Effect of interstitial nitrogen on magnetism and entropy change of LaFe11.7Si1.3 compound

Crystal structure, magnetism and magnetocaloric properties of LaFe11.7Si1.3Ny (y=0, 1.3) compounds have been studied by X-ray diffraction and magnetic measurements. The LaFe11.7Si1.3Ny compounds present a cubic NaZn13-type structure. Insertion of 1.3 nitrogen atoms per LaFe11.7Si1.3 formula increases the lattice parameter and Curie temperature from 11.467 to 11.733 A and from 190 to ∼230 K, respectively. Besides, the absorption of nitrogen drives drastically the magnetic transition from first to second order and accordingly strongly decreases the magnetocaloric effect compared to the parent alloy. Under an external field change of 5 T, the value of isothermal entropy change -ΔS is about 28 and 3.5 J/kg K for LaFe11.7Si1.3 and LaFe11.7Si1.3N1.3, respectively, close to their Curie temperature. However, the relative cooling power RCP(S) of the nitride is about half that of the parent alloy