The Exchange Bias, Magnetoresistance, Magnetocalaric Effect Research In Ni(Co)MnIn Systerm

NiMn-based magnetic shape memory alloy show a series of novel physical phenomenon across its martensitic transition, such as magnetic shape memory effect, magnetoresistance effect, magnetocaloric effect, exchange bias effect, which has attracted much attention for its potential application in sensors, actuators and spintronic devices. This work researched the related physical effect in Ni(Co)MnIn alloy system. The alloy sample was made by arc-melting and the film sample was fabricated by sputtering.Firstly as the austenite and martensite phase are co-exist in NiMnIn alloy in low temperature, and the austenitic ferromagnetism was formed on matensitic antiferromagnetic matrix, which would induce the exchange bias effect. This work tuned the volume fraction of ferromagnetic phase in the alloy by changing its field cooling history. In this way, it gained the tunable exchange bias effect. Using consistent rotation model, the exchange bias with the rule of magnetization of ferromagnetic phase was fitted, and confirmed that the magnetic field can control the size of the ferromagnetic phase in NiMnIn alloy.Secondly in NiMnIn alloy thin film, this work observed the linearity good magnetoresistance phenomenon. The film magnetoresistance still keeps very good linearity, though magnetic field up to 12 T. It confirmed that the ferromagnetic and antiferromagnetic phase are also coexistence in the film by curve fitting and the external magnetic field could make the antiferromagnetic moment on the interface between them along the field direction gradually, which produced linear magnetoresistance.Finally by doping Co atoms on Ni position in NiMnIn alloy to improve the saturated magnetization and Curie temperature. When Co content is about 5%, applying a big enough magnetic field on this composition sample, the high-temperature austenite phase can be arrested to low temperature. In the subsequent temperature arising, the sample experiences the process of austenite, martensite, austenitic phase transformation. Based on this arresting phase exploring the phase changing temperature method, it is the realization of giant magnetocaloric effect from an extrinsic, materials processing-induced phase evolution in NiCoMnIn alloy beyond its intrinsic phase transition temperature.