The magnetic phase transition and magnetocaloric effects in Fe-doped MnNiGe alloys are investigated. The substitution of Fe for Ni decreases the structural transition temperature remarkably, resulting in the magnetostructural transition occurring between antiferromagnetic and ferromagnetic states in MnNil_χFexGe alloy. Owing to the enhanced ferromagnetic coupling induced by the substitution of Fe, metamagnetic behaviour is also observed in TiNiSi-type phase of MnNil-xFezGe alloys at temperature below the structural transition temperature.
In Ni-Mn-X（X=In,Sn,Sb） ferromagnetic shape memory alloys,a ferromagnetic transition from paramagnetic to ferromagnetic austenite and a martensitic transformation from ferromagnetic austenite to weak magnetic martensite occur in some particular composition ranges,in which abundant physical properties have been observed by the abrupt change of magnetization and resistivity around their transition temperatures in these alloys.Therefore,tuning the martensitic transformation temperature（TM） and enlarging the workingtemperature interval for Ni-Mn-X（X=In,Sn,Sb） alloys,are of great importance.In the present paper,we will focus on the effect of external factors,including pre-deformation,annealing,and high pressure annealing,on the magnetic transitions and the related magnetocaloric properties in Ni-Mn-Co-Sn ferromagnetic shape memory alloys.Our approaches and the main results in this particular field will be reviewed.
This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn Co-Sn ribbons.
The magneto-transport properties are investigated in metamagnetic CoMnSi0.ssGe0.12 alloy. By applying a magnetic field or increasing temperature, a metamagnetic phase transition from antiferromagnetic to ferromagnetic is observed in this alloy. Around the metamagnetic phase transition, CoMnSi0.88Ge0.12 alloy exhibits a large and negative magnetoresistance effect （-32%） under a magnetic field of 20 kOe （1Oe = 79.5775 A/m）, which is ascribed to the spin-dependent scattering of conduction electrons.
