Stray magnetic field imaging of thin exfoliated iron halides flakes

TL;DR

This study uses NV center microscopy to image magnetism in exfoliated iron halide flakes, revealing the absence of stable ferromagnetic domains and showing how sample preparation influences magnetic behavior.

Contribution

First direct magnetic imaging of exfoliated iron halide flakes, demonstrating the lack of sustained ferromagnetic domains and the impact of sample preparation on magnetic properties.

Findings

No magnetic remanence observed in flakes

Weak induced magnetization under bias field

Magnetic behavior varies with sample preparation

Abstract

Magnetic van der Waals materials are often proposed for use in future spintronic devices, aiming to leverage the combination of long-range magnetic order and near-atomic thinness to produce energy-efficient components. One class of material that has been discussed in this context are the iron halides FeCl$_2$ and FeBr$_2$, which are A-type antiferromagnets with strong uniaxial magnetocrystalline anisotropy. However, despite characterization of the bulk materials, the possibility for sustaining the magnetic behaviors that would underpin such applications in thin flakes has not been investigated. In this work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image magnetism in individual exfoliated flakes of these iron halides, revealing the absence of magnetic remanence, a weak induced magnetization under bias field and variable behavior versus temperature. We show that our results are consistent with the antiferromagnetic behavior of the bulk material with a soft ferromagnetic uncompensated layer, indicating that extended ($>1~\mu$m) ferromagnetic domains are not sustained even at low temperatures (down to 4 K). Finally, we find that the magnetic order is strongly affected by the sample preparation, with a surprising diamagnetic order observed in a thin, hydrated sample.