Effect of Secondary Phases on Multi-Step Phase Transitions and Magnetocaloric Properties in MnFe-Based Alloys

Abstract

This study investigated the effect of the secondary phases on multi-step phase transitions and the magnetocaloric properties depending on the Ge content in the MnFeCoPSiGe alloys. Two-step phase transitions were observed by the variations of the Fe2P-type hexagonal structure (first-order) and secondary phases (second-order). The Curie temperature alters with non-linear behavior consistent with change of the lattice parameters. In addition, the magnetic entropy change decreased with the increase of the Ge content and, subsequently, fractions of the secondary phases. However, the morphological variation of microstructure, distributed as a circular-type shape of the Fe2P-type hexagonal structure in the Ge-rich matrix, increased the magnetic entropy change. Therefore, the addition of Ge enables the control of the Curie temperature to be applicable for high temperature operating devices. The control of the secondary phases and morphology of the microstructure are crucial to improve the phase transition and magnetic entropy change.