SURFACE LAYERING OF A MAGNETIC FLUID STUDIED BY X-RAY REFLECTIVITY. Isao Takahashi, Yasunori Tsukahara⁺, Koichi Akimoto⁺, and Ayahiko Ichimiya⁺, School of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan, Department of Quantum Engineering, Nagoya University, Chikusa-ku, Nagoya 464, Japan

X-ray surface scattering measurements on a free surface of a magnetic fluid were performed at various temperatures from 250K to 450K. The former temperature is close to the freezing point and the latter is near the decomposition temperature of the disperse medium. All reflectivity data, collected to momentum transfer as large as Q (= 4[[pi]]sin[[theta]]/[[lambda]]) = 0.15Å^-1, exhibit a broad maximum near 0.06Å^-1. This indicates a layer spacing which is comparable to the size of the mean value of the magnetic fine particles.

In the present study, an analysis was carried out based on kinematical scattering theory by adopting two steps: direct Fourier transformation from the reduced intensity to a density-gradient convolution function; followed by non-linear least squares fitting. In the second process, from the convolution function, we can obtain the electron density function. At 300K, the magnitude of the electron density oscillations decays with a characteristic length of 51Å. In addition, the amplitude of the first peak at the surface is l.9[[rho]]_o. This is much larger than that of monoatomic liquids like Hg or Ga. Surface effects of this interesting colloidal solution will be discussed through the temperature variation of the electron density function.