| X-ray Magnetic Circular Dichroism (XMCD) |
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| Beamline |
| XMCD measurements are performed on both the soft (4-ID-C) and hard (4-ID-D)
beamlines on sector4. The choice of beamline depends on the absoption edges of interest (see below). |
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| 4-ID local contacts |
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| What is XMCD? |
XMCD measures the difference in the absorption coefficient
(μc = μ+ - μ-) near an x-ray absorption edge, with the
helicity of the incident circulary polarized x-ray parallel (μ+) and antiparallel
(μ-) to the sample magnetization direction. XMCD spectra yield two basic types of
infromation:
- Element (& orbital) specific magnetization
- Separation of orbital <Lz> and spin<Sz>
moments
Since each x-ray absorption edge is associated with a particular element and final state orbital,
the magnetization of each constituent in a complex sample can be seperately studied. The strength
of the dichroic signal scales much the same way as for conventional magnetization measurements,
thus it can be used to obtain element specific hystersis and magnetization curves. For certain
edges, sum rules can be applied to quantitatively determine the orbital and spin contribution
to the magnetic moment.
Beamline 4-ID-C can access energies from 500 eV and 3000 eV.The absorption edges in this energy
range access the transition metal 3d and rare earth 4f states, which are the predominant magnetic
electrons in these elements. Therefore the observed dichroic differences at these energies are
typically large (~10%). Measurements at these energies however require UHV due to considerable
beam attenuation in air.
Beamline 4-ID-D can perform XMCD measurements from 3 keV up to 14 keV. Most absorption edges
in this energy range probe orbitals with are indirectly magnetized, thus the difference signals
are smaller (~0.1 to 1%). |
 |
| XMCD spectra of GaMnAs doped semiconductor showing the induced moment on the Ga and
As atoms. D. Keavney et al. Phys. Rev. Lett. 91 187203 (2003).
(more info) |
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| 4-ID Capabilities |
| The following table gives some general parameters for the beam line capabilites. Note
can't observe smallest difference signals on smallest samples. |
| Parameter |
Soft (4-ID-C) |
Hard (4-ID-D) |
| Temperature Range |
4.2 to 325 K |
4.2 to 325 K |
| Maximum Field |
7.0 Tesla |
4.0 Tesla |
| Smallest detectable difference |
<5x10-4 |
<5x10-5 |
| Minimum Sample Volume |
<0.01 Monolayers |
~500Å |
| Minimum magnetic moment |
~0.01μB |
~0.01μB |
| Time Resolution |
Yes (<10ns) |
No |
| <Lz> error |
~10% |
N/A |
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| References |
Work on 4-ID
- V.V. Krishnamurthy et al., Phys. Rev. Lett. 98 126403 (2007).
- V. Iota et al., Appl. Phys. Lett. 90 042505 (2007).
- J. Chakhalian et al., Nature Phys. 2 244 (2006).
- D. Keavney et al., Phys. Rev. Lett. 91 187203 (2003).
- P. Ryan et al., Phys. Rev. B 69 054416 (2004)
- D. Haskel et al., Phys. Rev. B 67 180406 (2003).
General XMCD
- J Stohr, J. Mag. Mag. Mat. 200, 470 (1999).
- G. Krill, et al., Physica Scripta T49, 295 (1993).
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