Simultaneous Optical and Electrical Spin-Torque Magnetometry with Phase-Sensitive Detection of Spin Precession

Spin-based coherent information processing and encoding utilize the precession phase of spins in magnetic materials. However, the detection and manipulation of spin precession phases remain a major challenge for advanced spintronic functionalities. By using simultaneous electrical and optical detection, we demonstrate the direct measurement of the spin precession phase of a permalloy device driven by the spin-orbit torques from adjacent heavy metals. The spin Hall angle of the heavy metals can be independently determined from concurrent electrical and optical signals. The phase-sensitive optical detection also allows spatially-resolved measurements of local spin-torque parameters and ferromagnetic resonance with comprehensive amplitude and phase information. Our study offers a route toward future advanced characterizations of spin-torque oscillators, magnonic circuits, and tunneling junctions, where measuring the current-induced spin dynamics of individual nanomagnets is required.

Figure 1

(a) Illustration of the microwave excitations and optical measurements of spin-torque FMR using our combined electrical and optical technique. (b),(c) Optical and electrical signals of spin-torque FMR spectra for $\mathrm{Pt}$(6 nm)/$\mathrm{Py}$(6 nm) bilayer devices from 5.6 to 7.4 GHz. (d),(e) Extracted optical and electrical phases, ${\varphi }_O$ and ${\varphi }_E$, from Eq. (3).

Figure 2

Left: Introduction of the phase shifter to the electrical path. Right: Evolution of ${\varphi }_O$ measured on a $\mathrm{Pt}$(6 nm)/$\mathrm{Py}$(6 nm) device at different phase tuning ranges $\eta$ and frequencies $\omega$. The dashed lines are linear fits to the data.

Figure 3

(a) Line shapes of optical signals of a $\mathrm{Pt}$(6 nm)/$\mathrm{Py}$(6 nm) device at different locations. (b) Spatial MOKE detection, with the extracted amplitudes and phases shown in color diagrams.

Figure 4

(a),(b) Extracted $H_{\mathrm{res}}$ and $\mathrm{\Delta }{H}_{1/2}$ values and the corresponding curve fittings of both electrical (crosses) and optical (dots) signals for the single- and dual-bar devices. (c),(d) Extracted ${\varphi }_O$ for (c) $\mathrm{Pt}$(6 nm)/$\mathrm{Py}$(6 nm) and (d) $\mathrm{Cu}$(10 nm)/$\mathrm{Py}$(6 nm) devices from the two single-bar samples and the two dual-bar samples, as illustrated in the bottom diagrams. Solid curves are guides to the eye.

Figure 5

(a) Comparison of all the optical phase offsets. The shaded areas indicate the upper and lower limits of the mean values plus errorbars of the measurement data. Different colors denote different spin Hall layers; empty circles denote the phases from magneto-optical effects; solid circles denote the spin Hall angles, which are shown also in (b) and (c). (b) Comparison of $\mathrm{\Delta }{\varphi }_O$ induced by $\mathrm{Pt}$ (blue) and $\mathrm{Ta}$ (magenta) heavy metals. (c) Comparison of $\mathrm{\Delta }{\varphi }_O$ and $\mathrm{\Delta }{\varphi }_E$ induced by $\mathrm{Pt}$ (blue) and $\mathrm{Pt}$/$\mathrm{Cu}$ (cyan) layers.