In this work, attention was focused on the inductive contribution to the real part of admittance G(T , f ) in (Fe 0.45 Co 0.45 Zr 0.10 ) x (PZT) (1−x) nanocomposite films deposited in a mixed argon-oxygen atmosphere. The observed G(x, f, T ) dependences for the films on the dielectric side of the insulator-metal transition demonstrated the negative capacitance (NC) effect that was maximal for the nanocomposites with 0.40 < x < 0.60, where the metallic FeCoZr nanoparticles were totally oxidized. The NC effect was explained by a specially developed model for the ac hopping conductance of the electrons between the fully oxidized nanoparticles embedded in the PZT matrix. In accordance with the model, under the determined conditions the observed structure of nanocomposites led to an increase in the hopping electron mean lifetime on nanoparticles and hence to the possibility of positive angles of the phase shifts θ and a proper NC (inductive-like contribution) effect.

The combined use of scanning electron microscopy, Mössbauer spectrometry, X‐ray diffraction and also DC/AC electrical and magnetic characterization techniques allowed this work to elucidate the influence of metal‐to‐dielectric component ration, and effect of oxygen in gas mixture on phase structure and properties of the Co0.45Fe0.45Zr0.10 ferromagnetic nanoparticles in amorphous dielectric Al2O3 matrix. The films of 3–5 µm thickness with compositions of 30 at.% < X < 60 at.% were sputtered on a single substrate from the compound target in the chamber containing either pure Ar or Ar‐O gas mixture. The films sputtered in Ar‐O mixture resulted in partial oxidation of metallic nanoparticles causing the shift of percolation threshold X c to 55 at.% as compared to 45–47 at.% for the samples deposited in pure Ar. Mössbauer studies of the films sputtered in Ar gas have shown that at X < X c metallic nanoparticles were at superparamagnetic state but for X > X c metallic phase showed a ferromagnetic behavior. DC carrier transport at the temperatures of 77–350 K were explained by hopping mechanisms and described by Mott and Shklowski‐Efros laws. That was also confirmed by the relationship power law of Z ′(f ) ∼ f –s (s ≤ 2) for real part of impedance at low temperatures (<120 K) for the samples on dielectric side of MIT. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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This paper investigates the inductive contribution to AC conductance in the granular nanocomposites (Fe0.45Co0.45Zr0.10)x(Al2O3)1−x. The initial nanocomposites studied were manufactured in Ar+O2 atmosphere by ion-beam sputtering of the target containing Fe0.45Co0.45Zr0.10 and alumina stripes and then subjected to the annealing procedure in air over the temperature range 373 K < Ta < 873 K. These samples, before and after annealing, were studied using the temperature 77 K < Tp < 300 K and frequency 50 Hz < f < 1 MHz dependences of a real part of the admittance σ(T, f ). Analysis of the observed σ(f, T p ) dependences for x < 0.5 demonstrated that in the studied samples the equivalent circuits with the capacitive and noncoil-like inductive contributions can be accomplished. Just in this case, the capacitive properties of RLC circuit with the phase angle −90• ≤ θ L < 0• are exhibited at low frequencies and the inductive properties with 0• become apparent at high frequencies. A value of the critical frequency f R , where θ H changes sign, depends on the metallic phase concentration x, measuring temperature T p , and annealing temperature T a .

We report the investigation of a real part of the admittance σ of granular nanocomposites (Fe 0.45 Co 0.45 Zr 0.10) x (Al 2 O 3) 1−x with 0.30 < x < 0.70 in the dielectric (hopping) regime. An analysis of the σ(T, f, x) dependences in the as-deposited and annealed films over the temperature 77 K < T < 300 K and frequency 50 < f < 10 6 Hz ranges displayed the predominance of an activation (hopping) conductance mechanism with dσ/ dT > 0 for the samples below the percolation threshold x C ≈ 0.76 ± 0.05. Based on the earlier models for hopping AC conductance, computer simulation of the frequency coefficient α f of hopping conductance depending on the probability of jump p, frequency f , and also on the shape of σ(f) curve was performed. The experimental and simulation results revealed a good agreement.