Magnetic properties of the Co-doped MnNiGe system in high magnetic field

Abstract

High-field magnetic properties of the Co-doped MnNiGe system, Mn0.9Co0.1NiGe, which undergoes a ferromagnetic and structural phase transition at Tt= 215 K, were investigated. Additionally, first-principles calculations were performed on Mn0.875Co0.125NiGe. The magnetic field, μ0H, dependence of magnetization, M(μ0H), of Mn0.9Co0.1NiGe saturates at ∼73 A⋅m2⋅kg−1 below Tt 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, ΔS, peaks around Tt, reaches -79.7 J⋅K−1⋅kg−1 for Δμ0H = 30 T. The density of states (DOS) calculated for Mn0.875Co0.125NiGe in the paramagnetic-hexagonal phase (Tt<T) exhibits a peak at the Fermi energy, EF, with significant contributions from the Mn 3d orbitals. In the ferromagnetic-orthorhombic phase, DOS at EF is suppressed, indicating that the structural phase transition at Tt in this system is primarily driven by the band Jahn-Teller effect.