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Fe3O4 thin films on Si (100) substrate were prepared by chemical solution deposition (CSD) technique. In the present work, we have investigated the control of magnetization of Fe3O4 thin films by N2 ion implantation. The dosage of N2 ion implantation in Fe3O4 thin films varies from 0 to 3 × 1016 ions/cm2. The magnetization decreased as a function of dosage concentration that changed the electronic and magnetic properties of the thin films. Advanced characterization techniques, such as X-ray absorption spectroscopy (XAS) X-ray magnetic circular Dichroism (XMCD), were used for the first time to estimate the electronic and magnetic properties of the thin films in surface-sensitive total electron-yield mode. The temperature-dependent XMCD measurement suggests that with an increase in the dosage of N2 from 0 to 3 × 1016 ions/cm2, Fe3O4 transitioned from a high-magnetization phase to a low magnetization phase. The observation was further supported by vibrating sample magnetometer (VSM) measurements, which pointed toward the same magnetic-phase transition in the films.

In this work, we report the electronic and magnetic properties of epitaxial BiFeO3 (BFO) thin film deposited on SrTiO3 (001) substrate via the chemical solution deposition technique. These properties of pure BFO thin films were characterized by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism techniques (XMCD). The large magnetization at Fe-edge could be due to annealing in nitrogen. Annealing in nitrogen atmosphere increases the grain size and porosity which lead to create more oxygen vacancy. The presence of oxygen vacancies which compensate the bismuth vacancies created due to bismuth volatilization. The origin of large orbital momentum in BFO thin film is also discussed. The O K-edge spectra display large spectral variation depending on the polarization vector E. The structural distortion at oxygen octahedral induces large anisotropy due to Fe 3d–O 2p hybridization. The hybridized Fe 3d orbitals contribute a much larger orbital momentum in BFO thin film.

It has long been a challenging task to observe surface chemical reactions proceeding in the depth direction without stopping the reaction (i.e., real-time observation), with subnanometer depth resolution. X-ray absorption spectroscopy (XAS) in the soft X-ray region is one of the most crucial methods to analyze the chemical states of light elements; however, simultaneous time- and depth-resolved XAS measurements during the reaction have not been realized before. Herein, we show the real-time observation of the time-evolving oxidation process of a Co thin film with a fluorescence-yield wavelength-dispersive XAS method, which also has subnanometer depth resolution. The series of Co L-edge XAS spectra show that the oxide component increases from the surface to deeper regions as the reaction proceeds. The progress of oxidation in the depth direction was interpreted by the reaction with O2 gas at the surface and the interlayer reaction by oxygen migration.

A fluorescence-yield wavelength-dispersive x-ray absorption spectroscopy technique in the soft x-ray region, by which the x-ray absorption spectra are recorded without scanning the monochromator, has been developed. The wavelength-dispersed soft x rays, in which the wavelength (photon energy) continuously changes as a function of the position, illuminate the sample, and the emitted fluorescence soft x rays at each position are separately focused by an imaging optics onto each position at a soft x-ray detector. Ni L-edge x-ray absorption spectra for Ni and NiO thin films taken in the wavelength-dispersive mode are shown in order to demonstrate the validity of the technique. The development of the technique paves the way for a real-time observation of time-dependent processes, such as surface chemical reactions, with much higher gas pressure compared to the electron-yield mode, as well as under magnetic and electric fields.

We study an electric field-induced redox reaction at the interface of GdOx/Co thin film, by means of soft X-ray absorption spectroscopy (XAS). The fluorescence-yield depth-resolved XAS analysis reveals that the interfacial Co layer at GdOx/Co is composed of ∼50% Co oxide when the negative field is applied, while metallic Co is dominant in the case of the positive field. We suppose that the interfacial layer is oxidized by oxygen migration from the GdOx layer with the negative field while the interfacial layer shows the metallic state with the positive field, which means that the redox reaction is induced by the electric field. In addition, it is found from the X-ray magnetic circular dichroism (XMCD) measurement that the orbital magnetic moment of Co is larger when the negative electric field is applied to the film, as compared to the positive field. Moreover, the depth-resolved XMCD analysis reveals that the interfacial Co layer shows no or little magnetization regardless of the electric field, while for the inner layer, an increase of the orbital magnetic moment is suggested with the negative field. The field-induced magnetic modification could be attributed to the change of the orbital moment in the inner Co layer due to interfacial modifications. We thus succeed in the direct observation of the redox reaction-induced change in the interface magnetic state.

