Using soft x-ray resonant magnetic scattering with a coherent beam, we find evidence for memory effects in the magnetic configuration of a periodic array of submicron ferromagnetic lines under external magnetic field. The memory effect is explained by the dipolar coupling between the lines which is lost when the sample is saturated by the external magnetic field.

We have studied bilayers and trilayers of FePd thin-film alloys. where each of the constituting layers has a different magnetic-anisotropy, as controlled by the growth conditions. The competition between the magnetocrystalline anisotropy and the shape anisotropy in these films lends to the formation of stripe domains with a period of similar to 100 nm, which has been imaged by magnetic force microscopy (MFM). The average magnetic anisotropy has been obtained from the in-plane and perpendicular magnetic field dependence, measured using vibrating sample magnetometry (VSM). We measured the soft x-ray resonant magnetic scattering (SXRMS) at the Fe L-3 edge using sigma linearly polarized light, which is sensitive to the magnetization profile in the layers. The magnetic configuration of the layer systems was modeled using micromagnetic software (GL-FFT, @CNRS). The results of the micromagnetic modeling were used for a numerical simulation of the reflectivity scan and the magnetic rod scans of the SXRMS. This allowed us to determine parameters, such as the lateral roughness, the magnetic period, the magnetic correlation length, and the magnetic layer thickness. The good agreement obtained with the experimental results demonstrates that SXRMS Provides in-depth information that cannot be obtained from either MFM or VSM.

Soft X-ray resonant magnetic scattering (SXRMS) was performed on a FePd alloy thin film at the L3-edge of Fe. This film exhibits perpendicular magnetic anisotropy giving rise to periodic alternation of up and down magnetisation domains with closure domains. Rocking curves performed in transverse geometry allowed us to measure the magnetic periodicity and correlation length of domains. Micromagnetic simulations of the FePd layers and SXRMS calculations were made to analyse the asymmetry ratio of magnetic satellite intensities, hence allowing us to quantify the magnetic anisotropy.

We describe a measurement technique for x-ray absorption spectroscopy, in which the sample is used as the detector. Co L2,3 absorption spectra were taken from cobalt films grown on n-GaAs by measuring the photovoltage generated by the x rays transmitted across the rectifying metal–semiconductor contact. After correcting the effects of signal saturation good agreement was obtained with spectra acquired using the conventional total electron yield method. X-ray magnetic circular dichroism measurements using the method gave values for the spin moment of cobalt between 1.48 and 1.89 μB/atom, compared to the value in the literature of 1.55 μB/atom for the bulk. An anomalously high average value of 0.39 μB/atom was found for the orbital moment and attributed to the presence of oxide in the films.

FePd thin-film samples with different perpendicular magnetic anisotropies have been studied with magnetic force microscopy (MFM), micromagnetic calculations and soft x-ray resonant magnetic scattering (SXRMS). The competition between perpendicular magnetic anisotropy (PMA) and shape anisotropy leads to the formation of highly ordered stripe domain patterns with a magnetization component perpendicular to the film plane. The magnetic stripes with a period of ∼100 nm, which are seen in the MFM images and can be modeled by micromagnetic calculations, give rise to magnetic peaks in the diffraction pattern. Closure domains occur in samples with a low to medium PMA, while a high PMA inhibits their formation. The in-plane magnetization component of the closure domains is not observable with MFM. In the presence of closure domains the interference between the scattering amplitudes in SXRMS from perpendicular and in-plane magnetized domains gives rise to a circular dichroism in the transverse geometry, where the scattering plane is along the stripes. We also recorded the magnetic speckle pattern from an 8 μm FePd wire using coherent x-rays and CCD detection. A high degree of coherence was obtained as evidenced from the observed intensity fluctuations. The speckle pattern can in principle provide information about the local disorder of the magnetic stripe domains.

We present combined experimental and theoretical results for the magnetic circular dichroism (MCD) in resonant 4f photoemission (RPE) from Tb metal in the perpendicular geometry at different photon energies across the whole of the M-4,M-5 resonance. The atomic calculations, which take into account the full multiplet structure and the coherent second-order optical process, give excellent agreement with new experimental results for the resonant photoemission decay. The angular dependence of the MCD-RPE and its strong spin polarization in the M-5 region are also reported. For a single-configuration state the variations in the spectral shape are found to be stronger as a function of angle than as a function of photon energy. Due to the presence of the multiplet structure in the intermediate state 3d(9)4f(9) the coherent second-order optical process is essential for a correct description of the RPE. While the analysis of the spectra in parallel geometry yields accurate values of the spin-orbit, Coulomb, and exchange interactions, only the angle dependent RPE provides the phase factors of the emitted photoelectron.

