Magnetic and structural transition of Ni 50+ xMn 25− x/2 Ga 25− x/2 ( x=2–5) alloys

Abstract

Magnetic and structural transitions of non-stoichiometric Ni 50+ x Mn 25− x/2 Ga 25− x/2 ( x=2–5) alloys are systematically investigated. Differential scanning calorimetry and modified thermogravimetry (TG) are used to measure magnetic and structural transitions simultaneously. The structural transition temperatures increase monotonically with increasing Ni substitution for Mn and Ga. Different magnetic transition sequences on heating were observed from ferromagnetic martensite to ferromagnetic autensite, then to paramagnetic autensite, from ferromagnetic martensite to paramagnetic austensite or from ferromagnetic martensite to paramagnetic martensite, respectively. Three kinds of NiMnGa alloys were obtained according to the sequence of the structural and magnetic transition, whose structural transition temperatures are lower, equal to or higher than the magnetic transition temperatures.