We develop bond-length mapping technique without two-dimensional scanning by combining photoelectron emission microscopy with extended x-ray absorption fine structure (EXAFS) analysis. Several tens of thousands of EXAFS data are simultaneously acquired, which corresponds to a data acquisition time less than 1 second per spectrum. We apply this technique to an Fe/BaTiO3 thin film, and two-dimensional distribution of the Fe-Fe bond length at the Fe surface is observed. From the Fe K-edge EXAFS analysis, we find that the Fe-Fe bond length is 2.52 A over the whole area with a Gaussian distribution of 0.01 A, which implies that this technique realizes a bond-length mapping with precise bond-length determination.

Surface ferromagnetic state of FeRh thin films irradiated with 1 keV Ar ion-beam has been investigated by using soft X-ray Magnetic Circular Dichroism (XMCD). It was revealed that the Fe atoms of the samples were strongly spin-polarized after Ar ion-beam irradiation. Due to its small penetration depth, 1 keV Ar ion-beam irradiation can modify the magnetic state at subsurface of the samples. In accordance with the XMCD sum rule analysis, the main component of the irradiation induced ferromagnetism at the FeRh film surface was to be effective spin magnetic moment, and not to be orbital moment. We also confirmed that the surface ferromagnetic state could be produced by thermal annealing of the excessively ion irradiated paramagnetic subsurface of the FeRh thin films. This novel magnetic modification technique by using ion irradiation and subsequent annealing can be a potential tool to control the surface magnetic state of FeRh thin films.

We develop a fluorescence-yield depth-resolved soft x-ray absorption spectroscopy (XAS) technique, which is based on the principle that the probing depth is changed by the emission angle of the fluorescence soft x rays. Compared with the electron-yield depth-resolved XAS technique, which has been established in this decade, we can observe wider range in-depth XAS distribution up to several tens of nm. Applying this technique to a 30 ML (∼4.3 nm) FeCo thin film, we observe Fe L-edge XAS spectra at the probing depth of 0.3–6 nm and find that the film has 22 ML (∼3.1 nm) surface oxide layer while its inner layer shows metallic state. We thus successfully obtain nanometer-resolution depth-resolved XAS spectra and further expect that operando measurement under the electric and/or magnetic fields is possible.

We have studied the effect of cobalt substitution in $L{1}_{0}\ensuremath{-}{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Pt}$ films by means of x-ray magnetic circular dichroism (XMCD) and first-principles calculations. The magnetic moments of Fe ($\ensuremath{\sim}2.5\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$) and Co ($\ensuremath{\sim}1.5\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$) deduced using XMCD were almost unchanged upon Co doping, and the net magnetization decreases with increasing Co content. Calculation also showed that the $3d$ electrons that have been added by Co substitution occupy only spin-down bands.

The strong perpendicular magnetic anisotropy of $L{\rm1_0}$-ordered FePt has been the subject of extensive studies for a long time. However, it is not known which element, Fe or Pt, mainly contributes to the magnetic anisotropy energy (MAE). We have investigated the anisotropy of the orbital magnetic moments of Fe 3$d$ and Pt 5$d$ electrons in $L{\rm1_0}$-ordered FePt thin films by Fe and Pt $L_{2,3}$-edge x-ray magnetic circular dichroism (XMCD) measurements for samples with various degrees of long-range chemical order $S$. Fe $L_{2,3}$-edge XMCD showed that the orbital magnetic moment was larger when the magnetic field was applied perpendicular to the film than parallel to it, and that the anisotropy of the orbital magnetic moment increased with $S$. Pt $L_{2,3}$-edge XMCD also showed that the orbital magnetic moment was smaller when the magnetic field was applied perpendicular to the film than parallel to it, opposite to the Fe $L_{2,3}$-edge XMCD results although the anisotropy of the orbital magnetic moment increases with $S$ like the Fe edge. These results are qualitatively consistent with the first-principles calculation by Solovyev ${\it et\ al.}$ [Phys. Rev. B $\bf{52}$, 13419 (1995).], which also predicts the dominant contributions of Pt 5$d$ to the magnetic anisotropy energy rather than Fe 3$d$ due to the strong spin-orbit coupling and the small spin splitting of the Pt 5$d$ bands in $L{\rm1_0}$-ordered FePt., Comment: 9 pages, 4 figures, 2 tables

