Search

The effect of the milling of virgin ZnO and MgO powders on structural, optical, and electrical properties of Mg0.2Zn0.8O ceramics is studied. In all Mg0.2Zn0.8O ceramics, both cubic and hexagonal phases of solid solution are formed simultaneously. The hexagonal phase is represented by densely sintered grains that are doped with magnesium homogeneously. The crystallites of cubic phase of solid solution turn out to appear in large pores. The infrared reflection spectra show that the milling of intial powders does not affect free carrier concentration in hexagonal grains. It is found to be close to that of ZnO being determined by Zn interstials. For ceramics sintered from virgin powders, a decrease of direct current conductivity of Mg0.2Zn0.8O in comparison with that of pure ZnO occurres, which is being caused by the appearance of barriers, the nature of which may be ascribed to the fluctuations in the bandgap and/or electron concentration. For ceramics sintered from milled powders, an increase in DC conductivity of all samples is found and attributed to the formation of conductive channels along the grain boundaries via their enrichment in Zn and Mg due to mechanical stress. A chemical mapping of the ceramics supports this effect. [ABSTRACT FROM AUTHOR]

The effect of calcination temperature ( TC = 500-1000 °C) and cooling rate on the dopant distribution in Cu-doped Y-stabilized ZrO2 nanopowders is studied. The powders are produced by co-precipitation technique and investigated by attenuated total reflection, UV-vis diffuse reflectance, electron paramagnetic resonance, and transmission electron microscopy methods. The cooling rate is found to affect the amount of Cu substances on grain surface, the powders subjected to fast cooling (quenching) showed higher amount of Cu-related complexes on the grains' surface than their counterparts cooled with furnace after calcination. It is observed that Cu impurities diffuse inside ZrO2 grains from Cu-related surface substances when TC < 800 °C. This process is accompanied by the enhancement of 275-nm absorption band caused by oxygen vacancies formation. For TC > 800 °C, outward migration of Cu dopants takes place. Simultaneously, the intensity of 275-nm absorption band decreases, the monoclinic ZrO2 phase forms and its contribution rises with TC. It is proposed that monoclinic phase formation is caused by the replacement of Cu atoms from lattice sites to interstitials leading to an appearance of the channels for Y out-diffusion via cation vacancies and destabilization of ZrO2 tetragonal phase. [ABSTRACT FROM AUTHOR]

Mechanisms of the recently demonstrated ex-situ thermal control of the indirect exchange coupling in magnetic multilayer are discussed for different designs of the spacer layer. Temperature-induced changes in the hysteresis of magnetization are shown to be associated with different types of competing interlayer exchange interactions. Theoretical analysis indicates that the measured step-like shape and hysteresis of the magnetization loops is due to local in-plane magnetic anisotropy of nano-crystallites within the strongly ferromagnetic films. Comparison of the experiment and theory is used to contrast the mechanisms of the magnetization switching based on the competition of (i) indirect (RKKY) and direct (non-RKKY) interlayer exchange interactions as well as (ii) indirect ferromagnetic and indirect antiferromagnetic (both of RKKY type) interlayer exchange. These results, detailing the rich magnetic phase space of the system, should help enable the practical use of RKKY for thermally switching the magnetization in magnetic multilayers. [ABSTRACT FROM AUTHOR]