Tuning magnetocrystalline anisotropy by cobalt alloying in hexagonal FeGe.

We show using both experimental and theoretical methods that cobalt substitution in the hexagonal ferromagnet FeGe suppresses the planar magnetic anisotropy and favors a uniaxial state. Uniaxial ferromagnetism is observed at room temperature for cobalt concentrations of only a few percent, and 10% substitution fully suppresses the planar magnetic structure at least down to 5 K, with only a small effect on the magnetization and Curie temperature. First principles calculations predict strong uniaxial magnetocrystalline anisotropy and promising permanent magnet properties for higher cobalt concentrations. Although these high Co concentrations were not realized experimentally, this work suggests that the rare-earth-free FeGe structure supports intrinsic magnetic properties that may enable promising permanent magnet performance.