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Vol 124, No 11 (2023)
ЭЛЕКТРИЧЕСКИЕ И МАГНИТНЫЕ СВОЙСТВА
Modern Magnetocaloric Materials: Existing Problems and Research Prospects
Abstract
Abstract—
A brief review of works related to a new and promising direction – magnetic cooling technology based on the magnetocaloric effect (MCE) is presented. The essence of the effect and the main publications related to this area are briefly considered. The materials in which the MCE is observed are reported and the corresponding diagrams of the main publications on the MCE for the last 5 years are presented. The latest results of research by Russian scientists working in this field are presented.
1019-1024
Advanced Non-Contact Optical Methods for Magnetocaloric Effect Measuring
Abstract
Abstract—
A big problem in magnetic and, in particular, magnetocaloric studies is the accurate measurement of the temperature of materials, especially in high pulsed and alternating magnetic fields. The disadvantages of the used contact temperature sensors (microthermocouples and film thermistors) are: (1) the influence of electromagnetic interference on their readings, proportional to the time derivative of the magnetic field, (2) their relatively long response time due to thermal inertia, (3) the impossibility of accurate measurement temperatures of thin and microstructured samples. The described difficulties can be avoided by using contactless optical methods for measuring the temperature of magnetic materials in high magnetic fields. This review describes advanced non-contact optical methods for measuring the magnetocaloric effect using known materials as an example, and provides a comparative analysis of the main characteristics of these methods, such as: maximum magnetic field, sampling frequency, time constant and spectral range of the detector, error and temperature resolution.
1025-1043
Baric Transformation of the Nature of Magnetic Ordering and Magnetocaloric Properties in the Mn1 – xCrxNiGe System
Abstract
Abstract—
The isobaric temperature dependences of the magnetization and the magnetocaloric characteristics of alloys of the Mn1 – xCrxNiGe system are studied in a constant magnetic field up to 10 kOe in the range of hydrostatic pressures up to 12 kbar. It has been established that, with increasing pressure, the implementation of helimagnetic ordering undergoes qualitative changes from smooth hysteresis-free 2nd order phase transition to 1st order phase transitions, accompanied by the appearance of a temperature hysteresis and an increase in the magnetocaloric effect. Based on the exchange-structural model, an explanation is given for the mechanism of baric transformation of magnetic and magnetocaloric properties.
1044-1050
Magnetization and Magnetostriction of LaFe11.2 – хMnxCo0.7Si1.1 (x = 0.1, 0.2, 0.3) Alloys In Pulsed Magnetic Fields
Abstract
Abstract—
The magnetization and magnetostriction of polycrystalline alloys LaFe11.2 – хMnxCo0.7Si1.1 (x = = 0.1, 0.2, 0.3) were measured in pulsed magnetic fields up to 180 kOe in the temperature range 80–270 K. The replacement of Fe atoms by Mn atoms shifts the TC towards low temperatures and does not affect the value of saturation magnetization. The observed field dependence of the magnetization M(H) near the TC is characteristic of second-order phase transitions, while the temperature dependence of the magnetization M(T) above the TC in strong magnetic fields indicates a first-order magnetic phase transition. The magnetic volume effect ΔV/V reaches 0.81% in a field of 180 kOe. The asymmetry of magnetostriction relative to the temperature of the maximum effect, manifested in strong magnetic fields, and the magnetic field hysteresis of magnetostriction bear signs of a first-order phase transition
1051-1057
Thermal Contact Resistance of the Copper–Copper Pair with Graphene Thermal Interface in Magnetic Fields up to 10 T
Abstract
Abstract—
The thermal contact resistance of a detachable connection in copper-copper contact pair with a thermal interface from layers of graphene synthesized by the method of a low pressure chemical vapor deposi-tion on the contact surface was studied. Obtaining the value of the thermal contact resistance of a detachable contact pair copper–graphene–copper by the method of transient heat flow, at a temperature of 15–150 K under the influence of an external magnetic field up to 10 T.
1058-1064
Magnetocalorical Effect and Phase Separation: Theory and Perspectives
Abstract
Abstract—
The problem of the magnetic phase separation effect on the magnitude of the magnetocaloric effect is considered. A general thermodynamic generalized Landau theory with a variable particle number is proposed, which allows simple and consistent treatment of the first order phase transition between the magnetically ordered and disordered phases, taking into account the phase separation. The calculation of the magnetic susceptibility and entropy of phases involved in the phase separation was considered. It is shown that the magnetic susceptibility of the magnetically ordered (disordered) phase participating in the phase separation is negative (positive) in the vicinity of the tricritic point, which can result in the inversion of the sign of the magnetocaloric effect.
