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(Sm,Zr)Fe$_{12-x}$M$_x$ (M=Zr,Ti,Co) for permanent-magnet applications: Ab initio material design integrated with experimental characterization

In rare-earth permanent magnets (REPM's), trade-off's between intrinsic magnetic properties are often encountered. A recent example is SmFe$_{12}$ where excellent magnetic properties can be achieved at the sacrifice of bulk structure stability. Bulk structure stability is sustained by the presence of the third substitute element as is the case with SmFe$_{11}$Ti, where Ti degrades magnetic properties. It is now in high demand to find out with which chemical composition a good compromise in the trade-off between structure stability and strong ferromagnetism is reached. We inspect the effects of representative substitute elements, Zr, Ti, and Co in SmFe$_{12}$ by combining ab initio data with experimental data from neutron diffraction. The trend in the intrinsic properties with respect to the concentration of substitute elements are monitored and a systematic way to search the best compromise is constructed. A certain minimum amount of Ti is identified with respect to the added amount of Co and Zr. It is found that Zr brings about a positive effect on magnetization, in line with recent experimental developments, and we argue that this can be understood as an effective doping of extra electrons.