First order magneto-structural transition and magnetocaloric effect in MnNiGe0.9Ga0.1

The first order magneto-structural transition (Tt≃95 K) and magnetocaloric effect in MnNiGe0.9Ga0.1 are studied via powder x-ray diffraction and magnetization measurements. Temperature dependent x-ray diffraction measurements reveal that the magneto-structural transition remains incomplete down to 23 K, resulting in a coexistence of antiferromagnetic and ferromagnetic phases at low temperatures. The fraction of the high temperature Ni2In-type hexagonal ferromagnetic and low temperature TiNiSi-type orthorhombic antiferromagnetic phases is estimated to be ∼40% and ∼60%, respectively at 23 K. The ferromagnetic phase fraction increases with increasing field which is found to be in non-equilibrium state and gives rise to a weak re-entrant transition while warming under field-cooled condition. The material shows a large inverse magnetocaloric effect across the magneto-structural transition and a conventional magnetocaloric effect across the second order paramagnetic to ferromagnetic transition. The relative cooling power which characterizes the performance of a magnetic refrigerant material is found to be reasonably high compared to the other reported magnetocaloric alloys.