Probing Thermal Magnon Current Mediated by Coherent Magnon via Nitrogen-Vacancy Centers in Diamond

At a Glance

Metadata	Details
Publication Date	2021-12-23
Journal	Physical Review Applied
Authors	Dwi Prananto, Yuta Kainuma, Kunitaka Hayashi, Norikazu Mizuochi, Ken‐ichi Uchida
Institutions	Japan Advanced Institute of Science and Technology, National Institute for Materials Science
Citations	16
Analysis	Full AI Review Included

Technical Documentation & Analysis: Probing Thermal Magnon Current via NV Centers in Diamond

This analysis reviews the experimental requirements and results of the research paper, “Probing thermal magnon current mediated by coherent magnon via nitrogen-vacancy centers in diamond,” highlighting 6CCVD’s advanced Material Science capabilities necessary for replication, extension, and commercialization of this spin caloritronics device platform.

Executive Summary

This research successfully demonstrates the use of Nitrogen-Vacancy (NV) centers in diamond as highly sensitive, nanoscale quantum sensors to detect and quantify thermal magnon currents (TMCs) in Yttrium Iron Garnet (YIG) films.

Core Achievement: Detection of TMC via the thermal magnon spin-transfer torque mechanism, which alters the magnetization dynamics of coherently excited Magnetostatic Surface Spin Waves (MSSWs).
Sensing Mechanism: TMC was probed using Optically Detected Magnetic Resonance (ODMR) via two distinct methods:
1. Resonant Excitation (Bulk Diamond): Observing modification in the Rabi oscillation frequency (amplitude change up to 18 ± 1 %) under an applied temperature gradient (∆T).
2. Non-Resonant Excitation (Nanodiamond): Observing corresponding changes in the longitudinal NV spin relaxation rate (Γ modulation up to 37.5 %).
Material Necessity: The success hinges on high-purity Single Crystal Diamond (SCD) with precisely engineered NV ensembles (mean depth 40 nm) and orientation control ((110) crystal face).
Technological Advantage: This diamond-based quantum sensing method overcomes the spatial resolution limitations inherent in conventional electrical methods (like the Inverse Spin Hall Effect, ISHE), enabling nanoscale probing of magnon dynamics critical for spin caloritronics and hybrid spin qubit platforms.
6CCVD Value: 6CCVD specializes in the custom, high-precision MPCVD diamond required (SCD films, controlled NV implantation, sub-µm thin films) to build next-generation spintronics sensors.

Technical Specifications

Key experimental parameters and quantified results extracted from the research paper, establishing necessary material performance benchmarks.

Parameter	Value	Unit	Context
Diamond Type 1 (Bulk Beam)	SCD, (110) oriented	N/A	Used for resonant Rabi oscillation measurements
Diamond Beam Dimensions	2.5 x 0.1 x 0.1	mm	Custom size for hybrid integration
NV Ensemble Depth (Mean)	40 (up to 70)	nm	Critical depth for efficient coupling to YIG MSSWs
Diamond Type 2	Nanodiamond	N/A	Approx. 40 nm diameter, used for local, non-resonant detection
Magnetic Insulator	YIG/GGG/YIG	Trilayer	Thicknesses: 100/550/100 µm
Maximum Temperature Gradient (∆T)	±10	K	Applied along the YIG longitudinal direction
External Magnetic Field (B_ext)	19	mT	Field applied perpendicular to MSSW propagation
Microwave Excitation Power (P_MW)	1	mW	Used for exciting MSSWs
Resonant Frequency (f_NV)	2.58 or 2.60	GHz	Matching condition for MSSW-NV coupling
Rabi Field Amplitude (b_R) Change	18 ± 1	%	Maximum observed change for ∆T = ±10 K (+B_ext)
Maximum Rabi Field Amplitude	26 ± 0.4	µT	Observed at ∆T = -10 K (+B_ext)
Thermal Magnon Damping (α_tm)	(10 ± 0.9) x 10^-4	N/A	Calculated for +B_ext geometry (effective ∆T_eff = 6.6 K)
Longitudinal Relaxation Rate Change (Γ)	37.5	%	Maximum observed change in nanodiamond (for +B_ext)

Key Methodologies

The experiment utilized a hybrid spintronic/quantum sensing platform to detect the subtle effects of temperature gradients on spin dynamics.

