Magnetic and magnetocaloric properties of Co2-xFexVGa Heusler alloys

K Schroeder,Y Huh,S Valloppilly,R Skomski,J Herran,D J Sellmyer,W Zhang,P Lukashev,P Kharel,J Waybright

doi:10.1063/1.5006646

Abstract

The magnetic and magnetocaloric properties of iron-substituted Co2VGa alloys, Co2-xFexVGa (x = 0, 0.1, 0.15, 0.2, 0.3), were investigated. The Fe-substituted samples, prepared by arc melting, melt spinning, and annealing, crystallized in the L21 Heusler structure, without any secondary phases. The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 μB/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 μB/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x ≤ 0.2, the highest value being 3.3 J/kgK at 7 T for Co1.85Fe0.15VGa. First-principle calculations show that Co2VGa retains its half-metallic band structure until at least 30% of the cobalt atoms are replaced by Fe atoms. The wide operating temperature window near room temperature and the lack of thermal and magnetic hysteresis are the interesting features of these materials for application in room-temperature magnetic refrigeration.

Highlights

Heusler compounds and alloys have attracted recent attention because of their many interesting properties with prospects for spintronics, energy technology and magnetocaloric applications.[1,2,3] the magnetic properties of these materials can be tuned to fit specific applications by adjusting the elemental composition
We performed density-functional calculations of bulk Heusler compound, Co8-xFexV4Ga4 (x = 0, 1, 2, 3, 4), using the projector augmented-wave method (PAW),[13] implemented in the Vienna ab initio simulation package (VASP)[14] within the generalized-gradient approximation (GGA).[15]
The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 μB/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 μB/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x ≤ 0.2

Summary

INTRODUCTION

Heusler compounds and alloys have attracted recent attention because of their many interesting properties with prospects for spintronics, energy technology and magnetocaloric applications.[1,2,3] the magnetic properties of these materials can be tuned to fit specific applications by adjusting the elemental composition. Co-based compounds including Co2MnSi, Co2FeSi and CoFeCrAl have shown promising properties such as high transport spin polarization at the Fermi level and Curie temperature much above room temperature.[5,6,7] One of the issues with the Heusler compounds is the difficulty of synthesizing them in completely ordered structures. The main obstacles to the application of these materials are the large hysteresis and limited operating temperature window.[10]. These considerations stimulated the current work, where we have investigated the magnetic and magnetocaloric properties of Co2VGa-based alloys.

Experimental methods

Computational methods

Experimental results

Computational results

CONCLUSIONS