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High Resolution Photoemission Study of the Spin-Dependent Band Structure of Permalloy and Ni

K. N. Altmann, D. Y. Petrovykh, and F. J. Himpsel

Surf. Sci. Spectra 6, 255 (1999); http://dx.doi.org/10.1116/1.1247929 (6 pages)

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High resolution, angular-resolved photoemission is used in a comparison of the energy bands of permalloy (Ni_0.8Fe_0.2) 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” and d bands in Ni. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
71.20.Be	Transition metals and alloys
75.50.Bb	Fe and its alloys

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Electronic Structures of the Heusler Compounds XMnSb (X = Ni, Pd, Pt) Using Photoemission Spectroscopy

J.-S. Kang and C. G. Olson

Surf. Sci. Spectra 6, 261 (1999); http://dx.doi.org/10.1116/1.1247932 (7 pages)

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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 4d core 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 fractured in situ and measured at about 60 K in a vaccum better than 4 × 10⁻¹¹ Torr. The instrumental resolution of the system is about 0.2 eV at hν=40 eV and about 0.4 eV at hν = 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 3d partial spectral weight (PSW) distribution. The extracted Mn 3d PSWs of PdMnSb and PtMnSb are found to be very similar to each other. The measured Sb 4d core level spectra are very similar for NiMnSb and PtMnSb. In contrast, the Sb 4d spectrum 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. © 2000 American Vacuum Society.

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71.20.Be	Transition metals and alloys
79.60.Bm	Clean metal, semiconductor, and insulator surfaces
75.50.Cc	Other ferromagnetic metals and alloys

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Soft X-ray Photoemission From Heusler Alloys

M. D. Crapper and D. Brown

Surf. Sci. Spectra 6, 268 (1999); http://dx.doi.org/10.1116/1.1247930 (6 pages)

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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-3d resonance in all three. Heusler alloys are magnetic alloys with localized moments on the Mn atoms. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
71.20.Be	Transition metals and alloys
75.50.Cc	Other ferromagnetic metals and alloys

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Electron Spectroscopic Data of La_1−xSr_xMnO₃ and La_1−xSr_xCoO₃

D. D. Sarma, Dinesh Topwal, and A. Chainani

Surf. Sci. Spectra 6, 274 (1999); http://dx.doi.org/10.1116/1.1247934 (18 pages)

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We report various high-energy electron spectroscopic data on sintered polycrystalline La_1−xSr_xMnO₃ and La_1−xSr_xCoO₃ with x=0.0, 0.1, 0.2, 0.3, and 0.4. The data presented consist of x-ray photoelectron transition metal 2p core level and valence band spectra, x-ray initiated transition metal L₃VV spectra, Bremsstrahlung isochromat spectra, and soft x-ray absorption spectra at the oxygen K-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. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
78.70.Dm	X-ray absorption spectra
71.30.+h	Metal-insulator transitions and other electronic transitions
75.50.Ee	Antiferromagnetics

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Strontium-doped Lanthanum Manganese Oxides Studied by XPS

T. Saitoh, A. E. Bocquet, T. Mizokawa, H. Namatame, A. Fujimori, Y. Takeda, and M. Takano

Surf. Sci. Spectra 6, 292 (1999); http://dx.doi.org/10.1116/1.1247937 (10 pages)

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La_1−xSr_xMnO₃ is a perovskite-type magnetic material. LaMnO₃ and SrMnO₃ are antiferromagnetic insulators while the system becomes a ferromagnetic metal in a certain Sr concentration. In ∼0.2<x<∼0.5, it shows a so-called colossal magnetoresistance (CMR) which is a phenomenon of a huge resistivity drop when a magnetic field is applied. This property has a potential application to the magnetic storage industry. The aim of this research was to understand the electronic structure of this system using photoemission spectroscopy and to elucidate the origin of the CMR phenomenon. The samples were polycrystalline and were prepared by solid-state reaction. XPS measurements were carried out using a Mg K_α source at liquid nitrogen temperature (∼80 K). In order to obtain a fresh, clean surface, the samples were scraped with a diamond file in situ, and surface aging was monitored by observing the intensity of a tail at the higher binding-energy side of the O 1s peak. The surface typically lasted for 1–2 h. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
71.20.Ps	Other inorganic compounds
75.47.Gk	Colossal magnetoresistance
81.05.Je	Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

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Strontium-doped Lanthanum Cobalt Oxides Studied by XPS

T. Saitoh, T. Mizokawa, A. Fujimori, Y. Takeda, and M. Takano

Surf. Sci. Spectra 6, 302 (1999); http://dx.doi.org/10.1116/1.1247936 (11 pages) | Cited 1 time

