Spin coherence on the ferromagnetic spherical surface

TL;DR

This paper investigates the spin dynamics of ferromagnetic materials on spherical surfaces, revealing finite-temperature order due to curvature and analyzing magnetization dynamics under magnetic fields using $SU(2)$ coherent states.

Contribution

It introduces a model for ferromagnetic spin coherence on spherical surfaces, highlighting curvature-induced finite-temperature order and systematic analysis of magnetization dynamics with magnetic fields.

Findings

Curvature enables finite-temperature ferromagnetic order on the sphere.

The model accurately describes magnetization dynamics using $SU(2)$ coherent states.

Potential applications in spin superfluidity and magnetoelectronics on spherical surfaces.

Abstract

Spintronics on flat surfaces has been studied over the years, and the scenario is relatively well-known; however, there is a lack of information when we consider non-flat surfaces. In this paper, we are concerned about the spin dynamics of the ferromagnetic model on the spherical surface. We use the Schwinger bosonic formalism for describing the thermodynamics of spin operators in terms of spinon operators. Opposite to the flat two-dimensional model, which is disordered at finite temperature, the curvature of the spherical surface provides non-zero critical temperature for Schwinger boson condensation, which characterizes order at finite temperature even in the absence of external magnetic fields. The thermodynamics is then analyzed in the low-temperature regime. In addition, we consider the presence of both static and oscillating magnetic fields, the necessary condition for inducing the ferromagnetic resonance, and we show systematically that the studied model is well-described by $SU(2)$ coherent states, which provides the correct dynamics of the magnetization. The archived results can be applied for describing a diversity of experiments such as spin superfluidity, angular momentum injection by spin pumping and spin-transfer torque in non-conventional junctions, magnon dissipation, and magnetoelectronics on the spherical surface.