Frequency Modulation of Spin-Transfer Oscillators

TL;DR

This paper demonstrates that adding an ac current to a spin-transfer oscillator induces frequency modulation, producing sidebands and frequency shifts, with potential applications in communications and signal processing.

Contribution

It introduces the concept of frequency modulation in spin-transfer oscillators through combined ac and dc currents, supported by experimental and simulation results.

Findings

Sidebands appear at the modulation frequency.

Center frequency shifts with drive amplitude.

Simulations show modulation of the magnetization cone angle.

Abstract

Spin-polarized dc electric current flowing into a magnetic layer can induce precession of the magnetization at a frequency that depends on current. We show that addition of an ac current to this dc bias current results in a frequency modulated (FM) spectral output, generating sidebands spaced at the modulation frequency. The sideband amplitudes and shift of the center frequency with drive amplitude are in good agreement with a nonlinear FM model that takes into account the nonlinear frequency-current relation generally induced by spin transfer. Single-domain simulations show that ac current modulates the cone angle of the magnetization precession, in turn modulating the frequency via the demagnetizing field. These results are promising for communications and signal processing applications of spin-transfer oscillators.