Graphene-based vertical spin valves (SVs) are expected to offer a large magnetoresistance effect without impairing the electrical conductivity, which can pave the way for the next generation of high-speed and low-power-consumption storage and memory technologies. However, the graphene-based vertical SV has failed to prove its competence due to the lack of a graphene/ferromagnet heterostructure, which can provide highly efficient spin transport. Herein, the synthesis and spin-dependent electronic properties of a novel heterostructure consisting of single-layer graphene (SLG) and a half-metallic Co2 Fe(Ge0.5 Ga0.5 ) (CFGG) Heusler alloy ferromagnet are reported. The growth of high-quality SLG with complete coverage by ultrahigh-vacuum chemical vapor deposition on a magnetron-sputtered single-crystalline CFGG thin film is demonstrated. The quasi-free-standing nature of SLG and robust magnetism of CFGG at the SLG/CFGG interface are revealed through depth-resolved X-ray magnetic circular dichroism spectroscopy. Density functional theory (DFT) calculation results indicate that the inherent electronic properties of SLG and CFGG such as the linear Dirac band and half-metallic band structure are preserved in the vicinity of the interface. These exciting findings suggest that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures, for realizing effective transport of highly spin-polarized electrons in graphene-based vertical SV and other advanced spintronic devices.

We measured X-ray absorption spectra of amorphous alumina with vacancy-type oxygen defects (AlOx) which exhibits the resistance random access memory (ReRAM) effect. We were able to detect changes in the electronic structure owing to the ReRAM effect. A major difference in the spectra near the O K-absorption edge was observed between a low resistance state (LRS) and a high resistance state (HRS). The subpeak profile within the band gap appeared in the LRS, while it was suppressed in the HRS. By contrast, the spectra near the Al K-absorption edge in the LRS and HRS appeared almost identical, indicating that no byproducts are generated. These findings imply that the distribution of charged electrons primarily changes near oxygen sites from the HRS to the LRS. The features of the subpeak profile are analogous to those of the mid-gap profile, as speculated by the first-principles calculation [Momida et al., Appl. Phys. Lett. 98, 042102 (2011)]. The LRS was mainly detected near the surface of the thin film.We measured X-ray absorption spectra of amorphous alumina with vacancy-type oxygen defects (AlOx) which exhibits the resistance random access memory (ReRAM) effect. We were able to detect changes in the electronic structure owing to the ReRAM effect. A major difference in the spectra near the O K-absorption edge was observed between a low resistance state (LRS) and a high resistance state (HRS). The subpeak profile within the band gap appeared in the LRS, while it was suppressed in the HRS. By contrast, the spectra near the Al K-absorption edge in the LRS and HRS appeared almost identical, indicating that no byproducts are generated. These findings imply that the distribution of charged electrons primarily changes near oxygen sites from the HRS to the LRS. The features of the subpeak profile are analogous to those of the mid-gap profile, as speculated by the first-principles calculation [Momida et al., Appl. Phys. Lett. 98, 042102 (2011)]. The LRS was mainly detected near the surface of the thin film.

We show from the depth-resolved X-ray absorption analysis that the degree of surface oxidation of Fe70Co30 thin films is reduced by Ar+ ion milling even if the film is exposed to air after ion milling. The milled film has thinner surface oxide layer and smaller ratio of Fe oxide component in the surface layer than those of the as-deposited film. It is also indicated that selective oxidation of Fe proceeds accompanied by the movement of Fe atoms toward the surface. The suppression of oxidation is explained by the obstruction of Fe movement toward the surface by the milling-induced disorder.

Spectral separation methods for X-ray absorption fine structure spectroscopy at the near carbon K-edge are examined for an n -C 36 H 74 monolayer adsorbed on a monolayer graphene grown on a Pt(1 1 1) surface. The spectra of n -C 36 H 74 and the monolayer graphene are separated by fitting decay curves obtained for all photon energies by detecting photoelectrons as a function of the ejection angle. The results are discussed in comparison with separation results obtained by subtracting the independently measured graphene spectra as a background.

