Giant magnetic field-induced strain due to rearrangement of variants in an ordered Fe3Pt

Abstract

abstractMagnetic field-induced strain due to rearrangement of martensite variants in a ferromagnetic Fe3Pt alloy single crystal with degree of order of about 0.8 has been investigated. The alloy exhibits a martensitic transformation from an ordered L12-type structure to a tetragonal one at 85 K. The tetragonality of the martensite decreases as temperature decreases, and is about 0.945 at 14 K. When a magnetic field is applied along the [001]P direction (‘P’ stands for ‘parent’ phase) at 4.2 K after cooling down to the temperature under zero magnetic field, the specimen contracts more than 1% along this direction due to the rearrangement of variants. In association with this contraction, the fraction of the variant whose easy axis (c axis) is parallel to the [001]P direction reaches 70%. On the other hand, when the magnetic field is removed, a part of the strain initially induced by the magnetic field recovers and its value is 0.6% at 4.2 K. This recoverable strain repeatedly appears in the subsequent field applying and removing processes. The rearrangement of variants by a magnetic field is also confirmed by an X-ray measurement under the magnetic field. The energy dissipated due to the rearrangement of variants by the magnetic field is obtained from the magnetization curve to be about 180 kJ/m3. Based on these results and the magnetocrystalline anisotropy constant of the martensite phase (Ku < 500 kJ=m3 at 4.2 K), the mechanism of rearrangement of variants under the magnetic field is discussed.