Hall micromagnetometry of two-dimensional ferromagnets

The recent advent of atomically-thin ferromagnetic crystals has allowed experimental studies of two-dimensional (2D) magnetism that not only exhibits novel behavior due to the reduced dimensionality but also often serves as a starting point for understanding of the magnetic properties of bulk materials. However, the experimental techniques that were used to explore two-dimensional ferromagnetism could not probe the magnetic field directly. Here we show that ballistic Hall micromagnetometry provides a reliable and convenient way to measure 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 multiterminal Hall bar made from encapsulated graphene. We apply the micromagnetometry to study atomically-thin chromium tribromide (CrBr₃). The material remains ferromagnetic down to monolayer thickness and exhibits strong out-of-plane anisotropy. 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.

M. Kim et al., Micromagnetometry of two-dimensional ferromagnets. Nat. Electron. 2, 457-463 (2019)