We report x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements of both paramagnetic and ferromagnetic Ti 1 − x Fe x O 2 − δ thin films. Fe L 3 , 2 edge XAS spectra showed that the Fe ions in our samples were in mixed valence states and that the Fe2+/Fe3+ ratio decreased with increasing oxygen partial pressure. Finite XMCD signals were observed only for the Fe2+ state in the ferromagnetic sample. These findings indicate that the observed ferromagnetism in Ti 1 − x Fe x O 2 − δ originates from ferromagnetic interactions between Fe2+ local spins.

Near edge X-ray absorption fine structure spectra at the carbon K-edge (C K-NEXAFS) of n-C12H26 films grown on graphite (0 0 0 1) were measured under ultrahigh vacuum conditions. In the normal incidence spectra, the 1 s → σ CH * / R resonance of n-alkane was identified at a lower energy than the absorption edge of graphite. The σ CH * / R resonance directed along the CH bond was observed at 286.9 eV for the first layer of the n-C12H26 film on graphite. This indicates that the CCC plane of the molecule is parallel to the surface (flat-on orientation). As the film thickness increases, another peak assigned to σ CH * / R ⊥ grows at 288.0 eV, suggesting an increase in the number of molecules with the CCC plane perpendicular to the surface in a multilayer film.

The present status of a new vacuum ultraviolet/soft X-ray (VUV/SX) beamline (BL-13A) used for the study of organic thin films adsorbed on surfaces is described. The base pressure of BL-13A is maintained below 1×10−8 Pa in order to prevent contamination of the optics by residual gases. The measured performance is as follows: photon-energy region, 30-1,200 eV; photon flux, 109-1011 photons s−1; photon-energy resolution (E/ΔE), 10,000 at a photon energy of 401 eV; spot size (horizontal\ imes;vertical) at the second focus, ≈630×120 μm; photon-energy drift, ≤±0.02 eV at a photon energy of 244.39 eV; reduction of photon flux in the C K-edge region, ∼50%.

The electronic and atomic structures of a 4-cyano-4′-iodobiphenyl (CIB) thin film on a GeS(0 0 1) substrate were studied by atomic force microscopy (AFM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. CIB molecules exhibit high crystallinity owing to halogen bonding and are grown as a microcrystal at a nominal thickness of 80 A. NEXAFS measurements suggest that, at a thickness of 0.4 A, the molecular plane tilts away from the surface plane at an angle of 12°, and the molecular axis tilts away from the GeS [0 1 0] direction by 35°. At a thickness of 80 A, the molecular plane tilts away from the surface plane by 51°, and the molecular axis tilts away from the GeS [0 1 0] direction by 43° on average. NEXAFS spectra show a drastic reduction in the π C C * and π C N * resonances in the thicker film. This is interpreted as electron transfer, which is induced by halogen bonding, from the halogen atom.

The origin of the focused single-pulse laser irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt film is investigated by the x-ray absorption near-edge structure and extended x-ray absorption fine structure techniques combined with the photoelectron emission microscope. A significant increase of the Co–Co bond length in both in-plane and out-of-plane directions is observed on the periphery of the laser spot, at which perpendicular magnetization appears. With increasing laser power density towards the center of the laser spot, anisotropic structural changes are observed accompanied by the reappearance of in-plane magnetization. The enhancement of perpendicular magnetization is attributed to the lattice expansion-induced magnetoelastic effect, while the in-plane compressive strain in the Co film is suggested to be the origin of the reappearance of in-plane magnetization at higher laser power densities.

The insertion effect of an interface NiO layer on magnetism in Fe/BaTiO3 is investigated by X-ray absorption spectroscopy (XAS). From X-ray magnetic circular dichroism (XMCD) analysis, the enhancement of remanent magnetization in Fe is observed with increasing NiO thickness. We also find that the NiO layer is partially composed of metallic Ni, and its thickness is estimated to be ~0.4 nm from the NiO-thickness dependence of the Ni XAS intensity by assuming that Ni is localized at the interface between Fe and NiO. Moreover, extended X-ray absorption fine structure data shows that the Ni–O distance of the interface NiO layer is shorter than that of bulk NiO, which leads to the pseudomorphic growth of NiO on BaTiO3. We thus suppose that the improved Fe growth promoted by the interface NiO layer enhances the magnetic moment in Fe.

