Effect of wavelength, deposition temperature and substrate type on cobalt ferrite thin films grown by pulsed laser deposition

In pulsed laser deposition, the laser irradiation wavelength and the substrate nature and temperature crucially affect the composition, crystallinity, structure and magnetic properties of the grown deposits. In this work, cobalt ferrite (CoFe₂O₄) thin films were deposited on Si (1 0 0) and SrTiO₃ (1 0 0) single crystal substrates at room temperature and 770 K using laser wavelengths of 213, 532 and 1064 nm. The deposited films were characterized by atomic force microscopy to determine the surface morphology, by X-ray diffraction to examine their crystallinity, and by micro-Raman, scanning electron microscopy/energy-dispersive X-ray spectroscopy, X-ray photoelectron and Mössbauer spectroscopies to investigate their composition and stoichiometry. Magnetic characterization was carried out by superconducting quantum interference device magnetometry. At 770 K and 1064 nm, the films consisted of single-crystal CoFe₂O₄ ((1 0 0) orientation) when grown on SrTiO₃, and of polycrystalline CoFe₂O₄ when grown on Si. The composition of the films became more complex at shorter wavelengths as they contained magnetite and other minority phases in different concentrations. The crystalline quality of the films also decreased with decreasing wavelength even including superparamagnetic species. In general, for the same wavelength, the deposits obtained at room temperature were less crystalline than those produced with the substrate heated at 770 K.