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

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 5 nm in thin surface layer of monocrystalline plate of BaTiO3. On the other hand, larger nanoparticles of cobalt with sizes from 5 up to 40 nm 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.