Antiferromagnetism and low-temperature specific heat of β-Mn1-xIrx alloys

The site preference of Ir, the temperature dependence of magnetic susceptibility and the low-temperature specific heat of β-Mn_1-xIr_x alloys have been investigated. In Mn_1-xIr_x alloys, the β-phase exists below x = 0.102. From x-ray diffraction patterns, almost all Ir atoms are substituted at site 1 in the β-Mn lattice. The electronic specific heat coefficient γ is proportional to the Néel temperature T_N in the form T_N ^3/4 in regions of low-Ir concentration. With increasing x, however, the gradual decrease in γ leads to a relative increase in γ from the straight line. Therefore, it is concluded that the magnetic state of the β-Mn_1-xIr_x alloys varies from a weak itinerant-electron antiferromagnet to an intermediate antiferromagnet with increasing Ir concentration. The point to observe is that the γ versus T_N ^3/4 plots give a universal line for all the β-Mn alloy systems over the entire concentration range.