Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy

TL;DR

This study uses micromagnetic simulations to demonstrate that spin transfer torque nano-contacts with strong perpendicular magnetic anisotropy can excite multiple propagating spin wave modes simultaneously, differing from in-plane systems.

Contribution

It reveals that PMA materials in nano-contacts support multiple propagating modes without solitonic bullets, enabling tunable magnonic waveguides.

Findings

Two propagating spin wave modes are excited simultaneously.

No solitonic self-localized spin-wave bullet observed in PMA systems.

Magnon transport can be controlled by tuning the applied current.

Abstract

Current induced spin wave excitations in spin transfer torque nano-contacts are known as a promising way to generate exchange-dominated spin waves at the nano-scale. It has been shown that when these systems are magnetized in the film plane, broken spatial symmetry of the field around the nano-contact induced by the Oersted field opens the possibility for spin wave mode co-existence including a non-linear self-localized spin-wave bullet and a propagating mode. By means of micromagnetic simulations, here we show that in systems with strong perpendicular magnetic anisotropy (PMA) in the free layer, two propagating spin wave modes with different frequency and spatial distribution can be excited simultaneously. Our results indicate that in-plane magnetized spin transfer nano-contacts in PMA materials do not host a solitonic self-localized spin-wave bullet, which is different from previous studies for systems with in plane magnetic anisotropy. This feature renders them interesting for nano-scale magnonic waveguides and crystals since magnon transport can be configured by tuning the applied current.