Microstructure and improved magnetocaloric properties: LaFeSi/LaAl magnets prepared by spark plasma sintering technique

Abstract

Bulk LaFeSi magnets with the addition of LaAl alloy showing excellent performance were prepared by the spark plasma sintering (SPS) technique. The effects of heat treatment and various amounts of LaAl on the microstructure and magnetocaloric properties were investigated in details. It was found that appropriate amounts of LaAl can promote the peritectic reaction, and LaFeSi magnets with a high 1:13 phase amount can be obtained. Due to the unfavorable effects of Al in the peritectic reaction, excess addition of LaAl alloy was not beneficial to the formation of the 1:13 phase. The addition of 5 wt.% LaAl was most favorable to the formation of the 1:13 phase. Furthermore, heat treatment had important effects on the formation of the 1:13 phase and magnetocaloric performance. For SPSed LaFeSi magnets with 5 wt.% LaAl, the maximum values of magnetic entropy change (−ΔS M)max and refrigerating capacity (RC) are 18.07 J kg−1 K−1 and 327.55 J kg−1 under the field changes of 0–5 T, respectively. The variation of Curie temperature (T C) depended on the joint effects from the antiferromagnetic interaction between Fe–Al atoms and the ferromagnetic interaction between Fe–Fe atoms.