Probing Thermal Magnon Current Mediated by Coherent Magnon via Nitrogen-Vacancy Centers in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-23 |
| Journal | Physical Review Applied |
| Authors | Dwi Prananto, Yuta Kainuma, Kunitaka Hayashi, Norikazu Mizuochi, Kenâichi Uchida |
| Institutions | Japan Advanced Institute of Science and Technology, Kyoto University |
| Citations | 16 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study demonstrates a novel quantum sensing method for detecting thermal magnon currents in magnetic insulators, bridging the fields of spin caloritronics and quantum sensing using Nitrogen-Vacancy (NV) centers in diamond.
- Core Achievement: Successful detection of thermal magnon current propagating in Yttrium Iron Garnet (YIG) under a temperature gradient (ÎT) using NV electron spins as a quantum sensor.
- Mechanism: Thermal magnons (high energy) exert a thermal magnon spin-transfer torque (Ïtm) onto coherent magnons (Magnetostatic Surface Spin Waves, MSSWs), altering their magnetization dynamics.
- Coherent Probing Result: Under resonant excitation (using a bulk diamond beam), the NV Rabi oscillation frequency was modulated, indicating an 18 ± 1 % change in the effective Rabi field amplitude (bR) across a 20 K ÎT range.
- Local Probing Result: Using a nanodiamond for non-resonant excitation, the NV longitudinal spin relaxation rate (Î) showed a significant modulation of up to 37.5 % across the same ÎT range, confirming modulation of the thermal magnon population.
- Validation: The estimated thermal magnon damping parameter (αtm) was (10 ± 0.9) x 10-4 for +Bext, consistent with values reported from conventional electrical Inverse Spin Hall Effect (ISHE) measurements.
- Technological Advantage: This NV-based technique offers nanoscale spatial resolution and non-perturbative operation, overcoming limitations of conventional ISHE methods which require large electrodes and specific geometries.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| YIG/GGG/YIG Trilayer Dimensions | 6 x 3 | mm | Overall sample size. |
| YIG Layer Thickness | 100 | ”m | Upper and lower YIG layers. |
| GGG Layer Thickness | 550 | ”m | Gadolinium Gallium Garnet substrate. |
| External Magnetic Field (Bext) | 19 | mT | Used for resonant MSSW/NV coupling. |
| Microwave (MW) Power (PMW) | 1 | mW | Used for coherent MSSW excitation (bulk diamond). |
| Applied Temperature Difference (ÎT) | Up to 10 | K | Applied across the YIG sample (20 K total range). |
| Effective ÎT (over 2 mm distance) | 6.6 | K | Used for calculating αtm. |
| Resonant Frequency (fMSW = fNV) | 2.58 | GHz | Matching condition for +Bext. |
| Rabi Field Amplitude Change | 18 ± 1 | % | Observed change in bR from ÎT = 10 K to -10 K. |
| Longitudinal Relaxation Rate Change | 37.5 | % | Maximum observed change using nanodiamonds (+Bext). |
| Thermal Magnon Damping Parameter (αtm) | (10 ± 0.9) x 10-4 | Unitless | Estimated for +Bext geometry via Rabi oscillation fitting. |
| Bulk Diamond Beam Orientation | (110) | Crystal Axis | Used for efficient resonant NV spin excitations. |
| Bulk Diamond NV Depth (Mean) | 40 | nm | Depth beneath the surface. |
| Nanodiamond Diameter (Averaged) | 40 | nm | Used for local, non-resonant detection. |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Fabrication: A single-crystalline YIG/GGG/YIG trilayer (100 ”m / 550 ”m / 100 ”m) was grown via liquid-phase epitaxy, with Yttrium partially substituted by Bismuth to improve lattice matching.
- Thermal Gradient Setup: Temperature gradient (âT) was established along the YIGâs longitudinal direction using Peltier modules to control temperatures at sites A (TA) and B (TB), maintaining a constant temperature at the center where the diamond sensor was placed.
- MSSW Excitation: Two 50 ”m diameter gold-wire antennas (A and B) were overlaid on the upper YIG surface, separated by 2 mm, to excite Magnetostatic Surface Spin Waves (MSSWs) using electrical microwave fields (PMW = 1 mW).
- NV Sensor Placement: Two types of NV sensors were used: a bulk diamond beam (NV ensemble) placed at the center for resonant probing, and 40 nm nanodiamonds (few NV spins) dropped onto the center for local, non-resonant probing.
- Coherent Probing (Rabi Oscillation): Optically Detected Magnetic Resonance (ODMR) spectroscopy was performed under resonant conditions (fMSW = fNV = 2.58 GHz). The Rabi oscillation frequency (ΩR) was measured as a function of ÎT, quantifying the change in the MSSW driving field (bR) due to the thermal magnon spin-transfer torque (Ïtm).
- Non-Resonant Probing (Relaxation Rate): Longitudinal spin relaxation measurements (T1) were conducted using nanodiamonds under non-resonant MW excitation (2.66 GHz). The relaxation rate (Î) was measured as a function of ÎT, providing a local measure of the thermal magnon population modulation via four-magnon scattering.
Commercial Applications
Section titled âCommercial ApplicationsâThis research, leveraging NV centers in diamond, directly supports advancements in quantum technology and spintronics, particularly relevant to high-quality diamond material suppliers.
- Spin Caloritronics and Energy Devices:
- Development of highly efficient thermoelectric conversion technologies and energy-saving computing devices by precisely controlling and measuring heat-driven spin currents.
- Quantum Sensing and Metrology:
- Enabling nanoscale probing and imaging of complex magnetic phenomena, such as the non-uniformity of thermal magnon currents, which is impossible using conventional macroscopic electrical methods (ISHE).
- Future implementation of scanning probe-based NV magnetometry for high-spatial-resolution mapping of spin dynamics in magnetic materials.
- Magnon Spintronics and Qubit Hybridization:
- Creating foundational device platforms that hybridize spin caloritronics (magnon transport) with solid-state spin qubits (NV centers), crucial for future quantum information processing architectures.
- Advanced Materials Characterization:
- Non-perturbative characterization of magnetic insulators (like YIG) to understand intrinsic damping mechanisms and spin-transfer effects at interfaces, guiding the design of next-generation magnetic films.
- Diamond Material Demand (6ccvd.com Relevance):
- Increased demand for high-purity, isotopically controlled Chemical Vapor Deposition (CVD) diamond substrates and nanodiamonds with precisely engineered NV center concentrations and depths, essential for reliable quantum sensing platforms.
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