Abstract
This work reports on first principles calculations of the electronic and magnetic structure of tetragonal Heusler compounds with the composition Rh$_2$Fe$_{x}$Co$_{1-x}$Sb ($0\leq x\leq1$). It is found that the magnetic moments increase from 2 to 3.4~$\mu_B$ and the Curie temperature decreases from 500 to 464~K with increasing Fe content $x$. The $3d$ transition metals make the main contribution to the magnetic moments, whereas Rh contributes only approximately 0.2~$\mu_B$ per atom, independent of the composition. The paper focuses on the magnetocrystalline anisotropy of the borderline compounds Rh$_2$FeSb, Rh$_2$Fe$_{0.5}$Co$_{0.5}$Sb, and Rh$_2$CoSb. A transition from easy-axis to easy-plane anisotropy is observed when the composition changes from Rh$_2$CoSb to Rh$_2$FeSb. The transition occurs at an iron concentration of approximately 40\%.
Highlights
Permanent or hard magnets are made of bulk materials with strong anisotropy, which may be based on magnetocrystalline anisotropy, shape anisotropy, or both
One advantage of Heusler compounds is that most of them do not contain rareearth elements; rather, the magnetic properties are provided by 3d transition metals
The electronic and magnetic structure of tetragonal Heusler compounds with the composition Rh2FexCo1−xSb were investigated by ab initio calculations
Summary
Permanent or hard magnets are made of bulk materials with strong anisotropy, which may be based on magnetocrystalline anisotropy, shape anisotropy, or both. The Rh2T M alloys (T = V, Mn, Fe, Co; M = Sn, Sb) crystallize in a regular tetragonal structure with space group I 4/mmm and are expected to exhibit uniaxial anisotropy when the 3d transition metals have large moments. Experiments on the crystal structure and magnetic properties of Rh2-based Heusler compounds were reported by Dhar et al [1], who observed a tetragonal structure and a magnetic moment of 1.4 μB in the primitive cell. This work proposed that thin films of Rh2CoSb exhibit uniaxial, perpendicular anisotropy with the easy direction along the c ([001]) axis. Experiments and calculations both suggest that Rh2CoSb might be a suitable hard magnetic material with uniaxial anisotropy.
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