# Presentation: 180568

## 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
- Proposed Upgrades (higher sensitivity and throughput)
- Existing beamline
- New soft x-ray magnetism sector
- Estimated Performance and Expected Issues

## Magnetic Studies at the APS – Sector 4

**4-ID-D**
**2.8-40 keV**

**4-ID-C**
**0.5-3.0 keV**

- XMCD
- Magnetic Imaging (PEEM)
- Reflectivity
- XPS

- XMCD
- High Field Scattering

- Helical undulator

- e-

- www.aps.anl.gov

## 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
- 500-3000eV 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

## Magnetic Semiconductors

- H. Ohno, et al. Appl. Phys. Lett. **69, **363 (1996).

- Mi et al., J. Appl. Phys. **101**, 023904 (2007).

- Mn:GaAs TC~120K

- Mn:ZnO TC>300K

- Controversies:
- Extrinsic vs. intrinsic magnetism
- Are conduction electrons involved?
- Second phase formation
- Contamination
- Source material, substrate, metal tools

## Spin Configuration in Mn:GaAs

- D.J. Keavney, D. Wu, J.W. Freeland, E. Johnston-Halperin, D.D. Awschalom, J. Shi,
- Phys. Rev. Lett. **91** 187203 (2003).

**Mn**

**As**

**Ga**

- Consistent with Density Functional Theory

## 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:TiO2

- Correlation with extrinsic defects

## 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 μB/Co
**Fluorescence Yield data:**
- XAS: Co2+
- XMCD: 0.8% signal

* **MOCVD-grown films, Zn-diffused, S. Chambers et al.*

- XMCD

- 100 nm film
- 10% Co

## Ferromagnetism in Cu-doped ZnO

- D.B. Buchholz, et al., APL 87, 082504 (2005).

- Ye et al., PRB 73, 033203 (2006).

## Cu-doped ZnO

-  PLD-grown with O2 or N2O atmosphere

- D. J. Keavney, D. B. Buchholz, Q. Ma, R. P. H Chang, Appl. Phys. Lett. **91** 012501 (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: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.

## Mixing Ferromagnetism and Superconductivity at the Atomic Scale

- J. Chakhalian, J.W. Freeland, et. al. Nature Physics** 2**, 244 (2006).

- Mn

- Cu (x10)

- YBa2Cu3O7-δ

-    La2/3Ca1/3MnO3

## 100ps magnetization dynamics via time-resolved PEEM

- 6 μm Ni80Fe20 disk

## Rationale for Upgrades

- Long Undulators & Efficient Optics
- Enhanced Detectors
- Fast Polarization Switching

- Proposed detection goal: 5x1012 μB/cm2
- (100nm film 1% doped with 0.0005μB/dopant ion)

- Current detection limit: 5x1015 μB/cm2
- (100nm film 10% doped with 0.05μB/dopant ion)

## 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.

## 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-

-  2-3 orders of magnitude more flux
-  Lock-in detection
-  Enhanced Instrumentation

## 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 1⁄2 flux
- Matching and aligning probably difficult

- RCP

- LCP

- LCP beam to user

- RCP beam to user

- LCP/RCP beam to user

## Expected Performance

- Higher Flux: x30
- Lock-in: x10 @ 40Hz
- Multi-element Si-drift detectors: x10

## 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 |  |  |
| --- | --- | --- |
|  | Milestone | Switching Time |
| March 2001 | Beamline operational, RCP mode only |  |
| Oct 2001 | LCP mode | 5 min |
| 2003 | Ramp rates increased | 30 sec |
| 2004 | AC mode at up to 0.5Hz periodic | 3 sec |
| 2006 | AC mode non-periodic up to 1Hz | 150 ms |

## 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