All-oxide ferromagnetic resonance and spin pumping with $\mathrm{SrIr}{\mathrm{O}}_3$

$\mathrm{SrIr}{\mathrm{O}}_3$ is a semimetallic complex oxide of interest for spintronic applications due to the large spin-orbit coupling arising from iridium. It has unusual charge transport properties derived from a complex multiband electronic structure, with electron and hole pockets both contributing to conductivity. We report ferromagnetic resonance of $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ and $\mathrm{SrIr}{\mathrm{O}}_3$ epitaxial bilayer films on ${\left(\mathrm{LaAl}{\mathrm{O}}_3\right)}_{0.3}{\left(\mathrm{S}{\mathrm{r}}_2\mathrm{AlTa}{\mathrm{O}}_6\right)}_{0.7}$ substrates. Anomalous trends in the out-of-plane magnetic anisotropy and Landé $g$ factor suggest that orbital magnetism is modified by proximity of $\mathrm{SrIr}{\mathrm{O}}_3$ at low temperatures, likely contributing to large (∼fivefold) enhancements in Gilbert damping. However, enhanced Gilbert damping due to spin pumping is also apparent in the temperature range 250–300 K. The effective spin-mixing conductance is evaluated to be $G_{\uparrow \downarrow }^{\mathrm{eff}}\sim 0.5\times {10}^{14}{\mathrm{\Omega }}^{-1}{\mathrm{m}}^{-2}$, and the spin scattering length scale of $\mathrm{SrIr}{\mathrm{O}}_3$ is of the order of ∼1 nm. Our work demonstrates the delicate interplay of pure spin current with interfacially mediated spin-orbit effects in a complex oxide heterostructure, exploiting temperature as a control parameter, and should be of interest for both spin pumping and understanding the electronic structure of thin film iridates.

Figure 1

(a) X-ray reflectometry of 8-nm-thick $\mathrm{SrIr}{\mathrm{O}}_3$ [SIO] deposited on a (001)-oriented ${\left(\mathrm{LaAl}{\mathrm{O}}_3\right)}_{0.3}{\left(\mathrm{S}{\mathrm{r}}_2\mathrm{AlTa}{\mathrm{O}}_6\right)}_{0.7}$ [LSAT] substrate. (b) X-ray diffraction near the (002) Bragg reflections of single layer and bilayer films deposited on LSAT. Upper curve: 9-nm-thick LSMO. Middle curve: 8-nm-thick SIO. Lower curve: bilayer film of 9-nm-thick $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ [LSMO] (lower layer) and 15-nm-thick SIO (upper layer). Curves are offset for clarity.

Figure 2

(a) Magnetization $M$ of a 9-nm-thick LSMO single layer film, on sweeping magnetic field ${\mu }_{0}H$ from ±6 T. (b) Remnant (zero field) magnetization of a 9-nm-thick LSMO single layer film on sweeping temperature $T$.

Figure 3

(a) Resistivity ρ as a function of temperature for an 8-nm-thick SIO single layer. (b) Hall resistance $R_{\mathrm{H}}$ as a function of temperature for the same sample as (a). To obtain these data, a magnetic field was swept in ±7 T and the measured Hall voltage was observed to be linear in field. (c) Room temperature sheet conductance ${\kappa }_{\square }$ as a function of $t$, for bilayer samples of 9-nm-thick LSMO and $t$-nm-thick SIO.

Figure 4

Ferromagnetic resonance (FMR) of 9-nm-thick LSMO. Red curves are fits to data (black). (a) Data show measured field dependence of FMR absorption at a frequency $f=10\mathrm{GHz}$. Due to the use of field modulation, the observed curve represents the field derivative of the physical resonance, and is fit with an asymmetric Lorentzian function to extract center $H_0$ and linewidth Δ$H$. The out-of-plane measurement geometry is indicated in the diagram showing the orientation of magnetic field H with respect to the coplanar waveguide (CPW). (b) Resonance center $H_0\left(f\right)$ is captured by a linear fit whose slope allows the Landé $g$ factor to be determined, and intercept is equal to the effective saturation magnetization $M_{\mathrm{eff}}$. (c) Resonance linewidth Δ$H\left(f\right)$ is captured by a linear fit whose slope is proportional to the Gilbert damping parameter α.

Figure 5

Results from fitting data from FMR measurements for bilayer samples of 9-nm-thick LSMO and $t$-nm-thick SIO. We show (a) effective saturation magnetization, (b) Landé $g$ factor and (c) Gilbert damping as a function of temperature.