Magnetic Properties of the Co-doped MnNiGe System in High Magnetic Field

High-field magnetic properties of the Co-doped MnNiGe system, Mn0.9Co0.1NiGe, which undergoes a ferromagnetic and structural phase transition at T-t = 215 K, were investigated. Additionally, first-principles calculations were performed on Mn0.875Co0.125NiGe. The magnetic field, mu H-0, dependence of magnetization, M(mu H-0), of Mn0.9Co0.1NiGe saturates at similar to 73 A.m(2).kg(-1) below T-t and shows significant hysteresis in the range of 215 <= T <= 230 K due to the magnetic-field-induced structural phase transition. The isothermal magnetic entropy change, Delta S, peaks around T-t, reaches -79.7 J.K-1.kg(-1) for Delta mu H-0 = 30 T. The density of states (DOS) calculated for Mn0.875Co0.125NiGe in the paramagnetic-hexagonal phase (T-t < T) exhibits a peak at the Fermi energy, E-F, with significant contributions from the Mn 3d orbitals. In the ferromagnetic-orthorhombic phase, DOS at E-F is suppressed, indicating that the structural phase transition at T-t in this system is primarily driven by the band Jahn-Teller effect.