Thickness-Driven Control of Room Temperature Ferrimagnetic Skyrmions and their Topological Hall signature in GdFe Single Layers

Abstract

Magnetic skyrmions are nanoscale, topologically protected spin textures with exceptional potential for high density data storage and energy efficient computing. Among various skyrmion hosting systems, rare earth transition metal ferrimagnets offer a promising platform due to their tunable magnetic properties and intrinsically low net magnetization. Despite this, the fundamental control of ferrimagnetic skyrmions in single layer films remains unexplored. Here, we demonstrate a viable route for engineering room temperature skyrmions in GdFe single layers through precise control of film thickness (60 to 80 nm). Thickness variation enables the systematic tuning of key magnetic parameters, including perpendicular magnetic anisotropy and saturation magnetization, thereby allowing precise control over skyrmion size and density. Magnetic force microscopy (MFM) reveals a clear thickness dependent evolution of isolated skyrmion characteristics, where skyrmion size decreases while skyrmion density increases with increasing GdFe film thickness, in agreement with micromagnetic simulations. At the same time, magnetotransport measurements show a systematic enhancement in the topological Hall resistivity with thickness, further corroborating the increased skyrmion density observed in MFM. Scanning transmission electron microscopy reveals a compositional gradient across the film thickness, indicative of structural asymmetry and potential inversion symmetry breaking, contributing to the emergence of a bulk Dzyaloshinskii Moriya interaction. Notably, sub 60nm skyrmions with high areal density are stabilized at room temperature. This work provides a viable route to tailor the properties of ferrimagnetic skyrmions in single-layer GdFe films, paving the way for the development of high-density ferrimagnetic skyrmionic devices.

Figures (7)

• Figure 1: In-plane and out-of-plane magnetization hysteresis loops for GdFe films with thicknesses of (a) 60 nm, (b) 70 nm, and (c) 80 nm. (d) Extracted anisotropy field ($H_{k}$) and uniaxial magnetic anisotropy ($k_{u}$) as a function of film thickness.
• Figure 2: Room temperature MFM imaging of magnetic spin textures and THE as a function of applied field (H) in a 60 nm GdFe single layer. $\boldsymbol{a}$ represents topological Hall resistivity ($\Delta \rho_{xy}(H)$) (green circles) obtained by subtracting the fitted ordinary and anomalous Hall contributions ($\rho_{xy}^{Fit}(H)$, red curve) from the total Hall resistivity ($\rho_{xy}(H)$, black curve) ($\Delta \rho_{xy}(H)$ = $\rho_{xy}(H)$ - $\rho_{xy}^{Fit}(H)$). The black arrow indicates the field sweep direction for $\Delta \rho_{xy}$ and MFM, while $\rho_{xy}$ and $\rho_{xy}^{Fit}$ are shown for both sweep directions. $\boldsymbol{b-m}$ Corresponding MFM images at selected OOP magnetic fields, as marked on the topological Hall curve and top-left corners of each panel. All MFM images share the same scale bar shown in panel l, corresponding to 1 $\mu m$.
• Figure 3: Room temperature MFM imaging of magnetic spin textures and THE as a function of applied field (H) in a 70 nm GdFe single layer. $\boldsymbol{a}$ represents topological Hall resistivity ($\Delta \rho_{xy}(H)$) (green circles) obtained by subtracting the fitted ordinary and anomalous Hall contributions ($\rho_{xy}^{Fit}(H)$, red curve) from the total Hall resistivity ($\rho_{xy}(H)$, black curve) ($\Delta \rho_{xy}(H)$ = $\rho_{xy}(H)$ - $\rho_{xy}^{Fit}(H)$). The black arrow indicates the field sweep direction for $\Delta \rho_{xy}$ and MFM, while $\rho_{xy}$ and $\rho_{xy}^{Fit}$ are shown for both sweep directions. $\boldsymbol{b-m}$ Corresponding MFM images at selected OOP magnetic fields, as marked on the topological Hall curve and top-left corners of each panel. All MFM images share the same scale bar shown in panel l, corresponding to 1 $\mu m$.
• Figure 4: Room temperature MFM imaging of magnetic spin textures and THE as a function of applied field (H) in a 80 nm GdFe single layer. $\boldsymbol{a}$ represents topological Hall resistivity ($\Delta \rho_{xy}(H)$) (green circles) obtained by subtracting the fitted ordinary and anomalous Hall contributions ($\rho_{xy}^{Fit}(H)$, red curve) from the total Hall resistivity ($\rho_{xy}(H)$, black curve) ($\Delta \rho_{xy}(H)$ = $\rho_{xy}(H)$ - $\rho_{xy}^{Fit}(H)$). The black arrow indicates the field sweep direction for $\Delta \rho_{xy}$ and MFM, while $\rho_{xy}$ and $\rho_{xy}^{Fit}$ are shown for both sweep directions. $\boldsymbol{b-m}$ Corresponding MFM images at selected OOP magnetic fields, as marked on the topological Hall curve and top-left corners of each panel. All MFM images share the same scale bar shown in panel l, corresponding to 1 $\mu m$.
• Figure 5: Depth-resolved microstructural analysis of GdFe films via STEM and EDS. High-angle annular dark field STEM images of GdFe films with thicknesses of (a) 60 nm, (b) 70 nm, and (c) 80 nm. (d–f), Corresponding elemental maps of the Fe K-edge. (g-i), Elemental maps of the Gd L-edge. (j-l), Elemental maps of the Cr K-edge. (m-o), Composite elemental maps showing the spatial distribution of Fe, Gd, Cr, Si, and Ni for each thickness. (p-r), Laterally averaged line profiles along the z-axis direction for all elemental components in the 60, 70, and 80 nm GdFe films, respectively. (s-u) Corresponding averaged line profiles of the Fe/Gd composition as a function of z-position. Solid lines represent linear fits, with the slope denoted by $\beta$. (v) Extracted slope $\beta$ plotted as a function of film thickness.