Dynamic unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling

Nicolas Josten, Thomas Feggeler, Ralf Meckenstock, Detlef Spoddig, Marina Spasova, Ke Chai, Iliya Radulov, Zi-An Li, Oliver Gutfleisch, Michael Farle & Benjamin Zingsem. SCIENTIFIC REPORTS. DOI: 10.1038/s41598-020-59208-8

Strong unidirectional anisotropy in bulk polycrystalline B20 FeGe has been measured by ferromagnetic resonance spectroscopy. Such anisotropy is not present in static magnetometry measurements. B20 FeGe exhibits inherent Dzyaloshinskii-Moriya interaction, resulting in a nonreciprocal spin-wave dispersion. Bulk and micron sized samples were produced and characterized. By X-band ferromagnetic resonance spectroscopy at 276K +/- 1K, near the Curie temperature, a distribution of resonance modes was observed in accordance with the cubic anisotropy of FeGe. This distribution exhibits a unidirectional anisotropy, i.e. shift of the resonance field under field inversion, of K-UD=960J/m(3)+/- 10J/m(3), previously unknown in bulk ferromagnets. Additionally, more than 25 small amplitude standing spin wave modes were observed inside a micron sized FeGe wedge, measured at 293K +/- 2K. These modes also exhibit unidirectional anisotropy. This effect, only dynamically measurable and not detectable in static magnetometry measurements, may open new possibilities for directed spin transport in chiral magnetic systems