Imaging AC magnetization response of soft magnetic thin films using diamond quantum sensors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-05-23 |
| Journal | Communications Materials |
| Authors | Ryota Kitagawa, Aoi Nakatsuka, Teruo KĂŽhashi, Takeyuki Tsuji, H. Nitta |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Diamond Quantum Sensors for High-Frequency Magnetometry
Section titled âTechnical Documentation & Analysis: Diamond Quantum Sensors for High-Frequency Magnetometryâ6CCVD Reference Document: CM-2025-00812-4 Application Focus: High-Frequency Power Electronics & Soft Magnetic Material Characterization 6CCVD Material Relevance: Single Crystal Diamond (SCD) for Nitrogen-Vacancy (NV) Quantum Sensing
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the use of diamond Nitrogen-Vacancy (NV) quantum sensors for simultaneous, wide-frequency imaging of AC magnetic field amplitude and phase, a critical capability for evaluating energy loss in soft magnetic materials used in high-frequency power electronics.
- Wideband Quantum Sensing: Developed a diamond quantum imager capable of simultaneous amplitude and phase mapping of AC magnetic fields across a wide range, from 100 Hz up to 2.3 MHz.
- Novel Protocols: Introduced two specialized measurement protocols: Qubit Frequency Track (Qurack, up to 200 kHz) and Quantum Heterodyne (Qdyne, up to 2.3 MHz), filling the critical kilohertz frequency gap for wide-field NV imaging.
- Material Validation: Successfully analyzed CoFeB-SiO2 thin films, demonstrating negligible energy loss (near-zero phase delay) when driven along the hard axis up to 2.3 MHz.
- Anisotropy Dependence: Confirmed that energy dissipation increases significantly when the magnetization is driven along the easy axis, evidenced by a phase delay increase with frequency.
- SCD Platform Requirement: The experiment relied on high-quality, MPCVD-grown, [111]-oriented Single Crystal Diamond (SCD) substrates to host the perfectly aligned, high-density NV ensembles necessary for high-sensitivity wide-field quantum microscopy.
- Core Value Proposition: Diamond quantum sensors provide a non-invasive, high-resolution method to directly image hysteresis loss (M-H loop area) over a wide frequency range, offering crucial feedback for developing next-generation soft magnetic materials.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper, detailing the experimental parameters and material properties achieved.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Total Frequency Range Imaged | 100 Hz to 2.3 | MHz | Simultaneous amplitude and phase imaging |
| Qurack Protocol Range | 100 Hz to 200 | kHz | Qubit Frequency Track (kHz range) |
| Qdyne Protocol Range | 237 kHz to 2.34 | MHz | Quantum Heterodyne (MHz range) |
| SCD Substrate Orientation | (111) | N/A | Used for perfectly aligned NV centers |
| NV Layer Thickness (Typical) | 5 (2) | ”m | Grown via MPCVD on SCD |
| NV Density (Ensemble) | 4 x 1017 (4 x 1016) | cm-3 | High-density ensemble |
| Spin Coherence Time (T2, XY8) | 3.6 (5.8) | ”s | Measured using dynamic decoupling sequence |
| Spatial Resolution (Typical) | 2 to 5 | ”m | Magnetic field imaging resolution |
| CoFeB-SiO2 Film Thickness | 150 | nm | Soft magnetic material under test |
| Hard Axis Phase Delay (Max) | Almost 0 | ° | Up to 2.3 MHz (negligible energy loss) |
| Easy Axis Phase Delay (Max) | -60 | ° | At 50 kHz (signifying high energy loss) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized advanced MPCVD diamond growth and quantum control protocols to achieve wideband AC magnetometry.
- SCD Substrate Selection: An Ib (111) Single Crystal Diamond (SCD) substrate was chosen to ensure the NV centers were perfectly aligned along the [111] direction, simplifying signal analysis and maximizing sensitivity.
- NV Center Formation: Nitrogen-Vacancy (NV) ensembles were formed via Microwave Plasma Chemical Vapor Deposition (MPCVD) on the (111) SCD, achieving high density (up to 4x1017 cm-3) and precise layer thickness control (5 ”m).
- Magnetic Film Integration: A 150 nm thick CoFeB-SiO2 soft magnetic thin film was deposited on a separate Si/SiO2 substrate and placed adjacent to the NV layer for stray field detection.
