We measured Faraday rotation of linearly polarized soft x rays across the Fe L23 edges transmitted through an Fe/Cr multilayer in an applied magnetic field; the maximum rotation of 6X 10 deg/mm is larger than that observed for Fe in other spectral regions. Rotation data agree well with Kramers-Kronig analysis of absorption data measured using left and right circular polarization. A tunable elliptically polarizing undulator source provided linearly and circularly polarized x-ray beams. The tunable multilayer polarizer used extends optical rotation techniques into the 50 -900-eV region, with element specificity from core resonances.Magneto-optical effects were first observed by Faraday (in 1845) and Kerr (in 1876) and helped confirm the electromagnetic nature of light. They have remained of fundamental scientific and practical interest, and with the development of computers are much studied in connection with data storage and retrieval technologies. Magneto-optical effects refer to various changes in the polarization state of light upon interaction with materials possessing a net magnetic moment, including rotation of the plane of linearly polarized light (Faraday, Kerr rotation), and the complementary differential absorption of left and right circularly polarized light (circular dichroism). In the near visible spectral range these effects result from excitation of electrons in the conduction band. Near x-ray-absorption edges, or resonances, magnetooptical effects can be enhanced by transitions from welldefined atomic core levels to transition symmetry selected valence-band states, and hence provide a means of obtaining element-and state-specific magnetic information in multicomponent samples.In the x-ray range, nonresonant magneto-optical effects have been observed in transition metals and rare earths. While resonant x-ray magneto-optical effects in transition metals were first observed at the Fe K edge, ' they are much larger at the L23 edges because of the large 2p to 3d dipole transition-matrix elements. At the L23 edges, large magnetic circular dichroism (MCD) using near-circular polarization has been observed, as have magneto-optical Kerr effects 6 -8 using linear polarization. These effects have generated great experimental and theoretical interest because they offer a means of separating electron-spin and orbital and magnetic dipole contributions to magnetism, ' as well as probing element-specific properties in materials of practical interest.Until now, soft-x-ray magneto-optical studies have had to rely on effects revealed by the intensities of signals coming from samples, since polarization or phase-sensitive optics had not been available. We used a newly developed tunable linear polarizer to make the measurement of Faraday rotation in the 500 -900-eV range that includes the Lz3 edges of the 3d transition metals V, Cr, Mn, Fe, Co, and Ni. For an Fecontaining film in an applied magnetic field, Faraday rotation larger than in the visible is observed. This large rotation provides new experimental pathways to...

The characteri=tion of nanometer-de phase sepamtion in sputterd amorphous meti-Ge and Fe-Si films has led to the observation of a new microstructure that extends through the meti-insulator transition. The phase separated regions, which are depndent on deposition conditions, are well-correlated and of the order of 1 nm in the growth plane but poorly-correlated and 1.5-2.0 nm in the growth direction. The resdts suggest that fluctuations during film growth play a pivoti role in preventing anticipate columnar structures, probably l~ing to unusti percolation properties.-. Vapor-depositi amorphous meti-germanium and meti-silicon films have been the subject : of extensive study over the past decade. Much of the effort is aired at understanding the meMinsulator (M-I) transition, since many view the films as relatively unique examples of homogeneous materials which undergo a continuous structural transition as the meti concentration is increased:: In contrast, Kortright and Bienenstoekl inferred from their structural study of amorphous MoCGel-c that films with &c4.23 consist of aGe and a Me-modified material that coexist on a size scak of less than 4 nm. These authors were unable to confirm their supposition definitively with small-angle x-ray scattering (SAXS), however, since the observed intensity patterns could arise from either defecm or such phase separation. In addition, they reference an unsuccessful attempt to detect phase separation with transmission electron microscopy. Subsequently, Yoshizumi et al.2 and Mael et d.3 notd that their observation of a metallic low tempemture specific heat in insulating (cd. 1) amorphous MoCGel-Cfilms is consistent with the coexistence proposal. Recently, Rice et d.4 have used anomalous small-angle x-my mttering (ASAXS) to show, definitively that a variety of Ge-nch amorphous meti-germanium films have SAXS patterns that arise _from composition fluctuations or phase separation, rather than from defec~. E1-tron microscopy has been used in the past to observe composition modulations in, for example, the Work supported in part by~epartment of Energy Contract DE-AC03-76S~515.

A tunable polarimeter using multilayer interference coatings as both reflection polarizer and transmission phase retarder is described. The portable device bolts onto existing chambers and its rotation axis is precisely aligned to the beam. The upstream transmission phase retarder is tunable by varying its incidence angle, and the downstream polarizer is tunable by translating a laterally graded multilayer. These optical components allow an unambiguous determination of the polarization state of any collimated beam entering the device over at least the 50–800 eV range.