Strong Magnetic Circular Dichroism in 4F Photoemission
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STRONG MAGNETIC CIRCULAR DICHROISM IN 4F PHOTOEMISSION KAI STARKE, E. NAVAS, L. BAUMGARTEN, AND G. KAINDL Institut fir Experimentalphysik, Freie Universitiit Berlin, Amimallee 14,
W-1000 Berlin 33, Germany ABSTRACT We report on strong magnetic circular dichroism (MCD) in 4f photoemission (PE) 6 7 from magnetized Gd(0001)/W(110) films. The shape of the 4f - Fj final-state PE multiplet depends on the relative orientation between photon spin and sample magnetization and can be described within an atomic model. The spectra rule out antiferromagnetic alignment of the (0001) surface layer and the bulk of Gd. This MCD in 4f-PE from rare-earth materials opens new perspectives in the analysis of surface and thinfilm magnetism and as a sensor for circular polarization of soft x-rays. The availability of intense circularly polarized x-ray beams has recently led to a number of studies of magnetic circular dichroism (MCD) in photoabsorption and photoemission17 of ferromagnetic materials. In case of MCD, the photoabsorption and photoemission (PE) processes depend on the relative orientation between photon spin and sample magnetization. MCD in PE was first observed in 2p core-level spectra from ferromagnetic Fe(1 10)1 and was explained in terms of spin-selective dipolar transitions in 1 the presence of spin-orbit coupling ,2. Several theoretical treatments of the observed 2 7 MCD effects in PE have been given ,6, . In the present contribution we report on the observation of MCD in 4f PE from magnetized Gd(0001) filns grown epitaxially on W(1 10). The shape of the 4f67-Fj finalstate PE multiplet exhibits a strong dependence on the relative orientation between photon spin and sample magnetization. Even with the circular polarization of the synchrotron radiation beam amounting to only 55%, a 30-% MCD effect has been observed. Due to the localized nature of the 4f states in Gd, this MCD in PE can be explained within an atomic model making use of the dipole-selection rules. From MCD spectra recorded with high surface sensitivity at hv=48 eV, antiferromagnetic alignment of the (0001) surface layer and the bulk of Gd can be ruled out8 . This strong MCD in 4f PE carries a substantial potential as an analytical tool in surface and thin-filn magnetism and for an absolute determination of the degree of circular polarization of soft x-rays. The experiments were performed with circularly polarized soft x-rays from two different monochromators at the Berliner Elektronenspeicherring ftir Synchrotronstrahlung (BESSY): the plane-grating SX700/1II at a bending magnet 9 and the U2FSGM at the crossed undulator 1 0. Epitaxial Gd(0001) films with a thickness of 80±10 A were prepared by vapor deposition of Gd onto a clean and well-ordered W(110) substrate at room temperature (base pressure
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