Surface layers investigation of Co-implanted $\mathrm{BaTiO}_3$

Monocrystalline $\mathrm{BaTiO}_3$ were implanted by cobalt ions with high fluence to create multiferroic material. Element composition, surface morphology, optical and magnetic properties of Co-implanted $\mathrm{BaTiO}_3$ were analyzed by scanning electron microscopy, optical spectroscopy, and inductive magnetometry. After the ion implantation the transparent samples of $\mathrm{BaTiO}_3$ became grey due to the radiation damage of their crystal structure and acquired a characteristic metallic luster due to the precipitation of implanted impurity in the form of metal cobalt nanoparticles. With the fluence growth the magnetic response of $\mathrm{BaTiO}_3$ samples changed from superparamagnetic to ferromagnetic. Further thermal anneal in the air atmosphere leaded to the reconstruction of crystal structure, suppressed ferromagnetism and coloured the samples in yellow. Magnetic measurements made it possible to define cobalt particle size and their concentration. Ferromagnetic response disappears after the anneal at $T=450^\circ$ C due to the oxidation of the cobalt nanoparticles.