Low-non-linearity spin-torque oscillations driven by ferromagnetic nanocontacts

TL;DR

This paper explores low-nonlinearity spin-torque oscillations driven by localized currents at ferromagnetic nano-contacts, achieving high-frequency, narrow-linewidth signals suitable for nano-scale microwave applications.

Contribution

It demonstrates a method to reduce non-linearity in spin-torque oscillators by using localized excitation at nano-contacts, leading to improved spectral properties.

Findings

High-frequency (15 GHz) oscillations with narrow linewidth (<3 MHz) at low magnetic fields.

Localized excitation induces optical-mode spin-waves and domain-wall oscillations.

Reduced phase noise due to low non-linearity in the system.

Abstract

Spin-torque oscillators are strong candidates as nano-scale microwave generators and detectors. However, because of large amplitude-phase coupling (non-linearity), phase noise is enhanced over other linear auto-oscillators. One way to reduce nonlinearity is to use ferromagnetic layers as a resonator and excite them at localized spots, making a resonator-excitor pair. We investigated the excitation of oscillations in dipole-coupled ferromagnetic layers, driven by localized current at ferromagnetic nano-contacts. Oscillations possessed properties of optical-mode spin-waves and at low field ($\approx$200 Oe) had high frequency (15 GHz), a moderate precession amplitude (2--3$^\circ$), and a narrow spectral linewidth ($<$3 MHz) due to localized excitation at nano-contacts. Micromagnetic simulation showed emission of resonator's characteristic optical-mode spin-waves from disturbances generated by domain-wall oscillations at nano-contacts.