Magnetic properties and magnetocaloric effects in NaZn₁₃-type La(Fe, Al)₁₃-based compounds

In this article, our recent progress concerning the effects of atomic substitution, magnetic field, and temperature on the magnetic and magnetocaloric properties of the LaFe_13-xAl_x compounds are reviewed. With an increase of the aluminum content, the compounds exhibit successively an antiferromagnetic (AFM) state, a ferromagnetic (FM) state, and a mictomagnetic state. Furthermore, the AFM coupling of LaFe_13-xAl_x can be converted to an FM one by substituting Si for Al, Co for Fe, and magnetic rare-earth R for La, or introducing interstitial C or H atoms. However, low doping levels lead to FM clusters embedded in an AFM matrix, and the resultant compounds can undergo, under appropriate applied fields, first an AFM-FM and then an FM-AFM phase transition while heated, with significant magnetic relaxation in the vicinity of the transition temperature. The Curie temperature of LaFe_13-xAl_x can be shifted to room temperature by choosing appropriate contents of Co, C, or H, and a strong magnetocaloric effect can be obtained around the transition temperature. For example, for the LaFe_11.5Al_1.5C_0.2H_1.0 compound, the maximal entropy change reaches 13.8 J·kg^-1·K^-1 for a field change of 0-5 T, occurring around room temperature. It is 42% higher than that of Gd, and therefore, this compound is a promising room-temperature magnetic refrigerant.