The magnetic properties of ferromagnetic Ni thin films grown on a Cu(001) single crystal are modified by the growth of a NiO overlayer, as well as by the voltage application through the NiO/Ni interface. A spin reorientation transition from in-plane to perpendicular magnetization is induced with increasing NiO thickness, and the coercive field significantly increases by further growth of the NiO overlayer. The remanent magnetization of the films is found to be modulated by the voltage application. Moreover, a small exchange-bias effect arising from the ferromagnetic–antiferromagnetic interaction at the interface is observed, and the amplitude of the effect is modified by the applied voltage.

Effect of energetic C60 cluster ion irradiation on magnetic properties in FeRh thin films was examined by SQUID and XMCD measurements. The XMCD signal for the C60 irradiated samples is larger than that for the C1 samples in the initial stage of the irradiation. In contrast, as for the irradiation with larger ion fluence, the XMCD spectrum for the sample irradiated with C1 ion is larger than that for the sample irradiated with C60 cluster ion. Although the magnetization for the C60 irradiation samples continuously decreases with increasing in the ion fluence, the saturation magnetization for the C1 irradiation samples increases with increasing in the ion fluence. Considering these different behaviors in the irradiation induced ferromagnetism, the cluster ion can effectively deposit the apparent elastic collision energy at the surface region in the film, which effectively causes the ferromagnetic state at the surface of the films.

Development and potential applications of a three-dimensional X-ray absorption fine structure (XAFS) technique are described showing some preliminary data. By combining an X-ray microbeam with a depth-resolved XAFS technique, one can observe atomic, electronic and magnetic structures of thin film samples with a three-dimensional spatial resolution. A 3-5 μm beam size was achieved by adopting a two-step focusing mirror system, and two-dimensional magnetic images for a wedge-shaped Fe/Ni/Cu(100) thin film were obtained. On the other hand, the surface and interface components of XAFS spectra were extracted by applying the depth-resolved XAFS technique to a Ni/Cu(100) thin film. These results indicate that the three-dimensional XAFS measurements are now possible. Future prospects of this novel technique are also described.

Molecular adsorptions affect on the magnetism of magnetic thin films. We have observed anomalous magnetic states in gas adsorbed Fe thin films. In this report, we present the CO or NO adsorption effects on the magnetism of 2-4 ML Fe thin films on Cu(001), which are typical magnetic thin films. The Fe(2 ML)/Cu(001) film does not change its magnetic structure upon CO adsorption, whereas the CO/Fe(3 and 4 ML)/Cu(001) films turned their easy axes of magnetization to in plane. Depth resolved XMCD measurements give us detailed information on the depth profile of the magnetic structures. The surface two layers of the CO/Fe(4 ML)/Cu(001) film lose the magnetization, and only the bottom two layers keep the magnetization. NO adsorbed Fe films have the in-plane easy axes of magnetization. Moreover, the magnetization of the topmost layer of the NO/Fe/Cu(001) films aligns in the opposite direction to the other layers. Thus, the antiferromagnetism in the surface layers has appeared in the NO/Fe/Cu(001) films.

The spin reorientation transition (SRT) of Ni / Cu ( 0 0 1 ) induced by Fe deposition was investigated using the X-ray magnetic circular dichroism (XMCD) method. In-plane magnetized Ni films ( ⩽ 9 ML ) undergo the SRT twice; first, a small amount ( 1 ML ) of Fe deposition causes a transition to perpendicular magnetization. Second, further Fe deposition (1–2 ML in total) causes a return to in-plane magnetization. Perpendicularly magnetized Ni films ( ⩾ 10 ML ) also exhibit a transition to in-plane by 1–2 ML Fe deposition. A precise magnetic anisotropy phase diagram was obtained using a combination of wedge-shaped Ni samples and stepwise Fe deposition. Magnetic anisotropy energies in the bulk, surface and interface layers of Ni films were separately determined using the depth-resolved XMCD technique, while values in the 1 ML and 2 ML portions of the Fe films were obtained from the conventional XMCD measurements. The origin of the SRTs is successfully explained with a simple phenomenological layer model using the obtained magnetic anisotropy energies.

