Current-Induced Modulation of Spin-Wave Propagation in a Y-Junction via Transverse Spin-Transfer Torque

Abstract

We report the transverse control of spin-wave propagation in the configuration where the spin-wave wavevector k is perpendicular to the charge-current density J. Building on theoretical predictions of spin-wave refraction by nonuniform spin-polarized currents, and guided by micromagnetic simulations used to optimize the device geometry and current distribution, we experimentally explore a Y-shaped Permalloy structure in which a locally injected current perturbs the spin-wave dispersion. Measurements reveal current-dependent amplitude differences between the two output branches, providing initial experimental indications consistent with transverse, spin-transfer-torque-driven deflection. Although the magnitude of the effect is modest and accompanied by significant uncertainties, the observed trends qualitatively follow expectations from the simulations. These results demonstrate the feasibility of influencing spin-wave routing through local current injection and establish a proof-of-concept basis for current-controlled manipulation of spin-wave propagation in reconfigurable magnonic circuits.

Figures (3)

• Figure 1: Simulation setup illustrating the two device geometries, along with the corresponding current density, magnetization distribution, and normalized spin-wave output asymmetries. a) Schematic of the simulated geometry g1 with rounded corners, showing the input/output ports and relevant geometric parameters. b) Simulated current density distribution for geometry g1. c) Spin-wave magnetization amplitude across the constriction in geometry g1, with the directions of wavevector $\mathbf{k}$ and current density $\mathbf{J}$ indicated. Here, the highlighted rectangle indicates the region where output transmissions are calculated. d–f) Corresponding panels for geometry g2. g) Normalized output asymmetry $(O_2 - O_1)/(O_2 + O_1)$ as a function of applied current for geometry g1, evaluated at excitation frequencies of 10.5, 11.0, and 11.5 GHz. h) Same as g), but for geometry g2.
• Figure 2: a) Optical micrograph of the spin-wave multiplexer device, showing the input connected to VNA port 1 and the two outputs ($O_1$) and ($O_2$) connected to port 2. DC current contacts for positive and negative polarity are also labeled. b) False-colored scanning electron micrograph of the central region. The direction of spin-wave propagation (white arrow), applied DC current (red arrow), and external magnetic field $\mu_0 \mathrm{H}$ (cyan arrow) are indicated. The two output branches correspond to transmitted signals $\Delta \mathrm{L_{21}}$, measured at different output antennas.
• Figure 3: a–b) Transmitted signal amplitude for $O_1$ and $O_2$, respectively. c–d) Integrated signal area for $O_1$ and $O_2$ as a function of applied current, with fits showing linear (red) and quadratic (blue) components. e) Extracted linear component for both $O_1$ and $O_2$, with corresponding error bands.