R. Y. Umetsu, H. Ishikawa, K. Kobayashi, A. Fujita, K. Ishida, R. Kainuma, Tohoku University, Sendai, Japan
Ni-based ferromagnetic shape memory alloys (FSMAs) such as Ni2MnGa have attracted considerable interest as a new type of materials exhibiting a large strain. It was reported that the magnetic properties of Ni2MnAl Heusler alloy are significantly sensitive to the annealing condition in contrast to those of the Ni2MnGa. In order to clarify origin of the differences in those properties between the Ni2MnGa and Ni2MnAl alloys, magnetic measurements and micro-structural examinations in Ni2Mn(GaxAl1-x) shape memory alloys were performed by SQUID magnetometry, electron and X-ray diffractions and transmission electron microscopic observation, respectively.
By the magnetic measurements using the specimens annealed at various temperatures, it was found that in all the specimens the saturation magnetic moment Is and the Curie temperature TC increase with decreasing annealing temperature. This fact suggests that the degree of long-range order of the Heusler-type structure mainly effects the Is and TC. On the other hand, anti-phase domains (APDs), which are introduced by annealing or quenching, strongly affect magnetization process of the alloys, because anti-phase boundary (APBs) act as pinning sites for the magnetic domain walls. It can be concluded that the magnetic properties of the Ni2Mn(GaxAl1-x) alloys can be controlled by the degree of order and the APDs size, which depend on the annealing condition.
Summary: In order to clarify the origin of the differences in magnetic properties between the Ni2MnGa and Ni2MnAl alloys, magnetic measurements and micro-structural examinations in Ni2Mn(GaxAl1-x) shape memory alloys were performed by SQUID magnetometry, electron and X-ray diffractions and transmission electron microscopic observation, respectively.
