Perpendicular Magnetic Anisotropy Revealed by c / a Ratio of Mn 2 NiB Heusler Alloy

c / a ratio effects on the magnetic properties of the Mn 2 NiB Heusler alloy are investigated by using effective field theory developed by Kaneyoshi. It is found that the Curie temperature and coercive fields of the Mn 2 NiB are obtained as Tc IT > Tc C > Tc NT = 0.92 and Hc IT > Hc C > Hc NT = 0.00 for c / a < 1 (inverse tetragonal), c / a = 1 (cubic), and c / a > 1 (normal tetragonal), respectively. These magnetic differences show that the c/ a ratio causes a perpendicular magnetic anisotropy (PMA). Therefore, we suggest that PMA strongly depends on the c/ a ratio, atomic distance, and exchange interactions between two atoms (Mn–Ni and Mn–B) on the ca surfaces of the Mn 2 NiB.