X-RAY Magneto-Optics in Lanthanide Materials
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X-RAY MAGNETO-OPTICS IN LANTHANIDE MATERIALS
K. Starke1 , F. Heigl1, A. Vollmer1 , and G. Kaindl1 Freie Universitat Berlin, Arnimallee 14, D-14195 Berlin, Germany We demonstrate the feasibility of element-speci c magnetization reversal studies applying x-ray magnetooptical Kerr e ect (XMOKE) to lanthanide systems. In particular, we will rst describe XMOKE spectra at 4d-4f excitation thresholds of Gd and Tb in some detail, before showing element speci city at the example of a Gd/Y/Tbtrilayer metal lm. On the basis of experimental Tb M4;5 absorption spectra, we may anticipate substantial MO signals in specular re ectivity at M4;5 edges of all lanthanide elements, provided they carry a non-vanishing net 4f-magnetization. Abstract.
1 Introduction Magneto-optical e ects in the visible-light range are widely used for analyzing magnetic systems [1]. They involve optical transitions between itinerant valence-electron states so that a spectral separation of di erent elements in compound materials is extremely diÆcult. This lack of element speci city can be overcome by employing optical transitions of core electrons. Large magneto-optical (MO) signals in the x-ray range were theoretically predicted to appear in x-ray resonant scattering (XRS), i.e. when x-rays are tuned to electric dipole (E1) transitions of core electrons into a partially lled shell which contains ordered magnetic moments [2]. Gibbs and coworkers have demonstrated the usefulness of XRS in many detailed analyses of helimagnetic lanthanide systems [3]. In specular re ectivity, sizable MO signals have been found at the 2p-3d excitation thresholds of iron [4,5] and other technologically important 3d-transition metals [6] . Generally speaking, the existance of large MO e ects in the x-ray regime is a consequence of the substantial spin-orbit interaction of inner-shell electrons. As for lanthanides, x-ray resonant magnetic scattering studies have so far been restricted to antiferromagnets [3] and in particular element-speci c investigations of the magnetizationreversal process in ferromagnetic lanthanide materials have not been reported.
2 Experimental Lanthanide metal lms and multilayers have been prepared in situ by vapor deposition in ultra-high vacuum on a W(110) single-crystal substrate. For remanent magnetization of the lms, an external eld of up to 2 kOe was applied, using a rotatable electromagnet with a soft-iron yoke [7]), along the substrate bcc[110] axis, which lies parallel to the easy axis of Gd and Tb metal lms. For details of lanthanide metal lm preparation the reader is referred to Ref. [8]. X-ray re ectivity experiments were performed at the undulator beamlines UE56/1 and UE56/2 for elliptically polarized radiation at the Berliner Elektronenspeicherring fur Synchrotronstrahlung (BESSY) [9]. The specularly re ected x-ray intensity was detected using a Si photodiode inside the vacuum chamber, mounted on a home-built goniometer. Visible-light EE7.7.1
MOKE data were measured in situ for comparison, using a standard laser diode ( = 635 nm) an
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