Diamond magnetometer enhanced by ferrite flux concentrators
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-06-24 |
| Journal | Physical Review Research |
| Authors | Ilja Fescenko, Andrey Jarmola, Igor Savukov, Pauli Kehayias, JÄnis Ć mits |
| Institutions | University of Latvia, Sandia National Laboratories |
| Citations | 145 |
| Analysis | Full AI Review Included |
Diamond Magnetometer Enhanced by Ferrite Flux Concentrators: A 6CCVD Technical Analysis
Section titled âDiamond Magnetometer Enhanced by Ferrite Flux Concentrators: A 6CCVD Technical AnalysisâThis document analyzes the research demonstrating sub-picotesla diamond magnetometry using magnetic flux concentration and dual-resonance modulation. It highlights how 6CCVDâs advanced MPCVD diamond materials and customization capabilities are essential for replicating and extending this breakthrough research into commercial applications.
Executive Summary
Section titled âExecutive Summaryâ- Breakthrough Sensitivity: Achieved a magnetic field sensitivity of $\sim 0.9 \text{ pT s}^{1/2}$ across the $10-1000 \text{ Hz}$ frequency range, significantly outperforming commercial vector magnetometers.
- Flux Concentration: Sensitivity was enabled by microstructured MN60 ferrite flux concentrators in a bowtie configuration, providing a $\sim 250$-fold amplification of the external magnetic field within the diamond sensor volume.
- Thermal Stability: Utilized a dual-resonance modulation technique to suppress the effect of thermal shifts in the NV zero-field splitting parameter ($D(\Delta T)$), crucial for stable, low-frequency operation at ambient temperature.
- Low Power Operation: The device operates efficiently using only $200 \text{ mW}$ of laser power and $\le 20 \text{ mW}$ of microwave power, promising future miniaturization potential.
- Material Limitation: The current sensitivity is limited by the broad FDMR resonances ($\Gamma \approx 9 \text{ MHz}$) of the commercially-available Type Ib HPHT diamond used.
- Optimization Path: Achieving multi-order sensitivity improvement requires state-of-the-art synthetic diamond (SCD) featuring significantly narrower resonances, a core material specialty of 6CCVD.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and simulations:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Achieved Sensitivity ($\eta$) | $\sim 0.9$ | $\text{pT s}^{1/2}$ | In $10-1000 \text{ Hz}$ range |
| Magnetic Field Enhancement ($\epsilon$) | $254 \pm 19$ | N/A | Experimental value (Simulated: 280) |
| Photoelectron Shot-Noise Limit ($\eta_{psn}$) | $0.72$ | $\text{pT s}^{1/2}$ | Projected limit for the current setup |
| Ferrite Material | MN60 Ferrite | N/A | Used for flux concentration |
| Relative Permeability ($\mu_r$) | $\sim 6500$ | N/A | For MN60 ferrite |
| Diamond Membrane Thickness ($\delta$) | $43$ | $\text{”m}$ | Gap width between ferrite cones |
| Diamond Membrane Lateral Size | $\sim 300 \times 300$ | $\text{”m}^2$ | [100] faces |
| Laser Power (532 nm) | $200$ | $\text{mW}$ | Optical excitation power |
| Microwave Power | $\le 20$ | $\text{mW}$ | Used for dual-resonance modulation |
| NV Zero-Field Splitting ($D$) | $\sim 2862$ | $\text{MHz}$ | Indicates local diamond temperature of $\sim 385 \text{ K}$ |
| Rabi Frequency ($f_{Rabi}$) | $16$ | $\text{MHz}$ | With ferrite cones (Enhanced by $\ge 2$-fold) |
| Thermal Magnetization Noise (1 kHz) | $\sim 0.02$ | $\text{pT s}^{1/2}$ | Projected limit before ferrite noise dominates |
Key Methodologies
Section titled âKey MethodologiesâThe experiment combined advanced material engineering with quantum sensing techniques:
- NV Center Creation: A commercially-available Type Ib HPHT diamond was irradiated with $2 \text{ MeV}$ electrons (dose $\sim 10^{19} \text{ cm}^{-2}$) and subsequently annealed ($800-1100^\circ \text{ C}$) to convert substitutional nitrogen into NV centers.
