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Spin-polarized scanning electron microscopy (spin-SEM, or SEMPA)
is an efficient technique to image the magnetization distribution
at surfaces and in thin films. An unpolarized monoenergetic electron
beam, focused by electromagnetic lenses, scans across the ferromagnetic
surface. At each scanned position, spin-polarized secondary electrons
are created near the surface, emitted into vacuum and transferred
to the spin analyzer by electrostatic lenses. There the electrons
are scattered at a gold foil into preferential directions depending
on their spin. A pair of detectors counts the electrons with "up"
and those with "down" spin. The spin polarization of the
emitted secondary electrons is a measure of the surface magnetization.
The total number of electrons yields the surface topography map;
typical beam energies are 2 to 10 keV with a beam current of 0.1
to 1 nA. This instrument is able to image the magnetization of specimens
with thicknesses down to a single atomic layer and a very high spatial
resolution of 20 to 40 nm. Thus very detailed magnetization maps
can be acquired.
References
| [1] |
R. Allenspach, J.
Magn. Magn. Mater. 129, 160 (1994). |
| [2] |
R. Allenspach, IBM J. Res. Develop.
44, 553 (2000). |
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