Martensitic transformation and magnetic properties in Heusler CoNiGa magnetic shape memory alloys

A series of samples of CoNiGa were studied with regard to their structure, martensitic transformation, magnetic properties, and thermally induced strains. Optical microscopy shows that a single martensite phase exists in the alloys, which accords with the X-ray diffraction result. The martensitic transformation temperature (higher than 350 K) decreases with increasing Co content when keeping the ratio of Ni/Ga constant; this was attributed to the size factor. The saturation magnetization, about 30 emu/g, increases with increasing Co content. In addition, a complete shape recovery with a phase transformation strain of 1% appears in the oriented martensitic variants.