Large microwave generation from d.c. driven magnetic vortex oscillators in magnetic tunnel junctions

TL;DR

This paper demonstrates enhanced microwave power generation from spin-transfer induced vortex oscillations in MgO-based magnetic tunnel junctions, providing clear experimental and theoretical insights into the mechanisms involved.

Contribution

It presents the first experimental evidence of strong microwave emission from vortex precessions in MgO-based junctions with detailed modeling comparison.

Findings

Microwave power is at least ten times stronger than in metallic systems.

Spectral quality of vortex oscillations is comparable to previous systems.

Provides a clear theoretical explanation of vortex precession mechanisms.

Abstract

Spin polarized current can excite the magnetization of a ferromagnet through the transfer of spin angular momentum to the local spin system. This pure spin-related transport phenomena leads to alluring possibilities for the achievement of a nanometer scale, CMOS compatible and tunable microwave generator operating at low bias for future wireless communications. Microwave emission generated by the persitent motion of magnetic vortices induced by spin transfer effect seems to be a unique manner to reach appropriate spectral linewidth. However, in metallic systems, where such vortex oscillations have been observed, the resulting microwave power is much too small. Here we present experimental evidences of spin-transfer induced core vortex precessions in MgO-based magnetic tunnel junctions with similar good spectral quality but an emitted power at least one order of magnitude stronger. More importantly, unlike to others spin transfer excitations, the thorough comparison between experimental results and models provide a clear textbook illustration of the mechanisms of vortex precessions induced by spin transfer.