AC electrical resonances in nanocomposites with partly oxidized FeCoZr grains embedded in CaF₂ ceramic matrix – effects of annealing

Abstract

This paper presents the frequency and temperature dependences of the phase shift angle, the active part of the admittance, the capacitance, and the dielectric loss factor tanδ for as-deposited and annealed (FeCoZr)x(CaF2)(100-x) nanocomposite films prepared via ion-beam sputtering of a complicated target in a mixed argon–oxygen gas atmosphere. For films with a metallic phase content of x = 62.7 at.%, after 15 min of annealing at a temperature of 398 K, a strong ‘negative capacitance’ effect occurred, indicating an inductive-like contribution to the admittance. This effect was accompanied by two types of resonances: a voltage resonance and two current resonances. It was determined that description of AC parameters of (FeCoZr)x(CaF2)(100-x) films can be made by using compound equivalent circuit, consisting of RLC series circuit and two conventional circuits differing in values of their RLC elements, which means that the material can be used in microelectronics instead of such circuits. The joint analysis of the σ(f), θ(f), Cp(f), and tanδ(f) curves allowed the resonances to be explained on the basis of the previously developed alternating current (AC)/direct current (DC) hopping model with three different characteristic times of electron hopping.