Quantum Barkhausen Noise Induced by Domain Wall Co-Tunneling

TL;DR

This paper explores quantum tunneling-driven domain wall dynamics in a ferromagnet, revealing quantum Barkhausen noise with unique avalanche behaviors and two distinct quantum mechanisms influenced by external magnetic fields.

Contribution

It introduces the concept of quantum Barkhausen noise and demonstrates how quantum tunneling affects domain wall motion and avalanche dynamics in a ferromagnet, extending beyond classical models.

Findings

Observation of avalanche dynamics in quantum regime

Identification of two quantum mechanisms for domain wall movement

Correlation of domain wall pairs influenced by transverse magnetic field

Abstract

Most macroscopic magnetic phenomena (including magnetic hysteresis) are typically understood classically. Here, we examine the dynamics of a uniaxial rare-earth ferromagnet deep within the quantum regime, so that domain wall motion, and the associated hysteresis, is dominated by large-scale quantum tunneling of spins, rather than classical thermal activation over a potential barrier. The domain wall motion is found to exhibit avalanche dynamics, observable as an unusual form of Barkhausen noise. We observe non-critical behavior in the avalanche dynamics that only can be explained by going beyond traditional renormalization group methods or classical domain wall models. We find that this ``quantum Barkhausen noise'' exhibits two distinct mechanisms for domain wall movement, each of which is quantum-mechanical, but with very different dependences on an external magnetic field applied transverse to the spin (Ising) axis. These observations can be understood in terms of the correlated motion of pairs of domain walls, nucleated by co-tunneling of plaquettes (sections of domain wall), with plaquette pairs correlated by dipolar interactions; this correlation is suppressed by the transverse field. Similar macroscopic correlations may be expected to appear in the hysteresis of other systems with long-range interactions.