Pressure Evolution of Magnetism in URhGa

In this paper, we report the results of an ambient and high pressure study of a 5f-electron ferromagnet URhGa. The work is focused on measurements of magnetic and thermodynamic properties of a single crystal sample and on the construction of the p-T phase diagram. Diamond anvil cells were employed to measure the magnetization and electrical resistivity pressures up to ~ 9 GPa. At ambient pressure, URhGa exhibits collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 1.1 {\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure below the Curie temperature TC = 41K. With the application of pressure up to 5GPa the ordering temperature TC initially increases whereas the saturated moment slightly decreases. The rather unexpected evolution is put in the context of the UTX family of compounds.Comment: arXiv admin note: text overlap with arXiv:1611.0327

Pressure dependence of magneto-structural properties of Co-doped off-stoichiometric Ni2MnGa alloys

A strong effect of pressure on magnetization and paramagnetic moment of the Co-doped Mn-rich Ni 50-x Co x Mn 25+y Ga 25-y (x = 5,7,9 and y = 5,6,7,8) Heusler alloys is presented and compared with very weak pressure sensitivity of magnetization of the stoichiometric Ni 2 MnGa alloy. The effects of both, the pressure and the magnetic field, on temperature of the structural martensitic transition in the alloys are discussed with a use of the Clausius-Clapeyron relations. An analysis of pressure and field effects provides a possibility to evaluate structural and magnetic parts of latent heat of the martensitic transitions in the studied alloys. The Curie temperature of martensite phase of the Co-rich alloys is not affected by pressure

Pressure-induced huge increase of Curie temperature of the van der Waals ferromagnet VI3

Evolution of magnetism in single crystals of the van der Waals compound VI3 in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four magnetic phase transitions, at T1 = 54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed at ambient pressure. The first two have been attributed to the onset of ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is characterized by the magnetic ordering transition at Curie temperature TC and the transition between two different ferromagnetic phases TFM, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa whereas TFM increases rapidly with increasing pressure and reaches TC at a triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase transition is observed moving to higher temperatures with increasing pressure to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa) suggesting a possible pressure-induced reduction of vanadium magnetic moment. We discussed these results in light of recent theoretical studies to analyze exchange interactions and provide how to increase the Curie temperature of VI3.Comment: 20 pages, 16 figure

Experimental Investigation of Small-Scale Magnetocaloric Refrigerator

The small-scale magnetocaloric cooling device was developed at Czech Technical University in Prague. The magnetocaloric small-scale cooling system was designed as push-pull system with two permanent magnets with field of about 0.85 T. The construction offers a possibility to alter independently many parameters of the cooling process and it ensures easy way to change working material and design of heat exchangers. The measurements were performed with 35 g of gadolinium as a working material and ethanol as heat transfer liquid. Device was successfully operated at room temperature with maximal heat span of 3.1 K. In the article we report design of the machine and first measurement performed on it

Effect of pressure on the magnetic and structural properties of Fe5SiB2 compound

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Magnetocaloric Effect of the Tb1−xYxNiAlTb_{1-x}Y_{x}NiAl and TbNiAl1−yInyTbNiAl_{1-y}In_{y} Series

We have studied the development of the magnetocaloric effect in the (Tb,Y)NiAl and TbNi(Al,In) series as determined from magnetization measurements. The transition from antiferromagnetic order in TbNiAl to ferromagnetic order in $Tb_{0.7}Y_{0.3}NiAl$ is accompanied by increase of the maximum entropy change from - 4.1 to - 4.4 J $kg^{-1} K^{-1}$. In the TbNi(Al,In) series, the change of uniaxial anisotropy in TbNiAl to the easy-plane anisotropy in TbNiIn leads to broadening of the magnetocaloric effect accompanied with large increase of the relative cooling power from 66 to 120 J $kg^{-1}$

Non-collinear antiferromagnetic structure in PrCuAl

International audienceWe report on the magnetic structure in PrCuAl as determined by powder neutron diffraction. This compound crystallizes in the hexagonal ZrNiAl-type structure and the bulk measurements indicated an antiferromagnetic order in PrCuAl below TN = 7.9 K. Our neutron-diffraction data confirmed the antiferromagnetic order below TN and revealed the propagation vector (1/3, 1/3, 1/3). The Pr magnetic moments lie within the basal plane and form a triangular structure. This magnetic structure differs from antiferromagnetic structures observed in other RCuAl or RNiAl compounds that are mostly characterized by (1/2, 0, q) propagation

Pressure Influence on Magnetic Properties of TbNiAl

We have investigated the effect of hydrostatic pressure on magnetic properties of TbNiAl, crystallizing in hexagonal ZrNiAl-type structure. TbNiAl orders antiferromagnetically below $T_{N}$=45 K and undergoes further magnetic phase transition to another AF phase at $T_{1}$=23 K. The magnetic field of $B_{c}$ ≅ 0.3 T applied along the c-axis at 2 K leads to the transition to ferromagnetic order. By applying the hydrostatic pressure, both $T_{N}$ and $T_{1}$ remain almost unaffected whereas $B_{c}$ shows a strong increase. The hydrostatic pressure stabilizes the antiferromagnetic state which can be related to development of structural parameters

Magnetocaloric Effect in Materials with the First Order Transitions - Direct Measurements

The results of direct measurements of the magneto-caloric characteristics Δ $T_{ad}$ and the indirect determination of Δ $S_{m}$ of pure Gd around the Curie temperature and of the $FeMnP_{0.45}As_{0.55}$ and $Ni_{45}Co_5Mn_{31}Ga_{19}$ intermetallics in the vicinity of the first order magnetic and structural phase transitions are presented and discussed. A pronounced temperature and field dependence of the first order transitions in the studied materials manifests restrictions applying these materials in magnetic refrigeration techniques. An effective use of the Ericsson and the Brayton refrigeration cycles with $FeMnP_{0.45}As_{0.55}$ in the role of a refrigerant is discussed

Spin disordered resistivity of the Heusler Ni₂MnGa-based alloys

Electrical resistivity of the selected Heusler off-stoichiometric (NiCo)₂Mn(GaIn) alloys was studied in a wide range of temperature and magnetic field. A step-like change of resistivity (Δρ ≈24 μΩcm) was detected in the off-stoichiometric Ni_{1.85}Mn_{1.21}Ga_{0.94} alloy at temperature of martensitic structural transition. This Δρ is much more significant than one in the stoichiometric Ni₂MnGa alloy. In the case of the off-stoichiometric (NiCo)₂Mn(GaIn) alloys, an enormous change of resistivity, Δρ ≈ 200 μΩcm, accompanies the structural transition. Simultaneously, the maximum of the spin disordered resistivity ρ_{sd}(T) of austenite phase of the alloys is slightly dependent on composition of the alloy and vary from ≈30 μΩcm up to ≈45 μΩcm, in good agreement with theoretical calculations. Due to high sensitivity of the structural transition temperature of the alloys to magnetic field, the very pronounced magnetoresistance effects have been observed in the studied alloys