Magnetic field-induced deformation in single- and poly-crystalline Ni/sub 2/MnGa

Summary form only given. The shape changes of ferromagnetic shape memory alloys (FMSMAs) induced by magnetic field associated with structural and magnetic properties have been investigated to understand the relation between martensite transformation and magnetic properties. In the present study, two mechanisms explaining magnetic field-induced strain behavior and their related energy terms were introduced and shape change under magnetic field application were observed at temperatures below M/sub f/ and above A/sub f/. Two alloys, a Ni-19.5at%Mn-27at%Ga single crystal and a Ni-19.5at%Mn-27at%Ga polycrystal, were chosen to observe shape change by application of magnetic field at temperatures below M/sub f/ and above A/sub f/.The authors show strain as a function of magnetic field of Ni-19.5at%Mn-27at%Ga single crystal at 23/spl deg/C below M/sub f/ (-13/spl deg/C). Strain was measured on a surface of the single crystal along [2~ 21] based on parent phase orientation and magnetic field was applied along [6~7~2]. As seen, the field-induced strain increase in a parabolic form with increasing magnetic field. In this case, the induced maximum strain at a magnetic field of 10 kOe is about 0.16%. The difference between the theoretical (0.67%) and measured (0.16%) strains indicate that shape change occurred in only some range of magnetic field on the condition that the total energy (E/sub total/) necessary for the movement of martensite variant interfaces is smaller than magnetic energy (E/sub magnetic energy/) produced by magnetic field. Martensite transformation takes places by the application of magnetic field of 10 kOe at high temperatures above A/sub f/ in a polycrystalline Ni-19.5at%Mn-27at%Ga. Maximum induced strain associated with the transformation was 0.82% for the polycrystalline alloy A under preloading of 126MPa.