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6CCVD Research

A magnon scattering platform

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-06-15
JournalProceedings of the National Academy of Sciences
AuthorsTony Zhou, Joris J. Carmiggelt, Lisa Maria GĂ€chter, Ilya Esterlis, Dries Sels
InstitutionsETH Zurich, Harvard University
Citations53
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research demonstrates a novel, table-top, two-dimensional (2D) scattering platform utilizing coherent magnonic waves (spin waves) to probe the magnetic properties of materials at mesoscopic length scales.

  • Core Innovation: The platform uses a thin film of Yttrium Iron Garnet (YIG) as the ‘vacuum’ medium for long-lived, coherent magnon propagation, replacing traditional free-space particle beams.
  • Advanced Detection: A scanning Nitrogen Vacancy (NV) center magnetometer is employed as a local sensor, providing nanometer resolution and operating from cryogenic to ambient temperatures.
  • Comprehensive Measurement: Unlike most scattering techniques that measure only intensity, this platform determines both the amplitude and phase of the scattered magnons via an interference scheme, allowing for systematic reconstruction of the target scattering potential.
  • Mesoscopic Capability: The technique is specifically designed to overcome limitations of traditional scattering methods when analyzing ultra-thin (e.g., 2D layered) materials that are only micrometers wide.
  • Key Results: Experiments scattering magnons off a Permalloy (Py) disk confirm theoretical predictions for Damon-Eshbach Surface Waves (DESW), including negligible backscattering and confinement of the scattered wave to a specific cone angle (Ξc ≈ 28°).
  • Target Characterization: Analysis of the phase-resolved images reveals intrinsic features of the target’s magnetic response, including suppression of response near the target edges and a quadrupolar character in the real component of the scattering source.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Magnon MediumYttrium Iron Garnet (YIG)N/A100 nm thick film grown on Gd3Ga5O12 (GGG) substrate
Target MaterialPermalloy (Py) diskN/A100 nm thick, 5 ”m diameter
Impinging ParticleCoherent Magnonic Waves (DESW)N/AGenerated via a micro stripline
Detector TypeSingle Nitrogen Vacancy (NV) centerN/AScanning probe magnetometer
Detector ResolutionNanometerN/ASpatial resolution for imaging scattered waves
Magnon Wavelength (Shortest Resolved)640 to 660nmAchieved using simple RF waveguide design
NV Center Ground State Splitting2.87GHzSplitting between ms = 0 and ms = ±1 states at zero field
Operating Frequency Range~2.0 to 2.5GHzMagnon excitation frequency
Measured Scattering Cone Angle (Ξc)28 ± 2Degrees (°)Measured at 2.18 GHz
Operating EnvironmentCryogenic to AmbientN/ATemperature range for NV center operation

Key Methodologies

Section titled “Key Methodologies”

The experimental methodology integrates nanofabrication, microwave excitation, quantum sensing, and advanced wave analysis to achieve phase-resolved magnon scattering.

  1. Sample Preparation: A 100 nm YIG film is grown on a GGG substrate. A micro stripline (for magnon generation) and a 100 nm thick, 5 ”m diameter Py disk (the scattering target) are deposited onto the YIG surface.
  2. Magnon Launching: A microwave current is driven through the micro stripline, launching coherent Damon-Eshbach Surface Waves (DESW) in the YIG film at the microwave frequency (ω).
  3. NV Center Tuning: An external magnetic field (Bext) is applied along the NV axis to tune the Electron Spin Resonance (ESR) frequency of the NV center to match the magnon frequency (ω).
  4. Amplitude Detection: The propagating magnons generate a local time-varying AC magnetic field above the YIG. This field drives transitions in the NV spin state, resulting in a measurable decrease in NV fluorescence (PL) proportional to the magnon amplitude.
  5. Phase Detection (Interference Scheme): A second, uniform RF reference field (Bref) is applied from a distant antenna. The NV center measures the interference pattern (Btotal = Bmagnon + Bref). By varying the relative phase (φ) of the reference source, the full spatial amplitude and phase profile of the scattered waves are mapped.
  6. Dispersion Extraction: The wavelength (λ) of the magnons is extracted from the spatial interference peaks, allowing for the direct determination of the magnon dispersion relation, ω(k).
  7. Scattering Potential Inversion: The scattered wave (Bscat) is modeled as a convolution of the Green’s function (G) of the DESW and the target source term (∇ · m). The source term is determined experimentally by fitting the measured intensity pattern using Gaussian basis functions, revealing the magnetic response characteristics of the Py target.

Commercial Applications

Section titled “Commercial Applications”

This platform and its underlying technologies are highly relevant for advanced research and development in quantum materials and information processing.

  • Magnonic Devices and Computing:
    • Characterization of low-loss magnetic materials (like YIG) essential for developing next-generation magnonic circuits, which use spin waves instead of electrons for information transfer, potentially offering lower power consumption.
    • Designing and optimizing magnonic waveguides, filters, and resonators by providing high-resolution, phase-sensitive feedback on spin wave propagation and scattering.
  • Quantum Sensing and Nanoscale Metrology:
    • Advancing the use of NV centers in diamond as robust, high-sensitivity, table-top magnetometers capable of imaging dynamic magnetic phenomena (AC fields) with nanometer resolution across a wide temperature range.
  • Condensed Matter Physics Research:
    • Enabling the study of exotic magnetic phases and correlated many-body systems in 2D and mesoscopic materials (e.g., superconductors, topological insulators, spin liquids) that are inaccessible to traditional large-scale scattering techniques (neutron, X-ray).
  • Non-Destructive Evaluation (NDE) of Thin Films:
    • High-resolution imaging and characterization of magnetic domain structures, spin textures (like skyrmions), and defects in thin magnetic films used in data storage and sensor applications.
View Original Abstract

Significance This work describes a general scattering platform that uses magnons to explore the underlying properties of target materials. In this work we show how both phase and amplitude of magnons can be imaged using a nitrogen vacancy center magnetometer and how the scattered pattern of waves can be used to infer geometric and magnetic properties of a target material. To demonstrate this new experimental methodology we use a permalloy disk as our target and show that even with such a simple target unexpected behavior is observed. In addition, we provide a theoretical framework to reconstruct the properties of the target.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2010 - Nonlinear Optics
  2. 1984 - Theory of Neutron Scattering from Condensed Matter
  3. 2009 - Spin Waves: Theory and Applications

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