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Reactive single-step hot-pressing at 1473 K and 35 MPa for 4 h produces dense, bulk, near single-phase, low-cost and low-criticality Fe$_2$Al$_{1.15}$B$_2$ and Fe$_2$Al$_{1.1}$B$_2$Ge$_{0.05}$Ga$_{0.05}$ MAB samples, showing a second-order magnetic phase transition with favorable magnetocaloric properties around room temperature. The magnetic as well as magnetocaloric properties can be tailored upon Ge and Ga doping, leading to an increase of Curie temperature $T_C$ and spontaneous magnetization $m_S$. The maximum isothermal entropy change $\Delta s_{T,max}$ of hot-pressed Fe$_2$Al$_{1.15}$B$_2$ in magnetic field changes of 2 and 5 T amounts to 2.5 and 5 J(kgK)$^{-1}$ at 287.5 K and increases by Ge and Ga addition to 3.1 and 6.2 J(kgK)$^{-1}$ at 306.5 K, respectively. The directly measured maximum adiabatic temperature change $\Delta T_{ad,max}$ is improved by the composition modification from 0.9 to 1.1 K in magnetic field changes of 1.93 T. Overall, we demonstrate that hot-pressing provides a much faster, more scalable and processing cost reducing alternative compared to conventional synthesis routes to produce heat exchangers for magnetic cooling devices. Therefore, our criticality assessment shows that hot-pressed Fe-based MAB phases provide a promising compromise of material and processing cost, criticality and magnetocaloric performance, demonstrating the potential for low-cost and low-criticality magnetocaloric applications around room temperature.

International audience; Anisotropy constants are obtained from an analysis of single crystal magnetization curves measured up to high fields. The anisotropy of the 3d transition metal (M) sublattice is considered, as well as molecular exchange field coupling between the rare-earth (R) and transition metal sublattices (M). This procedure allows for non colinear R and M magnetic moments, meaning that their angles with respect to the easy axis are independent variables. With this approach we obtain anisotropy constants that are larger than those reported in the literature, which reflects the anisotropy of the isolated R sublattice. Results for Co and/or Ce doped Nd2Fe14B single crystals are presented, showing the influence of such substitutions on the magnetocrystalline anisotropy. These results indicate that the enhanced performance of NdFeB-based magnets co-doped with Ce and Co is due to an improvement in intrinsic properties.

Novel multicaloric cooling utilizing the giant caloric response of Ni-Mn-based metamagnetic shape-memory alloys to different external stimuli such as magnetic field, uniaxial load and hydrostatic pressure is a promising candidate for energy-efficient and environmentally-friendly refrigeration. However, the role of microstructure when several external fields are applied simultaneously or sequentially has been scarcely discussed in literature. Here, we synthesized ternary Ni-Mn-In alloys by suction casting and analyzed the microstructural influence on the response to magnetic fields and uniaxial load. SEM-EBSD reveals a distinct core-shell microstructure with a radially symmetric solidification texture resulting in a two-step martensitic transformation. In correlation with temperature-dependent XRD a significant effect of grain orientation on the stress-induced martensitic transformation is demonstrated. The influence of microstructure on the magnetic-field-induced transformation dynamics is studied by strain measurements in static and pulsed fields. Temperature-stress and temperature-magnetic field phase diagrams are established and single caloric performances are characterized in terms of ${\Delta}s_{T}$ and ${\Delta}T_{ad}$. The cyclic ${\Delta}T_{ad}$ values are compared to the ones achieved in the multicaloric exploiting-hysteresis cycle. It turns out that a tailored microstructure and the combination of both stimuli enable outstanding caloric effects in moderate external fields which can significantly exceed the single caloric performances. In particular for Ni-Mn-In, the maximum cyclic effect in magnetic fields of 1.9 T is increased by more than 200 % to -4.1 K when a moderate sequential stress of 59 MPa is applied. Our results illustrate the crucial role of microstructure for multicaloric cooling using Ni-Mn-based metamagnetic shape-memory alloys.

