Effect of Gd doping on the microstructure and magnetocaloric properties of LaFe11.5Si1.5 alloy

Abstract

NaZn13-type La(Fe,Si)13 alloys are one of the most promising magnetocaloric materials near room temperature. However, the impact of lanthanide doping on their magnetocaloric properties has not been thoroughly investigated. Here, a series of Gd-doped La1−xGdxFe11.5Si1.5 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) alloys were designed and synthesized by arc melting and annealing. The microstructure of different phases and their influence on magnetic properties were investigated. The Gd doping at La sites was confirmed by the lattice contraction revealed by X-ray diffraction and elemental mapping analysis. After saturation at around x = 0.1, extra Gd leads to formation of Gd-rich Gd2Fe16Si phase. Moreover, doping of extra Gd inhibits the formation of La(Fe,Si)13 phase, resulting in significantly increased amount of the impurity phases (α-Fe and LaFeSi phase). The change of microstructure and composition causes the magnetic transition to shift from first order to second order. Because of Gd doping, the Curie temperature of La1−xGdxFe11.5Si1.5 increases, and the maximum entropy change decreases. Understanding the effect of Gd on the microstructure and magnetic properties can help us develop more rare-earth-doped La(Fe, Si)13 alloys.