Enhanced magnetic entropy change and refrigeration capacity of La(Fe,Ni)11.5Si1.5 alloys through vacuum annealing treatment

Abstract

The microstructure and magnetic properties including magnetocaloric performance of as-prepared and heat-treated La(Fe,Ni)11.5Si1.5 alloys were systematically investigated. The experimental results indicate that the as-prepared La(Fe,Ni)11.5Si1.5 alloys are composed of α-Fe phase and LaFeSi phase, and the saturation magnetization Ms can achieve 159.1 emu/g, as for the larger content of ferromagnetic α-Fe phase. The peritectic reaction occurs during vacuum annealing process, and the decrease of α-Fe phase content reduced the hysteresis loss, meanwhile the NaZn13-type structure (1:13 phase) generated. In particular, the magnetocaloric properties of La(Fe,Ni)11.5Si1.5 alloys annealed at 1373 K are superior to that of annealed at 1323 K. And the magnetic entropy change (-ΔSm) of the alloys annealed at 1373 K is up to 20.87 J kg−1 K−1, while Refrigeration Capacity (RC) reaches 415.59 J kg−1 at a magnetic field of 5 T. From the perspective of solid-phase reaction dynamics, the increase of annealing temperature could beneficially accelerate the peritectic reaction process, and result in the increasing content of 1:13 phase, thereby enhancing their magnetocaloric characteristics. Therefore, the microstructure and magnetocaloric properties of La(Fe,Ni)11.5Si1.5 alloys could be effectively modulated by optimizing the annealing process, and it also provides a significant technical reference for the practical application of room-temperature Magnetic Refrigeration (MR) technology.