International audience; Nd2Fe14B-type materials exhibit the highest energy product around room temperature and hence dominate the high-performance permanent magnet market. Intensive research efforts aim at alternative material systems containing less critical elements with similar or better magnetic properties. Nd-and Sm-based compounds with a ThMn12-type structure exhibit intrinsic properties comparable or even superior to Nd2Fe14B. However, it has not been possible to achieve technically relevant coercivity and remanent magnetization in ThMn12-based bulk sintered magnets. Using SmFe11Ti as a prototypical representative, we demonstrate that one important reason for the poor performance is the formation of twins inside micro-crystalline grains. The nature of the twins in SmFe11Ti was investigated in twinned "single crystals" and both bulk and thin film poly-crystalline samples, using advanced electron microscopy and atom probe tomography as well as simulations and compared with benchmark Nd2Fe14B. Both micro-twins and nano-twins show a twin orientation of 57±2 • and an enrichment in Sm, which could affect domain wall motion in this 2 material. Micromagnetic simulations indicate that twins act as nucleation centers, representing the magnetically weakest link in the microstructure. The relation between twin formation energies and geometrical features are briefly discussed using molecular dynamic simulations.

Cerium-based intermetallics are currently attracting much interest as a possible alternative to existing high-performance magnets containing scarce heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in these systems are poorly understood due to the difficulty of a quantitative description of the Kondo effect, a many-body phenomenon where conduction electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in Ce–Fe intermetallics is partially Kondo screened. The Kondo scale is dramatically enhanced by nitrogen interstitials suppressing the Ce-4f contribution to the magnetic anisotropy, in striking contrast to the effect of nitrogenation in isostructural intermetallics containing other rare-earth elements. We determine the full temperature dependence of the Ce-4f single-ion anisotropy and show that even unscreened Ce-4f moments contribute little to the room-temperature intrinsic magnetic hardness. Our study thus establishes fundamental constraints on the potential of cerium-based permanent magnet intermetallics.

We combined experimental investigations and theoretical calculations to unveil an abnormal magnetic behavior caused by addition of the nonmagnetic element Cu in face-centered-cubic FeNiCoMn-based high-entropy alloys (HEAs). Upon Cu addition, the probed HEAs show an increase of both Curie temperature and saturation magnetization in as-cast and homogenized states. Specifically, the saturation magnetization of the as-cast HEAs at room temperature increases by 77% and 177% at a Cu content of 11 and 20 at. %, respectively, compared to the as-cast equiatomic FeNiCoMn HEA without Cu. The increase in saturation magnetization of the as-cast HEAs is associated with the formation of an Fe-Co rich phase in the dendritic regions. For the homogenized HEAs, the magnetic state at room temperature transforms from paramagnetism to ferromagnetism after 20 at. % Cu addition. The increase of the saturation magnetization and Curie temperature cannot be adequately explained by the formation of Cu enriched zones according to atom probe tomography analysis. Ab initio calculations suggest Cu plays a pivotal role in the stabilization of a ferromagnetic ordering of Fe, and reveal an increase of the Curie temperature caused by Cu addition which agrees well with the experimental results. The underlying mechanism behind this phenomenon lies in a combined change in unit-cell volume and chemical composition and the related energetic stabilization of the magnetic ordering upon Cu alloying as revealed by theoretical calculations. Thus, the work unveils the mechanisms responsible for the Cu effect on the magnetic properties of FeNiCoMn HEAs, and suggests that nonmagnetic elements are also crucial to tune and improve magnetic properties of HEAs.

The magnetization of $\mathrm{Sm}{\mathrm{Fe}}_{11}\mathrm{Ti}$ single crystals has been measured along the principal crystallographic directions in steady (14 T) and pulsed (43 T) magnetic fields. The fourfold symmetry axis [001] is an easy magnetization direction. The magnetization curves measured in directions perpendicular to [001] are remarkable in two ways: (i) They do not depend on orientation of $\mathbit{H}$ within the basal plane; (ii) at low temperature they are $\mathsf{S}$ shaped, with an inflection point at about 0.6 times saturation magnetization. These two facts enable us to conclude that three out of five crystal field parameters of $\mathrm{Sm}{\mathrm{Fe}}_{11}\mathrm{Ti}$ are negligibly small; only ${A}_{2}^{0}$ and ${A}_{6}^{0}$ are essentially nonzero. A comparison with an isomorphous compound ${\mathrm{DyFe}}_{11}\mathrm{Ti}$ reveals a dramatic disparity of their crystal fields, especially as regards ${A}_{4}^{4}$, nearly zero in $\mathrm{Sm}{\mathrm{Fe}}_{11}\mathrm{Ti}$ but outstandingly large in ${\mathrm{DyFe}}_{11}\mathrm{Ti}$.

