Spin-transfer torque driven localized spin excitations in the presence of field-like torque

TL;DR

This paper analytically and numerically investigates localized spin excitations in a ferromagnetic chain influenced by external magnetic fields, currents, and torques, revealing damping removal, frequency enhancement, and stability against thermal noise.

Contribution

It provides exact solutions for spin excitations under combined effects of spin-transfer and field-like torques, including stability analysis and synchronization phenomena.

Findings

Damping can be removed by appropriate current introduction.

Field-like torque enhances the oscillation frequency.

One-spin excitation remains stable against thermal noise.

Abstract

We study the existence of localized one-spin excitation in the Heisenberg one-dimensional ferromagnetic spin chain in the presence of perpendicular and parallel external magnetic fields and current with spin-transfer torque and field-like torque. The Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation is exactly solved for the one spin excitation in the absence of onsite anisotropy for the excitations of spin with fields perpendicular and parallel to the chain. We show the removal of damping in the spin excitations by appropriately introducing current and also the enhancement of angular frequency of the oscillations due to field-like torque in the case of both perpendicular and parallel field. The exactness of the analytical results is verified by matching with numerical counterparts. Further, we numerically confirm the existence of in-phase and anti-phase stable synchronized oscillations for two spin-excitations in the presence of current with perpendicular field and field-like torque. We also show that the one-spin excitation is stable against thermal noise and gets only slightly modified against thermal fluctuations.