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

Phase equilibria at 800, 900 and 1000 degrees C, as well as order-disorder and magnetic transitions of Heusler-type ordered phase were investigated in the Co-Mn-Ga ternary system. The beta 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 Mn2CoGa is L2(1b)-type Fm (3) over barm (i.e., (Mn,Co)(2)MnGa), but not inverse-Heusler (Hg2CuTi) type F (4) over bar 3m. The L2(1)/B2 order-disorder transition temperature shows a maximum at the stoichiometric composition of Co2MnGa and the Curie temperature of the L2(1) phase decreases with increasing Ga content. Magnetic moments converted from magnetization curves at 4.2 K for CoxMn(76-x)Ga24 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. (C) 2015 Elsevier B.V. All rights reserved.