Электрофизические свойства поликристаллических пленок BiFe-=SUB=-0.95-=/SUB=-Co-=SUB=-0.05-=/SUB=-O-=SUB=-3-=/SUB=-

Semiconductor BiFe0.95Co0.05O3 thin-film compounds were obtained by a flare technique. The surface morphology of the films and the effect of electronic doping by replacing trivalent iron with cobalt ions on the structural, optical, magnetic, and kinetic properties in the temperature range 77-600 K in magnetic fields up to 12 kOe are studied. The existence of two relaxation channels in the impedance spectrum at frequencies of 0.1–1000 kHz has been established. The negative magnetoresistance in the anomalous magnetization region and the maximum magnetoimpedance in the vicinity of the surface phase transition has been found. Using the Hall effect measurements, carrier types prevailing in the magnetoresistance and magnetoimpedance effects has been found. The magnetization anomalies are explained using the model of superparamagnetic clusters and the magnetoresistance is attributed to the scattering of carriers by the spin fluctuations.

Magnetometric Study Of ZnO/CoO Nanocomposites

ZnO nanoparticles doped with transition metal ions are intensively studied nanomaterials, due to their charges and the spins of electrons that provides new magnetic, optical and transport properties. They find a vast range of applications, ranging from optoelectronics to spintronics. In this context especially important is the room temperature ferromagnetism observed for ZnO doped nanomaterials, although this phenomenon is still a controversial and open topic in material science, mostly due to low reproducibility of results from samples prepared by different techniques. In the first part of this article a short review of papers using magnetometric methods to determine the magnetic characteristics of Co-doped ZnO nanomaterials is presented. Different models introduced to explain room temperature ferromagnetism (carrier mediated ferromagnetism, Co2+-oxygen vacancy pairs, blocked superparamagnetic clusters, Co2+-Zn interstitial pairs, heterogeneous distribution of magnetic ions) are examined and discussed. In the second part, magnetisation study of a new series of nCoO/(1-n)ZnO nanocomposites synthesized by hydrothermal method under higher than previously applied pressure will be described. The obtained experimental results will be analysed and information on magnetic systems responsible for the observed characteristics and the involved magnetic interactions will be deduced.