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6CCVD Research

Scanning nitrogen-vacancy center magnetometry in large in-plane magnetic fields

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-02-14
JournalApplied Physics Letters
AuthorsPol Welter, J. Rhensius, Andrea Morales, M. S. Wörnle, Charles‐Henri Lambert
InstitutionsETH Zurich
Citations21
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research details the development and application of novel scanning Nitrogen-Vacancy (NV) diamond probes optimized for magnetometry in large in-plane magnetic fields (Bip).

  • Core Innovation: Fabrication of scanning NV probes from {110}-cut diamond crystals, aligning the NV anisotropy axis parallel (θ = 90°) to the sample surface.
  • Performance Breakthrough: These {110} probes maintain high Photoluminescence (PL) spin contrast and sensing capability up to applied in-plane fields of approximately 40 mT.
  • Limitation Overcome: Conventional {100}-cut probes lose all PL contrast above ~20 mT Bip due to spin mixing caused by the NV axis tilt (θ = 55°).
  • Demonstrated Application: Quantitative nanoscale imaging of magnetic domain patterns in a Co-NiO thin film across the full Bip range (0 to 38.7 mT).
  • Engineering Impact: The ability to apply purely in-plane bias fields without sensitivity loss is critical for studying phenomena in spintronics, such as current-induced switching of ferromagnetic layers.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Diamond Crystal Facet (New Probe){110}N/ASupports in-plane NV orientation.
Diamond Crystal Facet (Conventional){100}N/AStandard probe, supports tilted NV orientation.
NV Anisotropy Angle (New Probe)90°Angle relative to surface normal (z-axis); in-plane.
NV Anisotropy Angle (Conventional)55°Angle relative to surface normal (z-axis); tilted.
Maximum In-Plane Bias Field (Bip)~40mTField limit for maintaining full PL contrast with {110} probe.
Field Limit (Conventional Probe)~20mTField limit before total loss of PL contrast.
Ion Implantation Species15N+N/AUsed for NV creation.
Ion Implantation Energy7keVImplantation depth control.
Ion Implantation Dose3 * 1010ions/cm2Nitrogen concentration.
Vacuum Annealing Temperature880°CDefect activation.
Vacuum Annealing Pressure< 5 * 10-8mbarHigh vacuum required.
PL Saturation Count Rate (Isat)800 - 1200kCt/sMeasure of optical efficiency.
Spin Contrast (Typical)20 - 25%Measure of sensing fidelity.
Co-NiO Film Coercivity40 - 50mTCoercive field of the imaged sample.
Detectable Field (Bmin)~5nT/Hz1/2Estimated magnetic field sensitivity.

Key Methodologies

Section titled “Key Methodologies”

The NV probes were fabricated using high-purity diamond and standard nanofabrication techniques, optimized for the {110} crystal orientation.

  1. Starting Material: High-purity single-crystal diamond plates with a main {110} facet, grown via High-Pressure High-Temperature (HPHT) synthesis.
  2. NV Center Creation:
    • Ion implantation of 15N+ ions at 7 keV energy with a dose of 3 * 1010 ions/cm2.
    • Subsequent vacuum annealing at 880 °C for 2 hours under high vacuum (P < 5 * 10-8 mbar) to activate the NV centers.
  3. Probe Tip Fabrication:
    • A series of e-beam lithography steps were used to define the tip geometry.
    • Inductively-Coupled Plasma (ICP) etching (using an Oxford Instruments PlasmaPro 100) was employed to shape the diamond paddle and tip structure.
  4. Magnetometry Setup:
    • The finished diamond probe (mounted on an AFM cantilever) was scanned over the magnetic sample surface.
    • Optically-Detected Magnetic Resonance (ODMR) was used to monitor shifts in the NV spin transition frequencies (ω±) caused by the sample’s stray magnetic field.
    • A variable in-plane magnetic field (Bip) was applied using permanent magnets or electromagnets to bias the sample.
  5. Sample Preparation (Co-NiO): The magnetic sample was fabricated by magnetron sputtering, creating a multilayer stack: Si/SiO2(400)/Ta(3)/Pt(5)/NiO(5)/Co(2.5)/NiO(5)/Pt(3) (thicknesses in nm).

Commercial Applications

Section titled “Commercial Applications”

The ability to perform high-sensitivity nanoscale magnetometry in the presence of large, purely in-plane bias fields is crucial for advancing several areas of magnetic materials science and quantum technology.

  • Spintronics Research:
    • Studying current-induced switching mechanisms in ferromagnetic layers, which often require large in-plane fields to break symmetry.
    • Imaging and control of domain wall hopping and dynamics in magnetic racetracks.
  • Thin-Film Magnetism:
    • Quantitative imaging of complex magnetic structures (e.g., skyrmions, antiferromagnetic domains) under external field control.
    • Characterization of exchange bias systems (like Co-NiO) where high bias fields are necessary to reach saturation or coercive limits.
  • Quantum Sensing Technology:
    • Development of next-generation scanning probe microscopes capable of operating robustly in complex magnetic environments.
    • Characterization of magnetic materials for high-density magnetic memory (MRAM) and logic devices.
View Original Abstract

Scanning magnetometry with nitrogen-vacancy (NV) centers in diamond has emerged as a powerful microscopy for studying weak stray field patterns with nanometer resolution. Due to the internal crystal anisotropy of the spin defect, however, external bias fields—critical for the study of magnetic materials—must be applied along specific spatial directions. In particular, the most common diamond probes made from {100}-cut diamond only support fields at an angle of θ=55° from the surface normal. In this paper, we report fabrication of scanning diamond probes from {110}-cut diamond where the spin anisotropy axis lies in the scan plane (θ=90°). We show that these probes retain their sensitivity in large in-plane fields and demonstrate scanning magnetometry of the domain pattern of Co-NiO films in applied fields up to 40 mT. Our work extends scanning NV magnetometry to the important class of materials that require large in-plane fields.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2017 - Purely antiferromagnetic magnetoelectric random access memory [Crossref]
  2. 2019 - Nanomagnetism of magnetoelectric granular thin-film antiferromagnets [Crossref]
  3. 2018 - Magnetostatic twists in room-temperature skyrmions explored by nitrogen-vacancy center spin texture reconstruction [Crossref]
  4. 2017 - Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer [Crossref]
  5. 2018 - Nanoscale electrical conductivity imaging using a nitrogen-vacancy center in diamond [Crossref]
  6. 2016 - Quantitative nanoscale vortex imaging using a cryogenic quantum magnetometer [Crossref]
  7. 2013 - Imaging currents in HgTe quantum wells in the quantum spin hall regime [Crossref]
  8. 2017 - Nanoscale imaging of current density with a single-spin magnetometer [Crossref]
  9. 2020 - Imaging viscous flow of the Dirac fluid in graphene [Crossref]

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