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Abstract

This work had three aims. In the first part the influences of the sizes of the particles of
barium ferrite (BaM) and their magnetic properties on the stability of the suspension were
investigated. In second part the deposits were prepared by electrophoretic deposition
(EFN) and the influence of particle size, stability of the suspension, EFN conditions and
external magnetic field on the orientation of film was studied. In third part the influence
of the grain size and the sintering temperature on the density and the orientation of films
was studied.
The plate-like particles of BaM were synthesized using the hydrothermal method,
where the particle size was controlled by the synthesis temperature. The surfaces of the
particles were modified with a double layer of the surfactant dodecylbenzenesulphonic
acid (DBSk) and the particles were dispersed in organic solvents. The stability of the
suspension was influenced by the polarity of the organic solvent and the most appropriate
suspensions for EFN were prepared in 1-butanol. The adsorption of DBSk onto the
particle surfaces was observed with infra-red spectroscopy and the zeta-potential, which
was around 100 mV. The stability of the suspensions, which depends on the magnetic
properties of particles and the conductivity of suspension, was defined with a
sedimentation test.
The particles were deposited from the suspension by EFN onto the substrate. The mass
and the thickness of the deposit were linearly increased with the time of deposition and
the voltage. The mass of the deposit was influenced by the particle size and was higher
for larger particles. The theoretical electrophoretic velocity and the theoretical mass of the
deposit were calculated and they showed that the electrophoretic velocity of the
anisotropic particles increased with the particle size and depends on the orientation of the
particles during the migration to the electrode. The orientation of the particles in the
deposit is a consequence of the change of the direction of the hydrodynamic force near
the electrode. The influence of the forces on the orientation of the films was studied with
a different position of the electrodes with regard to the gravitational force. The deposit
had the highest orientation if it was prepared in the horizontal position of the electrodes
on the lower electrode. Here the orientation is increased due to the potential energy of
particles, which is the lowest when the particle lies parallel on the substrate. The highest
orientation came with the thinnest films, prepared at the lowest voltage and with the
shortest time. The orientation of the thicker films can be increased by EFN, where the
voltage was increased by steps. For the smallest particles the orientation of films can be
improved by applying an external magnetic field.
The films on the substrate were sintered to increase the density and the orientation. In
the oriented deposits, prepared by EFN, the larger, oriented particles grow at the expense
of the smaller mis-oriented particles and the orientation is increased with an increasing
grain size. The orientation of the sintered films was determined from the magnetic
properties and from x-ray diffraction measurements. The films with the best properties
were prepared in the horizontal position of the electrodes on the lower electrode and
sintered at 1150 °C. The ratio between the remanent magnetization and the saturation
magnetization of these films with thickness of 1 and 25 µm was 0.88.