Magnetocaloric Properties of AlFe2B2 Including Paramagnetic Impurities of Al13Fe4

Abstract

AlFe2B2 produced by using a conventional arc melter has a ferromagnetic material with a Curie temperature (T-C) of around 300 K, but the arc-melt generates paramagnetic Al13Fe4 impurities during the synthesis of AlFe2B2. Impurities are brought to cause a decrease in magnetocaloric effects (MCEs). To investigate the effects of Al13Fe4 impurities on MCEs, we prepared and compared ascast and acid-treated samples, where the acid treatment was performed to remove the Al13Fe4 impurities. For the structural analysis, powder X-ray diffraction was carried out, and the measured data were subjected to a Rietveld refinement. The presence of Al13Fe4 impurities in the as-cast sample was observed in the phase analysis measurements. Magnetic properties were investigated by using Superconducting Quantum Interference Device (SQUID) measurements for the as-cast and the acid-treated AlFe2B2 samples. From isothermal magnetization measurements, Arrott plots were obtained showing that the transition of AlFe2B2 has a second-order magnetic phase transition (SOMT). The T-C and the saturation magnetization increased for the acid-treated sample due to removal of the paramagnetic impurities. As a consequence, the magnetic entropy change (-Delta S) increased in the pure AlFe2B2 samples, but the full width at half maximum in the plot of -Delta S vs. T decreased due to the absence of impurities.