J. Phys. IV France 112 (2003) 93
Martensitic transformation in Fe-based shape memory alloys under magnetic fieldT. Kakeshita1, T. Fukuda1, T. Terai1, T. Takeuchi2 and K. Kishio3
1 Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
2 Low Temperature Center, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
3 Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8666, Japan
Effects of magnetic field on martensitic transformations have been examined in order to know a magnetic field-induced martensitic transformation by using Fe 3Pt and Fe-Ni-Co-Ti shape memory alloys and an Fe-Ni alloy polycrystals, and control of variants by magnetic field by using Fe-Pd, Ni 2MnGa and Fe 3Pt shape memory alloy single crystals. Following results were obtained: (i) The effects of magnetic field on the martensitic transformation start temperature is explained by the equation proposed by our group. (ii) Magnetoelastic martensitic transformation (maretensites are induced only while a magnetic field is applied and are transformed back to the parent phase when the magnetic field is removed) appears in an ausaged Fe-Ni-Co-Ti shape memory alloy. (iii) In Fe-31.2Pd(at.%), whose easy axis is the a-axis in martensite state, a large expansion of about 3% appears in [OOl] (P is the symbol of the parent phase) direction at 77 K by applying a magnetic field along  direction. In Ni 2MnGa, whose easy axis is the c-axis in martensite state, a large contraction of about 3.8% appears in  direction at 77 K by applying a magnetic field along  direction. These strains are nearly the same as those expected from perfect conversion to the preferred variants under magnetic field. In Fe 3Pt, whose easy axis is the c-axis in martensite state, a large contraction of about 2.3% appears in  direction at 4.2 K by applying a magnetic field along  direction, and a part of this contraction (0.6%) recovers as the field is removed. Considering results of (iii), the mechanism of conversion of variants by magnetic field is discussed.
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