Sample Fabrication and Assembly:
- A trilayer YIG/GGG/YIG structure (total thickness 750 µm) was used, with Bismuth substitution in YIG to improve lattice matching.
- A (110) oriented SCD diamond beam (2.5 mm length) was centered on the upper YIG layer, containing an ensemble NV layer 40 nm deep.
- Two 50 µm diameter gold-wire antennas (A and B) were overlaid 2 mm apart on the YIG surface to excite MSSWs via electrical microwave fields.
Temperature Gradient Application:
- A temperature gradient (∆T up to 10 K) was applied along the YIG’s longitudinal direction using temperature control systems (Peltier modules, inferred by NV thermometry).
MSSW Excitation and Mapping:
- Microwaves (P_MW = 1 mW) were applied via Antenna A or B, and the YIG’s global coherent spin-wave resonance (S₁₁ parameter) was mapped using a Vector Network Analyzer under increasing external magnetic fields (B_ext up to 40 mT).
Resonant NV Detection (Bulk Diamond):
- ODMR spectroscopy was performed using an in-house scanning confocal microscope to optically address the NV spins.
- The B_ext and microwave frequency were tuned (e.g., 2.58 GHz at 19 mT) to match the NV resonance transition (m_s = 0 ⇔ m_s = -1) with the MSSW frequency.
- Rabi oscillation pulse sequences were performed. The change in Rabi oscillation frequency (Ω_R) under varied ∆T was measured, quantifying the thermal magnon spin-transfer torque (τ_tm).
Local Non-Resonant NV Detection (Nanodiamond):
- 40 nm nanodiamonds were placed locally on the YIG surface.
- Longitudinal spin relaxation rate (Γ) measurements were taken under non-resonant MSSW excitation (2.66 GHz), observing the modulation of Γ as a function of ∆T.

6CCVD Solutions & Capabilities

The successful implementation of this thermal magnon detection platform relies fundamentally on advanced diamond engineering. 6CCVD provides the specialized SCD and processing capabilities required to replicate this foundational research and develop scalable commercial devices for spin caloritronics and quantum computing.

Applicable Materials

To replicate or advance this research, engineers require diamond materials with extreme control over crystal structure, purity, and NV defect placement.

Material Requirement	6CCVD Solution	Technical Benefit
High-Purity SCD Wafer	Optical Grade SCD (MPCVD Grown)	Provides the high crystalline purity necessary for long NV spin coherence times (T₂*) and T₁ needed for precise Rabi/relaxation measurements.
Custom SCD Thin Films	SCD Layers (0.1 µm - 500 µm)	Critical for integration. 6CCVD supplies thin SCD films to minimize interface effects and ensure high thermal conductivity for efficient gradient management.
Precise NV Control	Custom NV Engineering (Ion Implantation)	6CCVD works with partners to provide precise control over NV ensemble depth (40 nm in this study) and concentration, essential for optimizing coupling efficiency to the MSSWs propagating in the YIG.
Specialized Substrates	(110) or (100) SCD Orientation	The study required a specific (110) orientation for optimal NV axis alignment relative to the magnetic field. 6CCVD delivers SCD wafers/plates in required crystal orientations up to 125 mm.

Customization Potential

The experimental setup relied on highly specific geometrical and physical interfaces. 6CCVD’s engineering capabilities directly address the complexity of hybrid device fabrication:

Custom Dimensions and Shaping: The paper required a precise diamond beam geometry (2.5 mm x 0.1 mm x 0.1 mm). 6CCVD offers high-precision laser cutting and dicing services to achieve custom plates and beams for hybrid material integration.
Surface Quality: The SCD must interface seamlessly with the YIG trilayer. 6CCVD guarantees ultra-low roughness polishing (Ra < 1 nm) on SCD, maximizing interface coupling quality and ensuring minimal microwave scattering.
Integrated Metalization: While the antennas were external gold wires, future integrated spintronics devices require robust on-chip contacts. 6CCVD provides internal metalization capabilities, including Ti/Pt/Au, Pd, W, and Cu, allowing engineers to build integrated microwave structures directly onto the diamond sensor surface.

Engineering Support

This research pushes the boundaries of hybrid quantum/spintronic platforms. 6CCVD’s internal expertise ensures successful material implementation:

Expert Consultation: 6CCVD’s in-house PhD team can assist with material selection and NV creation protocol design specifically tailored for complex spin caloritronics, magnon spintronics, and quantum sensing projects.
Global Supply Chain: We offer global shipping (DDU default, DDP available) to research institutions and commercial developers worldwide, ensuring reliable delivery of high-quality, custom-engineered diamond solutions.

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

View Original Abstract

Currently, thermally excited magnons are being intensively investigated owing\nto their potential in computing devices and thermoelectric conversion\ntechnologies. We report the detection of thermal magnon current propagating in\na magnetic insulator yttrium iron garnet under a temperature gradient using a\nquantum sensor: electron spins associated with nitrogen-vacancy (NV) centers in\ndiamond. Thermal magnon current was observed as modified Rabi oscillation\nfrequencies of NV spins hosted in a beam-shaped bulk diamond that resonantly\ncoupled with coherent magnon propagating over a long distance. Additionally,\nusing a nanodiamond, alteration in NV spin relaxation rates depending on the\napplied temperature gradient were observed under a non-resonant NV excitation\ncondition. The demonstration of probing thermal magnon current mediated by\ncoherent magnon via NV spin states serves as a basis for creating a device\nplatform hybridizing spin caloritronics and spin qubits.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.16.064058