Spin scattering characteristics of nickel doped with manganese are compared to nickel doped with iron and chromium in nickel. Conclusions are made based on the spin characteristics of the nickel samples doped with manganese with varying percentages in a host nickel crystal. Manganese doping increases the magnetic exchange splitting of nickel, similar to doping with iron and opposite to doping with chromium. On the other hand, manganese doping behaves different from iron with respect the ratio of the majority to minority spin carriers and the ratio of their lifetimes. While iron doping affects both ratios strongly, manganese and chromium doping do not.

This study explores the consequences of structure on the electronic properties of magnetic multilayers. Epitaxial layers of Co and Cu are grown on Cu(100) in a new deposition system that couples sputter-deposition with MBE and contains a wide range of characterization tools, including RHEED, LEED, and Kerr effect. This system can be coupled in situ to spin-polarized, angle-resolved photoemission and to resonant, magnetic X-ray scattering, both employing synchrotron radiation. The interface structure turns out to be critical in determining the coercivity and the presence of quantum well states, which determine oscillatory magnetic coupling.

We report magnetic behavior of a dilute ferromagnetic alloy Ni1−xMnx, 0<x<25%. Magnetic circular dichroism (MCD) is used to examine the local magnetic moment on each element, and superconducting quantum interference device magnetometry is used to evaluate the magnetization of the alloy as a whole. Both MCD and hysteresis loops show a collapse in moment at x≈15% measured at 100 K. The Mn doping appears to disturb the long-range ordering of the host nickel spins which, in the concentration range studied, is a precursor disordered ferromagnet prior to a spin-glass phase.

There is much interest and debate concerning the origin of ferromagnetism in dilute alloys of MnxGa1-xAs and other magnetically doped semiconductors [1]. The Mn acts as an acceptor introducing itinerant holes into the semiconductor. The ferromagnetic (FM) coupling between the magnetic Mn is thought to be via RKKY screening by the itinerant hole gas [2]. This coupling induces FM order at concentrations less than 10%, but increasing antiferromagnetic (AFM) disorder at higher concentrations. The Curie temperature TC increases to a maximum of a few hundred K at around 8% alloying. What has not been appreciated is that a similar behavior is observed in dilute alloys of

We report angle-resolved photoemission measurements of the effects of alloying on the spin-polarized electronic states of ferromagnetic transition metals. We observe that the minimum energy for spin-flip scattering of d electrons (the so-called "Stoner gap" in itinerant ferromagnets) is governed by the upper limit of the majority d bands. This Stoner gap can be tuned by alloying, which correspondingly alters the polarization of spin currents and lifetime of spin states in designer magnetic alloys for spintronic devices.

Received 14 January 2004DOI:https://doi.org/10.1103/PhysRevLett.92.089902©2004 American Physical Society

This chapter contains sections titled: Introduction Band structure of magnetic materials Magnetic insulators Phase transitions Magnetic multilayers Magnetoelectronics

The band structure of the single-domain Si(111)-(3x1)-Li surface is investigated by angular resolved photoelectron spectroscopy (ARPES) with synchrotron radiation. Vicinal surfaces are used as templates for obtaining a single-domain (3x1) reconstruction. The surface band structure consists of a single, well-pronounced state at about 0.9 eV below the valence band maximum. Its dispersion matches local density calculations for the honeycomb-chain-channel (HCC) structure, but the calculated energy is 0.31 eV too high. This shift is reminiscent of localized surface states on other silicon surfaces, such as Si(111)-H.

A new chain structure of Au is found on stepped Si(111) which exhibits a 1/4-filled band and a pair of > or =1/2-filled bands with a combined filling of 4/3. Band dispersions and Fermi surfaces for Si(553)-Au are obtained by photoemission and compared to that of Si(557)-Au. The dimensionality of both systems is determined using a tight binding fit. The fractional band filling makes it possible to preserve metallicity in the presence of strong correlations.

Metallic surface states on semiconducting substrates provide an opportunity to study low-dimensional electrons decoupled from the bulk. Angle resolved photoemission is used to determine the Fermi surface, group velocity, and effective mass for surface states on $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Ag},$ $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Au},$ and $\mathrm{Si}(111)\sqrt{21}\ifmmode\times\else\texttimes\fi{}\sqrt{21}\ensuremath{-}(\mathrm{Ag}+\mathrm{Au}).$ For $\mathrm{Si}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Ag}$ the Fermi surface consists of small electron pockets populated by electrons from a few % excess Ag. For $\mathrm{Si}(111)\sqrt{21}\ifmmode\times\else\texttimes\fi{}\sqrt{21}\ensuremath{-}(\mathrm{Ag}+\mathrm{Au})$ the pockets increase their size corresponding to a filling by three electrons per unit cell. The $\sqrt{21}\ifmmode\times\else\texttimes\fi{}\sqrt{21}$ superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the $\sqrt{21}\ifmmode\times\else\texttimes\fi{}\sqrt{21}$ superlattice.

