Relaxation of a single defect spin by the low-frequency gyrotropic mode of a magnetic vortex

At a Glance

Metadata	Details
Publication Date	2021-08-25
Journal	Journal of Applied Physics
Authors	Jeremy Trimble, B. Gould, F. Joseph Heremans, Steven S.-L. Zhang, D. D. Awschalom
Institutions	Argonne National Laboratory, Case Western Reserve University
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: NV Spin Relaxation via Magnetic Vortex Gyrotropic Mode

6CCVD Analysis of arXiv:2105.00927v1

This research demonstrates a critical mechanism for coupling quantum defects (NV centers) in diamond to magnetic dynamics (magnons/vortices) in adjacent ferromagnetic structures. The findings are highly relevant to the development of hybrid quantum systems, spintronics, and nanoscale magnetic sensing, requiring ultra-high purity Single Crystal Diamond (SCD) substrates and precision fabrication capabilities.

Executive Summary

Research successfully observes enhanced spin relaxation of a Nitrogen-Vacancy (NV) defect in diamond driven by the low-frequency gyrotropic mode ($f_g$ = 0.15 GHz) of a permalloy magnetic vortex.
The interaction is highly localized, requiring the vortex core to be within approximately 250 nm of the NV center defect for strong coupling effects.
The coupling mechanism is attributed to the soliton-like nature of the driven gyrotropic mode, which generates high-frequency magnetic fringe fields that overlap with the NV spin transitions ($f_0$ ~ 2.87 GHz, $f_{ex}$ ~ 1.43 GHz).
The experiment relies on high-quality, isotopically pure ¹²C Single Crystal Diamond (SCD) with a precisely controlled 15 nm deep delta-doped ¹⁵N layer for optimal NV center formation and coherence.
6CCVD specializes in providing the necessary high-purity SCD substrates, custom doping profiles, and integrated metalization (Au CPW, Permalloy interface layers) required to replicate and advance this cutting-edge quantum spintronics research.

Technical Specifications

The following hard data points were extracted from the research paper, highlighting the material and physical parameters critical for system performance:

Parameter	Value	Unit	Context
Diamond Material	Isotopically pure ¹²C SCD	N/A	Substrate for NV center creation
Nitrogen Doping Profile	Delta-doped ¹⁵N₂	N/A	15 nm deep layer
Permalloy Disk Diameter	2	µm	Magnetic structure dimension
Permalloy Disk Thickness	35	nm	Magnetic structure dimension
CPW Metal Thickness	125	nm	Gold (Au) Co-Planar Waveguide
Gyrotropic Mode Frequency (f_g)	0.15 (Exp.) / 0.165 (Sim.)	GHz	Low-frequency vortex precession mode
NV Ground State Transition (f₀)	2.87	GHz	Zero-field splitting frequency
NV Excited State Transition (f_ex)	1.43	GHz	Zero-field splitting frequency
Critical Interaction Proximity	~250	nm	Maximum distance for enhanced spin relaxation
Electron Irradiation Dose	1e14	dose	Used for vacancy creation
Annealing Temperature	850	°C	Post-irradiation processing

Key Methodologies

The experimental success hinges on precise material engineering and nanoscale fabrication steps, summarized below:

SCD Growth and Doping: High-quality, electronic-grade Single Crystal Diamond (SCD) was grown via MPCVD, incorporating an isotopically pure ¹²C lattice. A 15 nm deep delta-doped layer of ¹⁵N₂ was introduced for precise NV precursor placement.
NV Center Creation: Vacancies were generated using 2 MeV electron irradiation (1e14 dose), followed by high-temperature annealing (850 °C) under forming gas (H₂/Ar) to mobilize vacancies and form NV centers.
Surface Preparation: A triacid clean (HClO₄:HNO₃:H₂SO₄) was performed to ensure an atomically clean surface, critical for subsequent lithography.
Magnetic Structure Fabrication: Electron Beam Lithography (EBL), electron beam evaporation, and liftoff were used to pattern 2 µm diameter, 35 nm thick Permalloy (Ni_0.81Fe_0.19) disks atop the diamond surface.
Microwave Circuit Integration: Photolithography was used to pattern a 125 nm thick Gold (Au) Co-Planar Waveguide (CPW) over the disk array to deliver the microwave magnetic field (b).
Measurement: Confocal Optically Detected Magnetic Resonance (ODMR) spectroscopy was used to initialize, drive, and monitor the NV spin state while the magnetic vortex core position was controlled by an external static magnetic field (B).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational diamond materials and integrated fabrication services necessary for replicating and scaling this advanced quantum sensing platform.

