We have investigated the crystal structure, the bulk magnetization characteristics and the magnetocaloric properties of Er1−xDyxCo2 compounds. X-ray diffraction (XRD) analyses confirm that all these Laves phase type compounds crystallize in the cubic MgCu2-type structure. First, the magnetization behaviour and the magnetic transition are analyzed in terms of Landau theory. Then, a direct correlation was pointed out between the character of the magnetic transition and the behaviour of the cell parameter versus x. Substitution of Dy to Er enhances markedly the Curie temperature TC from 35 to 142K, while ΔS the corresponding change of isothermal entropy decreases significantly. The refrigerant capacity of the Er1−xDyxCo2 compounds is discussed and our experimental data are compared with the corresponding theoretical results reported in the literature [de Oliveira, von Ranke, J. Magn. Magn. Mater. 264 (2003) 55].

Experimental results on the thermal expansion and magnetostriction of YFe12−xVx (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5 T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5 T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe12−xVx compounds.

The Gd2Cu3Sn6, Tb2Cu3.5Sn5.5, and Dy2Cu3.5Sn5.5 intermetallic compounds were prepared by arc melting, annealed at 670 K and characterized by XRPD and DSC analyses. Rietveld refinement showed that they crystallize in tetragonal Sm2Cu4Sn5 structure type (space group I4mm). The magnetic properties were studied in the temperature range 2-300 K and showed that in the paramagnetic state all studied compounds are Curie-Weiss paramagnets, among them Tb2Cu3.5Sn5.5 and Dy2Cu3.5Sn5.5 order antiferromagnetically at low temperatures and exhibit a metamagnetic transition. Electronic structure calculations were performed to evaluate chemical bonding. (C) 2011 Elsevier B.V. All rights reserved.

The crystal structure, density of electron states, electron transport, and magnetic characteristics of an intermetallic n-ZrNiSn semiconductor heavily doped with atoms of rare-earth metals (R) have been studied in the ranges of temperatures 1.5–400 K, concentrations of rare-earth metal 9.5 × 1019–9.5 × 1021 cm−3, and magnetic fields H ≤ 15 T. The regions of existence of Zr1 − x R x NiSn solid solutions are determined, criteria for solubility of atoms of rare-earth metals in ZrNiSn and for the insulator-metal transition are formulated, and the nature of “a priori doping” of ZrNiSn is determined as a result of redistribution of Zr and Ni atoms at the crystallographic sites of Zr. Correlation between the concentration of the R impurity, the amplitude of modulation of the bands of continuous energies, and the degree of occupation of potential wells of small-scale fluctuations with charge carriers is established. The results are discussed in the context of the Shklovskii-Éfros model of a heavily doped and compensated semiconductor.

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Stannides with general composition R5−xNi12Sn24+x (R=Y, La, Nd, Sm, Gd, and Dy) were prepared by arc melting and the crystal structure peculiarities for this series were studied. Intermetallics with R=Y, La, Nd, Sm, and Gd belong to the cubic GdNi2.67Sn5.44 structure type (space group Im−3), while Dy4Ni12Sn25 compound crystallizes in the Ce4Pt12Sn25 type, ordered variant of the GdNi2.67Sn5.44. Stannides with magnetic rare earths (Nd, Gd, and Dy) are characterized by Curie–Weiss behaviour, whereas La4.87Ni12Sn24 is Pauli paramagnet in the temperature range 2–300K. Their electrical properties were investigated by means of the electrical resistivity and Seebeck coefficient measurements in the temperature range 80–380K. All investigated compounds exhibit metallic-like type of conductivity. Electronic structure calculations were also carried out to obtain the density of states (DOS) using the full potential linearized augmented plane wave (FLAPW) method for La4.87Ni12Sn24 and Dy4Ni12Sn25 compounds and confirmed the metallic type of conductivity.

Ce dossier fait le point sur l'état actuel des recherches sur les matériaux magnétocaloriques les plus prometteurs pour la réfrigération. Après une première partie consacrée au contexte dans lequel se situent ces recherches, une description plus détaillée de l'effet magnétocalorique et sa déterminat

The structural and magnetic properties of LaFe11.31Si1.69 and LaFe11.31Si1.69H1.45 compounds have been studied by neutron diffraction. Besides, characterization and optimization of their magnetocaloric properties, we have investigated more fundamental aspects of their crystal and magnetic structures. From high statistics neutron powder diffraction experiments, we have determined the cell parameters, the atomic positions, the atom occupancies, the interatomic distances and the magnetic moments versus temperature. An increase of specific Fe–Fe distances upon hydrogen absorption was pointed out leading to the net increase of the Curie temperature, well supported by the strong dependence of the Fe–Fe exchange interaction with metal–metal distances.

