Robust Zero-Field Skyrmion Formation in FeGe Epitaxial Thin Films

$B20$ phase magnetic materials have been of significant interest because they enable magnetic Skyrmions. One major effort in this emerging field is the stabilization of Skyrmions at room temperature and zero magnetic field. We grow phase-pure, high crystalline quality FeGe epitaxial films on Si(111). Hall effect measurements reveal a strong topological Hall effect after subtracting the ordinary and anomalous Hall effects, demonstrating the formation of high density Skyrmions in FeGe films between 5 and 275 K. In particular, a substantial topological Hall effect was observed at a zero magnetic field, showing a robust Skyrmion phase without the need of an external magnetic field.

Figure 1

Semilog $2\theta \text{−}\omega$ XRD scans of 100, 65, and 36 nm FeGe films epitaxially grown on Si(111).

Figure 2

(a) STEM image of a 100 nm FeGe thin film viewed along the FeGe $⟨110⟩$ axis near the interface with Si(111). A 1.2–1.5 nm interfacial transition region is observed between the diamond structure of Si and the $B20$ structure of FeGe. (b) A high resolution STEM image of the FeGe film reveals the $B20$ ordering of Fe and Ge atoms. (c) Schematic of the cubic lattice and the $⟨110⟩$ projection of the $B20$ structure.

Figure 3

(a) Out-of-plane magnetic hysteresis loop of the 36 nm FeGe film at 5 K. (b) Total Hall resistivity (${\rho }_{xy}$) of the 36 nm FeGe film with a coercivity of 2400 Oe ($T=5\mathrm{K}$) reveals a dominant topological Hall effect, which has a path opposite of the expected anomalous Hall effect. (c) The topological Hall resistivity (${\rho }_{\mathrm{TH}}$) hysteresis loops for the 36, 65, and 100 nm FeGe films at 5 K show a clear Skyrmion phase, which exhibit substantial remanent values at $H=0$, demonstrating robust Skyrmion formation in the absence of magnetic field. (d) Semilog plot of the temperature dependence of the maximum ${\rho }_{\mathrm{TH}}$ for the three samples. (e) The squareness of the topological Hall resistivity ${\rho }_{\mathrm{TH}}(H=0)/{\rho }_{\mathrm{TH}}(\max )$ for the three FeGe films between 5 and 275 K, reflecting the stability of Skyrmions at zero field.

Figure 4

Contour plots of ${\rho }_{\mathrm{TH}}$ for the (a),(b) 100 nm, (c),(d) 65 nm, and (e)–(h) 36 nm FeGe films. The plots on the left have the field sweeping from $+7$ to $-7\mathrm{T}$, and the plots on the right have the field sweeping in the opposite direction. A zoom-in view of the 36 nm film in (g) and (h) highlights that nonzero topological Hall resistivity exists at a zero field for all temperatures, particularly at low temperatures with substantial remanence at $H=0$.