Revealing room temperature ferromagnetism in exfoliated Fe 5 GeTe 2 flakes with quantum magnetic imaging

At a Glance

Metadata	Details
Publication Date	2022-02-22
Journal	2D Materials
Authors	Hang Chen, Shahidul Asif, Matthew P. Whalen, Jeyson Támara-Isaza, Brennan Luetke
Institutions	Universidad Nacional de Colombia, University of Delaware
Citations	29
Analysis	Full AI Review Included

Technical Documentation & Analysis: Room Temperature Ferromagnetism in 2D Magnets using NV Diamond

This document analyzes the research detailing the use of Nitrogen Vacancy (NV) centers in Chemical Vapor Deposition (CVD) diamond for quantum magnetic imaging (QMI) of 2D van der Waals magnets. This application directly aligns with 6CCVD’s core expertise in providing high-quality, customized diamond materials for quantum sensing and spintronics research.

Executive Summary

Room-Temperature Ferromagnetism Confirmed: Quantum Magnetic Imaging (QMI) based on NV ensembles in diamond successfully confirmed long-range ferromagnetic (FM) order in exfoliated Fe₅GeTe₂ flakes down to 21 nm (7 unit cells).
High T_c Validation: The Curie temperature (T_c) was determined to be approximately 300 K, validating the potential of Fe₅GeTe₂ for room-temperature spintronic and quantum devices.
NV Magnetometry Platform: The study utilized high-purity CVD diamond with near-surface NV ensembles (≈ 20 nm depth) as a local, sensitive, and artifact-free magnetic sensor.
Anisotropy Insight: Stray field patterns confirmed perpendicular easy-axis anisotropy in the thin Fe₅GeTe₂ flakes, consistent with prior electrical transport measurements.
High-Throughput Characterization: The wide-field QMI setup demonstrated capability for rapid, parallel screening of multiple 2D flakes simultaneously and time-resolved monitoring of magnetic degradation (oxidation).
Integration Requirement: Successful integration required ultra-clean diamond surfaces and the deposition of a protective Platinum (Pt) layer (5 nm) to prevent 2D material degradation.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Minimum Flake Thickness	21	nm	Thinnest Fe₅GeTe₂ flake exhibiting room-temperature FM (7 unit cells).
Curie Temperature (T_c)	≈ 300	K	Determined via temperature-dependent ODMR imaging.
NV Implantation Energy	6	keV	Used to create near-surface NV centers.
Average NV Depth	≈ 20	nm	Critical depth for high-sensitivity stray field detection.
NV Implantation Density	10¹² - 10¹³	cm^-2	Density range for NV ensembles used in wide-field imaging.
Excitation Laser Wavelength	532	nm	Used for continuous-wave Optically Detected Magnetic Resonance (cw-ODMR).
Optical Spatial Resolution	570	nm	Resolution limit imposed by optical diffraction in the wide-field system.
Bias Magnetic Field (B₀)	30 - 40	G	Applied during ODMR measurements to split transitions.
Stray Field Amplitude (ΔB_z)	-40 to +40	µT	Measured change in magnetic stray field (B_z) from background.
Protective Layer Material/Thickness	Pt, 5	nm	Deposited via e-beam evaporation to prevent oxidation.

Key Methodologies

The experiment relies on precise material engineering of the diamond substrate and controlled integration of the 2D magnet.

