Susamu Taketomi

Transparent magnetic fluid: preparation of YIG ultrafine particles

Abstract In order to prepare transparent magnetic fluid, yttrium iron garnet ultrafine particles ranging in size from 10 through 30 nm are synthesized by hydrolysis of metal alkoxides. Differential thermal analysis, X-ray diffraction analysis, electron micrography and magnetization measurements are carried out on these particles to investigate the calcination condition and particle sizes.

Temperature and Concentration Dependence of Magnetic Birefringence of Magnetic Fluids

It was found experimentally that the magnetic birefringence of magnetic fluid thin films obeys a Curie-Weiss like law for all kinds of magnetic fluids except for a water-based one. The birefringence can be described by θ( T , H )=θ a f ( H )/[ T - T a + f ( H )], where θ( T , H ), H and T are the phase difference, the applied field and the temperature of the film, respectively, and θ a is a positive constant. T a and f(H) are also found to be expressed empirically by T a = T 0 +κ ln c , f ( H )=1-exp [-α( c ) H ], respectively, where c is a volume fraction of the colloidal particles, T 0 , κ are positive constants and α( c ) is a function of c . Taking the empirical expression of θ into consideration, the free energy of the magnetic fluid is discussed using Landaus phase transition theory.

FIELD DEPENDENCE OF MAGNETIC BIREFRINGENCE OF MAGNETIC FLUID IN LOW-MAGNETIC-FIELD REGION

The magnetic-field, H , dependence of the magnetic birefringence of two kinds of magnetic fluid thin-film samples was measured in a region with a low magnetic field of less than 150 Oe. While the magnetic fluid of one sample had been exposed in a vacuum state for several minutes before the optical measurement, that of the other had not. The birefringence Δ n of the former sample is proportional to H 2 , but Δ n of the latter is in proportion to H in the low-field region. The magnetic birefringence of the former sample is attributed to the interaction between an individual magnetic colloidal particle and the external field, but that of the latter is due to the interaction among the colloidal particles exerted by the field.

Electron diffraction of yttrium iron oxide nanocrystals prepared by the alkoxide method

Abstract Yttrium iron garnet (YIG) ultrafine particles of several nanometers in diameter were prepared by the alkoxide method. The phase transformation of the particles during the course of calcination was studied in detail by transmission electron microscopy. A small fraction of the uncalcined amorphous particles was spontaneously crystallized into e-Fe 2 O 3 . The amorphous phase undergoes incomplete crystallization by forming an intermediate phase at 660°C calcination. Complete crystallization to YIG does not occur at temperatures lower than 675°C. A small amount of YFeO 3 and Fe 32 Y 12 O 2 (intermetallic compound) nanocrystals were also formed at calcination temperatures as low as 660°C. In selected area electron diffraction (SAED) experiment of the present YFeO 3 nanocrystals, we found a peculiar selection rule; we observed strong diffraction from the lattice planes, (i, j, k) , if the sum, i + j + k was odd, and weak or no diffraction from other planes. In the SAED experiment of YIG nanocrystals, we found that the diffraction rings fluctuated in the radial direction.

PECULIAR SPONGE-LIKE STRUCTURE OF YTTRIUM-IRON-GARNET NANOCRYSTALS ON QUARTZ SUBSTRATE SURFACE

Nanoscale amorphous yttrium–iron–garnet (YIG) particles were prepared by the alkoxide method. They were dispersed in a kerosene solvent, coated on a quartz plate substrate, and calcined at a temperature of 1273 K for 2 h. Surface morphology and cross-sectional microstructure of the thin coated films were examined by atomic force microscopy and transmission electron microscopy, respectively. During the calcination, amorphous YIG particles were transformed to YIG nanocrystals of ≈25 nm in mean diameter, and no extended grain growth or fusion of the multigrains was observed. Each particle was individually crystallized, but interconnected to each other, forming a sponge-like structure of 600 nm in thickness. Electron diffraction and energy dispersion x-ray analysis verified that the sponge-like layer consisted of YIG nanocrystalline particles. A rather dense intermediate layer of ≈100 nm in thickness was formed as a result of interfacial reactions between YIG and SiO2 decomposing to α-Fe2O3 and Y2Si2O7. The c...

Light absorption spectra of YIG ultrafine particles prepared by alkoxide method

Quartz, glass plate samples dispersed with YIG ultrafine particles about 30 nm in mean dimension were prepared through synthesis by the alkoxide method. Using these samples, the light absorption spectra of the YIG ultrafine particles were measured from the wavelength /spl lambda/=450 nm up to 1800 nm. The peak of the spectra of the YIG ultrafine particles around /spl lambda/=600 nm is shifted to a lower wavelength, while the peak around /spl lambda/=900 nm is shifted to a higher wavelength compared with those of bulk YIG. In addition, the latter peak broadens. >