1065-1073
The Magnetocaloric Effect in La(Fe,Mn,Si)13Hx Based Composites: Experiment and Theory
Abstract
Abstract—
Samples of composites with different porosity and surface roughness based on LaFe11.4Mn0.3Si1.3H1.6 (LFMSH) alloy powders were obtained, their magnetocaloric properties were studied by a direct method in cyclic magnetic fields μ0H = 1.2 T at a frequency of 2 Hz. The maximum value of the adiabatic temperature change in pure LFMSH powder was ΔT = 3 K at Т0 = 287 K in the sample cooling mode; for composite samples, this value turned out to be approximately 2 times lower than in the powder. The effect of Mn and H atoms on the electronic structure and local magnetic characteristics of the initial La(Fe,Si)13 alloy has been studied by the methods of the electron density functional theory. Replacing some of the Fe atoms with Mn reduces the total magnetic moment and slightly lowers the Curie temperature. Hydrogenation, on the contrary, leads to an increase in exchange interactions between Fe atoms located at the vertices of the icosahedron and an increase in the Curie temperature.
1074-1085
Magnitocaloric Effect in RCO5 (R = Gd, Tb, Dy, Ho) Alloys
Abstract
Abstract—
Experimental studies of magnetic and magnetocaloric properties of polycrystalline RCo5 alloys (R = Gd, Tb, Dy, Ho) in external magnetic fields up to 3 Tesla have been carried out. The results of magnetic measurements have shown that these compounds have small coercivity and reach saturation in small fields. It was found that the magnetocaloric effect in the studied co-compounds is observed in a wide temperature range, and for the intermetallides TbCo5, DyCo5, HoCo5 has several regions of existence, comparable in magnitude of the effect. The presence of several MCE existence intervals is caused by a series of magnetic phase transitions in these ferrimagnetic compounds.
1086-1092
Magnetocaloric Effect in Rare-Earth Magnetic Materials
Abstract
Abstract—
A study of the magnetocaloric characteristics of rare-earth magnets was carried out. There were studied a systems Gd–H, (Gd,R)Ni–H containing hydrogen (R is a rare earth metal); system RCo2–H with the structure of Laves phases; and systems without hydrogen, such as RTX intermetalic compounds (T = Mn, Fe, Co; X = Si), R2(Fe,T)17 compounds (T = Al), which have a magnetic compensation point and exhibit an alternating magnetocaloric effect (MCE). The MCE was measured by the direct method and calculated indirectly from the field dependences of the magnetization. The main regularities are established and the specific features of the formation of magnetocaloric properties are revealed depending on the composition and structure.
1093-1101
Electronic Structure and Magnetic Properties of FeRhSn1 – xZx (Z = Ge, Si, Sb): Ab Initio Study
Abstract
Abstract—
Magnetic properties and electronic structure of FeRhSn1 – xZx alloys (x = 0, 0.25, 0.5, 0.75, 1) have been investigated by first-principles methods using the VASP software package. It is shown that for all alloys the γ phase is energetically favorable, except for the FeRhSi alloy, for which the β phase is equilibrium. It is shown that the addition of a fourth element to a three-component alloy leads to a change in the position of the valence zone and conduction zone relative to the Fermi level, which makes it possible to obtain new four-component alloys possessing one hundred percent spin polarization. It is shown that FeRhSn1 – xGex (x = 0, 0.25, 0.5, 0.75, 1), FeRhSn1 – xSix (x = 0, 0.25, 0.5, 0.75) and FeRhSn1 – xSbx (x = 0, 0.25) alloys are half-metallic ferromagnets.
1102-1107
Effect of Ga Partial Substitution on the Structural and Magnetic Properties of Heusler Ni–Mn–Ga Alloys
Abstract
Abstract—
The effect of doping with Cu and Zn atoms on the magnetic and structural properties of the cubic and tetragonal phase of the Heusler Ni2Mn1.125Ga0.875 alloy has been investigated in the framework of density functional theory. Partial substitution of Ga atoms by Cu and Zn atoms leads to a decrease in the energy difference between the ferromagnetic and ferrimagnetic states of the cubic phase and an increase in the energy barrier between the cubic and tetragonal phase. The latter observation indirectly points to the increase in the structural transition temperature observed experimentally. Within the framework of calculations of exchange interaction parameters from first principles and Monte Carlo modeling of temperature dependences of magnetization, a phase T–x diagram is constructed. It is shown that the Curie temperature of the tetragonal phase decreases significantly compared to the Curie temperature of the cubic phase with increasing Cu and Zn content due to an increase in the inter-sublattice antiferromagnetic interaction between Mn atoms.
