摘要:

High resolution, angular-resolved photoemission is used in a comparison of the energy bands of permalloy (Ni0.8Fe0.2) and single crystal Ni. The nickel was cleaned with a combination of Ar-ion bombardment and annealing. The permalloy was grown epitaxially on the clean single crystal Ni surface to minimize lattice mismatch. The magnetically split bands at the Fermi level that are responsible for spin-dependent transport are resolved in both systems. In addition, spectra are shown demonstrating both “s,p” anddbands in Ni.

ISSN:1055-5269    

DOI:10.1116/1.1247929

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

Mn-based Heusler alloys of NiMnSb and PtMnSb have been predicted to be half-metallic ferromagnetic metals, with 100% spin-polarized conduction electrons at the Fermi level. In this study, the valence-band and Sb 4dcore levels of the XMnSb-type Heusler alloys (X = Mi, Pd, Pt) have been investigated using synchrotron-radiation photoemission spectroscopy. Samples were made by melting the appropriate amount of constituent elements in vacuum-sealed quartz tubes at 1100 °C, and subsequent annealing at 600 °C for one week. Photoemission measurements were performed on the Mark V beamline at the Synchrotron Radiation Center at the University of Wisconsin-Madison. Polycrystalline samples were fracturedin situand measured at about 60 K in a vaccum better than 4 × 10−11Torr. The instrumental resolution of the system is about 0.2 eV athν=40 eV and about 0.4 eV athν= 150 eV, respectively. The incident photon flux was monitored by the yield from a gold mesh and all the spectra were normalized to the incident photon flux. Due to the photon energy dependence of the photoionization cross sections, the valence-band spectra around 120 and 150 eV in PdMnSb and PtMnSb, respectively, can be considered to represent the Mn 3dpartial spectral weight (PSW) distribution. The extracted Mn 3dPSWs of PdMnSb and PtMnSb are found to be very similar to each other. The measured Sb 4dcore level spectra are very similar for NiMnSb and PtMnSb. In contrast, the Sb 4dspectrum for PdMnSb is less structured, as compared to NiMnSb and PtMnSb, indicating a larger lifetime broadening and a smaller surface core level shift in PdMnSb.

ISSN:1055-5269    

DOI:10.1116/1.1247932

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

Synchrotron radiation based measurements of the soft x-ray photoemission spectrum of the valence band of Pd2MnSn, Co2MnSn, and Cu2MnAl are presented. The focus is on the Cooper minimum effect in Pd2MnSn and on the Mn 3p-3dresonance in all three. Heusler alloys are magnetic alloys with localized moments on the Mn atoms.

ISSN:1055-5269    

DOI:10.1116/1.1247930

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

We report various high-energy electron spectroscopic data on sintered polycrystalline La1−xSrxMnO3and La1−xSrxCoO3withx=0.0, 0.1, 0.2, 0.3, and 0.4. The data presented consist of x-ray photoelectron transition metal 2pcore level and valence band spectra, x-ray initiated transition metalL3VVspectra, Bremsstrahlung isochromat spectra, and soft x-ray absorption spectra at the oxygenK-edge. Substitution of trivalent La with divalent Sr introduces holes into the system, driving an insulator-to-metal transition along with magnetic transitions. The spectral changes with progressive hole doping reflect the evolution of electronic structure across the phase transition.

ISSN:1055-5269    

DOI:10.1116/1.1247934

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

La1−xSrxMnO3is a perovskite-type magnetic material. LaMnO3and SrMnO3are antiferromagnetic insulators while the system becomes a ferromagnetic metal in a certain Sr concentration. In ∼0.2

ISSN:1055-5269    

DOI:10.1116/1.1247937

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

La1−xSrxCoO3is a perovskite-type magnetic material. LaCoO3is a nonmagnetic semiconductor at low temperatures but it undergoes a gradual transition from the nonmagnetic ground state to a paramagnetic state above ∼90 K and then to a metal above ∼500 K. It has remained controversial whether the 90 K transition is a low spin-to-high spin transition or not. One aim of this research was to elucidate the origin of the magnetic transition and our conclusion was that it is not a low spin-to-high spin transition, but low spin-to-intermediate spin transition. By replacing La with Sr, the system changes from the nonmagnetic semiconductor to a ferromagnetic metal with increasing Sr concentration. This is similar to the colossal magnetoresistance (CMR) system La1−xSrxMnO3, and the system shows fairly large MR, in fact. However, in contrast to the manganese system, the present system shows only about a half of the full moment of the high spin Co ion. The other aim of this research was to understand the magnetic state of this system using photoemission spectroscopy. The samples were polycrystalline and were prepared by solid-state reaction. XPS measurements were carried out using MgKαsource at liquid nitrogen temperature (∼80 K). In order to obtain a fresh clean surface, the samples were scraped with a diamond filein situ, and surface aging was monitored by observing the intensity of a tail at the higher binding-energy side of the O 1speak. The surface typically lasted for 1–2 h.

ISSN:1055-5269    

DOI:10.1116/1.1247936

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

We present high resolution (40 meV) angle-resolved photoemission data from cleaved single-crystalline surfaces of the layered colossal magnetoresistive oxide La1.2Sr1.8Mn2O7. The sample was in the low temperature ferromagnetic state atT=10 K, well below the phase transition temperature ofT=126 K. Full valence bands containing Mn 3dand O 2pstates are shown, as well as blowups of the nearEFspectra which are made up of theegsymmetry Mn 3d-O 2phybrid states.k-vectors span the Brillouin zone center (0,0) to the zone face (π,0).

ISSN:1055-5269    

DOI:10.1116/1.1247933

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

In this article, x-ray photoelectron spectroscopy (XPS) spectra of iron chalcogenides, FeS, Fe7S8, and Fe7Se8are presented. FeS (troilite) and Fe7S8(pyrrhotite) are among the most common iron compounds on earth. FeS is antiferromagnetic below the Néel temperature ofTN=593–598 K. AboveTα=420 K, FeS is a metal with an NiAs-type crystal structure, but becomes an insulator with a narrow band gap of 0.04 eV belowTα. This transition known as theα-transition is accompanied by a small displacement of the Fe and S atoms from the regular NiAs-type structure. Fe7S8and Fe7Se8are ferrimagnetic metals with Néel temperatures ofTN=578 and 423–460 K, respectively. The crystal structures of Fe7S8and Fe7Se8are derived from the NiAs-type one by introducing ordered Fe vacancies. The polycrystalline samples were synthesized by the Bridgman method. Clean surfaces were obtained by scrapingin situwith a diamond file. All the XPS spectra of the iron chalcogenides are taken at room temperature.

ISSN:1055-5269    

DOI:10.1116/1.1247931

出版商:American Vacuum Society    

年代:1999

数据来源: AIP

摘要:

XPS core- and valence-level spectra of various nonstoichiometric Fe3−δO4films were measured systematically as a function of theδvalue. The films were prepared epitaxially on MgO(100) substrates by NO2-assisted molecular beam epitaxy and characterizedin situwith RHEED, LEED, and XPS. Stoichiometry of the films was controlled precisely by adjusting the NO2pressure during deposition and analyzedex situby conversion electron Mössbauer spectroscopy.

ISSN:1055-5269    

DOI:10.1116/1.1247938

出版商:American Vacuum Society    

年代:1999

数据来源: AIP