Influence of extra La and annealing temperature on microstructure and magnetocaloric properties of La–Fe–Co–Si alloys

The microstructure, phase constitution and magnetocaloric properties of non-stoichiometric La1.7Fe11Co0.8Si1.2 alloys were investigated. Compared with stoichiometric La(Fe,Co,Si)13 alloys, a complex phase, including La(Fe,Co,Si)13 phase, La5Si3 phase, La(Fe,Co)Si phase, α-Fe phase and La oxide, can rapidly form upon annealing at 1323 K for 24 h in the present alloy. The resulting alloy exhibits a large magnetic entropy change of 7.5 J kg−1 K−1 at 271 K in a magnetic field change of 2 T. In addition, the annealed La1.7Fe11Co0.8Si1.2 alloy shows a reversible magnetic phase transition with zero hysteresis. These characteristics indicate that the present La-rich La–Fe–Co–Si compounds have potential for the applications as ambient magnetic refrigeration materials.