Surface and interface magnetization of Fe/Ni/Cu(1 0 0) thin films was observed with the probing depth-dependent X-ray magnetic circular dichroism technique, in which the probing depth is controlled by changing the electron detection angle. An oscillatory behaviour of the surface magnetization dependent on the Fe thickness was directly revealed, while simple analyses indicated that the interface (bottom) Fe magnetization stays almost unchanged independent of the Fe thickness, and that the inner layers are basically nonmagnetic. These results suggest an oscillatory interlayer magnetic coupling between the surface and interface of the Fe film via the nonmagnetic inner layers. It was indicated that the observed oscillation can also be attributed to a rotatory interlayer coupling between the surface and interface. A temperature-dependent experiment indicated that the surface magnetization is reversed depending on the temperature, which might be attributed to the magnetic structural change in the inner layers.

X-ray magnetic circular dichroism (XMCD) is a powerful method to study the magnetic properties of magnetic thin films. However it provides depth-averaged information. Recently, we have developed a simple but effective depth-resolved technique in XMCD by using an imaging type microchannel plate detector. The performance of this method is demonstrated by applying to the depth-resolved analyses of Ni/Cu(100) and the effect of CO adsorption on Ni/Cu(100), Fe/Cu(100) and Fe/Ni/Cu(100) magnetic thin films. For Ni/Cu(100), magnetic orbital moments of the surface and internal layers are extracted to give deep insight for the spin reorientation transitions. For 7 ML Fe/Cu(100), the surface two layers are ferromagnetically coupled, while the inner layers are non-magnetic at 200 K and are in the spin density wave (SDW) state at 130 K. For Fe/Ni/Cu(100), magnetically live surface layers and some thickness-dependent magnetic coupling between the Fe surface and Ni film have been observed.

Magnetic anisotropy of alternately layered FeNi thin films grown on Ni(3--21 ML)/Cu(001) is investigated by means of the X-ray magnetic circular dichroism (XMCD). Perpendicular magnetic anisotropy is observed when the substrate Ni is thicker than 15 and 20 ML for 4 and 6 ML FeNi films, respectively, while in-plane magnetic anisotropy appears at the thinner substrate Ni region. By comparing with the magnetic phase diagram calculated from the magnetic anisotropy energies, which are obtained by the XMCD study [M. Sakamaki and K. Amemiya, Appl. Phys. Express 4, 073002 (2011)], we show that the phase boundary of the present samples shifts so as to prefer the in-plane magnetic anisotropy. This might be caused by the structural relaxation in the substrate Ni. [DOI: 10.1380/ejssnt.2012.97]

Structure and magnetic anisotropy of alternately layered FeNi thin films grown on Ni ($x=3$--21 ML)/Cu(001) are investigated by means of reflection high-energy electron diffraction (RHEED) and x-ray magnetic circular dichroism (XMCD). From the RHEED analysis, we find that $n$ ML FeNi films grow with a similar in-plane lattice constant, $a$, to that of Cu up to the total film thickness, $n+x$, of $\ensuremath{\sim}$13 ML, from which the decrease in $a$ occurs. For the Ni-sandwiched Fe layer, we find from the XMCD analysis that the perpendicular component of the orbital magnetic moment increases and the in-plane component decreases as the in-plane lattice constant gets smaller. This suggests that perpendicular magnetic anisotropy is enhanced when the compressive strain in the in-plane direction is applied to the Fe layer. On the other hand, in the case of the Fe-sandwiched Ni layer, the orbital magnetic moment in both directions shows a small dependence on $a$. The change in magnetic anisotropy of Ni as a function of the structural strain is within the error margins.

The magnetic anisotropy of the Co thin films on Ru(0001) and the effect of the Ru capping were studied by Co LIII,II‐edge x‐ray magnetic circular dichroism (XMCD). As‐deposited Co films show only surface parallel magnetization in the whole thickness range of the observation (1–15 monolayer), while a Ru capping on 1–6 ML Co/Ru(0001) causes a spin reorientation transition (SRT) from surface parallel to the perpendicular magnetization. The critical thickness of SRT by the Ru capping is ∼6 ML. The Ru capping causes the reduction of the parallel orbital magnetic moments and contributes to stabilize perpendicular magnetic anisotropy.

