Macroscopic quantum tunneling of magnetization explored by quantum-first-order reversal curves (QFORC)

TL;DR

This paper introduces QFORC, a new method inspired by FORC, to analyze quantum tunneling of magnetization in molecular magnets, providing detailed insights into quantum transitions and separating thermal and tunneling effects.

Contribution

The paper presents the first application of QFORC analysis to quantum magnetic systems, offering a faster and more detailed alternative to traditional matrix diagonalization methods.

Findings

QFORC accurately reproduces experimental magnetization curves.

It distinguishes thermal activation from quantum tunneling contributions.

It correlates magnetization jumps with specific quantum transitions.

Abstract

A novel method to study the fundamental problem of quantum double well potential systems that display magnetic hysteresis is proposed. The method, coined quantum-first-order reversal curve (QFORC) analysis, is inspired by the conventional first-order reversal curve (FORC) protocol, based on the Preisach model for hysteretic phenomena. We successfully tested the QFORC method in the peculiar hysteresis of the Mn12Ac molecular magnet, which is governed by macroscopic quantum tunneling of magnetization. The QFORC approach allows one to quickly reproduce well the experimental magnetization behavior, and more importantly to acquire information that is difficult to infer from the usual methods based on matrix diagonalization. It is possible to separate the thermal activation and tunneling contributions from the magnetization variation, as well as understand each experimentally observed jump of the magnetization curve and associate them with specific quantum transitions.