Effect of Co substitution on ferrimagnetic Heusler compound Mn3Ga

Abstract

Effect of Co substitution on Mn3Ga is investigated using first-principles study for structural and magnetic properties. Without Co, ferrimagnetic Heusler compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co concentration (x), Mn3Ga prefers tetragonal (cubic) phase when x≤0.5 (x≥0.5). Ferrimagnetism is robust regardless of x in both phases. While magnetic moments of two Mn do not vary significantly with x, magnetic moments of Co in two phases exhibit different behaviors, leading to distinct features in absolute value of total magnetic moment (|Mtot|). When x≤0.5, in tetragonal phase, magnetic moment of Co is vanishingly small, resulting in a decrease of |Mtot| with x. In contrast, when x≥0.5, in cubic phase, magnetic moment of Co is roughly 1 μB, which is responsible for the increase of |Mtot|. Electronic structure is analyzed with partial density of states for various x. To elucidate the counterintuitively small Co moment, the magnetic exchange interaction is investigated, where exchange coefficient between Co and Mn(II) in x≤0.5 is much smaller than that in x≥0.5.