Crystal structure, magnetic properties and electronic structure of the MnBiintermetallic compound

Abstract

The low-temperature phase of the MnBi alloy has a coercivity μ0Hcof 2.0 T at 400 K and exhibits a positive temperature coefficientfrom 0 to 400 K. In the higher temperature range it shows a muchhigher coercivity than that of the NdFeB magnets, which suggests thatit has considerable potential as a permanent magnet for use at hightemperatures. In the temperature range from 30 to 150 K, the Mn atomis found to change its spin direction from a perpendicular to aparallel orientation with respect to thec axis.The anisotropy field increases with increasing temperature which gives rise to ahigher coercivity at the higher temperatures. The maximum energy product(BH)maxof the magnet is 7.7 and 4.6 MG Oe at room temperature and 400 K, respectively. Theelectronic structure of MnBi indicates that the Mn atom possesses a magnetic moment of3.6μB,and that the Bi atom has a magnetic moment of −0.15μBwhich is due to the s–d and p–d hybridization between Bi and Mn atoms. Wehave also investigated the volume dependence of the magnetic moments of Mnand Bi. The results indicate that an increase in the intra-atomic exchangesplitting due to the cell volume expansion leads to a large magnetic momentfor the Mn atom. The Mn magnetic moment attains a value of 4.6μBat a volume expansion rate of ΔV/V ≈ 100%.