Tunable and enhanced Rashba spin-orbit coupling in iridate-manganite heterostructures

Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a platform for engineering magnetism and spin-orbit coupling at the ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$ $\left(3d\text{−}5d\right)$ oxide interface by tuning the ${\mathrm{LaMnO}}_3$ growth conditions, which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report a tunable and enhanced interface-induced Rashba spin-orbit coupling where the spin relaxation mechanism varies with magnetic behavior of the underlying ${\mathrm{LaMnO}}_3$ layer. The x-ray spectroscopy measurements reveal the quantitative valence states of Mn and their impact on charge transfer. Our angle-dependent magnetoresistance measurements also reflects the signature of magnetic proximity effect in ${\mathrm{SrIrO}}_3$ and can be tuned with the magnetic nature of ${\mathrm{LaMnO}}_3$ in a ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$ bilayer. Our work demonstrates a route to engineer the interface-induced Rashba spin-orbit coupling and magnetic proximity effect at the $3d\text{−}5d$ oxide interface for spintronics applications.

Figure 1

Schematic image of the layered structure of ${\mathrm{LaMnO}}_3$ deposited at $37.5\times {10}^{-3}$ mTorr (LP-LMO-SIO) and 37.5 mTorr (HP-LMO-SIO) bilayer samples (left). (a) Temperature dependence of resistivity ($\rho$) and (b) magnetization (M) at an applied magnetic field of 500 Oe infield-cooled (FC) protocol are demonstrated in (a) and (b), respectively, for HP- and LP-LMO-SIO bilayers. (c) Comparison of LP-/HP-LMO-SIO anomalous Hall effect (AHE) contribution deduced from transverse resistance data by subtracting the linear Hall contribution (Hall bar structure is shown as inset in Fig. 1). (d), (e) Carrier density ($n_{2D}$) and mobility ($\mu$) of LP/HP-LMO-SIO layer as a function of temperature extracted from Hall measurements, respectively.

Figure 2

(a), (b) Experimental magnetoconductance ($\mathrm{\Delta }G$) data (closed colored symbols) as a function of magnetic field B ($\perp$) interface; measured for different temperatures fitted (solid black curve) by the Hikami-Larkin-Nagaoka equation for HP-/LP-LMO-SIO samples, respectively. Evolution of fitting parameters $B_i$ (c), $B_e$ (d) and $B_{\text{SO}}$ (e) as a function of temperature for HP-/LP-LMO-SIO samples. The reported ${\mathrm{SrIrO}}_3$/LSAT [35] has also been plotted for comparison in (e).

Figure 3

(a) Rashba spin-orbit coupling ($\alpha$) extracted from $B_{\text{SO}}$ values using Eq. (2) is shown as a function of temperature for HP-/LP-LMO-SIO samples. (b) Spin relaxation (${\tau }_{\text{so}}$) versus momentum scattering timescale (${\tau }_p$) for HP-/LP-LMO-SIO as a function of temperature.

Figure 4

Schematic representation of charge transfer mechanism for ${\mathrm{Ir}}^{4+}$ to ${\mathrm{Mn}}^{4+}$ (a) and ${\mathrm{Ir}}^{4+}$ to ${\mathrm{Mn}}^{3+}$ (b). (c), (d) XAS spectra around Mn $L_{2,3}$ edge of HP- and LP-LMO-SIO samples along with corresponding HP- and LP-LMO samples without ${\mathrm{SrIrO}}_3$ layer. The respective Mn valence state position, as deconvoluted Mn L-3 edge is shown for ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ in the bilayer as a shaded area (valence states are quantified by XPS spectra analysis (see SM [34]), the shaded area is for representation). The dashed black lines in the figure are guide to the eye based on the shift of the $\mathrm{Mn}\text{−}L$ edge position of LP- and HP-LMO-SIO with their corresponding ${\mathrm{LaMnO}}_3$ samples.

Figure 5

(a), (b) The angle-dependent magnetoresistance (ADMR) measurements carried out as a function of the magnetic field for LP- and HP- LMO-SIO samples, respectively, in $\beta$ rotational plane (schematic of the $\beta$ rotational measurement configuration in inset). (c), (d) ADMR measurements as a function of different rotational configurations. The rotational planes are shown as an inset in (c) with respect to crystallographic orientation. The angles $\alpha ,\beta ,\gamma$ are defined as the angle subtended between the current direction $j$ with respect to the magnetic field rotation, and $n$ is represented as a direction cosine normal to the surface. $\alpha$ points to the in-plane (IP) rotation of magnetic field with respect to $n$. $\beta$ represent out of plane (OOP) rotation direction lying in the plane perpendicular to the current direction $j$. $\gamma$ shows the OOP direction with respect to the current direction plane $j$.