Valerii Prudnikov

The comparison of direct and indirect methods for determining the magnetocaloric parameters in the Heusler alloy Ni50Mn34.8In14.2B

The magnetocaloric properties of the Ni50Mn34.8In14.2B Heusler alloy have been studied by direct measurements of the adiabatic temperature change (ΔTAD(T,H)) and indirectly by magnetization (M(T,H)), differential scanning calorimetry, and specific heat (C(T,H)) measurements. The presence of a first-order ferromagnetic-paramagnetic transition has been detected for Ni50Mn34.8In14.2B at 320 K. The magnetocaloric parameters, i.e., the magnetic entropy change (ΔSM = (2.9-3.2) J/kgK) and the adiabatic temperature change (ΔTAD = (1.3-1.52) K), have been evaluated for ΔH = 1.8 T from CP(T,H) and M(T,H) data and from direct ΔTAD(T,H) measurements. The extracted magnetocaloric parameters are comparable to those of Gd.

Giant field-induced adiabatic temperature changes in In-based off-stoichiometric Heusler alloys

Direct measurements of the adiabatic temperature change (ΔTAD) of Ni50Mn35In14.5B0.5 have been done using an adiabatic magnetocalorimeter in a temperature range of 250–350 K, and with magnetic field changes up to ΔH = 1.8 T. The initial susceptibility in the low magnetic field region drastically increases with temperature starting at about 300 K. Magnetocaloric effects parameters, adiabatic temperature changes, and magnetic entropy changes were found to be a linear function of H2/3 in the vicinity of the second order transitions (SOT), whereas the first order transitions do not obey the H2/3 law due to the discontinuity of the transition. The relative cooling power based on the adiabatic temperature change for a magnetic field change of 1.8 T has been estimated. Maximum values of ΔTAD = −2.6 K and 1.7 K were observed at the magnetostructural transition (MST) and SOT for ΔH = 1.8 T, respectively. The observed ΔTAD at the MST exceeds the ΔTAD for Ni50Mn35In14X with X = In, Al, and Ge by more than 20% and is...

Hall effect in a martensitic transformation in Ni-Co-Mn-In Heusler alloys

The Hall effect, transverse magnetoresistance, and magnetization of Ni48Co2Mn35In15 Heusler alloys have been studied at T = 77–300 K in magnetic fields up to 15 kOe. It has been shown that a martensitic transformation is accompanied by a change in the sign of the constant of the ordinary Hall effect, which means a strong change in the electronic spectrum in the martensitic transformation, while the anomalous Hall effect (AHE) constant is positive in both the austenite and martensite phases. In both phases, there are no correlations between the AHE constant and the square of the resistivity, which are characteristic of the side jump mechanism in the AHE theory. In the near vicinity of the martensitic transformation, the field dependences of the Hall resistance are complex and nonmonotonic, indicating a change in the relative concentrations of the austenite and martensite phases in strong fields.

The Adiabatic Temperature Changes in the Vicinity of the First-Order Paramagnetic-Ferromagnetic Transition in the Ni-Mn-In-B Heusler Alloy

The magnetocaloric properties of Ni-Mn-In-B Heusler alloy have been studied using direct measurements of the adiabatic temperature change (Δ<i>T</i>_AD(<i>T</i>,<i>H</i>)) , and indirectly by magnetization (<i>M</i>(<i>T</i>,<i>H</i>)), differential scanning calorimetry, and specific heat (<i>C</i>_P(<i>T</i>,<i>H</i>)) measurements. The presence of a first-order ferromagnetic-paramagnetic transition has been detected for Ni₅₀Mn_34.8In_14.2B at 320 K. The magnetocaloric parameters, i.e., the magnetic entropy change, Δ<i>S</i>_M = (2.9-3.2) J/kgK, and the adiabatic temperature change, Δ<i>T</i>_AD = (1.3-1.52) K, have been evaluated for Δμ₀<i>H</i> = 1.8 T from <i>C</i>_P(<i>T</i>,<i>H</i>) and M(T,H), and from <i>C</i>_P(<i>T</i>,<i>H</i>) and direct Δ<i>T</i>_AD(<i>T</i>,<i>H</i>) measurements, respectively, in the vicinity of the first-order transition temperature. The extracted magnetocaloric parameters are comparable to that of Gd.

Effects of the partial substitution of Ni by Cr on the transport, magnetic, and magnetocaloric properties of Ni50Mn37In13

The structural, magnetic, and magnetotransport properties of Ni50-xCrxMn37In13 Heusler alloys have been synthesized and investigated by x-ray diffraction (XRD), field and pressure dependent magnetization, and electrical resistivity measurements. The partial substitution of Ni by Cr in Ni50Mn37In13 significantly improves the magnetocaloric effect in the vicinity of the martensitic transition (TM). This system also shows a large negative entropy change at the Curie temperature (TC), making it a candidate material for application in a refrigeration cycle that exploits both positive and negative magnetic entropy changes. The refrigeration capacity (RC) values at TM and TC increase significantly by more than 20 % with Cr substitution. The application of hydrostatic pressure increases the temperature stability of the martensitic phase in Ni45Cr5Mn37In13. The influence of Cr substitution on the transport properties of Ni48Cr2Mn37In13 is discussed. An asymmetric magnetoresistance, i.e., a spin-valve-like behavior...