1108-1116
Magnetostriction and Magnetocaloric Properties of the Mn1 – xFexAs System
Abstract
Abstract—
The results of studying the temperature dependence of the magnetocaloric effect (ΔТad), thermal expansion and magnetostriction in the Mn1 – хFexAs (х = 0.003, 0.006) system in magnetic fields up to 8 T are presented. It is shown that an increase in the iron concentration in the Mn1 – xFexAs system leads to a shift in the phase transition temperature towards low temperatures by 15 K. In a field of 8 T, the value ΔTad = 8.3 K for the Mn0.997Fe0.003As sample at the initial temperature T0 = 318 K, and ΔTad = 7.7 K for Mn0.994Fe0.006As at T0 = 307 K. The data on thermal expansion and magnetostriction show that the magnetostriction decreases with increasing iron concentration, which also leads to a decrease in the magnetocaloric effect.
1117-1121
Magnetocaloric Effect of Mn2YSn (Y = Sc, Ti, V) Alloys
Abstract
Abstract—
In this paper, the structural, magnetic, and thermodynamic properties of Mn2YSn (Y = Sc, Ti, and V) alloys are considered depending on the applied pressure using the density functional theory and the Monte Carlo method. It is shown that for each compound there are two magnetic states with a low and a high magnetic moment at a smaller and larger unit cell volume, separated by an energy barrier. The barrier value depends on the applied external pressure. The two phases become almost equal in energy at critical pressures of 3.4, –2.9, and –3.25 GPa for Mn2ScSn, Mn2TiSn, and Mn2VSn, respectively. The temperature behavior of the magnetization and magnetocaloric characteristics for the studied phases at various pressures is obtained. Accounting for pressure leads to an understanding of the mechanism of the increase in the magnetocaloric effect in the phase with a high magnetic moment. The greatest effect (ΔSmag ≈ 0.158 J/mol K and ΔTad ≈ 1.1 K) is predicted for Mn2TiSn at a pressure of –2.9 GPa and a change in the magnetic field from 0 to 2 T.
1122-1128
СТРУКТУРА, ФАЗОВЫЕ ПРЕВРАЩЕНИЯ И ДИФФУЗИЯ
Influence of Si on the Structure and Martensitic Transformation in Deformed Ni–Mn–Ga Alloys
Abstract
Abstract—
The studying the effect of multiaxial isothermal forging on the microstructure and martensitic transformation in the Ni58Mn18Ga24 alloy is presented. Forging was carried out in two stages: stage 1 − forging at 700°C (4 passes, true degree of deformation e ≈ 1.64), stage 2 − forging at 500°C (1 pass, e ≈ 0.24). Forging led to the transformation of the original equiaxed grain structure. As a result of the 1st stage of processing, no new grains are formed. The new recrystallized grains are observed only after the 2nd stage of deformation, the proportion of which is very small. Apparently, the mechanism of fragmentation of the grain structure at the first stage is not triggered due to insufficient defect density at a deformation of 700°C. The characteristic temperatures of martensitic transformation are shifted to the low temperature region. The anharmonic change in the sample length is observed in the region of martensitic transformation for the both treated states. In general, this indicates a low level of defect density and internal stresses in the sample.
1129-1136
Phase Stability of Ni–(Co)–Mn–Z (Z = Ga, In, Sb, Sn) Heusler Alloys
Abstract
Abstract—
This work is devoted to the first-principle studies of phase stability and segregation stability of austenitic and martensitic phases of Heusler alloys Ni2 – xCoxMn1 + yZ1 – y (x = 0, 0.25, 0.5 and y = 0, 0.25, 0.5, 0.75; Z = Ga, In, Sb, Sn) with different types of magnetic ordering. Among all the considered compounds, only alloys Ni1.5Co0.5MnGa and Ni2MnGa in cubic and tetragonal structures with ferromagnetic ordering, respectively, as well as Ni2Mn2 in tetragonal structure with staggered and layer-by-layer antiferromagnetic ordering demonstrate stability. For these compositions, the presence of zero convex hull energy and the absence of reactions with positive decomposition energy are shown. The remaining compounds appear to be metastable both due to the presence of stable reactions with negative decomposition energy and decay reactions with positive decomposition energy. The number of decay reactions increases with increasing chemical disorder, i.e., deviation from stoichiometry.
1137-1144