Ferromagnetic shape memory effects in an iron palladium alloy

This paper presents the results of an extensive series of experiments conducted on Fe₇₀Pd₃₀ using a recently developed apparatus, the Magneto-Mechanical Testing Machine. These experiments were designed to investigate the ferromagnetic shape-memory behavior of Fe₇₀Pd₃₀ and test the predictions of a theory that assumes the magnetizations of the material are constrained to lie in the easy directions and the material strains are constrained to be the shape-memory transformation strains. It was found that a specimen made of Fe₇₀Pd₃₀ single crystal lengthens when a magnetic field is applied along its c axis (short axis of FCT lattice) while the specimen is under uniaxial compression in the c direction. This behavior agrees with the predictions of the constrained theory and magnetic anisotropy measurements. The maximum field-induced strain change measured in this material is about 0.009 at 5500 G and -1 MPa, which is one fifth of the theoretical prediction. This is attributed to the magnetization rotation away from the easy directions caused by insufficient magnetic anisotropy. Under -12 MPa of compresssion the field-induced strain change is considerably smaller reaching only about 0.0008, but this change gives the largest work output observed of 9.6 × 10³ J/m³. This work output is very close to the work output of Terfenol-D under this amount of compressive stress.