Quantum Imaging of Ferromagnetic van der Waals Magnetic Domain Structures at Ambient Conditions

TL;DR

This study uses quantum magnetic microscopy to directly image ferromagnetic domain structures in 2D $ m Fe_{5}GeTe_{2}$ at ambient conditions, revealing thickness-independent magnetic phase transitions and new stripe features.

Contribution

It demonstrates the application of nitrogen-vacancy center based quantum imaging to study 2D magnetic materials at room temperature, uncovering new magnetic features and phase transition behaviors.

Findings

Transition temperature shows significant spread with no clear thickness dependence.

Identified new stripe features in magnetic and optical images.

Magnetic anisotropy does not significantly influence magnetic properties.

Abstract

Recently discovered 2D van der Waals magnetic materials, and specifically Iron-Germanium-Telluride ($\rm Fe_{5}GeTe_{2}$), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications for integration into devices such as magnetic memories and logic. Here we address key questions using a nitrogen-vacancy center based quantum magnetic microscope, enabling direct imaging of the magnetization of $\rm Fe_{5}GeTe_{2}$ at sub-micron spatial resolution as a function of temperature, magnetic field, and thickness. We employ spatially resolved measures, including magnetization variance and cross-correlation, and find a significant spread in transition temperature yet with no clear dependence on thickness down to 15 nm. We also identify previously unknown stripe features in the optical as well as magnetic images, which we attribute to modulations of the constituting elements during crystal synthesis and subsequent oxidation. Our results suggest that the magnetic anisotropy in this material does not play a crucial role in their magnetic properties, leading to a magnetic phase transition of $\rm Fe_{5}GeTe_{2}$ which is largely thickness-independent down to 15 nm. Our findings could be significant in designing future spintronic devices, magnetic memories and logic with 2D van der Waals magnetic materials.