1 / 19

Polarized Soft X-ray Science at the APS

Polarized Soft X-ray Science at the APS. David Keavney X-ray Operations and Research Advanced Photon Source. Workshop on Soft X-ray Beamlines at the NSLS-II Brookhaven, NY, February 4, 2008. Outline. Beamline 4-ID-C at the APS Recent science using XMCD at 4-ID-C

marjoriefoster
Télécharger la présentation

Polarized Soft X-ray Science at the APS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Polarized Soft X-ray Science at the APS David Keavney X-ray Operations and Research Advanced Photon Source Workshop on Soft X-ray Beamlines at the NSLS-II Brookhaven, NY, February 4, 2008

  2. Outline • Beamline 4-ID-C at the APS • Recent science using XMCD at 4-ID-C • Proposed Upgrades (higher sensitivity and throughput) • Existing beamline • New soft x-ray magnetism sector • Estimated Performance and Expected Issues

  3. 4-ID-C beamline: 7 T 0.1 T PEEM Station High-Field Station XMCD/Scattering Station Beamline Optics Magnetic Studies at the APS – Sector 4 XMCD Magnetic Imaging (PEEM) Reflectivity XPS 4-ID-C 0.5-3.0 keV XMCD High Field Scattering www.aps.anl.gov 4-ID-D 2.8-40 keV Helical undulator e-

  4. 4-ID-C Helical undulator M3-Sphere M2-Sphere M1-Plane K-B pair Sample • Source: • Fully Electromagnetic CPU • 12.8cm period, 2.47m • Linear H and V, Circular R and L modes • RCP/LCP Switching Rate: 1Hz • Optics: • Spherical Grating Monochromator • 500-3000eV Energy Range • E/∆E~5000 typical • ~100x100µm spot (variable focus) • 700 and 1200 l/mm gratings • Rh coatings Exit Slit Ent. Slit SG

  5. III GaAs V Metal (Ga,Mn)As Mn:GaAs TC~120K Magnetic Semiconductors Controversies: • Extrinsic vs. intrinsic magnetism • Are conduction electrons involved? • Second phase formation • Contamination • Source material, substrate, metal tools H. Ohno, et al. Appl. Phys. Lett. 69, 363 (1996). Mn:ZnO TC>300K Mi et al., J. Appl. Phys. 101, 023904 (2007).

  6. Spin Configuration in Mn:GaAs Consistent with Density Functional Theory Mn As Ga D.J. Keavney, D. Wu, J.W. Freeland, E. Johnston-Halperin, D.D. Awschalom, J. Shi, Phys. Rev. Lett. 91 187203 (2003).

  7. Doped oxides - correlation with carriers • Activation of FM order via carrier doping Co:TiO2 Slow-Grown Fast-Grown S.A. Chambers, Surf. Sci. Rep. 61, 345 (2006). • Correlation with extrinsic defects

  8. Co-doped ZnO • MOCVD-grown films, Zn-diffused, S. Chambers et al. Bulk Remanent Magnetization: ~0.04 µB/Co Fluorescence Yield data: XAS: Co2+ XMCD: 0.8% signal SQUID XMCD is consistent with bulk magnetization But, S/N~3, still too low to rule out Co(0) 100 nm film 10% Co XMCD

  9. Ferromagnetism in Cu-doped ZnO D.B. Buchholz, et al., APL 87, 082504 (2005). Ye et al., PRB 73, 033203 (2006).

  10. Fluorescence Yield Data: • Two Cu2+ spectral components • A: substitutions, paramagnetic • B: CuO inclusions, non-magnetic • Noise level ~0.6% (spectra) • Upper bound of <0.1 mB/Cu from XMCD • ~0.3-0.4 mB/Cu from SQUID Cu-doped ZnO • PLD-grown with O2 or N2O atmosphere 20 mTorr O2: n-type, non-FM 50 mTorr N2O: p-type, FM Similar results seen in Mn:ZnO, Co:ZnO, Cr:TiO2, V:SnO2, Mn:GaN, Cr:AlN, Co:TiO2, etc. Magnetism in doped semiconductors may be unrelated to the dopant ions. Except for Mn:GaAs Flux limits ability to say for sure. D. J. Keavney, D. B. Buchholz, Q. Ma, R. P. H Chang, Appl. Phys. Lett. 91 012501 (2007).

  11. Mixing Ferromagnetism and Superconductivity at the Atomic Scale YBa2Cu3O7-δ Cu (x10) La2/3Ca1/3MnO3 Mn J. Chakhalian, J.W. Freeland, et. al. Nature Physics 2, 244 (2006).

  12. B 100ps magnetization dynamics via time-resolved PEEM 6 µm Ni80Fe20 disk

  13. √N Fe K-edge XMCD @ 40Hz D. Haskel More Photons Lock-in detection Rationale for Upgrades Current detection limit: 5x1015 µB/cm2 (100nm film 10% doped with 0.05µB/dopant ion) • Long Undulators & Efficient Optics • Enhanced Detectors • Fast Polarization Switching Proposed detection goal: 5x1012 µB/cm2 (100nm film 1% doped with 0.0005µB/dopant ion)

  14. M3-Plane M1-Plane M2-Sphere Source (CPU) K-B pair Exit Slit Sample VLS-PG Proposed Upgrade to 4-ID-C 10% grating efficiency 95% of beamtime requests Proposed: varied line-spacing plane grating design Energy range: 400-2000eV Peak efficiency @ 1000eV Resolution: 5000-10000 Improved flux by 1-2 orders of magnitude between 500 and 1000 eV.

  15. High-sensitivity magnetism beamline on long straight section Fast-switching helical undulator 9+ T New high sensitivity beamline 0.8 T e- High-Field, sub-K Station Multipole XMCD/Scattering Station Beamline Optics • 2-3 orders of magnitude more flux • Lock-in detection • Enhanced Instrumentation

  16. Fast Polarization Switching Approaches 1. Long CPU LCP/RCP beam to user • Uses entire straight section • Max switching rate not clear (CPU: 1Hz) • Orbit corrections difficult • Power Supply (CPU: H:1600A, V:±400A) 2. Dual Apple Devices with Kickers RCP LCP LCP beam to user RCP beam to user • Possibly faster switching • Orbit corrections easier • Arbitrary polarization • Switching mode throws away ½ flux • Matching and aligning probably difficult

  17. Expected Performance • Higher Flux: x30 • Lock-in: x10 @ 40Hz • Multi-element Si-drift detectors: x10

  18. Orbit Corrections CPU creates significant orbit perturbations and beam size fluctuations Peaks represent about 250 µm of orbit error Corrected to 7 µm after some effort

  19. Summary • Sensitivity limits in soft x-rays • Small moments • Very dilute limits • Inefficient detection (PEEM) • Upgrade Existing beamline x~100 • New fast polarization switching beamline x~1000

More Related