Experimental and theoretical study of room temperature Heusler ferrimagnets: CuMnCrAl, NiFeCrAl, Ni0.5Fe1.5CrAl; An aliovalent analogs of the Co2CrAl compound

Some Heusler compounds, particularly Co${}_2$CrAl, have been extensively studied due to their potential spintronic applications related to their half-metallic ferromagnet (HMF) properties, as well as magnetic ordering near room temperature. Here, we report aliovalent analogs to that compound, where we replaced expensive and problematic cobalt with its neighboring elements in the periodic table, in a way that we conserved the number of valence electrons. These compounds were not studied experimentally before. Our XRD measurements show that they crystallize in the Heusler structure, whereas our magnetization measurements show that CuMnCrAl, NiFeCrAl, Ni_0.5Fe_1.5CrAl have higher magnetic ordering temperatures than Co${}_2$CrAl — 354 K, 541 K, and 465 K, respectively.

We also present data for Cu_0.5Mn_0.5Ni_0.5Fe_0.5CrAl which is magnetic too, but at lower temperatures. Susceptibility measurements at higher temperatures show that the magnetic order is ferrimagnetic, with some magnetic sublattices antiparallel to others. It is also confirmed by comparison of our DFT calculations with Mössbauer spectroscopy investigations and magnetization data. In our ab initio calculations, we also compare the three structural models possible for XX’YZ quaternary Heusler structure with Mössbauer and magnetization data, and conclude whether previously claimed HMF state in NiFeCrAl is possible. We also have shown that for completely disordered structure (alloy) the magnetic moments are preserved, and they are higher than experimentally observed.