Structural, magnetic and magnetoelectric studies of BaTiO3:Co nanocomposite films formed by ion-beam methods

Abstract

Thin-film samples of ferroelectric barium titanate (BaTiO3) with cobalt nanoparticles were obtained by using either ion implantation or ion beam sputtering deposition (IBSD) techniques. The samples were characterized using X-ray diffraction, transmission electron microscopy, magnetometry and ferromagnetic resonance to investigate the efficiency of above ion-beam methods in the synthesis of magnetoelectric nanocomposite materials. Our structural studies show that high-fluence implantation with Co+ ions results in the formation of cobalt nanoparticles with mean size of 5nm in thin surface layer of monocrystalline plate of BaTiO3. On the other hand, larger nanoparticles of cobalt with sizes from 5 up to 40nm are formed in polycrystalline BaTiO3 matrix only after high-temperature annealing of BaTiO3:Co composite film prepared by IBSD method. Both types of thin-film nanocomposite samples have similar magnetic hysteresis curves in the sample plane. However Co-implanted BaTiO3 reveals strong uniaxial magnetic anisotropy for out-of-plane orientation, while BaTiO3:Co nanocomposite film demonstrates almost isotropic magnetic response. Strong magnetoelectric effect are observed in Co-implanted BaTiO3, and no magnetoelectric coupling are detected in BaTiO3:Co nanocomposite film formed by IBSD with subsequent high-temperature annealing.