Bachelorthesis: Calculation of the magnetic properties of quarternary ThMn$_{12}$-type compounds with Zr as a substitution for Nd

Abstract

This research aims to identify an alternative solution for the Nd$_2$Fe$_{14}$B magnet in light of the scarcity of rare earth (RE) resources. The investigation uses density functional theory (DFT) calculations to assess the effect of partial substitution of Nd with the transition metal (TM) Zr within the ThMn$_{12}$ structure, focusing specifically on the (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{11}$Ti compound. In order to gain a comprehensive understanding, an investigation of intrinsic and magnetic properties, including saturation magnetisation ($M_S$), Curie temperature ($T_C$) and magnetic anisotropy energy (MAE), is carried out on binary to quinary compounds RFe$_{11-y}$Ti$_{y}$ (R: Nd, Zr and Zr$_{0.5}$Nd$_{0.5}$, y: $0 \leq y \leq 1$) and (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. The substitution of Ti at different concentrations for thermodynamic stabilisation is studied in ternary and quaternary compounds RFe$_{12-y}$Ti$_y$ ($0 \leq y \leq 1$). In addition, the influence of Co on phase stability and intrinsic magnetic properties is studied in the quinary compound (Zr$_{0.5}$Nd$_{0.5}$)Fe$_{10}$CoTi. Special attention is given to the treatment of the 4$f$-electrons of Nd and their interaction with the 3$d$-electrons. Theoretical results are compared with available experimental data, although the limited availability of data, especially for Zr-containing compounds, limits the scope of such comparisons. Based on the literature and the calculations of binary and ternary compounds, the calculations of quaternary and quinary compounds are encouraged. Promising magnetic properties of an Nd-lean quaternary compound suitable for engineering applications have been identified.