The effects of compositional variations and different annealing regimes in Nd(Fe,Ti)12 alloys were studied in terms of phase formation and magnetic properties analysis. NdxFe11Ti (x = 1.05, 1.10, 1.15, 1.20) alloys were produced by rapid solidification through suction casting technique. The effect of Nd content and post annealing were investigated in the temperature range of 700–1200 °C. Single 1:12 phase samples were obtained at temperatures between 1150 and 1200 °C for compositions with Nd concentration of 1.15 and 1.20. Intrinsic magnetic properties and magnetization reversal were studied for 1:12 single phase samples, revealing uniaxial anisotropy with anisotropy field (HA) of 1.08T and saturation magnetization of 137 Am2kg−1 at room temperature. In addition, the demagnetization mechanism in bulk polycrystalline samples was analyzed by means of Kerr microscopy under applied magnetic fields. Magnetization reversal process starts at the twin boundary, which acts as a nucleation center for the reversal domain, and coupling between adjacent grains is also observed. These may be part of the reasons for the observed low coercivity in the NdFe11Ti systems. The findings of the present study leads to a better understanding of the relation between magnetic properties and microstructure, and can open new strategies to obtain coercivity in this 1:12 phase system and, possibly, in the corresponding nitride.

This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database., This work was supported by the European Horizon 2020 Framework Programme for Research and Innovation (2014-2020) under Grant Agreement No. 686056, NOVAMAG., Nieves, P., Arapan, S., Maudes-Raedo, J., Marticorena-Sánchez, R., Del Brío, N.L., Kovacs, A., Echevarria-Bonet, C., Salazar, D., Weischenberg, J., Zhang, H., Vekilova, O.Y., Serrano-López, R., Barandiaran, J.M., Skokov, K., Gutfleisch, O., Eriksson, O., Herper, H.C., Schrefl, T., Cuesta-López, S.

The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to $62\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The maximum observed adiabatic temperature change is $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=60.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the initial temperature ${T}_{0}$ being just above $300\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The field dependence of $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ is found to follow the usual ${H}^{2/3}$ law, with a small correction in ${H}^{4/3}$. However, as $H$ is increased, a radical change is observed in the dependence of $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$ on ${T}_{0}$, at $H=\mathrm{const}$. The familiar caret-shaped peak situated at ${T}_{0}={T}_{\mathrm{C}}$ becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, ${\ensuremath{\mu}}_{0}H\ensuremath{\gtrsim}140\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, calculations predict a complete disappearance of the maximum near ${T}_{\mathrm{C}}$ and an emergence of a new very broad maximum far above ${T}_{\mathrm{C}}$.

The search for tunable, size-dependent properties and unique processability has triggered the development of new synthetic routes for transition metal borides. MnB is a soft to semi-hard ferromagnetic material. This boride is now available by bottom-up, low-temperature solution chemistry. It is obtained as an unexpected metastable α'-variant that crystallises with a stacking-fault dominated CrB-type structure, as shown by transmission electron microscopy and X-ray powder diffraction (space group Cmcm, a = 300.5(8), b = 768.6(2), and c = 295.3(4) pm). The nanostructured powder consists of agglomerates of small particles (mean diameter of 85(41) nm) and transforms into well-known β-MnB with FeB-type structure at 1523 K. The room temperature ferromagnetic behavior (TC = 545 K) is attributed to the positive exchange-correlation between the manganese atoms, that have many unpaired d electrons.

The ideal magnetocaloric material would lay at the borderline of a first-order and a second-order phase transition. Hence, it is crucial to unambiguously determine the order of phase transitions for both applied magnetocaloric research as well as the characterization of other phase change materials. Although Ehrenfest provided a conceptually simple definition of the order of a phase transition, the known techniques for its determination based on magnetic measurements either provide erroneous results for specific cases or require extensive data analysis that depends on subjective appreciations of qualitative features of the data. Here we report a quantitative fingerprint of first-order thermomagnetic phase transitions: the exponent n from field dependence of magnetic entropy change presents a maximum of n > 2 only for first-order thermomagnetic phase transitions. This model-independent parameter allows evaluating the order of phase transition without any subjective interpretations, as we show for different types of materials and for the Bean–Rodbell model., Magnetocaloric materials often perform best when their magnetic transitions are at the boundary between first- and second-order behavior. Here the authors propose a simple criterion to determine the order of a transition, which may accelerate future magnetocaloric material searches.