The composition and magnetic properties of two types of ultrathin Fe3-deltaO4(111) films grown epitaxially on Pt(111) have been characterized using conversion electron Mossbauer spectroscopy (CEMS) and x-ray magnetic circular dichroism (XMCD). CEMS data from both films indicate that the magnetic moments lie in-plane and that a paramagnetic contribution is present that is not seen in spectra of bulk magnetite samples. The XMCD results are in good agreement with theoretical calculations, enabling the stoichiometry of the films to be determined as Fe3O4 and Fe2.91O4. The concentrations of both the tetrahedral Fe3+ and octahedral Fe2+ ions are reduced in the nonstoichiometric film, the decrease in the tetrahedral site probably being due to disorder. CEMS consistently yields a high tetrahedral:octahedral ratio of about 0.7:1, probably because of a contribution from a nonstoichiometric FeO interface layer.

X-ray magnetic circular dichroism (XMCD) is an element-, site- and symmetry-selective spectroscopic technique that has the potential to provide quantitative information on site occupancies in ferri- and ferro-magnetic minerals. XMCD spectra derived from the Fe L(2,3) absorption edge of a series of synthetic spinel ferrites and natural magnetite were collected using synchrotron radiation and a 0.6 Tesla 'flipper' magnet. These spectra were used to assess their potential value to mineralogical investigations. By comparison with theoretical spectra, the site occupancies of the cations have been calculated and compared to previous studies using other techniques. The spectra of the Co, Ni, Zn and Mg ferrite spinels show considerable variation, reflecting differences in site occupancies. Although the cation ratios derived from the XMCD spectra are broadly similar to previous work, there are significant differences especially in the amount of octahedral Fe(2+) present. Incomplete inversion is recognised in all the spinels analysed and the affinity of Co, Ni and Mg for the octahedral site and Zn for the tetrahedral site is confirmed; the preference of Co over Ni for tetrahedral sites is also revealed. XMCD spectra proved relatively straightforward to analyse but further refinement of the quantitative calculations is needed and detailed comparison with the information derived from other methods, especially Mossbauer spectroscopy.

X-ray magnetic linear dichroism (XMLD) is shown to be an element-specific probe of the magnetocrystalline anisotropy (MAE). The anisotropy in the spin-orbit interaction, determined using XMLD, is related to the MAE using a sum rule for a series of stepped Co surfaces exhibiting increasing uniaxial magnetic anisotropy. A linear relationship between the MAE, determined using XMLD, and the step density driven increase in the magnetic anisotropy proves the link between XMLD and the MAE. The element-specific nature of the technique is demonstrated by determining the individual MAE for Co/Fe bilayers.

The in-depth distribution of the induced 5d magnetic moments across the Ce layers in Fe/Ce/La/Ce, Fe/La/Ce/La and Fe/CeH2-delta multilayers has been investigated by x-ray resonant magnetic scattering (XRMS) at the Ce L-2 edge. The determination of the composition profile across the period of the multilayer is required for a quantitative analysis of XRMS and has been derived from x-ray resonant reflectivity measurements. In Fe/Ce/La/Ce and Fe/La/Ce/La multilayers, Ce adopts an alpha-like electronic configuration and the local magnetization, across the Ce layer, is found to be highly nonuniform. The Ce 5d magnetic profile shows an oscillating behavior with an amplitude decreasing from the Fe interface in Fe/Ce/La/Ce. Conversely, in Fe/La/Ce/La, where the Ce atoms are not in direct contact with Fe atoms, it presents an oscillatory profile with, however, a nearly constant amplitude. In Fe/CeH2-delta multilayers, where hydrogen leads to a strain relaxation and to a 4f relocalization (Ce gamma-like configuration), a nonoscillating decreasing profile has been observed. These experiments allow one to evidence an antiferromagnetic component in a alpha Ce ultrathin layer and a sharply decreasing induced magnetization due to 5d-3d hybridization at the interface.

Using scanned-energy mode photoelectron diffraction from the O 1s level, the local structure around the adsorbed OH species resulting from the interaction of H2O with a Si(100)(2x1) has been determined, by a combination of direct data inversion using a "projection" method and multiple-scattering simulations. The O atom is bonded to a surface Si atom with a Si-O bond length of 1.67+/-0.03 Angstrom, the Si-O bond being tilted away from the surface normal by 19+/-4degrees. This bonding Si atom is at one end of a surface dimer, which lies parallel to the surface to within +/-9degrees, but there appears to be a lateral offset of the dimer along the dimer direction away from the fully symmetric position by approximately 0.3 Angstrom, possibly reflecting a residual asymmetry associated with the adsorbate bonding. The main structural parameters are in excellent agreement with the results of a previously published density-functional theory slab calculation.

