Experimental and computational study of FeCrVAl and related compounds*

Materials exhibiting high degree of spin polarization are in demand for spin-transport-based devices. Half-metallic Heusler compounds have attracted particular attention because they have tunable magnetic properties and exhibit high Curie temperature much above room temperature. We have synthesized one such predicted half metal, FeCrVAl, using arc melting and annealing. In addition, we also studied the effect of Mn substitution on the structural, magnetic, and electronic band properties of FeCrVAl synthesizing samples with compositions FeCr_0.5Mn_0.5VAl and FeCrV_0.5Mn_0.5Al. The room temperature, x-ray diffraction patterns indicate that FeCrVAl and FeCrV_0.5Mn_0.5Al are cubic in structure with A2 type disorder, whereas FeCr_0.5Mn_0.5VAl is more ordered as evidenced by the presence of superlattice peaks. All samples show small saturation magnetizations at room temperature and the thermomagnetic curves M(T) are similar to that of a paramagnetic material. At the same time, the M(T) of FeCr_0.5Mn_0.5VAl is different and shows a slow magnetic transition similar to that of a ferrimagnetic material at 800 K. Our first principles calculations indicate that FeCrVAl and FeCr_0.5Mn_0.5VAl exhibit nearly perfect spin polarization, which may be further enhanced by mechanical strain. Both of these alloys exhibit ferrimagnetic alignment. At the same time, FeCrV_0.5Mn_0.5Al exhibits a relatively small value of spin polarization of only 24%, making it less attractive for practical applications.