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La_1−xSr_xCoO₃ is a perovskite-type magnetic material. LaCoO₃ is 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 La_1−xSr_xMnO₃, 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 Mg K_α source at liquid nitrogen temperature (∼80 K). In order to obtain a fresh clean surface, the samples were scraped with a diamond file in situ, and surface aging was monitored by observing the intensity of a tail at the higher binding-energy side of the O 1s peak. The surface typically lasted for 1–2 h. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
75.30.Kz	Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck	Nonmetals
81.05.Je	Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

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Spin Dependent Electronic Structure of Doped Manganese Perovskites

J.-H. Park

Surf. Sci. Spectra 6, 313 (1999); http://dx.doi.org/10.1116/1.1247935 (4 pages)

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The spin-resolved photoemission spectra were successfully obtained from La_0.7Sr_0.3MnO₃ 190 nm thick epitaxial film on SrTiO₃(001). Well below T_c the results clearly manifest the half-metallic nature, i.e., for the majority spin, the photoemission spectrum clearly shows a metallic Fermi cut-off, whereas for the minority spin, it shows an insulating gap with disappearance of the spectral weight at ∼0.6 eV binding energy. On heating through T_c the spectra show no difference for different spins and the spectra weight at the Fermi level (E_F disappears, indicating that the Mn 3d spins become disordered) and the system undergoes the ferromagnetic metal to paramagnetic non-metal transition. © 2000 American Vacuum Society.

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79.60.Dp	Adsorbed layers and thin films
71.20.Ps	Other inorganic compounds
75.30.Kz	Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

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Low-Temperature Angle-Resolved Photoemission Spectra of the Layered CMR Oxide La_1.2Sr_1.8Mn₂O₇

D. S. Dessau and T. Saitoh

Surf. Sci. Spectra 6, 317 (1999); http://dx.doi.org/10.1116/1.1247933 (4 pages)

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We present high resolution (40 meV) angle-resolved photoemission data from cleaved single-crystalline surfaces of the layered colossal magnetoresistive oxide La_1.2Sr_1.8Mn₂O₇. The sample was in the low temperature ferromagnetic state at T=10 K, well below the phase transition temperature of T=126 K. Full valence bands containing Mn 3d and O 2p states are shown, as well as blowups of the near E_F spectra which are made up of the e_g symmetry Mn 3d-O 2p hybrid states. k-vectors span the Brillouin zone center (0,0) to the zone face (π,0). © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
71.20.Ps	Other inorganic compounds
75.47.Gk	Colossal magnetoresistance

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Fe Chalcogenides by X-ray Photoemission Spectroscopy

Kenya Shimada, Takashi Mizokawa, Kazutoshi Mamiya, Tomohiko Saitoh, Atsushi Fujimori, and Takashi Kamimura

Surf. Sci. Spectra 6, 321 (1999); http://dx.doi.org/10.1116/1.1247931 (16 pages)

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In this article, x-ray photoelectron spectroscopy (XPS) spectra of iron chalcogenides, FeS, Fe₇S₈, and Fe₇Se₈ are presented. FeS (troilite) and Fe₇S₈ (pyrrhotite) are among the most common iron compounds on earth. FeS is antiferromagnetic below the Néel temperature of T_N=593–598 K. Above T_α=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 below T_α. This transition known as the α-transition is accompanied by a small displacement of the Fe and S atoms from the regular NiAs-type structure. Fe₇S₈ and Fe₇Se₈ are ferrimagnetic metals with Néel temperatures of T_N=578 and 423–460 K, respectively. The crystal structures of Fe₇S₈ and Fe₇Se₈ are 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 scraping in situ with a diamond file. All the XPS spectra of the iron chalcogenides are taken at room temperature. © 2000 American Vacuum Society.

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79.60.Bm	Clean metal, semiconductor, and insulator surfaces
75.50.Bb	Fe and its alloys
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

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In situ XPS Spectra of Nonstoichiometric Fe_3−δO₄(100) Films

Tatsuo Fujii, Frans C. Voogt, Tjipke Hibma, and George A. Sawatzky

Surf. Sci. Spectra 6, 337 (1999); http://dx.doi.org/10.1116/1.1247938 (10 pages)

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XPS core- and valence-level spectra of various nonstoichiometric Fe_3−δO₄ films were measured systematically as a function of the δ value. The films were prepared epitaxially on MgO(100) substrates by NO₂-assisted molecular beam epitaxy and characterized in situ with RHEED, LEED, and XPS. Stoichiometry of the films was controlled precisely by adjusting the NO₂ pressure during deposition and analyzed ex situ by conversion electron Mössbauer spectroscopy. © 2000 American Vacuum Society.

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79.60.Dp	Adsorbed layers and thin films
71.20.Ps	Other inorganic compounds
61.66.Bi	Elemental solids
61.66.Dk	Alloys
81.05.Je	Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

BROWSE VOLUMES

Oct 1999

Volume 6, Issue 4, pp. 255-346

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