Quantum Sensing and Imaging of Spin–Orbit‐Torque‐Driven Spin Dynamics in the Non‐Collinear Antiferromagnet Mn3Sn
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-03-24 |
| Journal | Advanced Materials |
| Authors | Gerald Q. Yan, Senlei Li, Hanyi Lu, Mengqi Huang, Yuxuan Xiao |
| Institutions | Colorado State University, University of California, San Diego |
| Citations | 70 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research utilizes Nitrogen-Vacancy (NV) quantum sensing to investigate the microscopic spin dynamics in the noncollinear antiferromagnet Mn3Sn, a promising topological semimetal for advanced spintronics.
- Nanoscale Imaging Achievement: Successfully performed nanoscale imaging of Spin-Orbit Torque (SOT)-driven magnetic dynamics, including deterministic magnetic switching and continuous chiral spin rotation, overcoming the challenge of Mn3Sn’s vanishingly small magnetic moment.
- Switching Mechanism: NV wide-field magnetometry revealed that SOT-driven switching in polycrystalline Mn3Sn is nonuniform, occurring gradually in individual magnetic grains over a characteristic length scale of hundreds of nanometers.
- Chiral Spin Rotation: Electrical transport and NV relaxometry measurements confirmed the SOT-driven continuous rotation of the chiral spin structure, establishing a critical current density threshold (Jcrit) for this dynamic behavior.
- Quantum Coupling Demonstrated: Direct evidence of off-resonance dipole-dipole coupling between the low-frequency spin wave modes of Mn3Sn and proximate NV centers was observed via NV relaxometry.
- Technological Platform: The results validate NV centers as a powerful tool for accessing local magnetic information in emergent topological magnets and suggest a pathway for developing solid-state hybrid quantum architectures.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Mn3Sn Film Thickness | 50 | nm | Polycrystalline films prepared by UHV magnetron sputtering. |
| Néel Temperature (TN) | ~420 | K | Temperature below which Mn3Sn exhibits noncollinear order. |
| Remnant Magnetization | ~0.002 | µB per Mn atom | Vanishingly small weak bulk magnetization. |
| Hall Device Width | 10 | µm | Standard Hall cross geometry for electrical and NV measurements. |
| NV Center Density | ~1500 | /µm2 | Ensemble density used for wide-field magnetometry. |
| Spatial Resolution (Imaging) | Hundreds | nm | Length scale of characteristic multidomain features observed. |
| Critical Current Density (Jcrit, Theory) | 36 | MA/cm2 | Theoretical threshold for SOT-driven chiral spin rotation (Mn3Sn/Pt). |
| Critical Current Density (Jcrit, Exp.) | ≥ 38 | MA/cm2 | Experimental threshold for enhanced NV relaxation rate (onset of rotation). |
| Maximum Tested Current Density (Jmax) | 48 | MA/cm2 | Maximum current density used in relaxometry measurements. |
| Magnetic Domain Length Scale (Theory) | ~300 | nm | Characteristic length scale of magnetic domains in Mn3Sn. |
| SOT Switching Proportion (Mn3Sn/Pt) | ~25 | % | Proportion of magnetic domains flipped during deterministic switching. |
Key Methodologies
Section titled “Key Methodologies”-
Sample Growth and Device Fabrication:
- 50-nm-thick polycrystalline Mn3Sn films were prepared using ultra-high-vacuum (UHV) magnetron sputtering.
- Heavy metal layers (Pt or W) were deposited in-situ to generate spin currents via the Spin Hall Effect.
- Samples were patterned into 10 µm wide Hall cross devices for magneto-transport and NV measurements.
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Quantum Sensing Platform Setup:
- A diamond microchip containing shallowly implanted Nitrogen-Vacancy (NV) ensembles (~1500/µm2) was positioned on top of the Mn3Sn/metal Hall device.
- NV centers were initialized and read out using 1-µs green laser pulses.
-
Wide-Field Magnetometry (Static Imaging):
- Used to image the out-of-plane component of the magnetic stray field (Bz) generated by the Mn3Sn sample.
- SOT-driven deterministic switching was induced by millisecond write current pulses (Iwrite) applied along the x-axis in the presence of an external magnetic field (Bext).
- The variation of Bz maps was recorded after successive current pulses to visualize the evolution of local magnetic textures and domain structure.
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NV Relaxometry (Dynamic Sensing):
- Principle: SOT-driven chiral spin rotation generates low-frequency magnons which scatter with thermal magnons, establishing a quasi-equilibrium state with enhanced magnon density at the NV Electron Spin Resonance (ESR) frequency (fNV).
- Measurement Protocol: NV spins initialized (ms = 0), followed by an electric current pulse (0 to 4 ms) to drive rotation, and finally, a readout pulse to measure the NV occupation probabilities and determine the relaxation rate (Γ).
- Microwave-Assisted Relaxometry: An external microwave magnetic field (fMW) was applied; a peak in the measured relaxation rate (Γ) was observed when fMW matched the SOT-driven chiral spin rotation frequency (f), confirming coherent spin dynamics.
Commercial Applications
Section titled “Commercial Applications”The integration of topological antiferromagnets with quantum sensors opens new avenues for advanced computing and sensing technologies:
- Next-Generation Spintronics: Utilizing the low-moment, high-speed dynamics of Mn3Sn for ultra-fast (terahertz-scale) and high-density data storage and processing devices.
- Hybrid Quantum Systems: Developing solid-state architectures where topological magnets (hosting spin wave modes) are coupled to quantum spin processors (NV centers) for mutual communication and signal transduction.
- Quantum Information Science (QIS): Creation of novel functional materials for quantum memory, sensing, and computation, leveraging the robust coupling mechanism demonstrated.
- Topological Materials Characterization: NV centers offer a unique, non-invasive method for local diagnosis of magnetic order and dynamics in other emergent quantum materials that possess low or vanishing magnetic dipole moments.
- Energy Efficient Computing: Investigating the interplay between topology and magnetism to inform the design of energy-efficient neuromorphic computing hardware.
View Original Abstract
Abstract Novel non‐collinear antiferromagnets with spontaneous time‐reversal symmetry breaking, non‐trivial band topology, and unconventional transport properties have received immense research interest over the past decade due to their rich physics and enormous promise in technological applications. One of the central focuses in this emerging field is exploring the relationship between the microscopic magnetic structure and exotic material properties. Here, nanoscale imaging of both spin-orbit‐torque‐induced deterministic magnetic switching and chiral spin rotation in non‐collinear antiferromagnet Mn 3 Sn films using nitrogen‐vacancy (NV) centers are reported. Direct evidence of the off‐resonance dipole-dipole coupling between the spin dynamics in Mn 3 Sn and proximate NV centers is also demonstrated by NV relaxometry measurements. These results demonstrate the unique capabilities of NV centers in accessing the local information of the magnetic order and dynamics in these emergent quantum materials and suggest new opportunities for investigating the interplay between topology and magnetism in a broad range of topological magnets.