Magnetic imaging and statistical analysis of the metamagnetic phase transition of FeRh with electron spins in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-06-08 |
| Journal | Journal of Applied Physics |
| Authors | Guillermo Nava Antonio, Iacopo Bertelli, Brecht G. Simon, Rajasekhar Medapalli, D. Afanasiev |
| Institutions | Leiden University, Huygens Institute for History and Culture of the Netherlands |
| Citations | 12 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: NV Magnetometry in FeRh Thin Films
Section titled âTechnical Documentation & Analysis: NV Magnetometry in FeRh Thin FilmsâThis document analyzes the application of MPCVD diamond in advanced quantum sensing, specifically focusing on the use of Nitrogen-Vacancy (NV) centers for high-resolution magnetic imaging of phase transitions in FeRh thin films. The findings validate the critical role of high-purity Single Crystal Diamond (SCD) in enabling quantitative analysis of complex magnetic phenomena.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates the power of NV magnetometry in characterizing the metamagnetic phase transition (MMPT) of FeRh, providing both high-resolution spatial imaging and quantitative statistical analysis.
- Validated Sensing Platform: Nitrogen-Vacancy (NV) centers embedded in a diamond chip are confirmed as powerful, local-probe sensors for high-resolution magnetic stray field imaging in condensed matter systems.
- Quantitative Characterization: Statistical analysis, utilizing the Root-Mean-Square (RMS) deviation of stray-field maps, successfully extracted macroscopic properties: the transition temperature (Tt â 370 K) and the thermal hysteresis width (â 20 K).
- Domain Dynamics Insight: The two-dimensional autocorrelation function was employed to systematically track the nucleation, growth, coalescence, and reorientation of ferromagnetic (FM) domains and domain walls during the MMPT.
- High-Speed Imaging: A feedback scheme was implemented to accelerate data acquisition by an order of magnitude, enabling efficient mapping of 100x100 pixel images (0.5 ”m pixel size).
- Anisotropy Detection: The analysis detected a reorientation of domain walls across the phase transition, highlighting the changing balance between Zeeman energy and magnetocrystalline anisotropy (MCA) under external bias fields (up to 34.0 mT).
- Future Scaling: The methodology is directly applicable to studying other magnetic phenomena, including spin-wave excitations and phase transitions in 2D materials, requiring nanometric spatial resolution achievable with ultra-thin diamond membranes.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental setup and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| FeRh Film Thickness | 20 | nm | Epitaxial film grown on MgO |
| Transition Temperature (Tt) | â 370 | K | Antiferromagnetic (AFM) to Ferromagnetic (FM) transition |
| Thermal Hysteresis Width | â 20 | K | Measured under 150 mT in-plane bias field |
| Maximum DC Bias Field (Bâ) | 34.0 | mT | Applied along hard axis for domain analysis |
| Saturation Magnetization (”âMs) | â 1.5 | T | Bulk FeRh value (used for comparison) |
| NV-FeRh Distance | â 1 | ”m | Distance between sensing layer and sample surface |
| Spatial Resolution (Pixel Size) | 0.5 | ”m | Resolution of the magnetic field maps |
| Image Dimensions | 100 x 100 | pixels | Size of the analyzed stray-field maps |
| NV Center Zero-Field Splitting | 2.87 | GHz | Electron Spin Resonance (ESR) frequency |
| Polishing Requirement | Ra < 1 | nm | Implied requirement for nanoscale proximity (6CCVD capability) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise control of the diamond sensor environment and advanced statistical processing of the magnetic field data:
- Sensing Platform Construction: An NV-containing diamond chip was positioned directly on top of the 20-nm-thick epitaxial FeRh film (grown on MgO) to detect magnetic stray fields (BNV).
- Spin Control: NV spins were polarized using optical pumping (green laser) and manipulated using a microwave (MW) field applied via a nearby bonding wire.
- Field Measurement: The magnetic field projection onto the NV axis (BNV) was determined by measuring the Zeeman-split Electron Spin Resonance (ESR) frequencies.
