Influence of the oxygen pressure and annealing time in the magnetic and structural properties of Barium Ferrite thin films

C. I. ZANDALAZINI; M. I. OLIVA; J. C. FERRERO

Manizales

Workshop; IX Latin American Workshop On Magnetism, Magnetic Materials And Their Applications; 2010

Universidad Nacional de Colombia

The characteristic of the low losses at microwave frequencies, high resistivity and strong magnetic coupling obtained for Ferrite materials, making them irreplaceable constituents in microwave device technology. They can provide unique circuit functions that cannot be reproduced with any other materials. Moreover, the Ferrite is considered a material for the next generation magnetic microwave devices.Our present work is focused in the influence of the oxygen pressure in the growth of Barium Hexaferrite (BaM) films deposited by Pulsed Laser Deposition on substrates of SiO2/(100)Si using a BaM stoichiometric target.Three deposits in high purity oxygen atmosphere with pressure of 45, 100 and 850 mTorr were made samples A45, B100, and C850 respectively. For the deposition of each sample, we use a laser of Nd-YAG (wavelength 532 nm, 2.3 J/cm2 (p/pulse), 6 ns pulse duration and 10 Hz repetition rate) during 60 minutes.The deposits were carried out at room temperature, and later on they received an ex-situ annealing in air at 900ºC. The thermal treatment was carried out in four stages according to the annealing time, 2, 10, 60 and 180 minutes. In each one of these stages, magnetic properties were measured in a Vibrant Sample Magnetometer (VSM) with applied field in parallel and perpendicular direction to the surface of the film. Structural characterization was achieved by means of a X-ray Difractometer (XRD). The as-prepared films show amorphous structure and diamagnetic behavior. Fast annealing (2 minutes) was enough to crystallize the BaM polycrystalline phase in A45 and B100 films. The later annealing crystallize Barium ferrite in C850 film and increase the crystal size of the films. The topographical characteristics were studied by means of a Atomic Force Microscope (AFM) for fast and last annealing stage, corroborating an increment in the grain size. Magnetic behavior depends of both, oxygen pressure deposition and annealing time. Coercive field (HC) decreases with the increment in the pressure of O2 in the first annealing, but this difference is attenuated with the increment of annealing time. Beside, a decrease in the magnetic moment per area (mS [emu/cm2]) was observed with the increase oxygen pressure. Although the XRD patterns didn't show a preferential orientation, in the magnetic behavior it was found that the pressure of O2 has bigger influence over magnetic behavior when parallel applied field to the film was applied, however, this difference becomes smaller as the time of annealing is increased.