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The 5 to 15 μ thick nanocomposite films
(Co0.45Fe0.45Zr0.10)x(Al2O3)1-x
with 30 < x < 65 at.% sputtered in a chamber
evacuated with pure Ar gas were studied using Mossbauer spectroscopy,
magnetization, complex magnetic permeability, and magneto-force microscopy
(MFM) measurements. In particular, the films with x < 40 at.% displayed
superparamagnetic state at room temperature (the lack of sextets in
Mossbauer specta, non-hysteresis character of the magnetization curves,
invariability of real μ' and imaginary μ'' parts of magnetic permeabilities
with x and high resistivity. Near the percolation threshold ( x ~ 40 - 45
at.%) Mossbauer specta displayed features of the ferromagnetic sextet and
the values of μ' and μ'' increased, approaching the maximum, as x increasing
due to the decrease of inter-particle distances. Moreover, effects of
dipole-dipole and exchange interactions of the nanoparticles resulted in the
nucleation of the magneto-ordered granules (magnetoclusters) including a few
metallic nanoparticles. The MFM allowed to visualizing the presence of
magnetic labyrinth-like magnetic contrast that was formed by the metallic
nanoparticles near the percolation threshold. At x > 45 at.% the films
behave like the "bulk" ferromagnetic sample with occasional inclusions of
dielectric phase.
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