Off-resonant detection of domain wall oscillations using deterministically placed nanodiamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-12-13 |
| Journal | npj Spintronics |
| Authors | Jeffrey Rable, Jyotirmay Dwivedi, Nitin Samarth |
| Institutions | Pennsylvania State University |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research establishes a methodology for detecting localized, GHz-scale magnetic dynamics using Nitrogen-Vacancy (NV) centers in deterministically placed nanodiamonds, paving the way for integrated quantum spintronic devices.
- Core Achievement: Demonstrated off-resonant detection of GHz-scale oscillations of a single transverse Domain Wall (DW) pinned at an engineered defect in a Permalloy (Py) nanowire.
- Sensing Mechanism: Detection relies on enhanced NV spin relaxation (pulsed ODMR) caused by the broadband stray magnetic field noise generated by the oscillating DW.
- Platform Design: Utilizes 10 nm thick Py semicircular nanowires with lithographically patterned notch defects, allowing for controlled DW nucleation and pinning.
- Observed Dynamics: DW oscillation signals were observed in the 1.8 GHz to 2.3 GHz range, showing high sensitivity to nanofabrication imperfections (edge roughness) compared to idealized micromagnetic simulations.
- Quantum Potential: Micromagnetic simulations predict that achieving resonant NV-DW coupling could increase the local microwave driving field by a factor of >30, significantly reducing the required pi pulse time for NV qubit control.
- Future Direction: The platform is designed to enable the use of current-driven DWs as highly localized, nanoscale microwave generators for quantum computing applications.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Nanowire Material | Permalloy (NiFe) | N/A | Semicircular geometry |
| Nanowire Thickness | 10 | nm | Fabricated thin film |
| Nanodiamond Diameter | 100 | nm | AdĂĄmas Nanotechnologies, 3 ppm NV concentration |
| NV Ground State Transition | 2.87 | GHz | Zero-field splitting (fNV) |
| Observed DW Oscillation Freq | 1.8 to 2.3 | GHz | Device 1 (300 nm wide wire) |
| DW Nucleation Field (Device 2) | 11.25 | mT | Detected via 1.9 GHz pulsed ODMR signal onset |
| Py Saturation Magnetization (Ms) | 8 x 105 | A/m | Micromagnetic simulation input |
| Py Exchange Constant (Aex) | 1.3 x 10-11 | J/m | Micromagnetic simulation input |
| Py Gilbert Damping (α) | 0.0063 | N/A | Standard value for Py |
| Microwave Driving Power | +43 | dBm | Applied via 25 ”m diameter gold wire |
| Simulated Stray Field Magnitude | >3 | mT | Predicted at NV location under resonant coupling |
| Laser Excitation Wavelength | 532 | nm | CW laser for optical polarization and readout |
Key Methodologies
Section titled âKey Methodologiesâ- Nanowire Fabrication: Permalloy (Py) semicircular nanowires (e.g., 300 nm or 350 nm wide, 10 nm thick) were fabricated using standard electron beam lithography, thin film deposition, and a liftoff process, incorporating a notch defect for DW pinning.
- NV Center Placement: 100 nm diameter nanodiamonds containing NV centers were deterministically positioned directly over the nanowire defect site using an Atomic Force Microscopy (AFM) pick-and-place protocol.
- Domain Wall Control: DWs were nucleated by applying a magnetic field perpendicular to the wire (using an N52 permanent magnet) to exploit shape anisotropy, and denucleated by applying a tangential field.
- Static Magnetic Characterization (CW-ODMR): Continuous Wave Optically Detected Magnetic Resonance was used to monitor the Zeeman splitting of the NV ground state transition frequency, detecting the onset of DW nucleation via a discontinuity in the stray field.
- Dynamic Detection (Pulsed ODMR): Pulsed ODMR measurements (5 ”s microwave pulse, 500 ns readout) were employed to measure the enhanced spin relaxation caused by the broadband AC magnetic noise generated by the off-resonant DW oscillations.
- Micromagnetic Simulation (Mumax3): The Landau-Lifshitz-Gilbert equation was solved using Mumax3 (5 nm cell size) to model DW dynamics, predict oscillation frequencies, and calculate the time-dependent AC stray field produced at the NV center location.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Spintronics: Provides a foundational platform for integrating NV-based quantum sensors with magnetic dynamic sources, enabling the creation of hybrid quantum devices.
- Nanoscale Microwave Generation: DW oscillations, particularly when driven by electrical current, can serve as highly localized, tunable GHz-frequency microwave generators for addressing and controlling adjacent solid-state qubits.
- High-Speed Qubit Control: The predicted factor of >30 enhancement in local driving field strength under resonant coupling allows for drastic reduction of the pi pulse time, accelerating quantum gate operations.
- Advanced Spintronic Characterization: Enables ultra-local, dynamic characterization of complex magnetic textures (DWs, skyrmions) and their sensitivity to patterning imperfections (edge roughness), critical for optimizing spintronic memory and logic devices.
- Integrated Quantum Sensing: Development of highly sensitive, localized magnetic field sensors capable of measuring high-frequency (GHz) phenomena in condensed matter systems.