The behavior of satellite features appearing in the Ni $L$-edge x-ray absorption spectrum has been investigated for Cu-capped Ni films on Cu(100) by extracting the interface component of the absorption spectrum. By comparing the results with the surface component, it was revealed that the satellite feature at $\ensuremath{\sim}6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ above the ${L}_{\mathrm{III}}$ peak is suppressed only at the surface. This behavior was well reproduced by a one-electron multiple-scattering calculation. On the other hand, an enhancement in the $3\text{\ensuremath{-}}\mathrm{eV}$ satellite was observed at the surface, associated with an increase in the $d$-hole number. This is interpreted as an increase in the $3{d}^{8}$ configuration in the ground state.

The surface and interface magnetic structures of Fe thin films (4-11 ML) grown on a 6 ML Ni/Cu(100) film have been directly investigated with the depth-resolved x-ray magnetic circular dichroism technique. An oscillatory behavior in the Fe surface magnetization as a function of Fe thickness is found. The spectra were analyzed with a simple magnetic model, in which only surface two layers and interface (bottom) single layer are magnetically active. The analysis clearly shows existence of an oscillatory or rotational interlayer magnetic coupling between the surface and interface of the Fe film via the inner layers with the interface magnetization essentially unchanged. Temperature dependent experiments showed that the surface magnetization vanishes with increasing temperature, while the interface one stays unchanged.

The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples.

The effect of the lattice strain on magnetic anisotropy of alternately layered FeNi ultrathin films grown on a substrate, Cu(tCu = 0-70 ML)/Ni(48)Cu(52)(124 ML)/Cu(0 0 1) single crystal, is systematically studied by means of in situ x-ray magnetic circular dichroism (XMCD) and reflection high-energy electron diffraction (RHEED) analyses. To investigate the magnetic anisotropy of the FeNi layer itself, a non-magnetic substrate is adopted. From the RHEED analysis, the in-plane lattice constant, ain, of the substrate is found to shrink by 0.8% and 0.5% at tCu = 0 and 10 ML as compared to that of bulk Cu, respectively. Fe L-edge XMCD analysis is performed for n ML FeNi films grown on various ain, and perpendicular magnetic anisotropy (PMA) is observed at n = 3 and 5, whereas the film with n = 7 shows in-plane magnetic anisotropy. Moreover, it is found that PMA is enhanced with decreasing ain, in the case where a Cu spacer layer is inserted. We suppose that magnetic anisotropy in the FeNi films is mainly carried by Fe, and the delocalization of the in-plane orbitals near the Fermi level increases the perpendicular orbital magnetic moment, which leads to the enhancement of PMA.

The spin-polarized electronic structures across the interface between single-layer graphene and a Ni(111) thin film are explored by employing depth-resolved X-ray absorption and magnetic circular dichroism spectroscopy with atomic layer resolution. The depth-resolved Ni L2,3-edge analysis clarifies that the Ni atomic layers adjacent to the interface show a transition of the spin orientation to the perpendicular one in contrast to the in-plane one in the bulk region. The C K-edge analysis reveals the intensification of the spin–orbit interactions induced by the π–d hybridization at the interface as well as out-of-plane spin polarization in the π band region of graphene. The present study indicates the importance of the interface design at the atomic layer level for graphene-based spintronics.

Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt ultrathin film are investigated by means of the X-ray magnetic circular dichroism (XMCD) technique. A large difference in the Co orbital moment is observed between out-of-plane and in-plane directions of the film at moderate Ga+ fluences of ~1-2×1014 ions/cm2 , which corresponds to the perpendicular magnetic anisotropy (PMA), while further increased fluences reduce the orbital moment difference, resulting in in-plane magnetization. In contrast, at much higher Ga+ fluences of ~5×1015 ions/cm2 , at which PMA is observed again, no significant difference is found in the orbital moment of Co between out-of-plane and in-plane directions. Different origins are thus suggested for the appearance of PMA induced by the irradiation between moderate and high Ga+ fluences.

