Interfacial mechanism in the anomalous Hall effect of $\mathrm{Co}/{\mathrm{Bi}}_2{\mathrm{O}}_3$ bilayers

Oxide interfaces are a source of spin-orbit coupling which can lead to novel spin-to-charge conversion effects. In this Rapid Communication, the contribution of the $\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ interface to the anomalous Hall effect (AHE) of Co is experimentally studied in $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ bilayers. We evidence a variation of ∼40% in the AHE of Co when a $\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ capping layer is added to the ferromagnet. This strong variation is attributed to an additional source of asymmetric transport in $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ bilayers that originates from the $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ interface and contributes to the skew scattering.

Figure 1

(a) Temperature dependence of the longitudinal resistivity of Co(10) (purple line) and Co(10)/$\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ (golden line). Inset: Measurement configuration of the longitudinal resistivity. (b) Anomalous Hall effect measurement in Co(10) (purple line) and Co(10)/$\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ (golden line) at 10 K. Dashed lines are linear curves fitted to high magnetic field data. The intercept of the fit at positive (negative) magnetic fields defines $R_{xy}\left(H=0^{+}\right)\left[R_{xy}\left(H=0^{-}\right)\right]$, as indicated for the purple line that corresponds to Co reference. Inset: Measurement configuration of the transverse resistivity applying out-of-plane magnetic field. The applied current I is 1 μA in (a) and 10 μA in (b).

Figure 2

Anomalous Hall resistivity as a function of the square of the longitudinal resistivity of Co (solid purple squares) and $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ (open golden squares). Purple solid line (golden solid line) is the fitting of Co ($\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$) data to Eq. (1).

Figure 3

(a) Residual resistivity of Co as a function of the thickness for the Co reference layers (solid purple squares) and the $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ bilayers (open golden squares) at 10 K. (b) Anomalous Hall resistivity as a function of the square of the longitudinal resistivity of Co (solid squares) and $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ (open squares) for different Co thicknesses. The applied currents range from 1 to 10 μA in (a) and from 10 to 100 μA in the measurements that gave the results shown in (b).

Figure 4

Residual resistivity dependence of (a) the intrinsic anomalous Hall conductivity and (b) the extrinsic anomalous Hall resistivity of Co for the Co reference layers (solid purple squares) and the $\mathrm{Co}/\mathrm{B}{\mathrm{i}}_2{\mathrm{O}}_3$ bilayers (open golden squares). (c) Thickness dependence of the ratio of the additional anomalous Hall resistivity at the interface and the residual resistivity of Co. Red solid line is a fit to $t^{-1}$. (d) Thickness dependence of the ratio of the additional anomalous Hall resistivity at the interface and the square of the residual resistivity of Co.