Magnetic refrigeration relies on a substantial entropy change in a magnetocaloric material when a magnetic field is applied. Such entropy changes are present at first-order magnetostructural transitions around a specific temperature at which the applied magnetic field induces a magnetostructural phase transition and causes a conventional or inverse magnetocaloric effect (MCE). First-order magnetostructural transitions show large effects, but involve transitional hysteresis, which is a loss source that hinders the reversibility of the adiabatic temperature change DTad. However, reversibility is required for the efficient operation of the heat pump. Thus, it is the mastering of that hysteresis that is the key challenge to advance magnetocaloric materials. We review the origin of the large MCE and of the hysteresis in the most promising first-order magnetocaloric materials such as Ni–Mn-based Heusler alloys, FeRh, La(FeSi)13-based compounds, Mn3GaC antiperovskites, and Fe2P compounds. We discuss the microscopic contributions of the entropy change, the magnetic interactions, the effect of hysteresis on the reversible MCE, and the size- and time-dependence of the MCE at magnetostructural transitions.

Fe2 P-based magnetocaloric compounds are an important and industrially relevant material class for magnetic refrigeration, yet their microstructure and its influence on the magnetic properties is hardly discussed in literature. We prepared Mn-Fe-P-Si-based samples using a powder metallurgical process and analyzed their microstructural and thermomagnetic properties. XRD, SEM, EDX and EBSD analysis reveal a phosphorous depleted cubic secondary phase in many samples with distinct microstructural properties giving an insight into the phase formation process. A porous morphology was found, hindering the direct application of the materials a magnetocaloric heat exchanger in bulk-like structures. The “virgin” effect could be in-situ observed for the first time on a macroscopic scale using temperature-dependent optical microscopy. Thermomagnetic measurements reveal a difference in transition temperature T t in comparison to literature values which is attributed to a processing induced deviation from the nominal composition. The isothermal entropy change Δ S T and adiabatic temperature change Δ T a d were studied as well as their cyclic behavior. The effect of secondary phases is discussed and the importance of the metal/non-metal (M/NM)-ratio is shown. The article presents a road map for the preparation of Mn-Fe-Si-P-based alloys with highest quality.

International audience; Core–shell magnetic anisotropic particles were prepared by reduction of Sb acetate at the surface of cobalt nanorods dispersed in a solution consisting of 1,2 tetradecanediol in oleylamine. X-ray diffraction and local EDS analyses revealed a thin β-CoSb shell with a controlled thickness ranging from 5 to 15 nm that depended on the Sb/Co molar ratio and the reduction temperature. The shell completely coats the rod surface but does not alter the shape anisotropy or the hcp structure of the cobalt cores, and the hard magnetic properties are preserved after coating with a coercivity higher than 3 kOe. Consolidated nanostructured materials that exhibit properties of permanent magnets were prepared by compaction of the core–shell Co@CoSb nanorods. The thin CoSb shell was very efficient for preventing the cobalt anisotropic core from sintering at high temperatures (up to 300 °C) and high pressures (up to 1.5 GPa). These results indicate that the bottom-up approach is very promising for preparation of nanostructured hard magnetic materials.

Hysteresis is more than just an interesting oddity, which occurs in materials with a first-order transition. It is a real obstacle on the path from existing lab-scale prototypes of magnetic refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and therefore it is necessary to understand the mechanisms causing hysteresis and to find solutions how to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, we discuss fundamental aspects, which can contribute to thermal hysteresis and we are developing strategies for at least partially overcoming the hysteresis problem in some selected classes of magnetocaloric materials with large application potential. Doing so, we refer to the most relevant classes of magnetic refrigerants La-Fe-Si-, Heusler- and Fe2P-type compounds., article submitted to Philosophical Transactions A

The influence of magnetocrystalline anisotropy on the magnetocaloric effect (MCE) was studied on single crystals of CoB and compared to measurements on polycrystalline samples. Large differences in adiabatic temperature change Δ T a d and magnetic entropy change Δ S M were found along the different crystallographic directions. The magnetocaloric effect differs by 40% in the case of Δ T a d in a field change of 1.9 T when applying the field along the hard axis and easy plane of magnetization. In the case of Δ S M, the values differ 50% and 35% from each other in field changes of 1 and 1.9 T, respectively. It was found that this anisotropy effect does not saturate in fields up to 4 T, which is higher than the anisotropy field of CoB ( ≈2 T). A simple model was developed to illustrate the possible effect on magnetocrystalline anisotropy, showing large differences especially in application relevant fields of about 1 T. The results strongly suggest that the MCE could be maximized when orienting single crystalline powders in an easy axis parallel to the applied field in active magnetocaloric regenerator structures, and therefore the overall device efficiency could be increased.

