Switching the Magnetization in Quantum Antiferromagnets

TL;DR

This paper investigates the controlled switching of magnetization in quantum antiferromagnets using a theoretical approach that accounts for quantum and thermal fluctuations, revealing conditions for efficient data writing and the dynamics involved.

Contribution

It introduces a Schwinger boson mean-field theory approach to model magnetization switching in quantum antiferromagnets, capturing both ordered and intermediate phases.

Findings

Switching requires overcoming an activation energy related to the spin gap.

Switching time diverges near the threshold field, indicating inertia.

Dephasing occurs during the switching process, reducing coherence.

Abstract

The orientation of the order parameter of quantum magnets can be used to store information in a dense and efficient way. Switching this order parameter corresponds to writing data. To understand how this can be done, we study a precessional reorientation of the sublattice magnetization in an (an)isotropic quantum antiferromagnet induced by an applied magnetic field. We use a description including the leading quantum and thermal fluctuations, namely Schwinger boson mean-field theory, because this theory allows us to describe both ordered phases and the phases in between them, as is crucial for switching. An activation energy has to be overcome requiring a minimum applied field $h_\text{t}$ which is given essentially by the spin gap. It can be reduced significantly for temperatures approaching the N\'eel temperature facilitating switching. The time required for switching diverges when the field approaches $h_\text{t}$ which is the signature of an inertia in the magnetization dynamics. The temporal evolution of the magnetization and of the energy reveals signs of dephasing. The switched state has lost a part of its coherence because the magnetic modes do not evolve in phase.