Periodic arrays of silicon nanolines, covered by a Co/Pt multilayer, with perpendicular magnetization, have been studied by soft x-ray resonant magnetic scattering at the Co ${L}_{3}$ edge. At the resonance, magnetic signals appear both on top of the structural diffraction peaks, characteristic of the grating, and between these peaks. These superstructure satellites reveal an antiferromagnetic order, generated by the interline dipolar coupling. Their intensities are strongly sensitive to the magnetic history, and can be enhanced through specific demagnetization processes. By applying an in situ magnetic field, the evolution of the magnetic signal has been monitored through the entire hysteresis loop. The magnetic contribution of the structural superlattice peaks can be quantified by their asymmetry ratio, whose angular variation stems from the scattering factor. The change of the purely magnetic satellites with the magnetic field is completely reproducible and characterizes the modifications of the magnetic configuration during the reversal process. A model of Ising macrospins, from which the distribution of the magnetic reversal fields can be deduced, is shown to be in agreement with the measured results.

The anisotropy of the spin-orbit interaction, , in vicinal Co films has been measured using x-ray magnetic linear dichroism (XMLD). A linear increase in with Co step density is found using a new sum rule and represents the first experimental confirmation that XMLD probes the magnetocrystalline anisotropy energy (MAE). X-ray magnetic circular dichroism is used to confirm that the XMLD arises from changes in the local step-edge electronic structure. The XMLD sum rule gives a larger MAE compared to macroscopic values and is discussed with respect to other local probes of the MAE.

The spin and orbital magnetic moments of 33 and 8 ML epitaxial BCC Fe "lms grown on GaAs(1 0 0)-4 6 have been measured using X-ray magnetic circular dichroism. Both samples have approximately the same spin moments of about 2.0 close to that of the bulk value, which con"rms that there are no magnetic dead layers at the interface. A giant orbital moment enhancement of about 300% was observed in the 8 ML "lm, which may be partially due to an increased degree of localization of electronic states at the Fe/GaAs interface. 2001 Elsevier Science B.V. All rights reserved.

The spin and orbital magnetic moments and the perpendicular magnetic anisotropy of 8 and 33 monolayer epitaxial bcc Fe films grown on GaAs(100)-4×6 have been measured using x-ray magnetic circular dichronism and polar magneto-optical Kerr effect. Both the films have approximately the same spin moments of about 2.0μB close to that of the bulk value. The ultrathin film shows a giant orbital moment enhancement of about 300% with respect to the bulk value and a perpendicular interface anisotropy field HsFe–GaAs of the order of −5×104 Oe. This may be partially due to an increased degree of localization of electronic states at the Fe/GaAs interface associated with the atomic scale interface structure.

The spin and orbital magnetic moments of 33 and 8ML epitaxial BCC Fe films grown on GaAs(100)-4×6 have been measured using X-ray magnetic circular dichroism. Both samples have approximately the same spin moments of about 2.0μB close to that of the bulk value, which confirms that there are no magnetic dead layers at the interface. A giant orbital moment enhancement of about 300% was observed in the 8ML film, which may be partially due to an increased degree of localization of electronic states at the Fe/GaAs interface.

The spin and orbital magnetic moments of 33 and 8 ML epitaxial BCC Fe films grown on GaAs(1 0 0)-4 x 6 have been measured using X-ray magnetic circular dichroism. Both samples have approximately the same spin moments of about 2.0 mu (B) close to that of the bulk value, which confirms that there are no magnetic dead layers at the interface. A giant orbital moment enhancement of about 300% was observed in the 8 ML film, which may be partially due to an increased degree of localization of electronic states at the Fe/GaAs interface. (C) 2001 Elsevier Science B.V. All rights reserved.

X-ray magnetic circular dichroism (XMCD) studies of magnetic 3d transition metal samples require the recording of high quality absorption scans in high magnetic fields using circularly polarised soft X-rays of energies in the range 0.5–1 keV. A Gas Microstrip Detector is described which permits the option of using the X-ray fluorescence signal instead of the usual electron yield signal.

The element and electronic shell specificities of X-ray resonant magnetic scattering have been used to investigate the magnetization of Ce 5d and Fe 3d states in [CeH2(19.6 Å)/Fe(25.4 Å)]*38 a multilayer. We show that the measurement of the magnetic contribution to the intensities reflected at low angles at the Ce L2 and Fe L2,3 edges allows us to investigate the profile of the Ce 5d and Fe 3d magnetic polarization. The Fe 3d polarization is found to be uniform across the Fe layer and the Ce 5d polarization appears to be restricted close to the interface with Fe.