Kimiyoshi Goto

Preparation of small particles of SrFe 12 O 19 with high coercivity by hydrolysis of metal-organic complexes

Small particles (50-60nm) of Sr ferrite (SrFe 12 O 19 ) have been synthesized by the hydrolysis method of metal-organic complexes such as metal acetylacetonates or metal ethoxides and subsequent heat-treatments of the precipitates, and their magnetic properties have been studied. X-ray, Mossbauer and electron-microscope studies have been conducted to examine the mechanism of the formation. A coercive force of 6700 Oe, one of the highest values reported so far for isotropic SrFe 12 O 19 samples and close to the theoretical limit, has been obtained. Some of their magnetic properties have been discussed in terms of magnetism of small particles.

Studies on Magnetic Domains of Small Particles of Barium Ferrite by Colloid-SEM Method

Magnetic domains of barium ferrite particles less than 10 to 1 µm in size which are on surfaces of as-sintered blocks have been observed by colloid-SEM method, a modified Bitter method, with magnifications from 20000 to 45000. The number of domains in a particle decreases with reduction of particle size on average. Below about 2 µm in size each particle comprises two domains. It is shown that domain structure of the two-domain particle is plate-like, and the particle shape is found to be a double hexagonal pyramid with c-plane approximately. A single-domain particle 1.3 µm in size has been observed successfully. The possibility of the twisted domain wall in small multidomain particles is suggested from the obtained patterns of the magnetite powders.

Magnetic Properties of W-Type Hexaferrite Powders

An investigation was undertaken to elucidate the preparation conditions and magnetic properties of W-type hexaferrite powders with the formula AM2Fe16O27 (A=Ba or Sr, M=Fe2+, Zn+Cu, Zn+Cd, Zn+Mg). A pure W-phase was formed by firing a mixture of carbonates and oxides in the appropriate molar ratio at 1200^° ~1400^°C in an atmosphere of PO2 /(PO2 +PN2 )=10-2 ~10-6 or in air. The values σs=70 ~79 emu/g, Hc=400 ~2000 Oe, σr/σs ~0.90 and Tc=350^° ~500^°C were obtained for the oxide powders, aligned along the c axis.

Observations on Perpendicular Magnetic Recordings of High Recording Densities on Co-Cr Films by the Colloid-SEM Method

Perpendicular magnetic recordings of 5 to 100 kBPI densities on evaporated Co-24 wt%Cr films of 2200 A in thickness have been observed by the colloid-SEM method and by the conventional magnetic powder pattern technique. The latter technique, using an optical microscope, gives satisfactory results for recording densities of 5 and 10 kBPI. For high recording densities of 50 and 100 kBPI, clear recorded patterns have been successfully obtained by the colloid-SEM method where dried powder patterns are made under external magnetic fields of 200 to 300 Oe applied vertically to the film planes. It is shown that a better recording can be determined from the obtained patterns, even in high-density recordings. Some discussions are given regarding the relation between the single-domain behaviour of columnar grains in the films and obtained recorded patterns.

Influence of Substrate Temperature on Magnetic Properties and Domains of Amorphous Tb31Fe69 Films

Magnetic properties and domains have been studied for amorphous Tb31Fe69 films prepared by flash evaporation with substrate temperatures Tsub=77 K, 300 K and 473 K. With the increase of Tsub, the perpendicular uniaxial anisotropy conslant of 106 erg/cm3 order increases rapidly from negative to positive. From domain observations on films having positive perpendicular anisotropy, it is found that in film with Tsub=300 K the reversal of magnetization takes place by the rotation of magnetization without domain wall displacement, while when Tsub=473 K the reversal proceeds by nucleation and growth of narrow reverse domains.

A Study of the Magnetic Domains of Isolated Fine Particles of Ba Ferrite

Isolated Ba ferrite particles are prepared by the conventional powder metallurgical method, and the magnetic domains of about 200 particles 0.5 to 5 µm in size are investigated by the colloid-SEM method (the Bitter method using a scanning electron microscope). The relationship between the three-dimensional sizes of Ba ferrite particles and their magnetic domain states is clarified. It is found that the critical size of isolated single-domain particles of Ba ferrite is somewhat larger than the value calculated using the magnetic domain theory.

Magnetic Domains of Single-Domain Particles of SmCo5 Observed by the Colloid-SEM Method

Magnetic domains of ball-milled small particles of the SmCo5 phase below several microns in size have been observed by the colloid-SEM (scanning electron microscope) method, a modified Bitter method. Domains on the c plane of single-domain particles were found when the particle size decreased. Measurements show that sizes of two single-domain particles are 2.2 and 1.6 µm. These values are discussed with the theoretical critical sizes for the single-domain particles of SmCo5.

Magnetic properties and structures of amorphous Tb 31 Fe 69 thin films

Magnetic films of Tb 31 Fe 69 were prepared with substrate temperatures from 77K to 773k by flash evaporation and the perpendiculer anisotropy Ku has been studied with the amorphous nature. In a substrate temperature range of 77K to 623K, all films are amorphous and Ku increases up to 7×106erg/cm3with the increase of the substrate temperature. A columnar structure could not be found in this range. The annealing effect for Ku was examined together with structure analysis.

Preparation and Magnetic Properties of Sm-Co Films with High Substrate Temperatures

Thin magnetic films with an approximate composition of Sm2Co7.8 were prepared on quartz substrates at high temperatures from 150° to 750°C by rf sputtering method. Film structures and magnetic properties have been studied. With the increase of the substrate temperature, the coercive force increases and then decreases through a well-reproducible maximum value of 11 kOe at 400°±50°C. It is shown by X-ray analyses that fine crystallites of SmCo5, Sm2Co7 and Sm2Co17 phases coexist in films with high coercive forces.

Magnetic domains of a sintered SmCo5 magnet

Magnetic domains of a press‐sintered SmCo5 magnet with a high intrinsic coercivity (IHc = 12 700 Oe) and energy product [(BH)max = 18.0 MGOe] were observed in the demagnetized state by the powder pattern technique. The domains on the surfaces parallel and perpendicular to the alignment direction and at grain boundaries are shown in detail. The domain structures observed are of the same type as those for thick crystals with high uniaxial anisotropy, such as MnBi and BaFe12O19.