Magnetic, Structural, and Dielectric Properties of Bi1-xKxFeO3 Thin Films Using Sol-Gel

Bismuth iron oxide (Bi1-xKxFeO3) thin films are prepared using sol-gel and the spin coating method. Films are deposited onto copper substrates and are annealed in the presence of vacuum with 500 Oe magnetic field at 300 degrees C. Potassium has an ionic radius of 1.64 angstrom and replaces Bi, which has an ionic radius of 1.17 angstrom. Based on the ionic radii difference of Bi3+ and K+, the dopant concentration is varied in the range x = 0.0-0.3. X-ray diffractometer analysis shows that at x = 0.3 an impurity phase (K2O) appears, which was not present at low dopant concentrations. It is shown here that ferromagnetic behavior arises in doped BiFeO3 films due to suppression of helical spin structure. In addition, as K+ replaces Bi3+ the charge compensation mechanism gives rise to oxygen vacancies and to the formation of Fe4+ cations, thus inducing ferromagnetic behavior. Variation in dopant concentration strongly affects the dielectric properties. Increase in dielectric constant up to similar to 84 was observed with increase in dopant concentration up to 0.15. Decrease in dielectric constant (similar to 25), beyond 0.15 doping concentration, might have been observed because of the appearance of impurity phase as is observed in structural and magnetic properties.