Macroscopic Quantum Tunneling of a Topological Ferromagnet

TL;DR

This paper reports the first observation of quantum tunneling of magnetization in a macroscopic ferromagnetic domain within a topological insulator, highlighting quantum effects in topological magnetic states.

Contribution

It demonstrates quantum tunneling of magnetization in a large ferromagnetic macrospin in a topological insulator, combining topological matter with quantum magnetic phenomena.

Findings

Observation of telegraph noise from domain fluctuations

Temperature and magnetic field influence on domain switching

Quantum tunneling evidence in a macrospin state

Abstract

The recent advent of topological states of matter spawned many significant discoveries. The quantum anomalous Hall effect[1-3] is a prime example due to its potential for applications in quantum metrology[4, 5] as well as its influence on fundamental research into the underlying topological and magnetic states[6-11] and axion electrodynamics[2, 12-14]. Here, we perform electronic transport studies on a (V,Bi,Sb)2Te3 ferromagnetic topological insulator nanostructure in the quantum anomalous Hall regime. This allows us access to the dynamics of an individual ferromagnetic domain. The volume of the domain is estimated to be about 85 000 nm3, containing some 50 000 vanadium atoms, spread over a macroscopic distance of 115 nm. Telegraph noise resulting from the magnetization fluctuations of this domain is observed in the Hall signal. Careful analysis of the influence of temperature and external magnetic field on the domain switching statistics provides evidence for quantum tunneling of magnetization[15-22] in a macrospin state. This ferromagnetic macrospin is not only the largest magnetic object in which quantum tunneling has been observed, but also the first observation of the effect in a topological state of matter.