Estimating the magnetic moment of microscopic magnetic sources from their magnetic field distribution in a layer of nitrogen-vacancy (NV) centres in diamond

At a Glance

Metadata	Details
Publication Date	2016-02-01
Journal	The European Physical Journal Applied Physics
Authors	Jānis Šmits, Andris Bērziņš, F. Gahbauer, R. Ferber, Kaspars Ērglis
Institutions	University of Latvia
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Analysis: NV Center Magnetometry

This document analyzes the research paper “Estimating the magnetic moment of microscopic magnetic sources from their magnetic field distribution in a layer of nitrogen-vacancy (NV) centres in diamond” to provide technical specifications and highlight how 6CCVD’s advanced MPCVD diamond solutions can optimize and scale this critical research area.

Executive Summary

This research validates the use of synthetic diamond NV centers for high-resolution magnetic field imaging, while simultaneously identifying key material challenges that 6CCVD is uniquely positioned to solve.

Application Validation: Successfully imaged magnetic field distributions generated by microscopic ferromagnetic (4 µm, 2 µm) and superparamagnetic (500 nm) particles using Optically Detected Magnetic Resonance (ODMR) in a synthetic diamond substrate.
Material Used: A high-pressure, high-temperature (HPHT) {100} oriented Type 1b Single Crystal Diamond (SCD) was used, with NV centers created via multi-energy nitrogen ion implantation and annealing.
Key Discrepancy: Significant differences (3-4 times) were observed between magnetic moments derived from ODMR imaging versus bulk Vibrating Sample Magnetometer (VSM) measurements, highlighting the need for improved material calibration and measurement protocols.
Critical Material Challenge: The study emphasizes that precise control over the NV layer depth (estimated 100-200 nm) and surface quality is essential, especially for resolving the magnetic fields of nanoscale particles (500 nm).
6CCVD Value Proposition: 6CCVD offers custom MPCVD SCD substrates with superior surface finish (Ra < 1 nm) and precise control over nitrogen incorporation depth, enabling the creation of ultra-shallow NV layers necessary for high-fidelity nanoscale magnetometry.
Scalability: The experiment used small 3 mm x 3 mm plates; 6CCVD provides custom SCD dimensions and large-area PCD plates (up to 125 mm) for scaling up sensor arrays.

Technical Specifications

The following hard data points were extracted from the research paper detailing the experimental setup and results.

Parameter	Value	Unit	Context
Diamond Substrate Orientation	{100}	N/A	Type 1b Single Crystal Diamond (SCD)
Substrate Dimensions	3 x 3 x 0.1	mm	Used for NV layer creation
Nitrogen Content (Initial)	100 - 200	ppm	Used for NV precursor
Ion Implantation Energies	10, 35, 60	keV	Multi-energy implantation for vacancy distribution
Estimated NV Layer Depth	100 - 200	nm	Post-annealing distribution
Zero-Field Splitting (ZFS)	2.87	GHz	³A₂ ground state
Applied Magnetic Field (Ambient)	~12	mT	Perpendicular to diamond surface
Excitation Wavelength	532	nm	Green solid-state laser
Fluorescence Wavelength Range	650 - 800	nm	Red emission at room temperature
Ferromagnetic Particle Diameter (1)	4	µm	Spherotech SVFM-40
Ferromagnetic Particle Diameter (2)	2	µm	Spherotech SVFM-20
Superparamagnetic Particle Diameter	500	nm	Ademtech MasterBeads
PSF Standard Deviation (Deconvolution)	370	nm	Assumed Gaussian PSF
Fitted Height (z-r) for 4 µm particle	1.4 ± 0.1	µm	Above diamond surface (attributed to solute layer)
Fitted Magnetic Moment (4 µm particle)	6.0 ± 0.1 x 10^-14	A m²	3-4 times lower than VSM expected value

Key Methodologies

The experiment relied on precise material engineering and advanced optical detection techniques to map the magnetic field.

