Macroscopic Quantum Coherence in Ferrimagnets

TL;DR

This paper investigates how small uncompensated magnetic moments in ferrimagnets significantly influence macroscopic quantum coherence, revealing a crossover to ferromagnetic-like tunneling behavior and implications for experimental observations.

Contribution

It demonstrates that even tiny uncompensated moments drastically alter MQC in ferrimagnets, providing new insights into tunneling behavior and experimental interpretations.

Findings

Uncompensated moments cause a rapid crossover to ferromagnetic-like MQC.

Calculated tunnel splitting matches numerical evaluations.

Ferritin's small uncompensated moment significantly affects MQC behavior.

Abstract

We study macroscopic quantum coherence (MQC) in small ferrimagnets. Through semi-classical calculations we show that even a small uncompensated moment has a drastic effect on MQC. In particular, there is a rapid crossover to a regime where the MQC tunnel splitting is equal to that obtained for a ferromagnet, even though the system is still an antiferromagnet for all other aspects. We calculate this tunnel splitting via instanton methods and compare it with numerical evaluations. As an application we re-examine the experimental evidence for MQC in ferritin and show that even though the uncompensated moment of ferritin is small it greatly modifies the MQC behavior. We also discuss the implications of our results for MQC in molecular magnets.