Diamond Substrate Acquisition: Electronic grade SCD diamond with a {100}-front facet was obtained via Chemical Vapor Deposition (CVD).
NV Center Fabrication: Nitrogen ions were implanted at 6 keV to achieve an average NV depth of approximately 20 nm, followed by subsequent annealing to activate the NV centers.
Sample Exfoliation: Fe₅GeTe₂ flakes were mechanically exfoliated onto the NV-diamond surface in ambient air.
Protective Layer Deposition: Immediately following exfoliation, a 5 nm Platinum (Pt) layer was deposited via electron-beam evaporation to protect the air-sensitive Fe₅GeTe₂ from oxidation.
Magnetic Initialization: Flakes were magnetized ex situ using a cylindrical permanent magnet (0.6 T perpendicular field).
QMI Measurement: Wide-field QMI was performed using continuous-wave ODMR, mapping the magnetic stray field (B_z or B_NV) generated by the flakes.
Temperature Control: An electrical heater placed near the sample allowed temperature-dependent measurements (295 K to 330 K) to determine T_c.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, customized diamond substrates and precise material integration capabilities—areas where 6CCVD excels. We provide the foundational materials and engineering support necessary to replicate and advance NV-based quantum sensing platforms for 2D materials research.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for Quantum Sensing
High-Purity Diamond Substrate	Optical Grade Single Crystal Diamond (SCD)	Our MPCVD SCD offers ultra-low strain and high crystalline purity, minimizing decoherence and maximizing NV spin coherence time (T₂* and T₂), crucial for high-sensitivity magnetometry.
Custom NV Platform	Custom Nitrogen-Doped SCD	We provide SCD with precise control over nitrogen concentration (PPM to PPB) and orientation ({100} or {111}), offering ideal starting material for shallow NV creation via implantation or in situ growth.
Large-Area Sensing Platform	PCD and SCD Wafers up to 125 mm	For high-throughput characterization and rapid screening of multiple 2D flakes (as demonstrated in Figure 5), 6CCVD supplies large-format substrates, significantly increasing experimental efficiency.
2D Material Protection & Integration	Custom Metalization Services (Pt, Ti, Au, Pd, W, Cu)	The study required a 5 nm Pt protective layer. 6CCVD offers internal, high-precision e-beam evaporation and sputtering services for depositing Pt and other contact metals, ensuring robust device integration and protection against ambient degradation.
Surface Quality for Exfoliation	Ultra-Smooth Polishing (Ra < 1 nm)	Our SCD substrates are polished to an atomic-scale finish (Ra < 1 nm), which is essential for successful mechanical exfoliation and subsequent high-resolution optical access to the 2D material.
Engineering Support	In-House PhD Material Science Team	Our experts can assist researchers in optimizing diamond specifications (thickness, doping density, orientation) to meet the specific demands of similar 2D magnet/quantum sensing projects, including optimizing NV depth for desired spatial resolution.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract Van der Waals (vdW) material Fe 5 GeTe 2 , with its long-range ferromagnetic ordering near room temperature, has significant potential to become an enabling platform for implementing novel spintronic and quantum devices. To pave the way for applications, it is crucial to determine the magnetic properties when the thickness of Fe 5 GeTe 2 reaches the few-layers regime. However, this is highly challenging due to the need for a characterization technique that is local, highly sensitive, artifact-free, and operational with minimal fabrication. Prior studies have indicated that Curie temperature T C can reach up to close to room temperature for exfoliated Fe 5 GeTe 2 flakes, as measured via electrical transport; there is a need to validate these results with a measurement that reveals magnetism more directly. In this work, we investigate the magnetic properties of exfoliated thin flakes of vdW magnet Fe 5 GeTe 2 via quantum magnetic imaging technique based on nitrogen vacancy centers in diamond. Through imaging the stray fields, we confirm room-temperature magnetic order in Fe 5 GeTe 2 thin flakes with thickness down to 7 units cell. The stray field patterns and their response to magnetizing fields with different polarities is consistent with previously reported perpendicular easy-axis anisotropy. Furthermore, we perform imaging at different temperatures and determine the Curie temperature of the flakes at ≈300 K. These results provide the basis for realizing a room-temperature monolayer ferromagnet with Fe 5 GeTe 2 . This work also demonstrates that the imaging technique enables rapid screening of multiple flakes simultaneously as well as time-resolved imaging for monitoring time-dependent magnetic behaviors, thereby paving the way towards high throughput characterization of potential two-dimensional (2D) magnets near room temperature and providing critical insights into the evolution of domain behaviors in 2D magnets due to degradation.

Tech Support

Original Source

DOI: https://doi.org/10.1088/2053-1583/ac57a9

References

2018 - Two-dimensional itinerant ferromagnetism in atomically thin Fe3GeTe2 [Crossref]
2018 - The van der Waals ferromagnets Fe5-δ GeTe2 and Fe5-δ-x Ni x GeTe2—crystal structure, stacking faults, and magnetic properties [Crossref]
2018 - Hard magnetic properties in nanoflake van der Waals Fe3GeTe2 [Crossref]
2019 - First-principles study of ferromagnetic metal Fe5GeTe2 [Crossref]
2021 - Van der Waals heterostructures for spintronics and opto-spintronics [Crossref]
2017 - Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals [Crossref]
2017 - Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit [Crossref]
2016 - Magnetic structure and phase stability of the van der Waals bonded ferromagnetFe3−x GeTe2 [Crossref]
2017 - Wafer-scale two-dimensional ferromagnetic Fe3GeTe2 thin films grown by molecular beam epitaxy [Crossref]
2019 - Ferromagnetism near room temperature in the cleavable van der Waals crystal Fe5GeTe2 [Crossref]