The magnetostriction and thermal expansion of Er2Fe14−xCoxB (x=1, 3 and 5) intermetallic compounds were measured, using the strain gauge method in the temperature range 75–450K under applied magnetic fields up to 1.5T. For all samples the longitudinal magnetostriction (λl) undergoes an anomaly around the spin reorientation temperature (TSR). It is also observed that λl decreases with increasing the Co content. All compounds show saturation type behaviour in their anisotropic magnetostriction curves at different temperatures and applied fields. The saturation behaviour of the compound with x=3 occurs at higher temperatures than with x=1 and 5. The volume magnetostriction strongly increases below μ0H=0.3T, then monotonically rises with applied field up to the spin reorientation temperature. An invar type behaviour is observed above 200K in the compound with x=1. The results are discussed based on the temperature dependence of magnetocrystalline anisotropy of compounds below and above their TSR.

Recently, a so-called “colossal” magnetocaloric effect (MCE) was reported in Mn1−xFexAs [A. de Campos et al., Nat. Mater. 5, 802 (2006)]. However, the value of ΔS that was determined appears markedly overestimated since it results from the inadequate use of the Maxwell relation. Here, we report on recent measurements of ΔS in Mn1−xFexAs from which a correct MCE value is deduced by using the Clausius–Clapeyron equation. This result is asserted by careful use of the Maxwell relation.

The magnetic and magnetocaloric properties of LaFe11.9−yCoySi1.1 compounds with y=0.8 and 0.9 have been investigated. The temperature dependence of magnetization data revealed that LaFe11.1Co0.8Si1.1 and LaFe11Co0.9Si1.1 exhibit a second-order magnetic transition near room temperature at 282 and 294 K, respectively. Under a magnetic field change of 5 T, the maximum values of isothermal entropy change −ΔS are found to be 15 and 13.5 J/kg K for y=0.8 and 0.9, respectively. The refrigerant capacity has been calculated to be 320 J/kg for y=0.8 and 266 J/kg for y=0.9 under a field change of 5 T. Direct measurements of the temperature change for LaFe11.9−yCoySi1.1 compounds around room temperature were also performed. Measurements of ΔT were performed in adiabatic conditions with practice-oriented method by using a specially developed test bench. For both materials, the normalized temperature change was found to be about 1 K/T at their Curie temperatures.

In this paper, we present the giant magnetocaloric effect exhibited by the Mn1−x(Ti0.5V0.5)xAs compound with x=0.1. The ordering temperature decreases from 318K in the case of MnAs (x=0) to 266K in the case of Mn0.9Ti0.05V0.05As (x=0.1). A large magnetic entropy change −ΔSm attributed to a first order magnetic transition has been observed. For Mn0.9Ti0.05V0.05As, the maximum of −ΔSm occurs near TC=266K and is about 30J∕kgK for an applied field change of 2T, a value very close to that (∼31J∕kgK) measured in MnAs. For materials with a first order transition at TC, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to structural changes. A model based on the phenomenological approach of Bean and Rodbell [Phys. Rev. 126, 104 (1962)] has been developed in order to describe such a behavior. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by Mn1−x(Ti0.5V0.5)xAs (x=0, 0.1) materials.

NdFe10V2 composites were prepared and the influence of H and N interstitial modifications on their structural and magnetoelastic properties were studied. By hydrogenation, the thermal expansion trace is markedly affected so that hydrogen-induced modification can be proposed as an effective method for monitoring the thermal expansion coefficient of NdFe10V2. Besides, nitrogenation does not have pronounced effect on the thermal expansion behavior of the NdFe10V2 compound. Below the spin reorientation temperature TSR=130K, the anisotropic magnetostriction Δλ of the hydride is negligible, while above TSR the saturation value of Δλ considerably decreases by hydrogenation. Our results show that below TSR=130K nitrogenation changes the sign of the anisotropic magnetostriction, while above TSR the thermal behaviour of Δλ is similar to that of the host compound. These results are discussed as due to the influence of interstitial modifications on both the magnetic anisotropy and the magnetization.

Experimental results on the thermal expansion and magnetostriction of YFe10V2 composites are reported and the influence of H and N interstitial atoms is studied. The anisotropic magnetostriction is about 30% larger in the composite than in the starting alloy. Also, the anisotropic magnetostriction remains positive after insertion of H (N) ion while the sign of volume magnetostriction changes by hydrogenation. The anisotropic magnetoelastic interactions are enhanced by insertion of H and especially N interstitial atoms. The results are discussed considering the effect of H and N, and of temperature on magnetic anisotropy and microstructure.