Simultaneous magnetooptic observation and thermomagnetic analysis of phase transitions in shape-memory Ni–Mn–Ga alloys

Abstract Direct observations of the austenite and martensite twin and magnetic domain structures are combined with thermomagnetic analysis (low-field AC susceptibility temperature measurements) of phase transitions in ferromagnetic shape memory alloys Ni 2+ x Mn 1− x Ga. Thermal hysteresis and magnetization jumps are clearly resolved by both techniques. Large Barkhausen-like jumps associated with discontinuous phase boundary and martensite twin motion are observed during the austenite–martensite transformation in contrast to the smooth ferromagnetic–paramagnetic transition near the Curie temperature.