Quantum Stoner-Wohlfarth model

TL;DR

This paper investigates the quantum version of the Stoner-Wohlfarth model, revealing a dynamical quantum phase transition and a novel magnetization beating phenomenon as the spin size increases, combining theoretical analysis and simulations.

Contribution

It introduces a quantum analog of the classical Stoner-Wohlfarth model, identifying a quantum phase transition and a new quantum phase factor affecting magnetization dynamics.

Findings

Identification of a dynamical quantum phase transition related to Landau-Zener tunneling

Discovery of magnetization beating after the Stoner-Wohlfarth transition

Analytical derivation of the beating period from quantum phase factors

Abstract

The quantum mechanical counterpart of the famous Stoner-Wohlfarth model -- an easy-axis magnet in a tilted magnetic field -- is studied theoretically and through simulations, as a function of the spin-size $S$ in a sweeping longitudinal field. Beyond the classical Stoner-Wohlfarth transition, the sweeping field-induced adiabatic change of states slows down as $S$ increases, leading to a dynamical quantum phase transition. This result is described as a critical phenomenon associated with Landau-Zener tunneling gaps at metastable quasi-avoided crossings. Furthermore, a beating of the magnetization is discovered after the Stoner-Wohlfarth transition. The period of the beating, obtained analytically, arises from a new type of quantum phase factor.