Spin excitations in a monolayer scanned by a magnetic tip

TL;DR

This study explores how a magnetic tip causes energy loss through spin excitations in a magnetic monolayer, revealing temperature-dependent friction behaviors explained by spin polarization dynamics.

Contribution

It introduces a detailed model combining Heisenberg spins and LLG dynamics to analyze temperature effects on spin-induced friction during magnetic scanning.

Findings

Friction force is proportional to velocity at low temperatures.

Friction coefficient correlates with damping constant at low temperatures.

At high temperatures, friction coefficient decreases exponentially.

Abstract

Energy dissipation via spin excitations is investigated for a hard ferromagnetic tip scanning a soft magnetic monolayer. We use the classical Heisenberg model with Landau-Lifshitz-Gilbert (LLG)-dynamics including a stochastic field representing finite temperatures. The friction force depends linearly on the velocity (provided it is small enough) for all temperatures. For low temperatures, the corresponding friction coefficient is proportional to the phenomenological damping constant of the LLG equation. This dependence is lost at high temperatures, where the friction coefficient decreases exponentially. These findings can be explained by properties of the spin polarization cloud dragged along with the tip.