- Microstructure Assembly: A $43 \text{ ”m}$ thick diamond membrane was mechanically polished and cut, then positioned and glued between two micro-machined MN60 ferrite cones in a bowtie configuration.
- Microwave Field Enhancement: A two-turn copper loop was wound around one ferrite cone, providing $\ge 2$-fold enhancement of the microwave magnetic field amplitude within the diamond gap.
- Optical Setup: $200 \text{ mW}$ of $532 \text{ nm}$ laser light was focused to a $\sim 40 \text{ ”m}$ diameter beam, traversing the diamond membrane parallel to its faces. Fluorescence ($650-800 \text{ nm}$) was collected and measured using a balanced photodetector.
- Dual-Resonance Magnetometry: Two microwave signals, centered about the $f_+$ and $f_-$ NV transitions, were modulated with a $\pi$ phase shift. The resulting lock-in signal is proportional to the difference frequency ($f_+ - f_-$), which is insensitive to temperature-induced shifts in $D(\Delta T)$.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights a clear path for next-generation NV magnetometers: leveraging high-purity, low-strain SCD to drastically reduce the FDMR linewidth ($\Gamma$) and increase sensitivity beyond the current shot-noise limit. 6CCVD is uniquely positioned to supply the necessary materials and customization services.
| Requirement from Research Paper | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Need for Narrower FDMR Resonances (To improve $\eta_{psn}$ by orders of magnitude) | Optical Grade Single Crystal Diamond (SCD) | Our MPCVD SCD offers superior crystalline quality, low strain, and controlled nitrogen incorporation, enabling the narrowest possible FDMR linewidths ($\Gamma$) and maximizing the fractional contrast ($C$). This is the critical factor for achieving sub-femtotesla sensitivity. |
| Custom Diamond Membrane Dimensions (Used $43 \text{ ”m}$ thickness, $300 \text{ ”m}$ size) | Custom Dimensions & Precision Thickness Control | 6CCVD manufactures SCD and PCD plates/wafers up to $125 \text{ mm}$ in size. We provide custom thicknesses from $0.1 \text{ ”m}$ to $500 \text{ ”m}$, allowing researchers to precisely match the optimal gap width ($\delta$) of the flux concentrators for maximum enhancement ($\epsilon$). |
| Integrated Microwave/Thermal Management (Used external copper loop; high operating temperature) | Integrated Metalization Services (Au, Ti, W, Cu) | We offer in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu). This enables the integration of micro-coils, microwave transmission lines, or robust thermal contact layers directly onto the diamond surface for improved microwave field homogeneity and efficient heat dissipation. |
| High Optical Collection Efficiency (Requires low surface roughness) | Ultra-Low Roughness Polishing ($R_a < 1 \text{ nm}$) | Our proprietary polishing techniques achieve $R_a < 1 \text{ nm}$ for SCD. This minimizes light scattering and maximizes the excitation photon-to-photoelectron conversion efficiency ($\xi$), crucial for reducing the shot-noise floor. |
| Engineering Support for NV Projects | In-House PhD Material Science Team | 6CCVD provides expert consultation on optimizing diamond growth recipes for specific NV applications, including controlled nitrogen doping (for NV density) and post-processing (irradiation/annealing) to maximize coherence time ($T_2^*$) and NV yield. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Magnetometers based on nitrogen-vacancy (NV) centers in diamond are promising room-temperature, solid-state sensors. However, their reported sensitivity to magnetic fields at low frequencies (âŸ1 kHz) is presently âż10 pT s<sup>1/2</sup>, precluding potential applications in medical imaging, geoscience, and navigation. Here we show that high-permeability magnetic flux concentrators, which collect magnetic flux from a larger area and concentrate it into the diamond sensor, can be used to improve the sensitivity of diamond magnetometers. By inserting an NV-doped diamond membrane between two ferrite cones in a bowtie configuration, we realize a ~250-fold increase of the magnetic field amplitude within the diamond. We demonstrate a sensitivity of ~0.9 pT s<sup>1/2</sup> to magnetic fields in the frequency range between 10 and 1000 Hz. This is accomplished using a dual-resonance modulation technique to suppress the effect of thermal shifts of the NV spin levels. The magnetometer uses 200 mW of laser power and 20 mW of microwave power. This work introduces a new degree of freedom for the design of diamond sensors by using structured magnetic materials to manipulate magnetic fields.