Homogeneity of Curie Temperature in La (Fe, Si) $_{13}$ Compounds by Co and C Doping

The microstructure and magnetic properties for LaFe_10.85 Co_0.65Si _1.5C_0.2, LaFe_11.5Si_1.5C_0.2 and LaFe_10.85Co_0.65Si_1.5 compounds were investigated. The ingots were prepared by 5 kilogram Vacuum Induction Melting Furnace. Then LaFe _10.85Co_0.65Si_1.5C_0.2 and LaFe_11.5Si_1.5C_0.2 thin strips were prepared by the strip-casting process. The DSC measurement shows that the maximum latent heat of LaFe_11.5Si_1.5C_0.2 thin strips has been obtained after annealing at 1353 K for 12 h, longer time annealing seems to be no good for latent heat. Substitute Co for Fe could cause inhomogeneous distribution of Curie temperature (T_C) in the bulk ingots, but the inhomogeneity can be improved by preparing the strip from the ingot. Under magnetic field changes of 0-1.5 T, the magnetic entropy change near the Curie temperature was about -11.1 J/kg· K and -4.0 J/kg· K for LaFe_11.5Si_1.5C_0.2 and LaFe_10.85Co_0.65Si_1.5C_0.2, respectively.