Electronic structure of La0.5Ca0.5MnO3

Boer, P.K. de; Leuken, H. van; Groot, R.A. de; Rojo, Teófilo; Barberis, G. E.

doi:10.1016/s0038-1098(97)00055-0

Cited by 25 publications

(20 citation statements)

References 26 publications

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“…[3][4][5] Besides the Heusler alloys, the majority of HMF's have been identified among transition metal oxides on the basis of the local spin-density approximation ͑LSDA͒ to the densityfunctional theory. Predictions have been made for Fe 3 O 4 , 6,7 CrO 2 , 8,9 manganites, 10,11 and the double perovskite Sr 2 FeMoO 6 . 12 Only recently, values of the spin polarization of over 90% near E F were found for CrO 2 at 1.8 K using superconducting point-contact spectroscopy, 13,14 although values of 95% had been obtained earlier at 300 K at binding energies of 2 eV below E F using spin-polarized photoemission.…”

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Evidence for the half-metallic ferromagnetic state ofFe3O4by spin-resolved photoelectron spectroscopy

2002

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The spin-dependent electronic structure of thin epitaxial films of magnetite, Fe 3 O 4 (111), has been investigated at room temperature by means of spin-, energy-, and angle-resolved photoemission spectroscopy. Near the Fermi energy E F a spin polarization of Ϫ(80Ϯ5)% is found. The spin-resolved photoemission spectra for binding energies between 1.5 eV and E F show good agreement with spin-split band energies from densityfunctional calculations.PACS number͑s͒: 75.70. Ak, 75.50.Bb, 75.70.Cn, 79.60.Bm The materials class of half-metallic ferromagnets ͑HMF's͒ has attracted renewed interest recently in the search for efficient spin polarizers in spin electronics.1 The intriguing feature of metallic conductivity for one spin component and semiconducting behavior for the other was in most cases theoretically predicted on the basis of electron band structure calculations. An experimental struggle extended over many years and is still ongoing to convincingly verify the truly intrinsic spin-dependent electronic structure of HMF's and consequently the high-spin polarization at the Fermi energy E F . The use of surface-sensitive measurements like spinpolarized photoemission, tunneling into superconductors, or superconducting point-contact spectroscopy imposed severe constraints in addition to problems with sample stoichiometry and homogeneity. In many cases the preparation of highquality thin films was indispensable instead of bulk single crystals which are believed to be superior. Thus, from the first theoretical prediction of, e.g., HMF behavior in Heusler alloys in 1983, 2 it took almost two decades to find evidence for spin polarization values at E F which come close to the expected ones.3 However, problems with the stoichiometry and especially surface composition of the films used are prevailing. [3][4][5] Besides the Heusler alloys, the majority of HMF's have been identified among transition metal oxides on the basis of the local spin-density approximation ͑LSDA͒ to the densityfunctional theory. Predictions have been made for Fe 3 O 4 , 6,7 CrO 2 , 8,9 manganites, 10,11 and the double perovskite Sr 2 FeMoO 6 .12 Only recently, values of the spin polarization of over 90% near E F were found for CrO 2 at 1.8 K using superconducting point-contact spectroscopy, 13,14 although values of 95% had been obtained earlier at 300 K at binding energies of 2 eV below E F using spin-polarized photoemission. 15 The most straightforward evidence of a minority spin gap and a concomitant 95% spin polarization near E F was obtained in La 0.7 Sr 0.3 MnO 3 at 40 K by means of spin-polarized photoemission spectroscopy. 16In this paper we present experimental evidence for the half-metallic ferromagnetic state of magnetite (Fe 3 O 4 ) by means of spin-and angle-resolved vacuum ultraviolet ͑VUV, hϭ21.2 eV͒ photoemission spectroscopy. Using epitaxial Fe 3 O 4 (111) films we obtain at room temperature a negative spin polarization of Ϫ(80Ϯ5)% at E F . This value agrees within 6% with the magnetization at 300 K of a thin Fe 3 O 4 film. 17 M...

