Optimal uni-axial ferromagnetism in (La,Ce)${}_2$Fe${}_{14}$B for permanent magnets

Prospects for light-rare-earth-based permanent magnet compound R${}_2$Fe${}_{14}$B (R=La${}_{1-x}$Ce${}_x$ with $0\le x\le 1$) are inspected from first principles referring to the latest experimental data. Ce-rich 2:14:1 compounds come with good structure stability, reasonably good combination of magnetization and magnetic anisotropy, while a drawback lies in the low Curie temperature that is only 120~K above the room temperature at the Ce${}_2$Fe${}_{14}$B limit. Best compromise is inspected on the basis of ab initio data for (La${}_{1-x}$Ce${}_x$)${}_2$Fe${}_{14}$B referring to the magnetic properties of the champion magnet compound Nd${}_2$Fe${}_{14}$B and prerequisite conditions imposed by practical utility.