Spinfiltered PEEM using spindependent transmission

If a spin polarized electron beam travels through ferromagnetic material, the scattering rates for electrons with spin parallel or antiparallel to the majority spin direction are different. One reason is that the unoccupied density of states, being the final state density in scattering events, is much higher for minority spin electrons. As a consequence, majority electrons are characterized by a higher mean free path for inelastic scattering. On the basis of spin polarized photoemission from Fe on W(110) by Getzlaff et al. [1] It was possible to estimate the so called transport polarization of unpolarized photoelectrons from the W-substrate through the ferromagnetic films of different thicknesses [2].

The spinfilter effect is maximized at low energies. Therefore this project uses a special immersion-lens optics (tandem optics) that allows to reduce the energy of the incoming electrons down to the cut-off of the work function threshold.


Figure 1: (a) Schematic view of the electron optics of a regular PEEM. Photoelectrons are emitted from the sample and the 'electronic' image is magnified and transferred by a set of electrostatic lenses to the imaging unit (either a MCP/CCD-camera or a Delayline Detector [3]) at the end of the column (b) Tandem optics; the sample holder for the thin films replaces the sample stage from the regular PEEM and an additional set of lenses is used to transfer the image from the sample to this thin film filter in front of the regular PEEM optics.

Very low kinetic energies are reached with this setup at the position of the filter stage, thus providing a long mean free path and enhanced spinfilter effect.
Different materials were tested and palladium was found to provide high electron transmission rates and can therefore be used as baselayer for the filter. To achieve the spinfilter effect a ferromagnetic coating such as cobalt has to be used.

In some preliminary tests the palladium baselayer was coated with a cobalt film without breaking. Furthermore it was verified that there still is sufficient electron transmission through the Pd/Co system.



[1] M. Getzlaff, J. Bansmann, G. Schönhense; Spin polarization effects for electrons passing through thin iron and cobalt films, Sol. State Commun. 87, 467 (1993)
[2] G. Schönhense, H. C. Siegmann; Transmission of electrons through ferromagnetic material and applications to detection of electron spin polarization, Ann. Phys. 2, 465 (1993)
[3] Oelsner, A. et al: Rev. Sci. Inst., 2001,72(10):3968-3974





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