Magnetic Rigid Rotor in the Quantum Regime: Theoretical Toolbox

TL;DR

This paper develops a theoretical framework for understanding the quantum dynamics of a magnetic rigid rotor, specifically a nanoparticle, under conditions where the Einstein-De Haas effect dominates, providing tools applicable to other quantum rigid rotors.

Contribution

It introduces a bosonized Hamiltonian for a magnetic nanoparticle's quantum dynamics, capturing center-of-mass, angular momentum, and macrospin interactions in a simplified quadratic form.

Findings

Derived a bosonized Hamiltonian for the system

Captured the physics of a nearly not spinning nanomagnet

Applicable to other quantum mechanical rigid rotors

Abstract

We describe the quantum dynamics of a magnetic rigid rotor in the mesoscopic scale where the Einstein-De Haas effect is predominant. In particular, we consider a single-domain magnetic nanoparticle with uniaxial anisotropy in a magnetic trap. Starting from the basic Hamiltonian of the system under the macrospin approximation, we derive a bosonized Hamiltonian describing the center-of-mass motion, the total angular momentum, and the macrospin degrees of freedom of the particle treated as a rigid body. This bosonized Hamiltonian can be approximated by a simple quadratic Hamiltonian that captures the rich physics of a nanomagnet tightly confined in position, nearly not spinning, and with its macrospin anti-aligned to the magnetic field. The theoretical tools derived and used here can be applied to other quantum mechanical rigid rotors.