Geometrical frustration in the face-centered-cubic (fcc) lattice presents a fundamental challenge in determining antiferromagnetic order, as the ground state is highly sensitive to subtle differences in competing magnetic interactions and structural symmetry. Here, we explore the magnetostructural interplay in two halide double perovskites, Cs2NaFeCl6 and Cs2AgFeCl6. Although both materials have a cubic structure at room temperature, neutron diffraction shows that they adopt different antiferromagnetic structures upon cooling. Cs2NaFeCl6 experiences a transition to an AFM-III order below 2.6 K, governed by J 1 and J 2 (first and second nearest-neighbor) magnetic exchange interactions. Cs2AgFeCl6, however, adopts an AFM-I order below 17 K, accompanied by a significant tetragonal distortion confirmed from both neutron diffraction and polarized Raman spectroscopy. Thermal expansion measurements reveal anomalous lattice expansion at the magnetic transitions in both compounds but are substantially stronger in Cs2AgFeCl6. Combining these findings with density functional theory (DFT) studies, we conclude that the strength of magnetoelastic coupling dictates the magnetic ground state. A strong J 1 in Cs2AgFeCl6 induces a large tetragonal lattice distortion, relieving magnetic frustration and stabilizing the AFM-I phase. In contrast, weaker magnetoelastic coupling in Cs2NaFeCl6 causes minimal distortion, favoring the AFM-III phase via the J 1-J 2 mechanism. Our findings show that magnetic interactions can be a primary driving force for structural phase transitions in these materials, while the strong structural distortion could determine the selection of magnetic ground-state ordering.

Magnetic field-driven bionanomanipulation continues to be a challenging task because the force applied by current magnetic nanoparticles and nanoactuators is effectively limited to femto and pico Newtons at the proper field and gradient scales. Therefore, of particular interest is search for the new functional materials and new effects that provide a breakthrough opportunity for the influence of a remotely controlled magnetic field on a nano and micro Newton scale on living biological objects, such as bacteria, viruses, individual cells, etc. This work includes deep study of the structure, physical and multifunctional properties of a new family of Heusler Ni-Mn-In-V alloys demonstrating the magnetic shape memory effect responsible for actuation, shape change and the production of mechanical work on objects such as viruses and bacteria in a constant temperature environment. The possibilities of capturing, storing, processing of bionanoobjects are discussed.

The hysteresis that usually accompanies the first-order phase transition and its kinetics causes efficiency losses in any cyclical refrigeration processes. Establishing the correlation between time and hysteresis could provide insight into this issue. This study presents experimental results on the evolution of magneto-induced structures under different thermodynamic conditions and cycling in a magnetic field, and the subsequent effect on the magnetocaloric effect for the Ni2Mn0.74Cu0.26Ga Heusler alloy. The study reveals the impact of the evolution of the magneto-induced structural subsystem on the irreversibility of the magnetocaloric effect near the first-order magnetostructural transition. The presence of residual martensite, formed during the initial magnetization of the sample, is identified as the cause of the irreversibility of the magnetocaloric effect. The results demonstrate the difference in the course of the martensitic transition in adiabatic and isothermal conditions. It also highlights the dependence of the nucleation of the martensitic phase and the movement of the boundaries of the new phase on the magnetic field sweep rate.

The influence of as-cast and multiaxial isothermal forged structures on the sensitivity of martensite to the magnetic field and on the magnetocaloric effect in Ni-Mn-Ga-Si alloy has been studied. In the multiaxial isothermal forged state, a "necklace" structure is observed where large grains of 100-200 mu m are encompassed by a layer of fine-grained structure. In this state, the martensitic transformation occurs with a shift towards the lowtemperature region of about 10 K. Characteristic points of the martensitic transformation are evaluated in a magnetic field up to 12 T, revealing a sensitivity value of 0.6 K/T for both as-cast and multiaxial isothermal forged samples. Furthermore, an inverse magnetocaloric effect is identified within the martensitic transformation region for both as-cast and multiaxial isothermal forged samples under weak magnetic fields, up to 0.2 T. This inverse effect disappears at a magnetic field of 1.8 T, leaving only the direct magnetocaloric effect observable. These findings shed light on the intriguing interplay between microstructure, magnetic sensitivity, and magnetocaloric behavior in this Ni-Mn-Ga-Si alloy, offering valuable insights for potential applications in magnetic cooling technologies.

