V. Bondariev

Percolation threshold of granular metal-dielectric nanocomposites (FeCoZr)x(CaF2)1-x produced in atmosphere of argon and oxygen

The paper presents temperature-frequency dependencies of conductivity of the granular metal-dielectric nanocomposites (FeCoZr)x(CaF2)100-x. A series of nanocomposite samples with a different metallic phase content from range x = 41.3 – 86.1 at.% produced by twosources ion-beam sputtering in mixed atmosphere of argon and oxygen was tested. Analysis of results of temperature dependences of conductivity of the samples with metallic phase content x bellow 81.8 at.% obtained immediately after producing showed that nanocomposites (FeCoZr)x(CaF2)100-x exhibit dielectric properties, namely conductivity increases with the increase of measurement temperature. At the metal phase content x = 86,1 at.% inverse relationship of conductivity was observed, which menace that nanocomposite is characterized by metallic type of conductivity. Comparison of the conductivity at LNT (liquid nitrogen temperature) and at room temperature for different content of metallic phase allowed to set the percolation threshold for tested series of samples of nanocomposite (FeCoZr)x(CaF2)100-x. The change of type of conductivity from dielectric to metallic type takes place with metallic phase content about 82±0.2at.%.

Ion Irradiation of Oxidized FeCoZr-CaF2 Nanocomposite Films for Perpendicular Magnetic Anisotropy Enhancement

Ion Irradiation of Oxidized FeCoZr–CaF2 Nanocomposite Films for Perpendicular Magnetic Anisotropy Enhancement J. Kasiuka,∗, J. Fedotova, J. Przewoźnik, C. Kapusta, V. Skuratov, I. Svito, V. Bondariev and T.N. Kołtunowicz Institute for Nuclear Problems of Belarussian State University, 220030 Minsk, Belarus AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Department of Solid State Physics, al. Mickiewicza 30, 30-059 Krakow, Poland Joint Institute for Nuclear Research, 141980 Dubna, Russia Belarusian State University, 220030 Minsk, Belarus Department of Electrical Devices and High Voltage Technology, Lublin University of Technology, Nadbystrzycka 38A, 20-618 Lublin, Poland

High-temperature thermogravimetric analysis and differential scanning calorimetry of nanocomposites (FeCoZr)x(CaF2)100-x

In this work thermogravimetric-DTG/DSC analysis result for samples of nanocomposite metal-dielectric (FeCoZr)x(CaF2)100-x are presents. Series of samples with, metallic phase content x = 24 – 68 at.% were produced by ionbeam sputtering method in mixed atmosphere of gas argon and oxygen. Study of thermal properties, phase shifts and process of change in mass of nanocomposites were performed using the thermoanalytical system TGA/DSC-1/1600 HF (MettlerToledoInstruments). High-precision weight has a weighing range 1μg – 1g with an accuracy 1μg. The furnace makes it possible to regulate the temperature in range from room temperature to 1600°С and heating rate is 0.01 – 150°С/min. After analysis of the results established that initial and final mass of samples of the nanocomposite (FeCoZr)x(CaF2)100-x are different, namely the sample mass is increased by 2 – 20%. It is related to the oxidation of metallic phase particles of nanocomposite. DTG and DSC analysis demonstrated that oxidation of metallic phase is held in two steps, at first oxidized iron atoms, and followed oxidation of the cobalt atoms, what can be seen on the waveform in the form of two humps and whereby oxides Fe2O3, Fe3O4, Co2O3, Co3O4 are formed. Oxide coatings on the surface of atoms represents an additional barrier to electron transfer charges. When a voltage is applied to the layer of the nanocomposite are three possible ways to transfer of charges between atoms and particles of metal, whereby each has its own relaxation time.

AC electric properties of nanocomposite (FeCoZr)0.818(CaF2)0.182 annealed in the tubular furnace

In this paper the influence of 15-minutes annealing in temperature range 398 K – 723 K with step 25 K on the frequency dependence on conductivity of nanocomposite (FeCoZr)x(CaF2)(100-x) was exanimate. Nanocomposite with metallic phase content x = 81.8 at.% was produced by ion-beam sputtering in mixed argon and oxygen atmosphere. Measurement were made in frequency range 50 Hz – 5 MHz and temperatures from 15 K to 375 K. It was found that to annealing temperature 523 K in measurement temperatures a less than room temperature a weak dependence of dielectric type of conductivity occurs in materials – the conductivity increases with temperature increase. At temperatures above room temperature a phase transition dielectric-metal is observed and a conductivity decreases with temperature increase. Growth stage of conductivity was observed in the frequency range above 105 Hz. The relaxation time for this stage is of the order 10-6 s. Annealing in the temperature above 523 K led to the appearance of additional low temperature stage of conductivity, for which the relaxation time is of the order of 10-4 s. The appearance of the low-frequency stage of conductivity increase is associated with oxidation of surface of nanoparticles of metallic phase during annealing, the growing barrier of potential and relaxation time. Further increase of annealing temperature above 673 K causes a further increase of the width of the barrier, and activation energy becomes so much that relaxation times for low-frequency stage grown above 10-2 s. Therefore, low-frequency stage is moves further into the area of low frequency and it becomes unnoticeable because it go beyond the lower range (50 Hz) of used meter.

Electric properties of nanostructure (FeCoZr)x(CaF2)(100-x) produced in argon Ar atmosphere

The paper presents frequency f and temperature Tp dependences of conductivity σ, capacitance Cp and phase shift angle θ for the nanocomposite metal-dielectric (FeCoZr)x(CaF2)(100-x). Samples of nanocomposite were produced by ion-beam sputtering in pure argon Ar atmosphere. Partial pressure of gas Ar in the ion source pAr=1.1·10-1Pa. Contains of metallic phase in tested sample is x = 54.6 at.%. Studies carried out by stand to measuring of AC electrical properties of nanocomposites and semiconductors. The measurements have been performed using alternating current within the frequency range of 50 Hz - 1 MHz for measuring temperatures ranging from 77 K to 373 K. On the frequency-temperature dependence of phase shift angle θ at low frequencies phase shift have capacitive character and at high frequencies - inductive. Position of fmin on the frequency dependence on capacitance Cp corresponds exactly to the resonance frequency fR for which the angle θ crosses zero. Analysis of the results showed that phenomena similar to phenomena in conventional circuit RLC occur in the nanocomposite (CoFeZr)54.6(CaF2)45.4. Jumping recharging between the defects leads to the formation of dipoles and consequently to the increase of permittivity. After a time τ electron returns to the first defect and dipole disappears. The formation of inductance in nanocomposite is associated with return jumps of electrons from defect with negative charge to the defect with positive charge, set by the time, which are characterized by low values of activation energy.