Synthesis and characterization of LaFe11.57Si1.43 and LaFe11.57Si1.43H alloys for magnetic refrigeration applications

Abstract

This study is based on the need to consolidate environmentally friendly technology to overcome pollution problems caused by conventional refrigerators. Compounds based on La(Fe,Si)13 have attracted much attention in many fields of industry as low cost materials as well as bright prospects for practical applications. The alloys obtained in this study are based on the LaFe11.57Si1.43 and LaFe11.57Si1.43H systems. These alloys were produced by melt-spinning of samples initially melted in an electric arc furnace and homogenized by heat treatment at 1050 °C for 2 h. LaFe11.57Si1.43 alloys to be hydrogenated with very little amount of 0.9 MPa of 5% H2/Ar gas and heat-treated at 723 K for one hour. An analysis of the crystal structure using X-ray diffraction measurements revealed that all alloys showed La-Fe-Si (1:13 phase) as the majority one with 85.8 wt% and 83.1 wt% for LaFe11.57Si1.43 and LaFe11.57Si1.43H respectively. The hyperfine and magnetic behavior of the alloys were studied by means of Mössbauer spectroscopy, and it was observed that the LaFe11.57Si1.43 alloy was fitted with a singlet and a doublet corresponding to 1:13 phase with a total spectral area of 72.5%, and in the LaFe11.57Si1.43H alloy exhibited a ferromagnetic behavior at room temperature with a hyperfine field of 19.4 T. Using vibrating sample magnetometry, it was demonstrated that the essential magnetic parameters to optimize the magnetocaloric effect, Curie temperature, and saturation magnetization at room temperature, significantly improved from 228.23 K to 308.1 K and 37.03 A m2kg−1 to 120 A m2kg−1, respectively, with the addition of hydrogen. Endothermic peaks possibly associated with first-order magnetic phase transition were found in each of the La-Fe-Si alloys using differential scanning calorimetry, coinciding with its TC value of 315.1 K. These results demonstrate that hydrogenation under a poor hydrogen gas atmosphere is an effective and safer method for improve the magnetocaloric properties of the LaFe11.57Si1.43system.