Magnetic Field-Induced Strain of Martensite and Parent Phases in a Ferromagnetic Shape Memory Iron-Palladium Alloy

Abstract

We have investigated the magnetic field-induced strain (MFIS) of the martensite and the parent phases in an Fe-31.2Pd(at.%) single crystal, which exhibits a martensitic transformation at TM = 230K. Below TM, a large MFIS of several percent appears due to rearrangement of martensite variants and this strain remains when a magnetic field is removed. Such rearrangement depends on magnetic field direction; Variants are perfectly rearranged into the variant, which lowers the magnetocrystalline anisotropy energy most, when a magnetic field is applied along [001]P, and partially when [011]P and hardly when [111]P (“P” represents “parent” phase). The dependence on the field direction can be explained by comparing the magnetic shear stress tmag with the shear stress t req required for rearrangement of variants. Above the temperature, TM, a relatively large MFIS appears and it increases up to about 10-3 with decreasing temperature from 280 K toward TM. This MFIS is probably caused by anomalies of some physical properties, such as elastic constant and dipole-dipole interaction coefficient in the parent phase.