Frustrated ferromagnetic transition in AB-stacked honeycomb bilayer

TL;DR

This study investigates the complex magnetic phase transition in ABC-stacked CrBr3, revealing a frustrated ferromagnetic transition in bilayer due to competing anisotropies, with implications for 2D magnetic frustration research.

Contribution

It provides experimental evidence of a frustrated ferromagnetic transition caused by anisotropy competition in bilayer honeycomb CrBr3, highlighting the role of reduced dimensionality.

Findings

Identification of susceptibility plateau indicating crossover regime

Enhanced anisotropy competition in bilayer compared to bulk and monolayer

Observation of a strongly frustrated ferromagnetic transition in bilayer

Abstract

In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing anisotropies are present, the phase transition becomes nontrivial. Here, utilizing highly sensitive susceptometry of scanning superconducting quantum interference device microscopy, we probe the spin correlations of ABC-stacked CrBr3 under zero magnetic field. We identify a plateau feature in susceptibility above the critical temperature (Tc) in thick samples. It signifies a crossover regime induced by the competition between easy-plane intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The evolution of the critical behavior from the bulk to 2D shows that the competition between the anisotropies is magnified in the reduced dimension. It leads to a strongly frustrated ferromagnetic transition in the bilayer with fluctuation on the order of Tc, which is distinct from both the monolayer and the bulk. Our observation potentially offers a 2D localized spin system on honeycomb lattice to explore magnetic frustration.