| Nanometer-size CoFe2O4 nanoparticles have been synthesized by self-assembly within diblock co-polymer films, through a novel room-temperature templating strategy, easily amenable to large-scale fabrication processes. X-Ray diffraction, TEM, SQUID and Mössbauer measurements are combined in order to explore the morphological, structural, micromagnetic and interfacial characteristics of this nanocomposite system. TEM micrographs indicate low polydispersity, with average particle size of 9.6 nm diameter. Low temperature Mössbauer studies predict average sublattice saturation hyperfine magnetic fields Hhfs (A) = 501 kOe and Hhfs [B] = 527 kOe, respectively, for the tetrahedral and octahedral iron coordination sites of the ferrite spinel structure. Superparamagnetic relaxation processes, analyzed within a cubic magnetic anisotropy model, give an effective particle magnetic anisotropy density Keff = 3.23⋅105 J/m3, while SQUID magnetometry measurements predict a saturation coercivity Hcs = 6.1 kOe. Deviations of the above parameters from those of bulk CoFe2O4 and unsupported CoFe2O4 nanoparticles of comparable size are discussed in terms of finite-size effects and interfacial interactions. The results indicate that particle-support interactions at the ferrite/polymer interface can be profitably utilized for the stabilization of non-equilibrium phases and manipulation of the magnetic properties of this nanocomposite system. |
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