Martensitic transformation and magnetic properties of ferromagnetic shape memory Fe 66Pd 30Rh 4 alloys

Abstract

This study mainly shows that in the Fe 66Pd 30Rh 4 (at%) alloys, the L1 0 phase plays an important role in magnetostriction due to the interplay of L1 0 martensitic twins with magnetic domains. The L1 0 martensitic twin structure exhibits a strong magnetocrystalline anisotropy energy constant ( K u =1.27–2.84×10 6 (ergs/cm 3)) along the tetragonal c axis direction. In addition, the L1 0 tetragonal martensitic twin structure shows both a perfect shape memory and a reversible shape memory effect; therefore, it is expected to be applicable in magneto-mechanical applications (such as microactuators or springs). However, in this study, we discover that solution treatment (ST) and aging heat treatments of Fe 66Pd 30Rh 4 ferromagnetic shape memory alloys influence the behavior of the martensitic transition, which is associated with the change in magnetic properties. The process of a thermoelastic L1 0+L1 m twin phase decomposition→non-thermoelastic L1 0+L1 m + α bct structure in Fe 66Pd 30Rh 4 alloys during solution treatment and aging at 400–550 °C for various times is studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The relation of phase separation morphology to the magnetic property change is examined with a superconducting quantum interference device (SQUID) magnetometer, and magnetostriction measurement is performed with a strain gage method and magnetostrictive meter setup. The results indicate that the process of martensitic transformation during aging leads to an increase in coercivity and a decrease in magnetostriction, simultaneously.