A method of band mapping providing full control of the three-dimensional k is described in detail. Angledependent very-low-energy electron diffraction is applied to determine the photoemission final states along a Brillouin zone symmetry line parallel to the surface; photoemission out of these states is then utilized to map the valence bands in the constant-final-state mode. The method naturally incorporates the non-free-electron and excited-state self-energy effects in the unoccupied band, resulting in an accuracy superior over conventional techniques. Moreover, its intrinsic accuracy is less limited by lifetime broadening. As a practical advantage, the method provides access to a variety of lines in the Brillouin zone using only one crystal surface. We extensively tested the method on Cu. Several new aspects of the electronic structure of this metal are determined, including non-free-electron behavior of unoccupied bands and missing pieces of the valence band.

Ga 1Ϫx Mn x As, xϭ0.043, has been grown ex situ on GaAs͑100͒ by low-temperature molecular-beam epitaxy. On the reprepared p(1ϫ1) surface, resonant photoemission of the valence band shows a 20-fold enhancement of the Mn 3d contribution at the L 3 edge. The difference spectrum is similar to our previously obtained resonant photoemission at the Mn M edge, in particular a strong satellite appears and no clear Fermi edge ruling out strong Mn 3d weight at the valence-band maximum. The x-ray absorption lineshape differs from previous publications. Our calculation based on a configuration-interaction cluster model reproduces the x-ray absorption and the L 3 on-resonance photoemission spectrum for model parameters ⌬, U dd , and (pd) consistent with our previous work and shows the same spectral shape on and off resonance thus rendering resonant photoemission measured at the L 3 edge representative of the Mn 3d contribution. At the same time, the results are more bulk sensitive due to a probing depth about twice as large as for photoemission at the Mn M edge. The confirmation of our previous results obtained at the M edge calls recent photoemission results into question which report the absence of the satellite and good agreement with local-density theory.

We have obtained the Mn 3d partial density of states in Ga 1Ϫx Mn x As using the resonance photoemission technique as well as by means of the difference between Ga 1Ϫx Mn x As and GaAs. We have observed a strong satellite structure on the higher binding energy side of the main peak, as in Mn-doped II-VI compounds such as Cd 1Ϫx Mn x Te. Based on analysis using configuration-interaction calculation for a MnAs 4 cluster, we could ascribe the spectral features to strong Mn 3d-As 4p hybridization and Mn 3d-3d Coulomb interaction. ͓S0163-1829͑99͒50904-1͔ RAPID COMMUNICATIONS R2488PRB 59 J. OKABAYASHI et al.

Ferromagnetic nanoscale zinc-blende MnAs dots were successfully fabricated on a sulfur-passivated GaAs (001) surface by molecular-beam epitaxy. Transmission electron microscopy and selected area electron diffraction showed that the crystalline structure was not the same as that of bulk MnAs with NiAs-type hexagonal crystalline structure, but of zinc-blende type. In in situ photoemission spectroscopy of the zinc-blende MnAs dots, the Fermi edge was not clearly observed and the Mn 3d partial density of states was similar to that of the diluted ferromagnetic semiconductor Ga1−xMnxAs, which also supports the fabrication of zinc-blende MnAs in the nanoscale.

Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3dz2 and O 2pz states.

Resonance behaviors of the Ni and Fe 3d, 3p and 3s related satellite photoemission and Auger features are measured for the Ni and Fe 2p core excitation in NiS 2 and FeS 2. Chronological interpretation is proposed to the Ni and Fe 2p3p3d Auger features. A resonance satellite around the binding energy of 30 eV is identified as due to the plasmon satellite associated with the resonance-enhanced satellite of the 3d state. ͓S0163-1829͑99͒05131-0͔

The magnetic properties of as-grown Ga1−xMnxAs have been investigated by the systematic measurements of temperature and magnetic field dependent soft x-ray magnetic circular dichroism (XMCD). The intrinsic XMCD intensity at high temperatures obeys the Curie-Weiss law, but residual spin magnetic moment appears already around 100 K, significantly above Curie temperature (TC), suggesting that short-range ferromagnetic correlations are developed above TC. The present results also suggest that antiferromagnetic interaction between the substitutional and interstitial Mn (Mnint) ions exists and that the amount of the Mnint affects TC.PACS numbers: 75.50. Pp, 78.70.Dm, 75.25.+z, 79.60.Dp Ga 1−x Mn x As is a prototypical and most wellcharacterized diluted magnetic semiconductor (DMS) [1]. Because Ga 1−x Mn x As is grown under thermal nonequilibrium conditions, however, it is difficult to avoid the formation of various kinds of defects and/or disorder. In fact, Rutherford backscattering (RBS) channeling experiments for as-grown Ga 0.92 Mn 0.08 As samples has shown that as many as ∼ 17 % of the total Mn ions may occupy the interstitial sites [2]. It is therefore supposed that antiferromagnetic (AF) interaction between the substitutional Mn (Mn sub ) ions and interstitial Mn (Mn int ) ions may suppress the magnetic moment [3,4]. In addition, the random substitution of Mn ions may create inhomogeneous Mn density distribution, which may lead to the development of ferromagnetic domains above Curie temperature (T C ) [5]. The characterization of non-ferromagnetic Mn ions is therefore a clue to identify how they are related with the ferromagnetic ordering and eventually to improve the ferromagnetic properties of Ga 1−x Mn x As samples. However, it has been difficult to extract the above information through conventional magnetization measurement due to the large diamagnetic response of the substrate and the unavoidable mixture of magnetic impurities.X-ray magnetic circular dichroism (XMCD), which is an element specific magnetic probe, is a powerful technique to address the above issues. So far, several results of XMCD measurements on Ga 1−x Mn x As have been reported [6,7,8]. From H dependent XMCD studies, the enhancement of XMCD intensity by post-annealing implies AF interaction between the Mn sub and Mn int ions [8]. In the present study, in order to characterize the magnetic behaviors of the Mn sub and Mn int , we have extended the approach and performed systematic temperature (T ) and magnetic field (H) dependent XMCD studies in the Mn L 2,3 absorption edge region of Ga 1−x Mn x As. We have found that short-range ferromagnetic correlations develop significantly above T C and that AF interaction between the Mn sub and Mn int is important to understand the magnetic properties of Ga 1−x Mn x As.We prepared two as-grown samples with different Mn concentrations; x = 0.042 and 0.078, whose T C was ∼ 60 and 40 K, respectively, as determined by an Arrott plot of the anomalous Hall effect. To avoid surface oxidation, the sample had...

The sheet conductivity of a Au-covered Si͑557͒ facet surface was measured by microscopic four-point probe methods using an independently driven four-tip scanning tunneling microscope and temperature-variable monolithic probes. This surface is composed of a periodic array of Au chains and known to have a quasi-onedimensional metallic band structure. Its surface conductivities parallel to the Au chains ͑ ʈ ͒ and perpendicular to them ͑ Ќ ͒, were obtained separately at room temperature (RT), and the anisotropy ʈ / Ќ was ϳ3. The temperature dependence of the surface conductivity showed a semiconductive character below RT with an activation energy of ϳ55 meV. Then it can be concluded that the transport along the Au chains is not metallic band conduction.