About the interesting properties of mixed-valence defect spinel ferrites for mass storage media

Tailhades, Philippe; Bonningue, Corine; Rousset, A.; Bouet, L.; Pasquet, Isabelle; Lebrun, Stéphane

doi:10.1016/s0304-8853(98)00420-x

Cited by 18 publications

(9 citation statements)

References 3 publications

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“…The nanocrystals made for this study result from the oxidation of alloy particles under very mild conditions. The production of ferrites by the oxidation of particles has been shown to result in incomplete oxidation of the core, leading to large stress anisotropy and coercivity enhancement . Even point defects can significantly impede the growth of reverse domains and thus result in significant H c enhancement in materials with a large anisotropy constants, such as CoFe 2 O 4 .…”

Section: Resultsmentioning

confidence: 99%

Superparamagnetic Cobalt Ferrite Nanocrystals Synthesized by Alkalide Reduction

2004

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CoFe 2 O 4 nanocrystallites have been synthesized by alkalide reduction of Co 2+ and Fe 3+ to form nanoscale CoFe 2 , followed by oxidation with aerated water at room-temperature resulting in the nanocrystalline ferrite. As produced, the material consists of 2-4 nm nanocrystals that are superparamagnetic with an average blocking temperature of ∼350 K. Annealing at 100 °C in air results in a decrease in the blocking temperature to ∼250 K, with no detectable nanocrystallite growth. The dramatic change in the magnetic properties upon annealing is probably due to removal of crystal defects, namely oxygen vacancies. Further annealing to temperatures as high as 400 °C results in little change in the nanocrystallite size or the magnetic properties. Annealing at 500 °C results in the onset of significant growth in the nanocrystallite size, reaching 30 nm for material annealed at 1000 °C. The saturation magnetization, remanence, and squareness ratio, measured at 300 K, increase smoothly with increasing annealing temperature above 500 °C reaching 30 nm, 75 emu/g (94% of bulk value), 28 emu/g, and 0.37 respectively, for material that had been annealed at 1000 °C. The unannealed material has the largest coercivity observed in this study, 5.13 kOe at 5 K falling to 116 Oe at 300 K. The coercivity at 300 K declines dramatically to 0.9 Oe upon annealing at 100 °C, rising sharply to 67 Oe for material annealed at 500 °C, falling to 44 Oe for material annealed at 600 °C, and then steadily growing with increasing annealing temperature to 59 Oe for material annealed at 1000 °C. The anomalous increase in coercivity observed for samples annealed at 500 °C appears to be due to an increase in the average crystallite aspect ratio, which declines upon annealing at higher temperature.

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Section: Resultsmentioning

confidence: 99%

Superparamagnetic Cobalt Ferrite Nanocrystals Synthesized by Alkalide Reduction

2004

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“…These spinels have magnetic, magneto-optic and optical properties making them interesting materials for magnetic storage media, printing inks, color imaging, high-grade magnetic separation and ferrofluids [1][2][3][4][5][6]. The recent development of biocompatible, functionalized ferrofluids has led to new biomedical and diagnostic applications [7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 98%

Synthesis and characterization of spinelic ferrites obtained from coordination compounds as precursors

Culiță

Patron

Teodorescu

et al. 2007

Journal of Alloys and Compounds

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“…In general, the lattice parameters should primarily depend on cation distribution and possible oxidation/reduction of a polyvalent cation [25,28,29]. The Yb 3+ cations for S1-S3 are close to being exclusively in the C 3i position while the Y 3+ and Yb 3+ are extremely stable cations.…”

Section: Site Occupancies and Size/strain Analysismentioning

confidence: 99%

157-nm Resist Material Design for Improvement of Its Transparency Using Highly Precise Theoretical Calculation

Yamazaki¹,

Itani²

2003

Jpn. J. Appl. Phys.

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A Y 2 O 3 :Yb nanoscale magnet that belongs to the cubic C-type or bixbyite structure family was synthesized by high energy ball milling (HEBM). An as-prepared sample (S1) was annealed at 650 • C (S2) and 950 • C (S3). Cation populations were determined by the refinement of site occupancies. It was found that in S1 and S2 Yb 3+ ions occupy exclusively the 8b (or C 3i ) position, whereas in S3 a small amount of Yb 3+ is also located on Wyckoff-site 24d (or C 2 ). X-ray powder diffraction line broadening analysis was done by using the Rietveld method using regular TCH-pV functions (isotropic effects) and symmetrized cubic harmonics (anisotropic effects) for the refinement. The line broadening anisotropy decreases due to strain effects from S1 to S3, while the crystallite size anisotropy increases from S1 to S3. Transmission electron microscopy (TEM) and Raman spectroscopy were used to define the homogeneity, microstructure and to locally probe the structure of the samples S1-S3. Magnetic susceptibility results in the 2-300 K temperature regions were analysed by applying the first-order perturbation theory. The mean energy gap between ground and excited crystal field levels (E i ), and their effective magnetic numbers M ieff , were determined. The analysis of the paramagnetic temperature shows the absence of clusterization of the magnetic ions.

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About the interesting properties of mixed-valence defect spinel ferrites for mass storage media

Cited by 18 publications

References 3 publications

Superparamagnetic Cobalt Ferrite Nanocrystals Synthesized by Alkalide Reduction

Superparamagnetic Cobalt Ferrite Nanocrystals Synthesized by Alkalide Reduction

Synthesis and characterization of spinelic ferrites obtained from coordination compounds as precursors

157-nm Resist Material Design for Improvement of Its Transparency Using Highly Precise Theoretical Calculation

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