State of research in the study of magnetocaloric materials based on rare-earth metals that are promising for application in the technology of low-temperature magnetic cooling is reviewed. Physical principles and characteristics of the magnetocaloric effect in materials based on rare-earth metals with low-temperature magnetic phase transitions are presented.

Both temperature (T ) increase and/or application of an external magnetic field (H) are able to induce ferromagnetism in otherwise antiferromagnetic FeRh. We present a theory that allows us to predict H -T phase diagrams for FeRh, with a special emphasis on the canted antiferromagnetic phase. Both cases of in-plane and out-of-plane magnetic anisotropy in FeRh films are studied numerically, and the results of the simulations are compared with the results obtained via magneto-transport studies done in magnetic fields up to 34 T and x-ray magnetic circular dichroism measured at the Rh L2,3 and Fe K absorption edges in magnetic fields up to 17 T. The comparisons suggest examples of the simulated H -T phase diagrams that are most suitable to fit the case of FeRh.

In this study, we investigate the entropy change of magnetostructural transformation and associated magnetocaloric properties in a Ni50Mn18.5Ga25Cu6.5 Heusler alloy. In this alloy, the structural and magnetic components (i.e., lattice vibration and magnetic entropy changes) synergistically contribute to total entropy change during the magnetostructural transformation. The unique synergistic feature of the alloy results in a large phase transformation entropy change of -1.05 J/molK, in which the structural component accounts for -63% and the magnetic component primarily contributes the remaining -37%. Within the framework of a Landau model, simulative magnetocaloric entropy change increases with magnetic field due to the synergistic feature of the structural and magnetic components. In addition, an adiabatic temperature change up to +6.5 K is obtained in the Ni50Mn18.5Ga25Cu6.5 alloy under a magnetic field of 8 T.

The work is devoted to the study of the phenomenon of irreversibility of the magnetocaloric effect (MCE) in the vicinity of the magnetostructural phase transition (PT) in Ni-Mn-Ga Heusler alloys. For this purpose, the MCE was studied by the direct method in stationary (up to 14 T) and pulsed magnetic fields (up to 50 T), and a magnetic phase diagram was constructed. Using a specially designed microscope, in-situ studies of the magnetostructural phase transition were carried out in magnetic fields of up to 14 T. Comparing the results of the MCE with those of the phase diagram, as well as in-situ studies, made it possible to determine the width of the irreversible MCE region. In-situ studies have shown, that the main reason of the occurrence of the irreversible MCE is the presence of the residual martensite formed as a result of the first magnetization of the sample. The results are discussed within the framework of Landau's phenomenological PT theory, which predicts the disappearance of thermal hysteresis under a field of 30 T. Within the framework of the same theory, a recommendation is made to reduce the value of the critical field and, as a result, the width of the hysteresis.(c) 2022 Elsevier B.V. All rights reserved.

The Heusler alloys demonstrate magnetically induced strain and magnetocaloric properties, but the mechanical properties are poor. Therefore, in this work, the influence of thermomechanical treatment on the properties of Ni-Mn-Ga-Si Heusler alloys is considered. The effect of multi-axial isothermal forging on functional properties of the Ni2.30Mn0.73Ga0.90Si0.07 alloy at 973 K and true strain (e) of 3.9 is presented. It is shown that a unique two-phase microstructure is formed as a result of forging. The large grains in the size range of 100–200 µm are surrounded by a fine-grained structure. The study of the thermomechanical properties by the three-point bend test has shown that the alloy demonstrates a single-stage reversible deformation of 3.1% at a constant stress of 860 MPa as compared to the same alloy in the as-cast condition which shows 2% at 380 MPa. The specimen demonstrates a reversible deformation of 5% without any degradation during thermal cycling (with a base of up to 4000 thermal cycles) under a stress of 550 MPa and up to 5% with degradation occurring at 700 thermal cycles under a stress of 650 MPa. Thus, forging makes it possible to obtain a material with higher operational properties and greater resistance to fracture during multiple cycles of martensitic transformation. In this case, it is possible to obtain anisotropy of properties equal or close to that of the specimen in the as-cast state.

