Micromagnetometry of two-dimensional ferromagnets

TL;DR

This paper demonstrates that ballistic Hall micromagnetometry can directly measure the magnetization of atomically thin two-dimensional ferromagnets, revealing their magnetic properties and behaviors at the monolayer level.

Contribution

It introduces a novel micromagnetometry technique using van der Waals assembled devices to study 2D ferromagnets directly.

Findings

CrBr3 remains ferromagnetic down to monolayer

CrBr3 exhibits strong out-of-plane magnetic anisotropy

Magnetic response varies little with layer number

Abstract

The study of atomically thin ferromagnetic crystals has led to the discovery of unusual magnetic behaviour and provided insight into the magnetic properties of bulk materials. However, the experimental techniques that have been used to explore ferromagnetism in such materials cannot probe the magnetic field directly. Here, we show that ballistic Hall micromagnetometry can be used to measure the magnetization of individual two-dimensional ferromagnets. Our devices are made by van der Waals assembly in such a way that the investigated ferromagnetic crystal is placed on top of a multi-terminal Hall bar made from encapsulated graphene. We use the micromagnetometry technique to study atomically thin chromium tribromide (CrBr3). We find that the material remains ferromagnetic down to monolayer thickness and exhibits strong out-of-plane anisotropy. We also find that the magnetic response of CrBr3 varies little with the number of layers and its temperature dependence cannot be described by the simple Ising model of two-dimensional ferromagnetism.