First Principles Calculation of Magnetocrystalline Anisotropy Energy of MnBi and MnB_(1-x)Sn_x

We calculated the magnetic anisotropy constant Ku of MnBi using a first principles approach, and obtained a negative Ku in agreeable with experimental results. Furthermore, we also found a band filling dependence indicating that a slight decrease in the valence electron number will change Ku from negative to positive. When some of the Bi is replaced with Sn to decrease the valence electron number, the Ku value of MnBi1-xSnx drastically changes to a positive value, Ku~2 MJ/m3, for x > 0.05.