Ferromagnetic shape memory effects in an iron palladium alloy

Abstract

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 5500G and 1MPa, 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 12MPa of compression 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◊10 3 J/m 3 . This work output is very close to the work output of Terfenol-D under this amount of compressive stress.