Arrays of atomic wires can now be synthesized by self-assembly at stepped surfaces. They provide opportunities for exploring electrons in one dimension and to test predictions of exotic properties, such as spin charge separation in a Luttinger liquid.  2002 Elsevier Science B.V. All rights reserved.

High-quality vicinal Si(111) surfaces are used as templates to create single domains of the Si(111)3×1-Ca reconstruction which exhibit atomic chains parallel to Si steps. Scanning tunneling microscope images support the formation of honeycomb chains of Si atoms, rather than zigzag chains proposed in earlier models. Angle-resolved photoemission is used to map out the dispersion of valence band states parallel and perpendicular to the chains. A gap of ≈0.9 eV is found below the Fermi level with both in-plane and out-of-plane polarization of the synchrotron light. The observed semiconducting behavior suggests that the honeycomb chain channel model proposed for the alkali-induced 3×1 reconstruction be modified for divalent alkaline earths, e.g. a 3×2 structure with 1/6 monolayer coverage.

Electrons at noble metal surfaces can be confined within terraces leading to one-dimensional surface states. These can be studied with angle-resolved photoemission from vicinal surfaces with regular arrays of (111)-oriented terraces. Here we show the case of Au(23 23 21), which is vicinal to Au(111) and displays L=56 Angstrom wide terraces. The surface state band appears broken up into three quantum well levels that match to those of the infinite quantum well of the same width L. Their parallel momentum dependent photoemission intensity allows mapping the probability density of the confined wave function in reciprocal space using angle-resolved photoemission. By Fourier transformation, their respective experimental wave functions in real space are obtained and compared to the case of the infinite quantum-well, showing excellent agreement. Final state step superlattice diffraction effects have also been observed. Finally, we observe the quenching of the characteristic spin-orbit coupling of Au(111) in the confinement direction. This is another indication of the one-dimensional character of the surface state, as confirmed with first order perturbation theory.

Arrays of atomic wires can now be synthesized by self-assembly at stepped surfaces. They provide opportunities for exploring electrons in one dimension and to test predictions of exotic properties, such as spin charge separation in a Luttinger liquid.

Angle-resolved photoemission is used to determine the change in the electronic states of Ni induced by doping with Fe and Cr. Well-defined spin and k states are selected using high energy and k resolution combined with single crystal alloys. Iron suppresses the mean free path of minority spins only, while chromium suppresses both spins and decreases the magnetic splitting. The strong variation of these effects from one impurity to the other supports the concept of magnetic doping.

The photoemission cross section of quantum well states in thin Cu(1 0 0) films on Co(1 0 0) has been analyzed in normal emission as a function of photon energy. Assuming conservation of the perpendicular wave vector k⊥, the cross section maxima can be assigned to direct transitions from the (initial) quantum well state to bulk-like final states. The value of k⊥ is obtained from the sharp k⊥ distribution of specific quantum well states, which is centered about discretized k⊥ values. Our data are compared with free-electron-like models and a low energy electron diffraction calculation of high-energy states in bulk Cu.

Epitaxial magnetic multilayers are grown in a new deposition system that can be coupled to a variety of synchrotron-based spectroscopic tools at the SRC, such as angle-resolved photoemission with a Scienta analyzer, spin-polarized photoemission, and resonant magnetic x-ray scattering. It is possible to deposit materials by sputter-deposition and by evaporation in the same system, thereby allowing a comparison between industrial fabrication methods and laboratory techniques. The atomic structure is characterized by RHEED (including differentially-pumped RHEED during sputter-deposition), LEED, and resonant X-ray scattering at the L-edges of Fe, Co, Ni, and Cu. Magnetic properties are determined by the Kerr effect, spin-polarized, angle-resolved photoemission, and diffuse magnetic X-ray scattering. Electronic states are investigated by highresolution photoemission with particular emphasis on the states near the Fermi level.

One-dimensional electron systems can now be synthesized at stepped surfaces by self-assembly of atomic and molecular chains. A wide variety of adsorbate and substrate combinations provides opportunities for systematically tailoring electronic properties, such as the intra-chain and inter-chain coupling, the electron count, magnetic moment and the Coulomb interaction. Angle-resolved photoemission with synchrotron radiation is an ideal probe to reveal the complete set of quantum numbers for electrons at an ordered surface, i.e. energy, momentum parallel to the surface, spin and point group symmetry. Interesting electronic features are discussed, such as spin-charge separation in a Luttinger liquid, charge density waves, the Peierls gap, mixed dimensionality and one-dimensional quantum well states.