Amorphous transition metal oxide films

Heiman, Neil; Kazama, Noriaki

doi:10.1063/1.326868

Cited by 36 publications

(31 citation statements)

References 5 publications

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“…2) reveal a slightly broadened doublet of the non-Lorentzian shape indicating a quadrupole splitting distribution which arises from the electric field gradient distribution encountered in amorphous iron(III) oxides [6,8,15]. The widths of the spectral lines (Γ 1/2 = 0.52 mm/s, both in S250 and in W250 samples) reflect the narrower distribution of the electric field gradients than in other amorphous Fe 2 O 3 powders (Γ 1/2 = 0.60-0.70 mm/s) [7][8][9]12]. The same isomer shift value for both samples, δ = 0.33 mm/s, corresponds to highspin Fe 3+ in octahedral coordination.…”

Section: Resultsmentioning

confidence: 99%

“…The superparamagnetic blocking temperature (T B ) of about 80 K was found by Prozorov et al for amorphous nanopowder prepared by sonochemical method from Fe(CO) 5 . The magnetic behaviour of amorphous Fe 2 O 3 thin films has been interpreted as paramagnetic with the antiferromagnetic ordering below the Neel temperature, which is mentioned to be about 80-100 K [6][7][8][10][11]. This interpretation is based mainly on the magnetic susceptibility measurements revealing negative paramagnetic Curie temperature between -95 and -200 K, depending on the synthetic route and reduced effective paramagnetic moment (2.5-5µ B ) explained by the local clustering of spins [6][7][8] or by the mixing of various spin states [11].…”

Section: Introductionmentioning

confidence: 98%

“…The magnetic behaviour of amorphous Fe 2 O 3 thin films has been interpreted as paramagnetic with the antiferromagnetic ordering below the Neel temperature, which is mentioned to be about 80-100 K [6][7][8][10][11]. This interpretation is based mainly on the magnetic susceptibility measurements revealing negative paramagnetic Curie temperature between -95 and -200 K, depending on the synthetic route and reduced effective paramagnetic moment (2.5-5µ B ) explained by the local clustering of spins [6][7][8] or by the mixing of various spin states [11]. The complex study of magnetic properties of amorphous Fe 2 O 3 powder (∼3 nm) in applied field [2] led to the evidence of four magnetic regimes: pure paramagnetic at T>110 K at low applied field, field induced spin clusters (superparamagnetic like) at higher applied fields at the same temperatures, interacting spin clusters with progressive freezing over 35 to 110 K and collective freezing below 35 K. With increasing applied field, the freezing temperature of spin-clusters decreases.…”

Section: Introductionmentioning

confidence: 98%

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Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Zbořil

Machala

Mashlan

et al. 2004

phys. stat. sol. (c)

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PACS 75.50. Kj, 75.75+a, 76.80.+y, 81.07.Wx Monodispersed amorphous Fe 2 O 3 nanoparticles with the size ranging from 1 to 4 nm have been prepared by thermally induced oxidative decomposition of Prussian Blue, Fe 4 [Fe(CN) 6 ] 3 , in air. Amorphous nanopowders exhibit specific magnetic behaviour strongly affected by interparticle interactions and extremely low particle size with a high contribution of the surface anisotropy as illustrated by temperature dependent and external field Mössbauer spectroscopy and magnetization measurements (4-300 K). Some of the properties are in close similarity to those of spin glasses including the fast thermal variation of superparamagnetic fraction in the Mössbauer spectra, or the particle size independence of the blocking temperature, and non-saturation of magnetization even at 5 K and magnetic field of 10 T. The reduced value of internal magnetic hyperfine field (∼49 T at 5 K) and no indications of the tetrahedral Fe 3+ sites in the 5T/5K external field Mössbauer spectra are the principal found differences in comparison with the magnetic behaviour of nanocrystalline γ-Fe 2 O 3 .

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

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Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Zbořil

Machala

Mashlan

et al. 2004

phys. stat. sol. (c)

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“…The hyperfine parameters, especially the hyperfine magnetic field, related to iron ions belonging to the surface oxides, are thereby distributed. The hyperfine magnetic field values are very high, which means that the short-range order in this phase is similar as in ordered oxides, contrary to real amorphous oxides which show paramagnetic behaviour at room temperature [20,22]. …”

Section: Resultsmentioning

confidence: 99%

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction

Krajewski¹,

Lin²,

Lin³

et al. 2015

Beilstein J. Nanotechnol.

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SummaryThe main goal of this work is to study the structural and magnetic properties of iron nanowires and iron nanoparticles, which have been fabricated in almost the same processes. The only difference in the synthesis is an application of an external magnetic field in order to form the iron nanowires. Both nanomaterials have been examined by means of transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffractometry and Mössbauer spectrometry to determine their structures. Structural investigations confirm that obtained iron nanowires as well as nanoparticles reveal core–shell structures and they are composed of crystalline iron cores that are covered by amorphous or highly defected phases of iron and iron oxides. Magnetic properties have been measured using a vibrating sample magnetometer. The obtained values of coercivity, remanent magnetization, saturation magnetization as well as Curie temperature differ for both studied nanostructures. Higher values of magnetizations are observed for iron nanowires. At the same time, coercivity and Curie temperature are higher for iron nanoparticles.

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“…This effect can be attributed to an increasing destruction of the surface order with increasing sputtering time, i.e. the sputtering process eventually produces an amorphous non-magnetic topmost layer of CrO 2 [74]. A following annealing process of the sputtered CrO 2 (100) film at 150…”

Section: Chromium Dioxidementioning

confidence: 98%

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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Amorphous transition metal oxide films

Cited by 36 publications

References 5 publications

Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction

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

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Amorphous transition metal oxide films

Cited by 36 publications

References 5 publications

Magnetism of amorphous Fe 2 O 3 nanopowders synthesized by solid‐state reactions

Magnetism of amorphous Fe 2 O 3 nanopowders synthesized by solid‐state reactions

Structural and magnetic properties of iron nanowires and iron nanoparticles fabricated through a reduction reaction

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

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Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions

Magnetism of amorphous Fe ₂ O ₃ nanopowders synthesized by solid‐state reactions