In this paper, we illustrate the dilemma of inverse magnetocaloric materials using the example of Heusler alloys. For such materials, the magnetic and lattice contribution to the total entropy change are competing with each other. For the two paradigmatic Heusler systems of Ni-Mn-In and Ni-Mn-In-Co, we provide a systematic comparison of experimental data under different magnetic fields and hydrostatic pressures with magnetic and the magnetocaloric properties obtained from the Heisenberg model. This allows us to separate the lattice and the magnetic contribution to the total entropy of the martensitic transition. Our analysis reveals that a large magnetization change is parasitic, but at the same time it is necessary to drive the magnetocaloric effect. This contradicting role of the magnetic contribution-the dilemma-is a general characteristic of inverse magnetocaloric Heusler materials.

Under the terms of the Creative Commons Attribution 3.0 Unported License., An investigation of the Y2Fe17 compound belonging to the class of intermetallic alloys of rareearth and 3d-transition metals is presented. The magnetization, magnetostriction, and thermal expansion of the Y2Fe17 single crystal were studied. The forced magnetostriction and magnetostriction constants were investigated in the temperature range of the magnetic ordering close to the room temperature. The giant field induced volume magnetostriction was discovered in the room temperature region in the magnetic field up to 1.2 T. The contributions of both anisotropic singleion and isotropic pair exchange interactions to the volume magnetostriction and magnetostriction constants were determined. The experimental results were interpreted within the framework of the Standard Theory of Magnetostriction and the Landau thermodynamic theory. It was found out that the giant values of the volume magnetostriction were caused by the strong dependence of the 3delectron Coulomb charge repulsion on the deformations and width of the 3d-electron energy band., The work was supported by RFBR Grant Nos. 13-02-00916 and 12-02-31516.

Manganese containing La–Fe–Si alloys are important magnetocaloric compounds, since Mn atoms prevent segregation of hydrogen in partially hydrogenated La–Fe–Mn–Si alloys when their Curie temperature is tuned to room temperature by hydrogen. The effect of Mn alloying on the Fe atomic magnetic moment μ Fe is still rather unexplored. Therefore, we investigated the (local) magnetic and electric hyperfine interactions in the strongly magnetocaloric compound LaFe11.3Mn0.3Si1.4 and, for comparison, LaFe11.6Si1.4 by 57Fe Mossbauer spectroscopy, and the global magnetic properties by vibrating sample magnetometry. The NaZn13 structure was confirmed by x-ray diffraction. Two non-equivalent Fe lattice sites are known to exist in this material: the (96i) sites (FeII) of low local symmetry, and the highly symmetrical (8b) sites (FeI). At room temperature in the paramagnetic state, the electric hyperfine parameters of Fe atoms on both sites were obtained. At low temperatures (4.8 K), the observed magnetically split nuclear Zeeman sextets with broad apparent lines were analyzed in terms of a distribution P(B hf) of hyperfine magnetic fields B hf. The average hyperfine field 〈B hf〉, originating predominantly from FeII sites, was found to be rather high (30.7(1) T at 4.8 K) for LaFe11.6Si1.4, and the approximate relation 〈B hf〉 = Aμ Fe is confirmed for FeII sites, with A = 14.2 T/μ B. 〈B hf〉 is significantly reduced (to 27.7(1) T at 4.8 K) for the Mn-containing sample LaFe11.3Mn0.3Si1.4, providing evidence for a reduction by 9.7% of the average Fe atomic moment μFe from ~2.16 μ B to a value of ~1.95 μ B by Mn substitution of Fe. Our Mossbauer results are in good agreement with magnetometry, which reveals a reduction of the saturation magnetization of M s = 163.1(1) Am2 kg−1 of LaFe11.6Si1.4 by 10.5% due to Mn substitution.

This work reports the influence of heat treatment on the magnetocaloric effect of cold-rolled Gd ribbons. A significant depression of magnetic and thermodynamical properties occurs in severely deformed ribbons. However, it is possible to recover the initial values, characteristic of polycrystals by way of heat treatment. The heat treatment regimes are directly connected with the degree of plastic deformation. The proposed approach is convenient for manufacturing magnetocaloric materials in the form of thin ribbons for magnetic refrigerators. © 2013 American Institute of Physics.

