The properties of mechanically activated powders consisting of 17.0 wt% Fe<inf>2</inf>O<inf>3</inf>, 4.4 wt% MnCO<inf>3,</inf> 3.6 wt% ZnO and 75.0 wt% BaTiO<inf>3</inf>

Abstract

A novel multiferroic composite material, composed of a mixture of nanocrystals of BaT1-xMexO3 and MeFe12O19 (Me = Zn and Mn) and an amorphous phases of BaTi1-xMexO3, MeFe12O19 and MeFe2O4, is synthetized. The composite material consisting of the mixture of nanocrystals of Fe2O3, ZnO and BaTiO3 embedded into the amorphous phase of MnCO3 is obtained by grinding the powder mixture of 17.0 wt% Fe2O3, 4.4 wt% MnCO3, 3.6 wt% ZnO and 75.0 wt% BaTiO3 for 20 min. The powders as-ground for 80 min and more are composed of the mixture of nanocrystals of Fe2O3 and BaTiO3 embedded in the amorphous phase of Fe2O3, ZnO, BaTiO3 and MnCO3. With increasing grinding time, formation of the composite with finer particles, a lower mean size of nanocrystals, higher content of the amorphous phase and higher magnetization is observed. The magnetization of the pressed samples increases with increasing grinding time. Grinding declines the amount of large weakly-ferromagnetic crystals of hematite, however it increases the quantity of paramagnetic small nanocrystals and the amorphous phase. The powder is thermostable up to 280 °C. Annealing above 280 °C results in the decrease in the magnetization of the cooled sample as a consequence of crystallization of the amorphous phase and enlargement of the size of nanocrystals. When sintering for 2 h at 1200 °C, the mixture of nanocrystals of BaTi1-xMexО3 and MeFe12O19 embedded into the amorphous matrix composed of BaTi1-xMexO3, MeFe12O19 and MeFe2О4 is formed. The sintered samples ground for longer periods of time are mainly composed of the amorphous phase and fine nanocrystals. Grinding of powders for less than 100 min results in the sintered samples with a granular structure, whereas the samples obtained from powders ground for more than 160 min are relatively compact. The magnetization of the sintered samples declines with increasing grinding time to 180 min due to transformation of nanocrystals into the amorphous phase. Further increase in grinding time from 180 to 240 min causes the increase in the magnetization, resulting from the effect of sintering. The magnetization of the sintered samples ground for more than 240 min declines with increasing grinding time, since the amount of the amorphous phase rapidly increases when grinding above 240 min. The samples sintered from the powders ground for 240 min show the compact structure and maximum magnetization.