Thermal-activated escape of the bistable magnetic states in 2D Fe3GeTe2 near the critical point
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2023-12-05 |
| Journal | Communications Physics |
| Authors | Chen Wang, Xi Kong, Xiaoyu Mao, Chen Chen, Pei Yu |
| Institutions | Nanjing University, University of Science and Technology of China |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive Summaryā- Quantitative Phase Transition Analysis: The study provides a quantitative description of the phase transition and thermal activation dynamics in two-dimensional (2D) Fe3GeTe2 ferromagnets near the critical point (Tc).
- NV Center Magnetometry: Nitrogen-Vacancy (NV) centers in diamond were used as a non-perturbative quantum magnetometer to measure random spin switching between bistable magnetic states.
- Arrhenius Law Validation: The auto-correlation time (lifetime, Ļ) of the spin states follows the Arrhenius law, exhibiting an extreme sensitivity where a temperature change of only 0.8 K alters the lifetime by three orders of magnitude.
- Ginzburg-Landau (GL) Parameter Determination: By tuning the energy landscape with a weak out-of-plane magnetic field, all parameters of the empirical GL model were quantitatively determined.
- Energy Landscape Control: A weak external magnetic field of 1 G was shown to induce a large energy splitting of approximately 51.3 meV between the spin states, confirming occupation probability governed by Boltzmannās law.
- Critical Dynamics Insight: The work paves the way for investigating critical fluctuation, non-equilibrium phase transitions, and spatial correlation of magnetization in 2D materials.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Critical Temperature (Tc) | 173.6 | K | Determined for Fe3GeTe2 sample #2. |
| Temperature Sensitivity (ĪT) | 0.8 | K | Change required to shift spin state lifetime by 3 orders of magnitude. |
| Energy Splitting Coefficient | 51.3 | meV G-1 | Energy difference (2Ī“Em) achieved per unit magnetic field (Bbias). |
| Barrier Height Coefficient (Ī±) | 31 | meV K-2 | Fitted parameter for the Arrhenius law (Eq. 2). |
| Minimum Lifetime (Ļ0) | 13 | ms | Extrapolated lifetime at the critical point (Tc). |
| Fe3GeTe2 Thickness (Sample #1) | 4.8 | nm | Measured via Atomic Force Microscopy (AFM). |
| NV Center Implantation Dose | 1 x 1013 | cm-2 | 14N2 ions implanted at 16 keV. |
| NV Center Zero Field Splitting (D) | 2876.5 | MHz | Used for ODMR calculation. |
| Electron Spin Gyromagnetic Ratio (Ī³e) | 2.8 | MHz G-1 | Standard NV parameter. |
| Magnetization (Mz) (Sample #1, 165 K) | 29.2 | ĀµB nm-2 | Reconstructed from stray field imaging. |
| Stray Field Sensitivity (Īµtp) | 0.038 | GHz-1/2 | Theoretical sensitivity for the three-point sampling method. |
| Correlation Decay Length (Ī¾) | ~1 | Āµm | Spatial correlation length of magnetization fluctuations. |
| Domain Width (Ī») | ~1 | Āµm | Spatial domain width observed near Tc. |
| GL Parameter a2 (Sample #2) | 2.7 x 10-6 | meV nm2 K-1 ĀµB-2 | Determined at ĪT = 1.54 K. |
| GL Parameter a4 (Sample #2) | 5.7 x 10-8 | meV nm6 ĀµB-4 | Determined at ĪT = 1.54 K. |
Key Methodologies
Section titled āKey Methodologiesā- Fe3GeTe2 Crystal Growth: Crystals were grown using the Chemical Vapor Transport (CVT) method with a stoichiometric ratio of Fe:Ge:Te = 3:1:2. Source and growth zones were maintained at 750 Ā°C and 700 Ā°C, respectively.
- NV Center Fabrication: NV centers were generated in ultra-pure [100]-faced diamond by implanting 16 keV 14N2 ions (1 x 1013 cm-2 dose), followed by 1000 Ā°C annealing.
- Sample Preparation and Transfer: Ultrathin Fe3GeTe2 was mechanically exfoliated and transferred onto the diamond substrate in an inert gas glovebox. The FGT multilayer was encapsulated on both sides with hexagonal Boron Nitride (hBN) to prevent degradation and proximity artifacts.
- Low-Temperature NV Magnetometry: Measurements were performed using a homemade scanning confocal microscope cooled by liquid nitrogen. A 532 nm laser was used for NV initialization and readout, and continuous microwave (MW) fields were applied via a gold wire.
- Stray Magnetic Field Measurement (ODMR): The stray magnetic field (Bs) was measured by monitoring the Zeeman splitting of the NV electron spin states using Optically Detected Magnetic Resonance (ODMR) spectroscopy.
- Fast Fluctuation Detection: A high-speed three-point sampling method was used to measure temporal magnetization fluctuations, tracking fluorescence changes at three preselected frequencies near the resonance peak.
- Data Modeling: Experimental data (lifetime Ļ and occupation probability P) were fitted using the Arrhenius law and Boltzmann distribution, respectively, to extract and quantify all parameters (a2, a4, and the barrier height Ī“E) of the Ginzburg-Landau model.
Commercial Applications
Section titled āCommercial Applicationsā- Quantum Computing and Memory: The ability to precisely control and quantify the thermal stability and switching rates of 2D magnetic states is crucial for designing robust, low-power spintronic memory and logic devices.
- Nanoscale Magnetic Sensing: NV center magnetometry provides a platform for high-resolution, non-perturbative magnetic imaging, applicable in quality control and characterization of advanced magnetic materials and integrated circuits.
- Fundamental Condensed Matter Research: The methodology offers a unique tool for studying critical phenomena, such as phase transitions and critical fluctuations, in low-dimensional systems, which is vital for developing next-generation materials.
- Cryogenic and Wide-Temperature Electronics: NV sensors are robust across a wide temperature range (from low temperature to hundreds of Kelvin), making them ideal for characterizing magnetic components used in cryogenic quantum systems.
- 2D Material Device Engineering: Provides quantitative feedback necessary for optimizing the thickness, encapsulation, and external field control of van der Waals magnets for practical device integration.
View Original Abstract
Abstract Great effort has been made recently to investigate the phase transitions in two-dimensional (2D) magnets while leaving subtle quantification unsolved. Here, we demonstrate the thermal-activated escape in 2D Fe 3 GeTe 2 ferromagnets near the critical point with a quantum magnetometry based on nitrogen-vacancy centers. We observe random switching between the two spin states with auto-correlation time described by the Arrhenius law, where a change of temperature by 0.8 K induces a change of lifetime by three orders of magnitude. Moreover, a large energy difference between the two spin states about 51.3 meV is achieved by a weak out-of-plane magnetic field of 1 G, yielding occupation probability described by Boltzmannās law. Using these data, we identify all the parameters in the Ginzburg-Landau model. This work provides quantitative description of the phase transition in 2D magnets, which paves the way for investigating the critical fluctuation and even non-equilibrium phase transitions in these 2D materials.