Broadband multi-magnon relaxometry using a quantum spin sensor for high frequency ferromagnetic dynamics sensing
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-10-16 |
| Journal | Nature Communications |
| Authors | Brendan McCullian, Ahmed M. Thabt, Benjamin Gray, Alex L. Melendez, Michael Wolf |
| Institutions | United States Air Force Research Laboratory, The Ohio State University |
| Citations | 64 |
| Analysis | Full AI Review Included |
Technical Analysis: Broadband Multi-Magnon Relaxometry using NV Centers
Section titled âTechnical Analysis: Broadband Multi-Magnon Relaxometry using NV CentersâThis document analyzes the research paper âBroadband multi-magnon relaxometry using a quantum spin sensor for high frequency ferromagnetic dynamics sensingâ to provide technical documentation and specific material solutions offered by 6CCVD for advanced quantum sensing and magnonics applications.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates the use of Nitrogen-Vacancy (NV) centers in nanodiamonds as quantum spin sensors to probe high-frequency ferromagnetic dynamics, overcoming traditional frequency limitations.
- Core Achievement: First demonstration of broadband multi-magnon NV relaxometry, extending NV sensing capability beyond the inherent few GHz resonance frequency of the NV spin.
- Application: Sensitive local probing of spinwave (magnon) generation, propagation, scattering, and relaxation in insulating magnetic films (NZAFO).
- Sensing Mechanism: NV spin relaxation is caused by magnetic field noise generated by multiple magnons participating in four-magnon scattering processes.
- Broadband Capability: The technique detects magnetic noise from spinwaves driven via nonlinear instability, even when all spinwave modes are at frequencies higher than the NV frequencies.
- Wavevector Probing: Successfully probed spinwave wavevectors up to $3 \times 10^{6}$ m-1, reaching the exchange-dominated regime of the spinwave spectrum.
- Material Requirement: Requires high-quality NV centers in diamond positioned within 300-600 nm of the ferromagnetic sample surface for near-field coupling.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental setup and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensor Material | Nanodiamond Powder | N/A | ~100 nm diameter, ~30 ppm NV concentration |
| Ferromagnetic Film | NZAFO (Ni0.65Zn0.35Al0.8Fe1.2O4) | N/A | Grown on MgAl2O4 substrate |
| Film Thickness | 23 | nm | Epitaxial growth via Pulsed Laser Epitaxy (PLE) |
| NV-Sample Separation | 300 - 600 | nm | Estimated range for drop-cast nanodiamonds |
| NV Ground State Splitting | 2.87 | GHz | Zero-field splitting (D) |
| Microwave Drive Frequencies | 2.2, 4.0 | GHz | Used for parametric excitation |
| High Microwave Power | +18 | dBm | Used for 4.0 GHz multi-magnon regime |
| Maximum Probed Wavevector | $3 \times 10^{6}$ | m-1 | Achieved by varying microwave power |
| FMR Field (2.2 GHz) | 94 | Gauss | Uniform mode FMR condition |
| FMR Field (4.0 GHz) | 206 | Gauss | Uniform mode FMR condition |
| Antenna Metalization Stack | Ti(5 nm)/Ag(285 nm)/Au(10 nm) | N/A | 15 ”m wide tapered microstrip |
| Laser Excitation | 532 | nm | Continuous wave green laser (30 mW) |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on a highly integrated setup combining thin-film growth, microwave engineering, and quantum optical detection.
- Thin Film Growth: A 23 nm thick Nickel Zinc Aluminum Ferrite (NZAFO) film was grown on a MgAl2O4 substrate using Pulsed Laser Epitaxy (PLE).
- Microwave Structure Fabrication: A 15 ”m wide tapered microstrip antenna (Ti/Ag/Au stack) was fabricated on the NZAFO film using lithography to excite ferromagnetic dynamics.
- NV Sensor Placement: Nanodiamond powder (~100 nm diameter, ~30 ppm NV) was drop-cast onto the stripline and NZAFO surface, creating a sensor layer a few hundred nm thick.
- Magnetic Field Control: An electromagnet applied an in-plane static magnetic field (H) along the NZAFO [100] crystalline axis, which was swept during measurements.
- Optical Excitation & Collection: A 532 nm laser (30 mW) was focused onto the nanodiamond ensemble via a 20x objective; red NV photoluminescence (PL) was collected through the same objective.
- Lock-in Detection Protocol: Microwaves were 100% amplitude modulated (fmod ~ 1 kHz). Lock-in amplifiers simultaneously recorded:
- Microwave transmission (via diode).
