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Injection Locking of the Gyrotropic Vortex Motion in a Nanopillar

Spin-torque oscillators (STOs) are a promising application for the spin-transfer torque effect. The major challenge lies in pushing the STO’s microwave output power to useful levels, e.g. by operating an array of STOs in a synchronized, phase-locked mode. Our experiment on metallic, giant magnetoresistance-type nanopillars focuses on the influence of external high-frequency signals on current-driven vortex dynamics and demonstrates the injection locking of the gyrotropic mode. We detected a gap of approximatelyt three orders of magnitude between the high-frequency power emitted by one oscillator and the power needed for phase-locking.


Figure: Injection locking of the gyrotropic vortex motion. Power spectra (fdet, vertical axis) of the current-induced gyrotropic mode as a function of HF excitation frequency (fext, horizontal axis) measured for different excitation amplitudes as indicated. The intensity at fext exceeds the colour scale and appears as diagonal white lines.

R. Lehndorff, D. E. Bürgler, C. M. Schneider, and Z. Celinski
Injection locking of the gyrotropic vortex motion in a nanopillar
Appl. Phys. Lett. 97, 142503 (2010).