Substrate Selection: A {100} oriented Type 1b SCD plate (100-200 ppm N) was chosen as the host material.
NV Center Creation: Nitrogen ion irradiation was performed at three distinct energies (10 keV, 35 keV, and 60 keV) to distribute vacancies near the surface, followed by high-temperature annealing to mobilize vacancies and form NV centers.
Magnetic Particle Deposition: Ferromagnetic and superparamagnetic particles were suspended in buffer solutions, applied to the diamond surface, and dried under an external magnetic field to orient the particles.
Optical Setup: An inverted microscope setup was used. NV centers were excited by a 532 nm laser, and the resulting red fluorescence was collected via a filter cube (515-560 nm excitation filter, 580 nm dichroic mirror, 590 nm long-pass suppression filter).
Microwave Delivery: Microwaves were generated (SG386) and amplified (+45 dB gain, up to 3 W output) and delivered via a thin wire loop placed directly on the diamond surface.
ODMR Imaging: The magnetic field was mapped by measuring the ratio of fluorescence intensity with the MW on (I_on) versus off (I_off) for each pixel across a range of MW frequencies (0.5 MHz steps for ferromagnetic, 0.2 MHz steps for superparamagnetic).
Data Analysis: Images were deconvoluted using a Richardson-Lucy algorithm (assuming a 370 nm Gaussian PSF). The resulting ODMR peak frequency maps were fitted to a magnetic dipole model to determine the particle’s magnetic moment (m) and its height above the NV layer (z-r).

6CCVD Solutions & Capabilities

The challenges identified in this research—specifically the need for ultra-shallow NV layers, high-purity substrates, and superior surface preparation—are directly addressed by 6CCVD’s specialized MPCVD diamond manufacturing capabilities.

Applicable Materials

To replicate and extend this research, the following 6CCVD materials are recommended:

Optical Grade SCD (Single Crystal Diamond): Essential for minimizing strain and maximizing the coherence time (T₂) of the NV centers, which is crucial for achieving high magnetic field sensitivity.
Custom Nitrogen-Doped SCD: 6CCVD utilizes MPCVD growth, allowing for precise control over the nitrogen concentration during the growth phase, ensuring uniform doping tailored for subsequent implantation and annealing processes.

Customization Potential

Research Requirement / Challenge	6CCVD Customization Capability	Technical Advantage for NV Magnetometry
Precise NV Layer Depth	Custom Thickness Control (SCD: 0.1 µm - 500 µm): We can grow SCD with a thin, highly controlled nitrogen-doped layer near the surface, eliminating the need for high-energy implantation and achieving NV layers < 50 nm deep.	Crucial for maximizing coupling efficiency and spatial resolution when imaging nanoscale sources (e.g., 500 nm particles).
Surface Quality & Particle Separation	Ultra-Low Roughness Polishing (Ra < 1 nm): Our SCD plates are polished to an atomic level.	Minimizes the separation distance (z-r) between the magnetic particle and the NV layer, overcoming the 1.4 µm separation issue caused by solute layers noted in the paper.
Scaling Experimental Setup	Custom Dimensions & Large Plates: While the paper used 3 mm x 3 mm, 6CCVD provides custom SCD dimensions and Polycrystalline Diamond (PCD) plates up to 125 mm in diameter.	Enables the fabrication of large-area sensor arrays and commercial-scale NV magnetometers.
Integrated Microwave Delivery	Custom Metalization (Au, Pt, Ti, W, Cu): We offer in-house metal deposition and patterning.	Allows researchers to integrate microwave striplines or coplanar waveguides directly onto the diamond surface, replacing external wire loops and improving MW field homogeneity and efficiency.
On-Chip Sensing	Boron-Doped Diamond (BDD): We supply highly conductive BDD films.	BDD can be used to create integrated microwave circuitry or ground planes, further simplifying the experimental setup and enhancing signal integrity.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers are experts in MPCVD diamond growth parameters, nitrogen incorporation, and surface preparation techniques optimized for quantum applications. We offer consultation services to assist researchers in selecting the ideal material specifications (doping concentration, thickness, and orientation) for similar NV Center Magnetometry projects, ensuring optimal coherence times and maximum magnetic sensitivity.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

\n\t\t\t\tWe have used a synthetic diamond with a layer of nitrogen-vacancy (NV) centres to image the magnetic field distributions of magnetic particles on the surface of the diamond. Magnetic field distributions of 4 µm and 2 µm ferromagnetic and 500 nm diameter superparamagnetic particles were obtained by measuring the position of the optically detected magnetic resonance peak in the fluorescence emitted by the NV centres for each pixel. We fitted the results to a model in order to determine the magnetic moment of the particles from the magnetic field image and compared the results to the measured magnetic moment of the particles. The best-fit magnetic moment differed from the value expected based on measurements by a vibrating sample magnetometer, which implies that further work is necessary to understand the details of magnetic field measurements on the micro scale. However, the measurements of two different types of ferromagnetic particle gave internally consistent results.\n\t\t\t

Tech Support

Original Source

DOI: https://doi.org/10.1051/epjap/2016150449