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 Magnetic Studies at the APS – Sector 4 4-ID-D keV 4-ID-C keV XMCD Magnetic Imaging (PEEM) Reflectivity XPS XMCD High Field Scattering PEEM Station Beamline Optics High-Field Station 0.1 T 7 T XMCD/Scattering Station 4-ID-C beamline: Helical undulator e-e-

4 4-ID-C 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 eV Energy Range E/∆E~5000 typical ~100x100µm spot (variable focus) 700 and 1200 l/mm gratings Rh coatings M1- Plane M2- Sphere M3- Sphere SG K-B pair Sample Exit Slit Ent. Slit Helical undulator

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

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

7 Doped oxides - correlation with carriers S.A. Chambers, Surf. Sci. Rep. 61, 345 (2006). Activation of FM order via carrier doping Fast-Grown Slow-Grown Co:TiO 2 Correlation with extrinsic defects

8 Co-doped ZnO XMCD is consistent with bulk magnetization But, S/N~3, still too low to rule out Co (0) SQUID Bulk Remanent Magnetization: ~0.04 µ B /Co Fluorescence Yield data: XAS: Co 2+ XMCD: 0.8% signal MOCVD-grown films, Zn-diffused, S. Chambers et al. XMCD 100 nm film 10% Co

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

10 Cu-doped ZnO Fluorescence Yield Data: Two Cu 2+ spectral components A: substitutions, paramagnetic B: CuO inclusions, non-magnetic Noise level ~0.6% (spectra) Upper bound of <0.1  B /Cu from XMCD ~  B /Cu from SQUID PLD-grown with O 2 or N 2 O atmosphere D. J. Keavney, D. B. Buchholz, Q. Ma, R. P. H Chang, Appl. Phys. Lett (2007). 20 mTorr O 2 : n-type, non-FM 50 mTorr N 2 O: p-type, FM Similar results seen in Mn:ZnO, Co:ZnO, Cr:TiO 2, V:SnO 2, Mn:GaN, Cr:AlN, Co:TiO 2, etc. Magnetism in doped semiconductors may be unrelated to the dopant ions. Except for Mn:GaAs Flux limits ability to say for sure. Magnetism in doped semiconductors may be unrelated to the dopant ions. Except for Mn:GaAs Flux limits ability to say for sure.

11 Mixing Ferromagnetism and Superconductivity at the Atomic Scale J. Chakhalian, J.W. Freeland, et. al. Nature Physics 2, 244 (2006). Mn Cu (x10) YBa 2 Cu 3 O 7-δ La 2/3 Ca 1/3 MnO 3

12 100ps magnetization dynamics via time-resolved PEEM B 6 µm Ni 80 Fe 20 disk

13 Rationale for Upgrades Long Undulators & Efficient Optics Enhanced Detectors Fast Polarization Switching Proposed detection goal: 5x10 12 µ B /cm 2 (100nm film 1% doped with µ B /dopant ion) Current detection limit: 5x10 15 µ B /cm 2 (100nm film 10% doped with 0.05µ B /dopant ion) More Photons √N Lock-in detection Fe K-edge 40Hz D. Haskel

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

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

16 Fast Polarization Switching Approaches 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 1. Long CPU Possibly faster switching Orbit corrections easier Arbitrary polarization Switching mode throws away ½ flux Matching and aligning probably difficult RCP LCP LCP beam to user RCP beam to user LCP/RCP beam to user

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

18 Orbit Corrections Peaks represent about 250 µm of orbit error Corrected to 7 µm after some effort CPU creates significant orbit perturbations and beam size fluctuations Approximate Timeline MilestoneSwitching Time March 2001Beamline operational, RCP mode only Oct 2001LCP mode5 min 2003Ramp rates increased30 sec 2004AC mode at up to 0.5Hz periodic 3 sec 2006AC mode non-periodic up to 1Hz 150 ms

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