Spin Polarized Electron Spectroscopies of 3d and At Systems
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Spin Polarized Electron Spectroscopies of 3d and 4f Systems H. HOPSTER Department of Physics and Institute for Surface and Science, University of California, Irvine, CA 92717
Interface
Abstract Recent results from spin polarized electron spectroscopic studies of surfaces and ultrathin films are presented. The magnetic coupling of 3d transition metals (Cr,Mn) to the Fe(100) surface is studied by spin polarized electron energy loss spectroscopy. The first atomic layer of Cr and Mn aligns antiparallel to the Fe. For larger thicknesses we find evidence for layer-by-layer antiferromagnetic order. In the range of 1-6 atomic layers the behavior is more complex with the surface of the Cr films showing preferential ferromagnetic alignment while the Mn surface aligns antiparallel to the Fe substrate. Secondary electrons from Gd(O001) surfaces are shown to be highly spin polarized. However, no enhancement mechanism at low kinetic energy as in the 3d transition metals is observed indicating the absence of strongly spin dependent inelastic scattering in Gd. Temperature dependent spin polarized 4f photoemission results show almost complete polarization demonstrating ferromagnetic surface coupling. However, a perpendicular surface magnetization component is found indicating surface spin canting. A large enhancement of the surface Curie temperature is also present. I.
Introduction
Spin polarized electron spectroscopies have played a major role in the studies of magnetism of surfaces and ultrathin films[l]. One of the main advantages of electron spectroscopies is their intrinsic surface sensitivity due to the short mean free path of low-energy electrons in solids. This paper reviews recent results using three different spin polarized electron techniques. Spin polarized electron energy loss spectroscopy (SPEELS) was used to study the magnetic structure of ultrathin epitaxial 3d transition metal layers (Cr and Mn) on Fe(lO0) substrates. The intriguing magnetic properties of the Gd(0001) surface were studied by spin polarized secondary electron emission spectroscopy (SPSEES) and spin polarized photoemission spectroscopy (SPPES) on thick epitaxial Gd films on W(11O). II. The magnetic order of 3d transition Fe(100) studied by SPEELS
metal overlayers on
In spin polarized electron energy loss spectroscopy (SPEELS) a polarized electron beam is scattered off a surface and the intensity and polarization of the scattered electrons are measured as a function of energy loss. In the case of a ferromagnetic surface the scattering intensity depends on the alignment between the surface majority-spin direction and the incident beam polarization. One defines a scattering asymmetry A as the normalized difference between scattering intensities for beam
Mat. Res. Soc. Symp. Proc. Vol. 313. c 1993 Materials Research Society
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polarization parallel and antiparallel to the sample majority spin direction: A=(I/P0 ) (It-I4)/(It+I•) SPEELS experiments on elemental 3d ferromagnetic surfaces (Ni,Fe,Co) have shown large negative asymmetries in the ra
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