Quantum rescaling, domain metastability and hybrid domain-walls in two-dimensional CrI3 magnets

TL;DR

This study reveals that quantum effects and higher-order exchange interactions in 2D CrI3 magnets lead to complex domain structures and metastability, challenging the simple Ising model assumptions.

Contribution

It demonstrates the importance of biquadratic exchange and quantum rescaling in accurately modeling the magnetic properties of 2D CrI3.

Findings

Quantum rescaling is necessary for accurate thermal property predictions.

Metastable magnetic domains form due to quantum fluctuations.

Hybrid Neel and Bloch domain walls with 3-5 nm width are observed.

Abstract

Higher-order exchange interactions and quantum effects are widely known to play an important role in describing the properties of low-dimensional magnetic compounds. Here we identify the recently discovered two-dimensional (2D) van der Waals (vdW) CrI3 as a quantum non-Heisenberg material with properties far beyond an Ising magnet as initially assumed. We find that biquadratic exchange interactions are essential to quantitatively describe the magnetism of CrI3 but requiring quantum rescaling corrections to reproduce its thermal properties. The quantum nature of the heat bath represented by discrete electron-spin and phonon-spin scattering processes induced the formation of spin fluctuations in the low temperature regime. These fluctuations induce the formation of metastable magnetic domains evolving into a single macroscopic magnetization or even a monodomain over surface areas of a few micrometers. Such domains display hybrid characteristics of Neel and Bloch types with a narrow domain wall width in the range of 3-5 nm. Similar behaviour is expected for the majority of 2D vdW magnets where higher-order exchange interactions are appreciable.