Magnetocaloric effect in Ni_{2.19}Mn_{0.81}Ga Heusler alloys

Abstract

The results of direct measurements of the magnetic field induced entropy change in the Ni _{2.19} Mn _{0.81} Ga alloy are presented. It is shown that the largest entropy change in the magnetic field 2.6 T is equal to 11 J/kgK. The experimental data are compared with the theoretical results, obtained with the help of the statistical and molecular field theory.

Magnetocaloric and thermomagnetic properties of Ni2.18Mn0.82Ga Heusler alloy in high magnetic fields up to 140 kOe

“…It is important to note that although Heusler alloys of Ni 2 MnGa system have been at the center of attention for almost two decades, thanks to their magnetic-field controlled martensitic transition governing GMCE and shape memory effect, no data on direct measurement of MCE have been published attributed to complete magnetostructural PT by magnetic field. [13][14][15][16][17][18][19] We demonstrate by the direct method that even though a magnetic field, as strong as H ¼ 140 kOe, does not lead to complete PT from paramagnetic austenite to ferromagnetic martensite, the maximal value of heat transferred DQ ¼ 4900 J/kg obtained at 343 K in this field (Fig. 4(b)) exceeds the highest values reported in previously published works.…”

Magnetocaloric effect in La1−xAgyMnO3(y⩽x): direct and indirect measurements

“…When comparing different magnetocaloric materials it is useful to calculate the relative cooling power (RCP) based on the magnetic entropy change and the adiabatic temperature change. The RCP of a magnetocaloric material can be, in simple cases, evaluated by considering the magnitude of S M or T ad and its full-width at half maximum (δT FWHM ), RCP(S) = − S M (T , H ) × δT FWHM [3,25]. The results of this estimation are shown in table 1.…”

“…Until recently, the rare earth metal gadolinium (Gd) with a large MCE has been considered as the most active magnetic refrigerant in room temperature magnetic refrigeration (MR) [1,2]. For this reason, there is an extensive search for new materials suited for solid state cooling machines working in this temperature range, for example, Ni-Mn-Ga alloys [3,4], Mn-As-Sb alloys [5], La-Fe-Co-S alloys [6], Mn-Fe-P-As alloys [7] and various compounds of manganites [8][9][10][11][12][13][14].…”

Unusual Kinetic Properties of Usual Heusler Alloys

“…The inset shows the field dependences of the coefficients A, B, and C [55] Under these conditions, a high degree of polarization of current carriers can occur with a polarization coefficient P close to 1. The spin polarization coefficient P is given by the following expression: P = (N↑(EF) − N↓(EF))/(N↑(EF) + N↓(EF)), (7) where N↑(EF) and N↓(EF) are densities of electronic states at the Fermi level EF with the spin up and spin down, respectively. Then, in a simple mean-field approximation, the presence of only one type of carriers can mean 100% spin polarization of current carriers, which somewhat decreases when non-quasiparticle states are taken into account [10,56,57].…”

“…This is largely due to the fact that Heusler alloys are multifunctional materials, i.e. compounds with a combination of two or more functional properties and characteristics, such as giant magnetoresistivity [2,3]; shape memory effect [4,5]; large magnetocaloric effect (MCE) [6][7][8]; a high degree of spin polarization of current carriers (in half-metallic ferromagnets [9,10] and spin gapless semiconductors [11,12]); anomalous thermal properties [13,14]; large thermoelectric effect in thermoelectrics and semiconductors [15][16][17][18]; superconductivity [19,20]; giant anomalous Hall and Nernst effect in topological semimetals (see reviews [21,22] and references therein), etc.…”