Macroscopic Quantum Tunneling in Small Antiferromagnetic Particles: Effects of a Strong Magnetic Field

TL;DR

This paper investigates how strong magnetic fields influence macroscopic quantum tunneling in small antiferromagnetic particles, revealing various tunneling regimes and providing exact solutions and numerical analysis.

Contribution

It introduces new analytical instanton solutions and explores the dependence of tunneling rates on magnetic field orientation in anisotropic antiferromagnetic particles.

Findings

Tunneling regimes vary with magnetic field direction.

Exact instanton solutions are constructed for uniaxial symmetry.

Tunneling rates increase or decrease depending on field orientation.

Abstract

We consider an effect of a strong magnetic field on the ground state and macroscopic coherent tunneling in small antiferromagnetic particles with uniaxial and biaxial single-ion anisotropy. We find several tunneling regimes that depend on the direction of the magnetic field with respect to the anisotropy axes. For the case of a purely uniaxial symmetry and the field directed along the easy axis, an exact instanton solution with two different scales in imaginary time is constructed. For a rhombic anisotropy the effect of the field strongly depends on its orientation: with the field increasing, the tunneling rate increases or decreases for the field parallel to the easy or medium axis, respectively. The analytical results are complemented by numerical simulations.