Evidence of stress anisotropy and role of oxygen pressure in growth of pulsed-laser-deposited hexaferrite films

BaFe12O19 films have been grown by pulsed laser deposition (PLD) on (001) sapphire using two different conditions (with and without oxygen). Layers grown in O-2 atmosphere exhibit an epitaxial structure (stressed at the interface) with a perpendicular easy axis whereas magnetic anisotropy is randomly oriented in those deposited without O-2. The random structure is a consequence of the high energy of ions in the PLD plume which damage the smoothness of the substrate at an earlier stage of growth. Oxygen pressure can reduce the energy of arriving atoms and prevent deterioration of the interface sharpness, and lead to epitaxial growth. Stress induces in-plane anisotropy with the coercivity strongly dependent on the temperature (T-0.75 law). An estimate of the stress confirms that it is too low to compete with magnetocrystalline anisotropy. (C) 2003 American Institute of Physics.