Applicable Materials

To achieve the high coherence and precise defect placement demonstrated in this research, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): We provide high-purity SCD substrates (up to 500 µm thick) with low native strain, essential for maintaining long NV spin coherence times (T₂).
Custom Isotopic Purity: 6CCVD can supply SCD with specific isotopic enrichment (e.g., highly enriched ¹²C) to minimize decoherence caused by nuclear spin bath noise, a requirement for high-fidelity quantum experiments.
Precision Doping Control: We offer advanced MPCVD capabilities to replicate the critical 15 nm deep delta-doped ¹⁵N layer, ensuring NV centers are formed at the optimal distance from the magnetic interface.

Customization Potential

The integration of the magnetic structure and microwave delivery circuit requires precision material handling and metalization, areas where 6CCVD excels:

Research Requirement	6CCVD Capability	Technical Advantage
Substrate Size	Plates/wafers up to 125mm (PCD)	Enables scaling from research prototypes to commercial devices.
Surface Quality	Polishing: Ra < 1nm (SCD)	Ultra-smooth surfaces are critical for high-resolution EBL and reliable thin-film deposition (Permalloy/Au).
Metalization Stack	Internal capability: Au, Pt, Pd, Ti, W, Cu	We can deposit the 125 nm Au CPW and assist in designing the necessary adhesion layers (e.g., Ti or W) required for robust Permalloy integration.
Thickness Control	SCD/PCD thickness from 0.1µm to 500µm	Provides flexibility for optimizing substrate thickness for optical access (532 nm excitation) and thermal management.
Precision Cutting	Custom laser cutting and shaping	Allows for the creation of specific geometries required for microwave delivery or integration into larger experimental setups.

Engineering Support

The successful coupling of the NV spin to the gyrotropic mode depends heavily on achieving nanoscale proximity and minimizing material defects.

Spintronics Expertise: 6CCVD’s in-house PhD team offers consultation on material selection and processing optimization for hybrid quantum systems and spintronics projects.
Integration Assistance: We provide engineering support to address challenges related to achieving the critical 250 nm NV-vortex core proximity, including optimizing surface preparation and metalization stacks to ensure high-fidelity lithography.
Defect Engineering: We assist researchers in defining the optimal doping concentration and post-processing parameters (irradiation dose, annealing temperature) to maximize the yield and coherence of near-surface NV centers.

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

View Original Abstract

We excite the gyrotropic mode of a magnetic vortex and observe the resulting effect on the spin state of a nearby nitrogen-vacancy (NV) defect in diamond. Thin permalloy disks fabricated on a diamond sample are magnetized in a vortex state in which the magnetization curls around a central core. The magnetization dynamics of this configuration are described by a discrete spectrum of confined magnon modes as well as a low-frequency gyrotropic mode in which the vortex core precesses about its equilibrium position. Despite the spin transition frequencies being far-detuned from the modes of the ferromagnet, we observe enhanced relaxation of the NV spin when driving the gyrotropic mode. Moreover, we map the spatial dependence of the interaction between the vortex and the spin by translating the vortex core within the disk with an applied magnetic field, resulting in steplike motion as the vortex is pinned and de-pinned. Strong spin relaxation is observed when the vortex core is within approximately 250 nm of the NV center defect. We attribute this effect to the higher frequencies in the spectrum of the magnetic fringe field arising from the soliton-like nature of the gyrotropic mode when driven with sufficiently large amplitude.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0055595

References

2013 - Long-distance entanglement of spin qubits via ferromagnet [Crossref]
2016 - Fast nanoscale addressability of nitrogen-vacancy spins via coupling to a dynamic ferromagnetic vortex [Crossref]
2016 - Exploiting bistable pinning of a ferromagnetic vortex for nitrogen-vacancy spin control [Crossref]
2017 - Long-range spin wave mediated control of defect qubits in nanodiamonds [Crossref]
2017 - Strong driving of a single coherent spin by a proximal chiral ferromagnet [Crossref]
2018 - Single-nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet [Crossref]
2020 - Predicted strong coupling of solid-state spins via a single magnon mode [Crossref]
2015 - Nanometre-scale probing of spin waves using single-electron spins [Crossref]
2016 - Spatially resolved detection of complex ferromagnetic dynamics using optically detected nitrogen-vacancy spins [Crossref]