Weak ferromagnetic – Antiferromagnetic transition in MnFe0.25Sb

Magnetic properties of intermetallic MnFe0.25Sb through magnetization and heat capacity measurements with the support of powder XRD patterns and electronic structure calculations are presented in this paper. Fe atoms occupy the vacant 2d sites in MnSb and as a result, the a-parameter increases and the c-parameter decreases. Both the magnetic ordering temperature and the saturation magnetization are smaller than those of MnSb. An A-type antiferromagnetic behaviour, where the Mn moments order ferromagnetically in the ab-plane (intra-layer) and the interlayer (along the c-direction) exchange is antiferromagnetic, was observed below 25 K. Specific heat data too revealed a small change in entropy at 28 K, consistent with the observations from the magnetization data. Furthermore, at 241 K a ferrimagnetic to paramagnetic transition was observed. Electronic structure calculations showed that MnFe0.25Sb stabilized in an A-type antiferromagnetic (AFM) like ground state. In this state, the exchange interactions between the moments of (i) Mn atoms along the c direction and (ii) Mn and Fe atoms are antiferromagnetic and is ferromagnetic between the moments of Mn atoms in the ab-plane. The competition between these interactions leads to magnetic frustration, which also emphasizes the near-degeneracy of different magnetic states.