Hysteresis features of the direct and inverse magnetocaloric effect associated with first-order magnetostructural phase transitions in Ni-Mn-X (X $=$ Ga, Sn) Heusler alloys have been disclosed by differential calorimetry measurements performed either under a constant magnetic field, $H$, or by varying $H$ in isothermal conditions. We have shown that the magnetocaloric effect in these alloys crucially depends on the employed measuring protocol. Experimentally observed peculiarities of the magnetocaloric effect have been explained in the framework of a model that accounts for different contributions to the Gibbs energy of austenitic ${g}_{A}$ and martensitic ${g}_{M}$ phases. Obtained experimental results have been summarized by plotting a phase fraction of the austenite ${x}_{A}$ versus the driving force ${g}_{M}\ensuremath{-}{g}_{A}$. The developed approach allows one to predict reversible and irreversible features of the direct as well as inverse magnetocaloric effect in a variety of materials with first-order magnetic phase transitions.

6 páginas, 6 figuras.-- PACS number(s): 75.30.Sg, 75.50.Cc.-- et al., Magnetocaloric properties of a Ni50Mn36Co1Sn13 ferromagnetic shape memory alloy have been studied experimentally in the vicinity of a first-order magnetostructural phase-transition low-temperature paramagnetic martensite↔high-temperature ferromagnetic austenite. The magnetic entropy change ΔSm calculated from the magnetization M(T) data measured upon cooling is higher than that estimated from M(T) measured upon heating. Contrary to ΔSm, the adiabatic temperature change ΔTad measured upon cooling is significantly smaller than that measured upon heating. The apparent discrepancy between ΔSm and ΔTad (larger ΔSm, smaller ΔTad upon cooling, and smaller ΔSm, larger ΔTad upon heating) is caused by the hysteretical behavior of this magnetostructural transition, a feature common for all the alloys in the family of Ni50Mn25+xZ25−x (Z=In,Sn,Sb) ferromagnetic shape memory Heusler compounds. The hysteresis causes the magnetocaloric parameters to depend strongly on the temperature and field history of the experimental processes., This work was partially supported by RFBR (Grants No. 07-02-13629, No. 08-02-91317, and No. 09-02-01274), FANI (Grant No. 02.513.123097), the EU Seventh Framework Programme (Contract No. 214864), MICINN and FEDER funding of Projects No. MAT2007-61621, No. MAT2008-1077, and No. CSD2007-00010.

La(Fe,Si)13 alloys display a giant magnetocaloric effect when a magnetic field is applied near the Curie temperatureT C. However, to use these alloys for domestic refrigeration based on magnetic cooling, it is vital to increase T C near to the room-temperature range while simultaneously maintaining a large magnetocaloric effect. With this aim, we studied the effect of interstitialcarbon on the microstructure and magnetocaloric effect in LaFe11.6Si1.4C x (x = 0–0.4). The investigation was carried out in cast samples annealed for seven days at 1323 K. The study of microstructure shows that annealing led to about 90 wt. % of 1:13 magnetocaloric phase. Magnetization data revealed that the addition of carbon leads to an increase in T C and a decrease of the thermal hysteresis width. For x > 0.2, the magnetic transition changes from first-order to second-order, with a corresponding reduction in magnetocaloric effect. A small amount of C (x up to 0.2) improves the magnetocaloric properties of the parent alloy La(Fe,Si)13, and, furthermore, the carbon addition leads to an increase in the thermal stability of hydrided LaFe11.6Si1.4C x . The onset of hydrogen desorption increases from 460 K for the x = 0 (carbon-free alloy) to 500 K and 540 K, respectively, for x = 0.1 and x = 0.2.

The net entropy change corresponding to the free charge carriers in a Ni-doped FeRh bulk polycrystal was experimentally evaluated in a single sample using low-temperature heat capacity experiments with applied magnetic field and using Seebeck effect and Hall coefficient measurements at high temperatures across the first-order phase transition. From the heat capacity data, a value for the electronic entropy change ΔSel≈8.9 J kg−1K−1 was extracted. The analysis of the Seebeck coefficient allows tracing the change of the electronic entropy jump with applied magnetic field directly across the transition. The difference in electronic entropy contribution obtained is as high as 10% from 0.1 to 6 T. © 2019 Elsevier Ltd. The authors thank Dr. Sebastian Fahler for insightful discussions. TU Darmstadt acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant no. 743116 project Cool Innov).