Tunable Magnonic Thermal Hall Effect in Skyrmion Crystal Phases of Ferrimagnets

TL;DR

This paper theoretically investigates the tunable magnonic thermal Hall effect in skyrmion crystal phases of ferrimagnets near the angular momentum compensation point, revealing a sign change in thermal conductivity that enables control of heat flux.

Contribution

It introduces a theoretical framework for magnon dynamics in skyrmion phases of ferrimagnets and predicts a tunable thermal Hall effect with a sign change across the compensation point.

Findings

Magnonic thermal Hall conductivity changes sign across the compensation point.

Derived equations of motion interpolate between relativistic and nonrelativistic regimes.

Proposed experimental method to detect the compensation point via thermal Hall measurements.

Abstract

We theoretically study the thermal Hall effect by magnons in skyrmion crystal phases of ferrimagnets in the vicinity of the angular momentum compensation point (CP). To this end, we start by deriving the equation of motion for magnons in the background of an arbitrary equilibrium spin texture, which gives rise to the fictitious electromagnetic field for magnons. As the net spin density varies, the resultant equation of motion interpolates between the relativistic Klein-Gordon equation at CP and the nonrelativistic Schr{\"o}dinger-like equation away from it. In skyrmion crystal phases, the right- and the left-circularly polarized magnons with respect to the order parameter are shown to form the Landau levels separately within the uniform skyrmion-density approximation. For an experimental proposal, we predict that the magnonic thermal Hall conductivity changes its sign when the ferrimagnet is tuned across CP, providing a way to control heat flux in spin-caloritronic devices on the one hand and a feasible way to detect CP of ferrimagnets on the other hand.