Enhancement of negative capacitance effect in (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films deposited by ion beam sputtering in argon and oxygen atmosphere

Abstract

The paper presents frequency f and temperature T-p dependences of phase shift angle Theta, admittance sigma and capacitance C-p for the as-deposited and annealed (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films deposited by ion-beam sputtering of a compound target in a mixed argon-oxygen gas atmosphere in vacuum chamber. The studied films presented metallic FeCoZr cores covered with FeCo-based oxide shells embedded into oxygen-free dielectric matrix (fluorite). It was found for the metallic phase content within the range of 52.2 at.% LT = x LT = 84.3 at.% in low-f region that Theta values were negative, while in the high-f region we observed the Theta LT 0 degrees. It was obtained that the f-dependences of capacitance module displayed minimum at the corresponding frequency when the Theta(f) crossed its zero line Theta = 0 degrees. It was also observed that the sigma(T-p) dependence displayed the occurrence of two minima that were related to the values of Theta(1) = 90 degrees (the first minimum) and of Theta(2)= -90 degrees (the second one). Some possible reasons of such behavior of (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films are discussed. (C) 2013 Elsevier B.V. All rights reserved.