Study and implementation of innovative systems of environmentally friendly and energy-efficient transport based on magnetic levitation, the principle of operation of which is based on the use of new solid-state magnetic materials based on compounds of rare earth materials, in particular materials with high-temperature superconductivity based on Y, permanent magnets based on Nd and Sm and magnetocaloric alloys based on Dy, Tb are of great interest throughout the world. In this work, the basic principles of magneto-levitation transport with the most economical principle of acceleration and deceleration - gravitational - are studied experimentally on mock-ups. The strength characteristics were measured: the levitation force and the lateral stabilization force, as well as losses during periodic translational motion of a cryostat with high-temperature superconducting elements made of ceramic material Y-Ba-Cu-O over the paths of permanent magnets made of the rare-earth compound Nd-Fe-B. A system for measuring the speed and compensation of losses for the implementation of continuous motion has been created and tested. The presented results indicate the possibility of scaling the layout project. It is concluded that the investigated scheme may be of practical interest for intracity and local transport communication with high comfort, environmental friendliness and record economy in the case of a successful solution of the problem of cooling HTSC elements to the temperature of the phase transition to the superconducting state, for example, using new principles of solid-state magnetic cooling based on compounds Dy-N, Tb-Ni, etc.

В работе представлены результаты исследований микро- и наноструктуры поверхности быстрозакаленных лент сплавов Гейслера (NiMnAl,NiMn AlSi, NiCoMn Al) методами сканирующей электронной и атомно-силовой микроскопии. Рассмотрено влияние химического состава на размер, геометрию границ и структуру зерен. Показано, что все исследуемые образцы обладают наноразмерным мартенситным рельефом, определены его параметры. Установлено, что поперечное сечение лент представлено кристаллическими зернами разной формы и размера, что обусловлено отличием скоростей охлаждения по краям и в центре ленты. Проведено элементное картирование поверхности поперечного сечения лент с помощью рентгеновского энергодисперсионного спектрометра, установлено равномерное распределение химических элементов в образцах. Показано, что легирование лент состава NiMnAl кобальтом вызывает изменение микроморфологии поверхности и оказывает значительное влияние на ход полевых зависимостей намагниченности и доменную структуру образцов. The paper describes the results of the scanning electronic and atomic force microscopy research of the surface structure of the NiMn Al, NiMn AlSi, NiCoMnAl rapidly quenched ribbons. The influence of the chemical composition on the size, boundary geometry and structure of the grains is considered. It is shown that all the test samples have a nano-sized martensitic relief, and its parameters are determined. It has been established that the cross section of the ribbon is represented by crystalline grains of different shapes which are due to differences in the cooling rates along the edges and in the center of the samples. Elemental mapping of the cross-sectional surface of the ribbons was carried out using an X-ray energy dispersive spectrometer, and a uniform distribution of chemical elements in the samples was established. It is shown that the cobalt doping of NiMn Al ribbon causes changes in the micromorphology of the surface and has a significant effect on the magnetic properties of rapidly quenched ribbons: field dependences of themagnetization and domain structure.

Systematic studies of magnetic entropy change ΔSm and adiabatic temperature change ΔTad have been performed for ferromagnetic shape memory alloys Ni2 + xMn1−xGa (0.18 ≤ x ≤ 0.27) undergoing coupled magnetostructural phase transition from ferromagnetic martensite ↔ paramagnetic austenite. The magnetic entropy change calculated from isothermal magnetization measurements has the highest value (for the magnetic field change of ΔH = 5 T), ΔSm = −29 J/kg K, in a Ni2.20Mn0.80Ga composition. The decrease in ΔSm observed in the alloys with the larger Ni excess (0.22 ≤ x ≤ 0.27) is attributed to the progressive reduction in both the saturation magnetization and the total entropy change at the martensitic transition temperature. The adiabatic temperature change ΔTad measured upon heating in the Ni2 + xMn1−xGa (0.18 ≤ x ≤ 0.27) alloys does not exceed 0.8 K (for the magnetic field change of ΔH = 1.85 T). A higher value of ΔTad measured upon cooling has been explained as caused by the contribution of the structural subsystem to ΔTad, i.e., to a partial magnetic field-induced structural transformation that has, for the given magnetic field change, an irreversible character in the alloys studied.

The results of in situ studies of the magnetostructural transition occurring in single crystals of an Ni2.19Mn0.81Ga Heusler alloy are presented in this paper. The formation of martensitic twins on exposure to high magnetic fields up to 10T in the magnetostructural transition regime was observed using an indigenously developed optical microscope. Experiments on magnetization were performed on single crystals of Ni2.19Mn0.81Ga in high magnetic fields, a phase diagram between magnetic field and temperature was constructed, and the isothermal entropy change was estimated. Based on the experimental data and the results from optical microscopic examination, the influence of magnetic field and thermal cycling on martensitic twins and, in turn, on the magnetocaloric effect, is discussed.

