Minoru Satou

Epitaxial growth of ferromagnetic CrO2 films in air

Abstract Epitaxial growth of CrO2 films under atmospheric pressure has been investigated. Single crystal films of CrO2 were obtained by the thermal decomposition of gaseous CrO3 onto the substrates of rutile single crystals in air. The optimum temperature of the substrate for the pure CrO2 epitaxial films was found to be 390°C. At the substrate temperature of 380°C, the obtained film included Cr2O5 as impurities, and Cr2O3 appeared at 400°C. Magnetic domain patterns of these films were observed by longitudinal Kerr effect. The growth patterns of domain were obtained with applied field.

Anomalous increase of coercivity in iron oxide powder coated with sodium polyphosphate

An anomalous increase of coercivity in a non-stoichiometric acicular iron oxide powder which was treated with a chain like sodium metaphosphate was investigated. The coercivity increased by a factor of about 2 in the acicular iron oxides and about 3 in the granular one, respectively. The magnetization decreased in inverse proportion to the increased coercivity. The coercivity of the treated iron oxides which was washed with water to remove the sodium metaphosphate returned to the value or to less than the value of the untreated iron oxides. The large magnetic anisotropy was estimated from the magnetic hysteresis loop. A constricted hysteresis loop was observed in treated iron oxides. The experiment suggests that an origin of the increased coercivity is due to the surface magnetic anisotropy which is based on the electrostatic coupling, participating in a absorbed compound.

High Frequency Conductivity in Cobalt-Iron Ferrite

The frequency dependence of the ac conductivity of polycrystalline cobalt-iron ferrite Co3-xFexO4(1.89x2.08) has been measured in the frequency range 1 kHz~200 MHz and the temperature range 130~300 K. The measured conductivity can be expressed as the sum of two kinds of conductivity σ1 and σ2. σ1 corresponds to the drift of free carriers and σ2 is related to the dispersion of weakly bound carriers. The activation energy of σ1 is much larger than that of σ2. The frequency dependence of σ2 is described as ωn(0.7n0.8). σ1 is independent of frequency in this frequency range. The distribution of the relaxation processes of bound carriers was determined from the frequency dependence of σ2.

Formation of ferrite thin films by vacuum evaporation with annealing process

Cobalt ferrite thin films were prepared in successive processes by vacuum evaporation of cobalt on hematite (αFe 2 O 3 ) films and annealing at relatively low temperature. The surfaces of these films were observed by transmission electron micrograph(TEM) and scanning electron micrograph(SEM), also their structures were identified using transmission electron diffraction(TED) and reflection electron diffraction(RED) methods. Then, a diffusion profile of depth distribution of cobalt ions into (αFe 2 O 3 ) layer was investigated by Auger electron spectroscopy(AES) analysis. Magnetic properties were measured with a vibrating sample magnetometer. Results showed that cobalt ions migrated easily into a (αFe 2 O 3 ) layer at relatively low temperature and formed ferrite thin films in the form of Co x Fe 3-x O 4 . Their magnetic properties, such as high coercive force, large residual magnetization and smooth surface, indicate considerable possibilities to obtain excellent magnetic medium for high density recording disk.

Crystal growth of YAlO3 coexisting with Y3Al5O12 by flux method

Abstract In flux growth by slow cooling, YAlO3 was obtained only when the PbO content of the PbO-PbF2 flux was more than 80 wt%. In the flux evaporation method, however, YAlO3 was grown for a wider range of PbO-PbF2. However Y3Al5O12 was obtained for a PbF2 content of more than about 50 wt%. The influence of the components of the flux on the crystal growth was investigated using X-ray powder diffraction. In the evaporation experiments, Y3Al5O12 started to grow after about 30 h at 1260°C and continued to the 50–60 h mark; after that YAlO3 began to grow as a result of the depletion of flouride in the melt.

Effects of Co-Ti on the crystal growth of rare earth orthoferrite and orthoaluminates

Abstract Co-Ti ions prevented the crystal growth of ErFeO 3 . In the RA1O 3 , however, Co-Ti ions promoted the crystal growth. Among the YAlO 3 , EuAlO 3 and GdAlO 3 the tendency to substitute Co-Ti for Al 3+ increased with increasing the ionic radius of R 3+ .