscience try to describe these mechanisms from an organic point of view. Until now, different researchs had given a model about control motor that describes how the union between the senses’s information allows adaptable movements. One of this sense is the proprioception, the sense which has a quite big factor in the orientation and position of the body, its members and joints. For this reason, research for new strategies to explore proprioception and improve the theories of human motion could be done by three different vias. At first, the sense is analysed in a case-study where three groups of persons are compared in a controlled enviroment with three experimental tasks. The subjects belong to each group by the kind of sport they do: sedentary, normal sportsmen (e.g. athletics, swimming) and martial sportmen (e.g. karate, judo). They are compared thinking about the following hypothesis: “Martial Sportmen have a better proprioception than of the other groups’s subjects: It could be due to the type of exercises they do in their sports as empirically, a contact sportsman shows significantly superior motor skills to the members of the other two groups. The second via are records from encephalogram (EEG) while the experimental tasks are doing. These records are analised a posteriori with a set of processing algorithms to extract characteristics about brain’s activity of the proprioception and motion control. Finally , the study tries to integrate graphic tools to make easy to understand final scientific results which allow us to explore the brain activity of the subjects through easy interfaces (e.g. space-time events, activity intensity, connectivity, specific neural netwoks or anormal activity). In the future, this application could be a complement to assist doctors, researchers, sports center specialists and anyone who must improve the health and movements of handicapped persons. Keywords: proprioception, EEG, assesment, rehabilitation.References: Röijezon, U., Clark, N.C., Treleaven, J. (2015). Proprioception in musculoskeletal rehabilitation. Part 1: Basic science and principles of assessment and clinical interventions. ManualTher.10.1016/j.math.2015.01.008. Röijezon, U., Clark, N.C., Treleaven, J. (2015). Proprioception in musculoskeletal rehabilitation. Part 2: Clinical assessment and intervention. Manual Ther.10.1016/j.math.2015.01.009. 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Pipelines from remote frontier regions are increasingly required to have adequate resistance to large deformations such as that caused by ground movement. In response to this, �strain-based design"� has been developed to enable assessment of imperfections at applied strains beyond yield. In addition, it is proposed to take advantage of the increased apparent toughness of pipe under low constraint, such as girth weld imperfections under axial tension, compared with the high-constraint toughness measured in conventional tests such as ASTM E1290 [1]. Application of low-constraint testing has been dvantageously applied in assessment of toughness for offshore pipeline projects. Also in the pipeline industry, demands on new pipeline projects include low design temperatures as well as high strain capacity. At the same time, increased strength is specified, which increases the level of required toughness. These factors make it increasingly important to assure weldment toughness, in particular to ensure that the failure mode remains ductile. It is well known that brittle cleavage is especially sensitive to constraint, and the availability of a toughness test that would reproduce field conditions would enable more rational development and acceptance of candidate welds and, in particular, enable more appropriate testing of weld heat-affected zones. This work was performed for specific application to surface circumferential cracks in pipe under strain-based design, for which the best constraint matching has been found to occur for clamped single-edge tension (SE(T)) specimens with H/W=10. For this geometry, a test procedure similar to that of ASTM E1820-06 for single-edge bend (SE(B)) and compact tension (C(T)) specimens was developed for J-resistance tests using a single-specimen technique. All the equations used in the procedure, including those for evaluation of J-integrals from the area under load/plastic crack mouth opening displacement (CMOD) curves, and evaluation of crack length from unloading compliance including rotation correction, were developed using finite element analysis (FEA) with a range of crack depths, focusing on a/W= 0.2 to 0.5 which is of most practical interest. The present procedure is compared with that of E1820 for SE(B) testing regarding evaluation of J-integral with crack growth correction, crack length evaluation, and correction of compliance for rotation.