Nanoscale magnetic imaging with single spins in diamond

Transcription

1 Nanoscale magnetic imaging with single spins in diamond Ania Bleszynski Jayich UC Santa Barbara Physics AFOSR Nanoelectronics Review Oct 24, 2016

2 Single spin scanning magnetometer Variable temperature operation (~ 1 K 700 K) Minimal measurement backaction High sensitivity (~ nt/hz 1/2 ) and high resolution (~ 10 nm) Proposals: Degen APL 92, (2009), Taylor et al, Nature Physics 4, 810 (2009)

3 Cryogenic NV magnetometry T = 6 K 100 nm Cryogenic opreation allows for high spatial resolution studies of a wide range of materials systems with nanoscale magnetic order.

4 Cryogenic NV magnetometry T = 6 K 100 nm Spatial resolution: 6 nm Pelliccione, ABJ et al, Nature Nano 11, 700 (2016) Magnetic field sensitivity: 3 μt/ Hz

5 Scanned probe imaging of superconducting vortices Vortices in BaFe 2 (As 0.7 P 0.3 ) 2 Field cooled in 10 G External B=0 for measurement 2862 MHz (5.9 G) contour 400 nm T = 6 K Sample grown by Eve Emmanuelidu, Yi group (UCLA)

6 NV fluorescence ratio NV fluorescence ratio NV fluorescence ratio NV fluorescence ratio Comparison to simulation Data: aa bb cc G G contour dd G G contour Simulation: NV height: 300 nm λ = 150 nm (London penetration depth) 200 nm

7 Motivation: Probing magnetic systems at the nanoscale Understand fundamental materials properties Magnetism at oxide interfaces (GdTiO 3 /SrTiO 3 ), multiferroics (BiFeO 3 ) Many potential technologies rely on magnetism at nanoscale Skyrmions (FeGe), Single molecule magnets (Fe 4 ) Probe biological systems at the nanoscale Structural determination of macromolecules, neuronal activity

8 Skyrmions magnetic topological defects Skyrmions are topologically protected, vortex-like spin excitations O. Janson, et al., Nat. Comm. 5, 5376 (2014) Review article: N. Nagaosa and Y. Tokura, Nature Nanotech 8, 899 (2013). Skyrmions are promising for logic and memory devices Small, robust to disorder, and easy to move (low power)

9 CoFeB/Ta/MgO thin film skyrmions Skyrmion density Magnetic multilayer sample with engineered interfacial DMI Perpendicular magnetic anisotropy (H k ) tuned with Ta thickness t Ta(t) Sample structure MgO CoFeB Ta Skyrmion phase stable at room temperature and at low B fields (Ta thickness (t)) ~ G. Yu, et al., Nano Lett. 16, 1981 (2016) Sample grown by Wang group, UCLA

10 NV imaging of CoFeB/Ta/Mgo: Evolution from stripe phase to skyrmion phase Normalized NV photoluminescence Normalized NV photoluminescence Normalized NV photoluminescence Applied H z tunes phase from stripe, to skyrmion, to ferromagnetic Dark lines are 0 G contours along NV axis Stripe Phase H z = 0 G 6.5 G Skymrion Phase μm μm

11 Field Field magnitude along NV axis (G) Magnetic field image of a single skyrmion: nm 0

12 Domain wall structure of the skyrmions? Bloch wall Néel wall

13 Domain wall structure of CoFeB/Ta/MgO skyrmions? Linecut of skyrmion NV-magnetic image: (CoFeB/Ta/MgO) CoFeB/Ta/MgO Data indicates right-handed Néel wall for CoFeB/Ta/MgO structure

14 Domain wall pinning B z = 5 G 5.5 G 6 G 6.5 G 7 G 7.5 G 8 G Domain wall moves between two stable positions ( & ) as B z is increased Important to understand for device applications (moving skyrmions)

15 PL (kcounts/s) PL (kcounts/s) PL (kcounts/s) Domain wall bistability NV ESR curves 34 6 G G Frequency (GHz) NV spin resonance shows two discrete magnetic field values: domain wall jumping Frequency (GHz) 8 G Frequency (GHz) Currently looking into the timescale of these dynamics using NVbased noise spectroscopy

16 NV centers with scanning probes Two scanning approaches: Sample on Tip NV on Tip

17 NV Local conductivity sensing with NV sensors Metal film Z Ag film diamond NV (~5 nm deep) σ Ag = 8.0±0.4 x 10 6 S/m σ Au = 7±2 x 10 6 S/m σ Ti = 3±2 x 10 6 S/m NV T 1 relaxation caused by Johnson noise-induced fluctuating B fields Promising for future nanoscale studies of local conductivity

18 Nanoscale conductivity imaging T 1 (ms) NV relaxometry image of nanopatterned Ag 4 SEM image of nanopatterned Ag nm Conducting silver nanostructures locally reduced NV T 1

19 Summary and next steps: T 1 (ms) 1 μm Imaged local nanoscale magnetic order in superconductors and skyrmionic systems Directly imaged domain wall type Observed domain wall depinning NEXT: measure dynamics 4 Demonstrated local, nanoscale conductivity imaging using NV relaxometry NEXT: probe inhomogeneous local conductivity in bulk materials, eg at domain walls 200 nm More future work: improve probe sensitivity

20 UCSB Group Preeti Alec Matt Bryan