Nanoscale Magnetic Domains in Polycrystalline Mn3Sn Films Imaged by a Scanning Single-Spin Magnetometer
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-05-23 |
| Journal | Nano Letters |
| Authors | Senlei Li, Mengqi Huang, Hanyi Lu, Nathan J. McLaughlin, Yuxuan Xiao |
| Institutions | Colorado State University, University of California, San Diego |
| Citations | 19 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research utilizes scanning Nitrogen-Vacancy (NV) single-spin magnetometry to directly image and analyze the nanoscale magnetic domains and switching behavior in polycrystalline Mn3Sn films, a prototypical noncollinear antiferromagnet (AFM).
- Core Achievement: Direct visualization of magnetic domains in Mn3Sn films at nanoscale resolution (~60 nm), overcoming the limitations of conventional magnetometry techniques constrained by the AFMâs nearly compensated magnetization.
- Domain Structure: Multidomain signatures were observed across all film thicknesses (30 nm to 400 nm). The average domain size (Ddomain) was found to increase systematically with film thickness, reaching 400 nm in the 400 nm film.
- Field-Driven Switching: Large perpendicular magnetic fields (up to 2.5 T) successfully reversed the polarity of the local stray field (Bz maps). Crucially, the domain wall boundaries remained stationary, indicating a âheterogeneousâ switching behavior due to weakly coupled magnetic grains.
- Current-Driven Switching (SOTs): Electrically driven switching in Mn3Sn/W Hall cross devices (via Spin-Orbit Torques, SOTs) showed inhomogeneous and âpartialâ magnetic switching features, suggesting complex local thermal effects and nonreversible domain reconstruction.
- Efficiency: Current-induced switching achieved a robust ~40% switching efficiency for the polycrystalline Mn3Sn films.
- Technological Impact: The results provide a comprehensive microscopic understanding of inhomogeneous magnetic orders in noncollinear AFMs, essential for developing next-generation, transformative spintronic applications like ultrahigh-density magnetic memory.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes key quantitative parameters and performance metrics extracted from the study.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material System | Mn3Sn / Mn3Sn/W | N/A | Prototypical noncollinear antiferromagnet. |
| Film Thickness Range (Mn3Sn) | 30 to 400 | nm | Polycrystalline films studied on Al2O3 and Si substrates. |
| Bilayer Thickness (Mn3Sn/W) | 70 nm / 7 nm | N/A | Used for Spin-Orbit Torque (SOT) switching experiments. |
| Measurement Temperature | 300 | K | Room temperature operation. |
| Spatial Resolution (NV) | ~60 | nm | Primarily determined by the NV sensor-to-sample distance. |
| NV Measurement Bias Field | ~15 | G | Static external field applied during scanning to distinguish ESR splitting. |
| Magnetic Training Field (Bext) | ±2.5 | T | Large perpendicular field used for pre-magnetization/switching. |
| Anomalous Hall Resistivity (ÏH) | ~2 | ”Ω cm | Measured for the 70-nm-thick Mn3Sn film. |
| Current Switching Efficiency | ~40 | % | Observed for polycrystalline Mn3Sn films. |
| Longitudinal Bias Field (Current Switching) | 500 | G | Applied to provide deterministic switching polarity during SOT experiments. |
| Maximum Stray Field (Bz) Magnitude | ±8 to ±10 | G | Measured Bz variation across domains. |
| Average Domain Size (Ddomain) | 400 | nm | Measured for the 400 nm thick Mn3Sn film. |
Key Methodologies
Section titled âKey MethodologiesâThe study employed a combination of thin-film deposition, device patterning, and advanced quantum sensing techniques.
- Sample Preparation: Polycrystalline Mn3Sn films (30 nm to 400 nm thick) were prepared using magnetron sputtering techniques on Al2O3 and Si substrates.
- Device Fabrication: Mn3Sn (70 nm)/W (7 nm) bilayer samples were patterned into standard Hall cross devices for magneto-transport characterizations and current-induced switching studies.
- NV Scanning Microscopy: A single nitrogen-vacancy (NV) center in a diamond cantilever was used as a local magnetic probe. The cantilever was attached to a quartz tuning fork for force-feedback Atomic Force Microscopy (AFM) to maintain a constant tip-sample distance (~60 nm).
- Magnetic Stray Field Detection: The local magnetic stray field component along the NV axis (longitudinal field projection) was detected via the Zeeman splitting of the NV electron spin resonance (ESR) energy, which is optically detected.
- Field-Driven Switching Protocol: Samples were subjected to large perpendicular magnetic fields (up to 2.5 T) for âfield training.â Stray field maps (Bz) were then measured in the remnant state after the external field was removed.
- Current-Driven Switching Protocol (SOTs): Electrical write current pulses (Iwrite) were applied through the Hall cross current channel, generating transverse spin currents via the Spin Hall Effect in the W capping layer, driving magnetic switching in the Mn3Sn layer, assisted by a longitudinal bias field (500 G).
Commercial Applications
Section titled âCommercial ApplicationsâThe findings are highly relevant to the development of next-generation microelectronic and quantum technologies, particularly those leveraging the unique properties of noncollinear antiferromagnets.
- Spintronic Memory: Developing ultrahigh-density, non-volatile magnetic memory devices utilizing the robust stability and fast dynamics inherent to antiferromagnetic materials (AFMs).
- AFM-Based Logic and Computing: Harnessing unconventional magnetic switching strategies (like SOT-driven reversal) for advanced information processing and transfer, potentially leading to faster and more energy-efficient logic circuits.
- Topological Quantum Materials Research: Utilizing NV quantum metrology for non-invasive, high-resolution study of microscopic spin properties in a broad range of emergent condensed matter systems, including topological magnets (Mn3X compounds).
- Quantum Sensing Technology: Advancing the application of NV centers as highly sensitive, nanoscale magnetic field sensors for characterizing complex magnetic textures and dynamics in novel materials.
- Magneto-Transport Devices: Engineering devices that exploit exotic AFM properties such as the robust anomalous Hall and Nernst effects, which rely on precise control over magnetic domain structure.
View Original Abstract
Noncollinear antiferromagnets with novel magnetic orders, vanishingly small net magnetization, and exotic spin related properties hold enormous promise for developing next-generation, transformative spintronic applications. A major ongoing research focus of this community is to explore, control, and harness unconventional magnetic phases of this emergent material system to deliver state-of-the-art functionalities for modern microelectronics. Here we report direct imaging of magnetic domains of polycrystalline Mn<sub>3</sub>Sn films, a prototypical noncollinear antiferromagnet, using nitrogen-vacancy-based single-spin scanning microscopy. Nanoscale evolution of local stray field patterns of Mn<sub>3</sub>Sn samples are systematically investigated in response to external driving forces, revealing the characteristic âheterogeneousâ magnetic switching behaviors in polycrystalline textured Mn<sub>3</sub>Sn films. Our results contribute to a comprehensive understanding of inhomogeneous magnetic orders of noncollinear antiferromagnets, highlighting the potential of nitrogen-vacancy centers to study microscopic spin properties of a broad range of emergent condensed matter systems.