- Change in NV PL (via photodiode), phased such that a decrease in PL (due to NV relaxation) gives a positive signal.
- Data Normalization: NV signals were reported as percent changes in NV PL (Lock-in PL / DC PL) to mitigate effects of PL quenching by off-axis magnetic fields.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for high-quality diamond materials and precision fabrication for next-generation quantum sensing platforms. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond substrates, thin films, and custom metalization required to replicate and advance this work toward integrated devices.
Applicable Materials
Section titled âApplicable MaterialsâTo transition from drop-cast nanodiamond powder to a robust, high-performance integrated sensor, the researchers require high-purity, low-strain diamond.
| Material | 6CCVD Specification | Application in Magnonics Sensing |
|---|---|---|
| Single Crystal Diamond (SCD) | Optical Grade, Ra < 1 nm polishing, Low Nitrogen (Type IIa). | Ideal for controlled NV creation (e.g., via ion implantation) to achieve high NV density and long spin coherence times (T2), crucial for sensitive relaxometry. |
| Thin SCD Films | Thicknesses from 0.1 ”m to 500 ”m. | Allows precise control over the NV layer depth and the critical NV-NZAFO separation (300-600 nm range) for optimized near-field coupling and high spatial resolution imaging. |
| Boron-Doped Diamond (BDD) | SCD or PCD, tunable doping levels. | Potential use as a conductive layer or integrated microstrip line, replacing the metal antenna for specific high-frequency or high-power applications. |
Customization Potential
Section titled âCustomization PotentialâThe experimental design relies heavily on precision fabrication, which is a core strength of 6CCVD.
- Custom Metalization Services: The paper utilized a Ti(5 nm)/Ag(285 nm)/Au(10 nm) stack for the microstrip antenna. 6CCVD offers in-house metalization capabilities, including the precise deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to optimize microwave transmission and coupling efficiency for high-frequency experiments (e.g., 10+ GHz).
- Precision Dimensions: 6CCVD supplies custom diamond plates and wafers up to 125 mm (PCD) and large-area SCD, enabling the fabrication of complex, inch-scale integrated quantum devices, moving beyond the small-spot measurements described in the paper.
- Ultra-Smooth Polishing: Our SCD wafers feature surface roughness Ra < 1 nm, which is essential for subsequent high-quality epitaxial growth (like NZAFO) and minimizing surface defects that can degrade NV spin properties.
Engineering Support
Section titled âEngineering SupportâThe demonstration of broadband multi-magnon relaxometry opens new avenues in high-frequency magnonics. 6CCVDâs technical team is ready to support these advanced projects.
- Material Consultation: 6CCVDâs in-house PhD team can assist researchers in selecting the optimal diamond material (SCD vs. PCD, NV concentration, isotopic purity) required to replicate or extend this research, particularly for projects aiming to push broadband relaxometry into the 10 GHz and higher frequency regimes.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of custom diamond materials, supporting international research collaborations.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Development of sensitive local probes of magnon dynamics is essential to further understand the physical processes that govern magnon generation, propagation, scattering, and relaxation. Quantum spin sensors like the NV center in diamond have long spin lifetimes and their relaxation can be used to sense magnetic field noise at gigahertz frequencies. Thus far, NV sensing of ferromagnetic dynamics has been constrained to the case where the NV spin is resonant with a magnon mode in the sample meaning that the NV frequency provides an upper bound to detection. In this work we demonstrate ensemble NV detection of spinwaves generated via a nonlinear instability process where spinwaves of nonzero wavevector are parametrically driven by a high amplitude microwave field. NV relaxation caused by these driven spinwaves can be divided into two regimes; one- and multi-magnon NV relaxometry. In the one-magnon NV relaxometry regime the driven spinwave frequency is below the NV frequencies. The driven spinwave undergoes four-magnon scattering resulting in an increase in the population of magnons which are frequency matched to the NVs. The dipole magnetic fields of the NV-resonant magnons couple to and relax nearby NV spins. The amplitude of the NV relaxation increases with the wavevector of the driven spinwave mode which we are able to vary up to 3 Ă 10 6 m â1 , well into the part of the spinwave spectrum dominated by the exchange interaction. Increasing the strength of the applied magnetic field brings all spinwave modes to higher frequencies than the NV frequencies. We find that the NVs are relaxed by the driven spinwave instability despite the absence of any individual NV-resonant magnons, suggesting that multiple magnons participate in creating magnetic field noise below the ferromagnetic gap frequency which causes NV spin relaxation.