Abstract
We show using both experimental and theoretical methods that cobalt substitution in the hexagonal ferromagnet Fe3Ge 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 Fe3Ge structure supports intrinsic magnetic properties that may enable promising permanent magnet performance.
Highlights
Magnets that perform better at elevated temperatures while tolerating strong demagnetizing fields are required for improving electric motors and generators for transportation and energy applications, while magnets comprising abundant elements are required to keep costs low and ensure supply stability[1]
Large magnetic moments and high Curie temperatures are associated with 3d transition metals, and the magnetocrystalline anisotropy is closely related to the crystallographic symmetry; in particular, cubic compounds generally exhibit weak magnetic anisotropy
At room temperature the magnetocrystalline anisotropy is planar, so that the ordered moments lie in the ab-plane, but a spin reorientation occurs near TSR = 380 K and the anisotropy is uniaxial at higher temperature with the moments along the hexagonal c-axis[10]
Summary
Magnets that perform better at elevated temperatures while tolerating strong demagnetizing fields are required for improving electric motors and generators for transportation and energy applications, while magnets comprising abundant elements are required to keep costs low and ensure supply stability[1]. We have recently shown that substitution of Si for Ge in Fe3Ge has the effect of extending the stability range of the uniaxial ferromagnetism, suppressing TSR by about 70 K (to 312 K) and TC by about 30 K (to 595 K), with little effect on the saturation magnetization[11] This is consistent with predictions from first principles calculations, which indicate uniaxial behavior could be realized over the whole temperature range for high Si concentrations; the solubility was found to be limited in experiments to about 6%. We observe uniaxial ferromagnetism at room temperature with only a few percent Co substitution, and complete suppression of the planar phase near 10% Co. First principles calculations confirm this trend, and predict the potential for good permanent magnet properties if the hexagonal phase can be stabilized for higher cobalt concentrations
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