Development and recent progress of a depth-resolved X-ray absorption spectroscopy (XAS) technique are presented, together with future prospects. The technique has been developed by controlling the probing depth of the electron-yield XAS data, which depends on the electron emission angle. This novel technique enables us to achieve depth profiling of the magnetic structure of thin films with a sub-nm depth resolution by using X-ray magnetic circular dichroism (XMCD) in X-ray absorption, which provides quantitative information on the element-specific spin and orbital magnetic moments. The chemical state and electronic structure at the surface and interface are also investigated by depth-resolved XAS analysis. As for future prospects, a three-dimensional micro XAS technique is being developed by combining an X-ray microbeam with depth-resolved XAS. Moreover, it is expected to manipulate magnetic anisotropy by using element-specific and depth-resolved magnetic anisotropy energies obtained from the depth-resolved XMCD to design thin films and multilayers with proper elements and proper thicknesses. The observation of the spin dynamics at the interface will be also possible in future by adopting the pump-probe method.

The element specific magnetic anisotropy energy (MAE) of alternately layered FeNi thin films grown on Ni (4–20 MLs)/Cu(001) is investigated by means of the X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE). Although surface Fe is known to show strong perpendicular magnetic anisotropy, the Ni-sandwiched Fe layer has a tiny MAE of 10±40 µeV. On the other hand, the Fe-sandwiched Ni layer has a positive MAE of 60±30 µeV. The total MAE simulated from the XMCD analysis shows good agreement with the MOKE result. We demonstrate that in-situ analysis of the element specific MAE gives a possible strategy for manipulating the magnetic anisotropy of multilayers.

The principle and applications of the depth-resolved x-ray magnetic circular dichroism (XMCD) technique are demonstrated, by which depth profiling of the magnetic structure of thin films is achieved with sub-nm resolution. The formation of a NiO-like layer at the surface of a Ni/Cu(1 0 0) thin film is revealed by this technique. Moreover, a small uncompensated magnetic moment in the surface layer is suggested, which shows an antiparallel coupling to that in the inner Ni layers. Development of a three-dimensional XMCD technique is also demonstrated, in which an x-ray microbeam is combined with the depth-resolved XMCD. A preliminary study on the magnetic anisotropy of Fe/Ni/Cu(1 0 0) is shown using this new technique.

The formation of a 1-ML-thick NiO-like layer on a 5.5 ML Ni ultrathin film by Ni deposition on oxygen precovered Cu(001) is revealed by the depth-resolved x-ray absorption spectroscopy, and its magnetic properties are investigated. The surface layer exhibits a NiO-like x-ray absorption spectrum, while the underlying layers show a typical spectrum for a metallic Ni film. An uncompensated spin moment is observed in the NiO-like layer, which is antiparallel to the spin moment in the underlying Ni layers. These results demonstrate a potential to fabricate a sharp interface between ferromagnetic and antiferromagnetic materials.

Recent progresses in the depth-resolved X-ray magnetic circular dichroism (XMCD) and X-ray absorption fine structure (XAFS) techniques are presented. The depth-resolved atomic and magnetic structures of Co films grown on Ru(0001) was investigated by using the depth-resolved XMCD and extended X-ray absorption fine structure EXAFS. The three-dimensional magnetic structure of a micro-patterned Fe/Ni/Cu(100) film was studied by combining the depth-resolved XMCD with the X-ray microbeam. The technique was also applied to Co thin films covered with a relatively thick Mo overlayer, in order to demonstrate the possibility to investigate ex-situ samples with a protection layer.

The effect of CO adsorption on the magnetic easy axis of Co/Pd(111) magnetic thin films has been studied by C 1s x-ray photoelectron spectroscopy (XPS) and Co L-edge x-ray magnetic circular dichroism (XMCD) in absorption spectroscopy. We found by the XMCD measurements that the CO adsorption at 200 K induces the spin reorientation transition of a 4–6 monolayer (ML) Co thin film, but it does not cause spin reorientation at 300 K. Simultaneous XPS measurement showed that the C 1s spectrum has a single peak at 285.8 eV at 300 K, while it has an additional shoulder at 285.3 eV at 200K. The main peak is associated with the CO atop adsorption, and the shoulder might be ascribed either to bridge or hollow site adsorption. Temperature and CO coverage dependences of XMCD and C 1s XPS spectra reveal that the bridge or hollow site CO adsorption is responsible for the spin reorientation of the Co thin film. This is the first direct observation to correlate the magnetic anisotropy of a magnetic thin film with the molecular adsorption site.