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Evidence for the half-metallic ferromagnetic state ofFe3O4by spin-resolved photoelectron spectroscopy

2002

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“…Band structure calculations show results which depend on the approximations involved. For example, for La 0.5 Ca 0.5 MnO 3 the local density approximation leads to a band structure where the Fermi energy just intersects the bottom of the minority t 2g band, 5,12 while a genuine half-metal is obtained in the generalized gradient approximation ͑GGA͒.…”

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Spin-polarization in half-metals (invited)

Fang

Wijs

Groot

2002

Journal of Applied Physics

217

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Half-metals are defined by an electronic structure, which shows conduction by charge carriers of one spin direction exclusively. Consequently, the spin polarization of the conduction electrons should be 100%. In reality this complete spin polarization is not always observed. Since the experimental search for half-metals is tedious and the verification of the expected spin polarization is involved, electronic structure calculations have played an important role in this area. So, an important question is, how the approximations in such calculations influence the resulting spin polarization of the conduction. Another aspect is the well-known fact that bulk properties can be very different from surface and interface properties. Indeed, measurements of the spin polarization in the bulk for, e.g., NiMnSb, show results different from surface sensitive measurements. In this respect it is important to realize that the origin of half-metallic behavior is not unique. Consequently, the deviations from the bulk behavior at the surface/interface can be important. Three different categories of half-metals can be distinguished and their expected surface properties will be discussed. Finally, ways will be described to control the properties at interfaces.

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“…Besides Heusler alloys, the majority of HFMs was identified among transition metal oxides. Band structure calculations on the basis of local spin density approximation (LSDA) to the density functional theory predict a HMF state for CrO 2 [1], Fe 3 O 4 [4,5], Sr 2 FeMoO 6 [24], and mixedvalence manganites [25,26].…”

Section: Half-metallic Ferromagnetsmentioning

confidence: 99%

Growth and Room Temperature Spin Polarization of Half-metallic Epitaxial CrO2 and Fe3O4 Thin Films

Fonin¹,

Dedkov²,

Rüdiger³

et al. 2005

Local-Moment Ferromagnets

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Abstract. Potential applications of systems based on half-metallic ferromagnets (HMFs) in magneto-and spinelectronics including spin injectors, magnetic field sensors and magnetic memory devices stimulated the investigation of the electronic properties of HFMs by a multitude of experimental and theoretical approaches. The main question remains however if the 100% spin polarization at the Fermi level (EF) theoretically predicted for HFMs can be confirmed experimentally. This article gives a short overview on the half-metallic ferromagnets with special emphasis on magnetite (Fe3O4) and chromium dioxide (CrO2). The spin-resolved electronic structure of thin epitaxial Fe3O4(111) and CrO2(100) films has been investigated at 293 K by means of spin-resolved photoemission spectroscopy (SP-PES). Epitaxial Fe3O4(111) films have been grown on different substrates by oxidizing epitaxial Fe(110) films. High surface quality and chemical homogeneity as well as high crystalline order in the bulk of Fe3O4(111) films were confirmed by means of STM and LEED. The Fe3O4(111) epitaxial films show a maximum spin polarization value of −(80±5)% near EF at 293 K confirming the half-metallic nature of Fe3O4 in the [111] direction. High-quality epitaxial CrO2(100) films have been prepared by a chemical vapor deposition technique. Near EF an energy gap was observed for spin-down electrons and a spin polarization of about +(90 ± 10)% was found at 293 K by means of SP-PES. This value and the magnitude of the gap in the minority spin channel are in good agreement with the prediction of the half-metallic nature of CrO2.

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Electronic structure of La0.5Ca0.5MnO3

Cited by 25 publications

References 26 publications

Evidence for the half-metallic ferromagnetic state ofFe3O4by spin-resolved photoelectron spectroscopy

Evidence for the half-metallic ferromagnetic state ofFe3O4by spin-resolved photoelectron spectroscopy

Spin-polarization in half-metals (invited)

Growth and Room Temperature Spin Polarization of Half-metallic Epitaxial CrO2 and Fe3O4 Thin Films

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