Ni43Mn37.8In12.2Co7 and Ni43Mn37.65In12.35Co7 polycrystalline alloys were tested mechanically in uniaxial compression in order to determine the stress–strain response and accompanying changes of electrical resistivity. Compression of the specimen by 9% at room temperature resulted in a 250% increase of resistivity followed by almost full recovery to its predeformation level upon heating to 400 K. Microstructural observations revealed that giant reversible changes of electrical resistivity occurred due to stress-induced martensitic transformation and shape recovery of plastically deformed grains induced by heating.

The magnetocaloric effect (MCE) in single crystals of MnAs compound was studied both experimentally and theoretically. Direct measurement of MCE showed that the adiabatic temperature change (Delta T-ad) in a magnetic field of 10 T was 15 K. But direct measurement of the quasi-adiabatic heat transfer (Delta Q) of the sample yielded a value of 9500 J/kg in a magnetic field of 10 T. To date, it is the highest experimentally recorded value for Delta Q by direct measurement. Phenomenological considerations that take into account the interaction of magnetic and structural order parameters explain a number of anomalies in the magnetic and magnetocaloric properties of MnAs that were observed during the experiments. (C) 2019 Elsevier B.V. All rights reserved.

The paper presents results of study of the dependence of the Ni-Mn-In film’s composition on the annealing parameters, data of scanning electron microscopy and energy dispersive analysis (EDX spectroscopy). The Influence of annealing of a film in vacuum on the chemical composition is shown. The content of manganese and indium decreases sharply with a rise in temperature up to 900 °C, and in a heating time up to 2 hours. The ferromagnetic Curie point in the investigated Ni-Mn-In films is observed. A decrease of the width of the ferromagnet-paramagnet transition results in the improvement of the crystallinity of the sample after annealing.

Recently the new scheme of layered composite with shape memory effect (SME) for thermal and magnetic actuation was suggested and proved to demonstrate the reversible actuation on micro- and nanoscale. The principles of magnetic field induced martensitic transition (MFIMT) and magnetic field controlled shape memory effect (MFCSME) have the advantages of magnetic-field-controlled actuation at constant temperature, extremely small size of an actuator and compatibility with modern nanotechnologies. The present paper is devoted to experimental study of MFCSME in two ferromagnetic Heusler alloys Ni54Mn21Ga25 and Ni50Mn41.2In8.8 with positive and negative shift of the martensitic transition temperature in a magnetic field. The three points bending device for dilatometric tests of plate-like samples of the alloys was designed and placed in the field of Bitter coil magnet. The bending deformations versus temperature were measured at various magnetic fields up to 10 T and at mechanical stresses up to 45 MPa. The temperature shifts of thermoelastic martensitic phase transition were found to be 0.55 K/T and -0.95 K/T for Ni54Mn21Ga25 and Ni50Mn41.2 In-8.(8) respectively. For direct MFCSME study the dependences of the bending deformation on magnetic fields up to 14 T were also obtained at constant temperatures for these alloys. Practically complete recoverable deformation of 0.2% due to MFIMT was obtained at 14 T in Ni54Mn21Ga25 alloy in temperature range 316-318 K and stress 8.6 MPa. The new variant of the layered functional composite actuator scheme based on the alloys with MFCSME is suggested. The proposed functional composite combines the layers of the alloys with positive and negative temperature shifts of martensitic transition temperature in magnetic field. It is argued that this combination of the alloys can improve the performance of the composite actuators driven by MFCSME, particularly, it can provide higher generated force, actuation stroke, sensitivity to magnetic field and frequency of actuation.

The ingot of Fe40.71Ni27.33Co17.13Al12.05Ta2.73B0.05 alloy was produced by arc melting technique followed by heat treatment. The alloy ingot was cut by electro-discharge machining and was further subjected to rolling. The microstructure of surface, thermomechanical and magnetic properties were studied. The alloy exhibits superelasticity at temperature lower than 330 K. The hysteretic behavior of magnetization was observed. These properties can be explained by combination of states of the spin- and strain-glasses.