Temperature- and magnetic-field-induced phase transitions in Fe-rich FePt alloys

Abstract

Structural and magnetic properties of the FexPt100-x (x=78–88) alloys have been investigated. It is found that for all of the investigated compositions, a phase transition occurs from the disordered γ phase to the ordered α phase during cooling, while a reverse process takes place during heating. Moreover, magnetic fields also induce a phase transition from the γ phase to the α phase near the transition temperature. The temperature- and magnetic-field-induced phase transitions give rise to a huge negative thermal expansion and thus a giant magnetic entropy change (up to 39.8 J/kg K for the alloy with x=79). The contribution of the magnetic field induced phase transition to the total magnetic entropy change is estimated to be around 20%–25%.