Robust Zero-Field Skyrmion Formation in FeGe Epitaxial Thin Films*

Magnetic skyrmions have attracted significant interests in recent years due to their potential for magnetic storage applications. B20 phase materials enable magnetic skyrmions due to the spin-orbit coupling and non-centrosymmetric structure. One major effort in this emerging field is the stabilization of skyrmions at room temperature and zero magnetic field. We grow high quality FeGe epitaxial films of 100, 65, and 36 nm thicknesses on Si by UHV off-axis sputtering, which exhibit pure B20 phase [1]. STEM images clearly reveal the B20 lattice of the FeGe film and its epitaxial relationship with Si. The FeGe films were patterned into a Hall bar structure for longitudinal and Hall resistivity measurements. The Hall resistivity loops show three regions of distinct features: 1) a linear background at large fields (> 2 T) due to the ordinary Hall effect, 2) a magnetic reversal at intermediate fields that follows the magnetization hysteresis loop due to the anomalous Hall effect, and 3) a hysteresis loop within ±3000 Oe due to the topological Hall effect. The topological Hall resistivity was extracted by subtracting the anomalous and ordinary Hall effect, demonstrating the existence of the skyrmion phase in FeGe films between 5 and 275 K. The topological Hall resistivity reaches 918 nOhm cm at 250 K, the highest reported to date. In particular, a large remanent topological Hall resistivity (77%) was observed at zero field and 5 K, indicating a robust skyrmion phase without the need of an external magnetic field. In addition, our recent results on skyrmions in oxides bilayers will be discussed.
[1] J. C. Gallagher, et al. Phys. Rev. Lett. 118, 027201 (2017).