Influence of synthesis parameters and thermal treatment on functional properties of Fe3O4-BaTiO3 multiferroics obtained by mechanical activation

Abstract

Mechanical activation of a mixture of polycrystalline powders Fe3O4 (50% wt.) and BaTiO3 (50% wt.) was performed in a planetary ball-mill, with different milling times (3 h, 6 h and 12 h). Average crystallite size determined by XRD analysis ranges from 12 to 30 nm, depending on the milling time. The activated powders were pressed into disc-shaped samples, 8 mm in diameter and 1.5 mm thick, applying the pressure of 500 MPa,. Thermoelectric measurements conducted in the temperature range from room temperature to 350 °C revealed that the electrical resistivity of the sample depends on temperature and activation time. At room temperature, the maximum value of specific electrical resistivity (ρ0 = 1 MΩm) was observed for the sample obtained by pressing the powder activated for 6 h. Magnetic properties of pressed powder samples were studied using a modified Faraday method. At room temperature, the pressed powder activated for 3 h exhibited the maximum value of magnetization, M0= 0.86 Am2/kg. Multiple heating of the pressed samples, for 10 min, was performed in a magnetic field of 20 KA/m. After cooling, the highest magnetization values were observed for the samples previously heated at 380 °C, while the maximum one (M’= 1.04 Am2/kg) corresponds to the sample activated for 3 h.