- Qurack Protocol (kHz): For lower frequencies, the Qubit Frequency Track (Qurack) protocol was employed. This method tracks the oscillation of the NV qubit frequency using microwave (MW) frequency modulation, deriving amplitude and phase from the minimum photoluminescence (PL) signal (matching condition).
- Qdyne Protocol (MHz): For higher frequencies, the Quantum Heterodyne (Qdyne) protocol was used. This involves undersampling the AC magnetic field by synchronizing MW pulses (specifically the XY8 dynamic decoupling sequence) with the AC field period, effectively down-converting the MHz signal for capture by a standard CCD camera.
- Optical Readout: The NV centers were initialized and read out using a 532 nm green laser, with the resulting red PL imaged by a CCD camera for wide-field mapping.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the high-specification diamond materials and fabrication services required to replicate, extend, and commercialize this advanced quantum sensing technology for power electronics analysis.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the high-performance quantum sensor demonstrated in this study, researchers require highly controlled, high-purity diamond material.
| 6CCVD Material | Specification Match | Relevance to Research |
|---|---|---|
| Optical Grade SCD (111) | Matches the required Ib (111) orientation and high purity. | Essential platform for growing perfectly aligned NV ensembles with long coherence times (T2). |
| Custom MPCVD Growth | Replicates the NV layer thickness (e.g., 5 ”m) and high NV density (4x1017 cm-3) achieved via MPCVD. | Ensures maximum magnetic field sensitivity and signal contrast for wide-field imaging applications. |
| High-Purity SCD Substrates | Available in thicknesses from 0.1 ”m up to 500 ”m, and substrates up to 10 mm thick. | Provides flexibility for optimizing the NV depth relative to the magnetic sample under test, crucial for spatial resolution (2-5 ”m achieved here). |
Customization Potential
Section titled âCustomization Potentialâ6CCVDâs in-house capabilities directly address the engineering challenges inherent in integrating quantum sensors into complex measurement systems.
- Custom Dimensions and Scaling: The paper used a small field of view (FOV). 6CCVD offers PCD plates up to 125mm and large-area SCD, enabling the scaling of wide-field quantum imagers for industrial applications or larger magnetic samples.
- Precision Polishing: The success of wide-field imaging relies on excellent optical access. 6CCVD provides SCD polishing to Ra < 1nm and inch-size PCD polishing to Ra < 5nm, minimizing scattering and maximizing the signal-to-noise ratio (SNR) for PL detection.
- Integrated Device Fabrication: The experiment requires precise integration of MW antennas and drive coils. 6CCVD offers in-house metalization services (including Au, Pt, Ti, W, Cu) for patterning microwave structures directly onto the diamond surface or adjacent components, simplifying the fabrication of integrated quantum devices.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in MPCVD diamond growth and material science for quantum applications. We can assist engineers and scientists in:
- Material Selection: Optimizing the SCD orientation and purity to achieve target T2 and T2* coherence times for high-sensitivity magnetometry.
- NV Recipe Optimization: Tailoring the MPCVD growth parameters to achieve specific NV density and depth profiles required for high-resolution AC magnetic response imaging projects.
- Integration Consultation: Providing technical guidance on mechanical and thermal integration, particularly concerning heat dissipation for strong MW irradiation used in high-frequency Qdyne protocols.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract The energy loss in inductor core is a significant limitation in high-frequency power electronics. For evaluating and optimizing soft magnets, simultaneous imaging of both amplitude and phase of AC stray fields beyond 10 kHz is crucial. Here, we develop an imaging technique for analyzing AC magnetization response using diamond quantum sensors. For frequencies up to 200 kHz, we propose a measurement protocol, Qubit Frequency Track (Qurack), where microwave frequency modulation tracks qubit frequency oscillations. For higher frequencies above MHz, quantum heterodyne (Qdyne) imaging is employed. The soft magnetic CoFeB-SiO2 thin films, developed for high-frequency inductors, exhibit near-zero phase delay up to 2.3 MHz, indicating negligible energy loss. Moreover, the energy loss depends on the anisotropy: when the magnetization is driven along the easy axis, phase delay increases with frequency, signifying higher energy dissipation. These results suggest potential applications in analyzing soft magnets and improving the performance of power electronics.