Monoclinic YFe${}_{12}$ phases predicted from first principles

Abstract

We searched for stable crystal structures of YFe${}_{12}$ using a crystal structure prediction technique based on a genetic algorithm and first-principles calculations. We obtained two monoclinic $C2/m$ structures as metastable phases that are different from the well-known ThMn${}_{12}$ structure. These two phases have advantages in their magnetism over the ThMn${}_{12}$ structure: The total magnetization $M$ is increased from 25.6 ${\mu }_{\text{B}}$/f.u. up to 26.8 ${\mu }_{\text{B}}$/f.u. by the transformations. We also calculated Curie temperature $T_{\text{C}}$ for these structures within the mean-field approximation and predicted the increase of $T_{\text{C}}$ from 792 K up to 940 K, which is mainly caused by the increase of intersite magnetic couplings within the distance of 2.3--3.1Å. The similar enhancements of $M$ and $T_{\text{C}}$ are also obtained in the pseudo-binary system Y(Fe${}_{1-x}$Co${}_x$)${}_{12}$ with $x$ of 0--0.7.

6 pages, 5 figures