- High-Speed Imaging: A feedback scheme was implemented where photoluminescence was measured at only two symmetric MW frequencies (v±) per pixel, significantly reducing the time required to generate 100x100 pixel magnetic maps.
- Transition Characterization: The temperature dependence of the phase transition was quantified by calculating the Root-Mean-Square (RMS) deviation of the stray-field maps (BRMS), which abruptly increases at Tt.
- Anisotropy Analysis: The magnetocrystalline anisotropy and domain wall orientation were analyzed using the two-dimensional autocorrelation function (RBB). The ratio of the Full Width at Half Maximum (FWHM) along different crystalline directions (e.g., FWHM[110]/FWHM[100]) served as a figure of merit for tracking domain wall realignment.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the need for high-purity, precisely engineered Single Crystal Diamond (SCD) substrates for quantum sensing applications. 6CCVD is uniquely positioned to supply the materials and customization required to replicate and advance this NV magnetometry work.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, the following 6CCVD materials are essential:
- Optical Grade Single Crystal Diamond (SCD): Required for the NV sensing platform. Our MPCVD process ensures high purity, low birefringence, and controlled nitrogen incorporation necessary for high-density, high-coherence NV center creation.
- Ultra-Thin SCD Substrates: For future nanometric spatial resolution (as noted in the conclusion), the NV layer must be closer to the sample. 6CCVD provides SCD substrates and membranes down to 0.1 ”m thickness, enabling nanometric standoff distances for scanning-probe NV magnetometry.
Customization Potential
Section titled âCustomization PotentialâThe complexity of the experimental setup (requiring precise alignment, MW delivery, and thermal control) necessitates custom material engineering, which 6CCVD provides:
| Research Requirement | 6CCVD Capability | Engineering Advantage |
|---|---|---|
| Custom Dimensions | Plates/wafers up to 125mm (PCD) and large-area SCD | We supply custom-cut diamond chips in the exact dimensions required for integration into cryostats, optical setups, and magnetometry systems. |
| Surface Quality | Polishing Ra < 1 nm (SCD) | Achieving the required â 1 ”m NV-FeRh distance (and future nanometric distances) demands an atomically flat surface. Our ultra-smooth polishing minimizes surface roughness and maximizes magnetic field coupling. |
| On-Chip Integration | Custom Metalization Services | The experiment requires nearby bonding wires for MW delivery. 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu for creating integrated microwave transmission lines or ohmic contacts directly on the diamond surface. |
| Advanced Doping | Controlled Nitrogen Doping | We offer precise control over nitrogen concentration during growth, optimizing the density of NV centers for either ensemble (wide-field) or single-NV (scanning-probe) applications. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond quantum systems. We can assist researchers and engineers with:
- Material Selection: Optimizing SCD grade and thickness based on target magnetic sensitivity and spatial resolution requirements.
- NV Creation Protocol: Consulting on post-growth processing (irradiation and annealing) to maximize NV yield and coherence times (Tâ).
- Integration Challenges: Providing technical support for metalization patterns and substrate mounting for similar NV Magnetometry and Metamagnetic Phase Transition projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Magnetic imaging based on nitrogen-vacancy (NV) centers in diamond has emerged as a powerful tool for probing magnetic phenomena in fields ranging from biology to physics. A key strength of NV sensing is its local-probe nature, enabling high-resolution spatial images of magnetic stray fields emanating from a sample. However, this local character can also form a drawback for analyzing the global properties of a system, such as a phase transition temperature. Here, we address this challenge by using statistical analyses of magnetic-field maps to characterize the first-order temperature-driven metamagnetic phase transition from the antiferromagnetic to the ferromagnetic state in FeRh. After imaging the phase transition and identifying the regimes of nucleation, growth, and coalescence of ferromagnetic domains, we statistically characterize the spatial magnetic-field maps to extract the transition temperature and thermal hysteresis width. By analyzing the spatial correlations of the maps in relation to the magnetocrystalline anisotropy and external magnetic field, we detect a reorientation of domain walls across the phase transition. The employed statistical approach can be extended to the study of other magnetic phenomena with NV magnetometry or other sensing techniques.