Magnetic correlations in non-percolated Co–SiO2 granular films

Sankar, S.; Berkowitz, A. E.; Dender, D. C.; Borchers, J. A.; Erwin, R. W.; Kline, S. J.; Smith, David J.

doi:10.1016/s0304-8853(00)00391-7

Cited by 77 publications

(55 citation statements)

References 35 publications

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“…The observed mean particle diameters are smaller and their growth with increasing concentration is less pronounced as compared to the data reported by Abeles and coworkers in co-sputtered Ni-Al 2 O 3 ͑D varies from 1.5 nm for x = 0.08 to 4 nm for x = 0.44͒ and Ni-SiO 2 ͑D = 3.5 nm for x = 0.40͒ granular systems, 30 15,33 This may be related to the choice of the matrix oxide: the ZrO 2 seems to coat the Co nanoparticles well confining them in small globules, thereby avoiding the growth of large clusters. The fact that our films have been prepared by means of laser ablation and not with the usual cathode sputtering may also explain the observed different microstructure, although similar sizes and concentration dependences have also been observed in co-sputtered Co-AlO x films by Ohnuma and co-workers, who reported an average particle diameter of about 2 nm almost independent of the Co concentration in a range from 20 up to 50 at.…”

Section: A DC Susceptibilitycontrasting

confidence: 52%

“…31,32 This feature seems to indicate the absence of strong magnetic interactions between particles for Co concentrations up to about x = 0.30, as may also be deduced from the relatively small values of . Sankar et al 33 reported = −29 K and = −34 K for Co-SiO 2 granular films with x = 0.32 and x = 0.41, respectively. These values are opposite in sign and much larger than the ones we found and may be related to stronger interactions in granular Co-SiO 2 than in Co-ZrO 2 , which support the suggestion of our samples being clean samples with a very reduced degree of particle-matrix intermixing.…”

Section: A DC Susceptibilitymentioning

confidence: 98%

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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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Section: A DC Susceptibilitycontrasting

confidence: 52%

Section: A DC Susceptibilitymentioning

confidence: 98%

Tunneling magnetoresistance inCo−ZrO2granular thin films

et al. 2006

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“…6 shows the spin structure of approximately 100 particles in zero field after ZFC from 300 to 5 K. The simulation area is 50 × 50 nm 2 . One observes FM correlated regions including several particles [12,29], which can be interpreted as SFM domains. This study neglects higher-order multipole terms of the dipolar interaction [5,6].…”

Section: Superferromagnetic (Sfm) Orderingmentioning

confidence: 99%

Collective states of interacting ferromagnetic nanoparticles

Petracic

Chen

Bedanta

et al. 2006

Journal of Magnetism and Magnetic Materials

164

129

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Discontinuous magnetic multilayers [CoFe/Al 2 O 3 ] are studied by use of magnetometry, susceptometry and numeric simulations. Soft ferromagnetic Co 80 Fe 20 nanoparticles are embedded in a diamagnetic insulating a-Al 2 O 3 matrix and can be considered as homogeneously magnetized superspins exhibiting randomness of size (viz. moment), position and anisotropy. Lacking intra-particle core-surface ordering, generic freezing processes into collective states rather than individual particle blocking are encountered. With increasing particle density one observes first superspin glass and then superferromagnetic domain state behavior. The phase diagram resembles that of a dilute disordered ferromagnet. Criteria for the identification of the individual phases are given.

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“…3 Similar, though only twodimensional ͑2D͒ SFM states are found, e.g., in Co͑t n ͒ /Cu͑100͒ thin films at coverages t n Ͻ 1.8 monolayers 9 or in ultrathin Fe films grown on CaF 2 /Si͑111͒. 10 In several cases, the ferromagnetic interparticlecorrelations could be imaged, e.g., by small-angle neutron scattering in nonpercolated Co-SiO 2 granular films 11 or by magnetic force microscopy ͑MFM͒ in self-assembled ⑀-Co nanoparticle layers. 12 However, in DMIMs the conjectured domain structure 8 has not yet been evidenced in a direct way.…”

Section: Introductionmentioning

confidence: 94%

Superferromagnetic domain state of a discontinuous metal insulator multilayer

et al. 2005

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Polarized neutron reflectivity ͑PNR͒ and magnetometry studies have been performed on the granular multilayer ͓Co 80 Fe 20 ͑1.3 nm͒ /Al 2 O 3 ͑3 nm͔͒ 10 . Due to strong interparticle interactions, a collective superferromagnetic state is encountered. Cole-Cole plots drawn from the complex ac susceptibility are measured as functions of frequency, temperature, and field amplitudes that hint at the relaxation, creep, sliding, and switching regimes of pinned domain walls that are in close agreement with results obtained from simulations. Very slow switching with exponential relaxation under near-coercive fields is confirmed by PNR measurements. The complete absence of spin-flip scattering confirms that the magnetization reversal is achieved merely by domain nucleation and growth.

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Magnetic correlations in non-percolated Co–SiO2 granular films

Cited by 77 publications

References 35 publications

Tunneling magnetoresistance inCo−ZrO2granular thin films

Tunneling magnetoresistance inCo−ZrO2granular thin films

Collective states of interacting ferromagnetic nanoparticles

Superferromagnetic domain state of a discontinuous metal insulator multilayer

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