Magnetic domains and domain wall pinning in two-dimensional ferromagnets revealed by nanoscale imaging

TL;DR

This study uses advanced cryogenic scanning magnetometry with nitrogen-vacancy centers to image and analyze magnetic domains and domain wall pinning in atomically thin CrBr3, revealing key mechanisms of magnetic behavior at the nanoscale.

Contribution

It demonstrates the use of nitrogen-vacancy center magnetometry for quantitative, nanoscale imaging of magnetic domains and pinning effects in two-dimensional ferromagnets, a significant advancement over previous methods.

Findings

Magnetic domains in bilayer CrBr3 are imaged at nanoscale resolution.

Pinning by defects is identified as a dominant coercivity mechanism.

Micromagnetic simulations confirm the experimental observations.

Abstract

Magnetic-domain structure and dynamics play an important role in understanding and controlling the magnetic properties of two-dimensional magnets, which are of interest to both fundamental studies and applications[1-5]. However, the probe methods based on the spin-dependent optical permeability[1,2,6] and electrical conductivity[7-10] can neither provide quantitative information of the magnetization nor achieve nanoscale spatial resolution. These capabilities are essential to image and understand the rich properties of magnetic domains. Here, we employ cryogenic scanning magnetometry using a single-electron spin of a nitrogen-vacancy center in a diamond probe to unambiguously prove the existence of magnetic domains and study their dynamics in atomically thin CrBr$_3$. The high spatial resolution of this technique enables imaging of magnetic domains and allows to resolve domain walls pinned by defects. By controlling the magnetic domain evolution as a function of magnetic field, we find that the pinning effect is a dominant coercivity mechanism with a saturation magnetization of about 26~$\mu_B$/nm$^2$ for bilayer CrBr$_3$. The magnetic-domain structure and pinning-effect dominated domain reversal process are verified by micromagnetic simulation. Our work highlights scanning nitrogen-vacancy center magnetometry as a quantitative probe to explore two-dimensional magnetism at the nanoscale.