Phase equilibria and magnetic properties of Heusler-type ordered phases in the Co–Mn–Ga ternary system

Abstract Phase equilibria at 800, 900 and 1000 °C, as well as order–disorder and magnetic transitions of Heusler-type ordered phase were investigated in the Co–Mn–Ga ternary system. The β phase with bcc structure including the Heusler-type ordered phase exists in a wide composition range of the ternary system. It was confirmed by STEM–HAADF observation that the crystal structure of the Heusler-type ordered alloy Mn 2 CoGa is L 2 1b -type Fm 3 ¯ m (i.e., (Mn,Co) 2 MnGa), but not inverse-Heusler (Hg 2 CuTi) type F 4 ¯ 3 m . The L 2 1 / B 2 order–disorder transition temperature shows a maximum at the stoichiometric composition of Co 2 MnGa and the Curie temperature of the L 2 1 phase decreases with increasing Ga content. Magnetic moments converted from magnetization curves at 4.2 K for Co x Mn (76− x ) Ga 24 alloys well follow the generalized Slater–Pauling rule in the composition of 25 ⩽  x  ⩽ 50, and magnetization curves indicate very small high-field magnetic susceptibility.