Microstructure of Co–Al–O granular thin films

Ohnuma, M.; Hara, Kazuhiro; Abe, Eiji; Onodera, Hidetoshi; Mitani, Seiji; Fujimori, H.

doi:10.1063/1.366425

Cited by 116 publications

(50 citation statements)

References 13 publications

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“…%. 38 We note that our results are also in accordance with other works on systems containing ͑various͒ discontinuous ͑less than one monolayer͒ Co layers embedded in Al 2 O 3 . 39,40…”

Section: A DC Susceptibilitysupporting

confidence: 82%

Tunneling magnetoresistance inCo−ZrO2granular thin films

et al. 2006

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Granular films composed of well defined nanometric Co particles embedded in an insulating ZrO 2 matrix were prepared by pulsed laser depositon in a wide range of Co volume concentrations ͑0.15Ͻ x Ͻ 0.43͒. High-resolution transmission electron microscopy ͑TEM͒ showed very sharp interfaces between the crystalline particles and the amorphous matrix. Narrow particle size distributions were determined from TEM and by fitting the low-field magnetic susceptibility and isothermal magnetization in the paramagnetic regime to a distribution of Langevin functions. The magnetic particle size varies little for Co volume concentrations x Ͻ 0.32 and increases as the percolation limit is approached. The tunneling magnetoresistance ͑TMR͒ was successfully reproduced using the Inoue-Maekawa model. The maximum value of TMR was temperatureindependent within 50-300 K, and largely increased at low T, suggesting the occurrence of higher-order tunneling processes. Consequently, the tunneling conductance and TMR in clean granular metals are dominated by the Coulomb gap and the inherent particle size distribution.

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“…%. 38 We note that our results are also in accordance with other works on systems containing ͑various͒ discontinuous ͑less than one monolayer͒ Co layers embedded in Al 2 O 3 . 39,40…”

Section: A DC Susceptibilitysupporting

confidence: 82%

Tunneling magnetoresistance inCo−ZrO2granular thin films

et al. 2006

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“…The diffraction pattern of the Co 59 Al 11 O 30 thin film has several peaks: most of them are assigned to metallic cobalt with a hexagonal closepacked (hcp) structure. Ohnuma et al 6 suggested the existence of metallic cobalt with a face-centred-cubic (fcc) structure in a Co 52 Al 20 O 28 alloy thin film based on highresolution TEM observation. In the present specimens, fcc Co could exist as indicated in Fig.…”

Section: X-ray Diffractionmentioning

confidence: 99%

“…5 The microstructures of several Co 72 Al 28 -O films with different oxygen concentrations were examined by high-resolution electron microscopy, etc. 6 However, information on chemical states of constituent elements are also needed for more understanding of their behaviour. Some of the present authors have shown that combined use of XPS and x-ray diffraction (XRD) methods gives quite complementary information on nanogranular materials to the results obtained by transmission electron microscopy.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Co-Al-O magnetic thin films by combined use of XPS, XRD and EPMA

Asami

Mitani

Fujimori

et al. 1999

Surf. Interface Anal.

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Several Co–Al–O alloy thin films with different physical properties were prepared by reactive r.f. sputtering of Co85Al15 and Co70Al30 alloy targets in Ar + O2 atmospheres and were characterized by XPS, x‐ray diffraction (XRD) and electron probe microanalysis (EPMA). The alloy films contained metallic Co, mainly of hexagonal phase, and also CoO. The Al oxide in the Co–Al–O thin films did not give any detectable diffraction peaks. The EPMA results showed that [Al]/([Co] + [Al]) ratios, where [M] denotes molar fraction of element M in the alloy, were almost the same as the compositions of the targets used for sputtering. However, quantitative XPS analysis resulted in much higher values of [Al]/([Co] + [Al]) ratios in comparison with the bulk values, suggesting enrichment of Al in the surface region. Aluminium detected by XPS was all in the oxidized state, and was in the form of hydroxide in the top surface region. Cobalt in the topmost region was in the form of oxyhydroxide, which was easily reduced to the metallic state by Ar+ etching. By taking the XPS, XRD and EPMA results into consideration, the difference of Co–Al–O alloys in electric resistance was explained qualitatively by the difference in microstructure of the alloy films, i.e. the difference in thickness of the oxide films on nanoscale particles of metallic Co embedded in an oxidized Al matrix together with the clearance between the nanoscale Co particles. Copyright © 1999 John Wiley & Sons, Ltd.

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“…2 Therefore, granular systems with different magnetic nanoparticles embedded in various kinds of inorganic insulating matrix with different fabricating technique were studied in detail in the last decade. [3][4][5][6] On the other hand, magnetic nanoparticles composite systems utilizing polymer as the insulating matrix have also been investigated with the focus on their optical, electrical magnetic properties, and microstructures. [7][8][9][10] Their magnetoresistance and its temperature dependence have not gained much attention.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of magnetoresistivity of cobalt-polytetrafluoroethylene granular composite films

Kwong

Wong

2007

Journal of Applied Physics

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Heterogeneous granular films consisting of ferromagnetic cobalt particles embedded in a polytetrafluoroethylene polymer matrix were fabricated by the pulsed laser deposition technique carried out with a Nd-doped yttrium aluminum garnet laser at 355 nm. The samples exhibit a magnetoresistance ͑MR͒ change of 4% ͑at 8 kOe͒ at room temperature. An enhancement of MR to a value of 6% was observed at 20 K which is attributed to the increasing order of magnetic moments in the ferromagnetic state at low temperature. Significant loop opening of the MR profile at low temperature and the temperature dependence of MR reveal the interplay of superparamagnetic relaxation behavior and spin-dependent electron tunneling.

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Microstructure of Co–Al–O granular thin films

Cited by 116 publications

References 13 publications

Tunneling magnetoresistance inCo−ZrO2granular thin films

Tunneling magnetoresistance inCo−ZrO2granular thin films

Characterization of Co-Al-O magnetic thin films by combined use of XPS, XRD and EPMA

Temperature dependence of magnetoresistivity of cobalt-polytetrafluoroethylene granular composite films

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