ULTRASMALL MAGNETIC PARTICLES IN LANGMUIR-BLODGETT-FILMS

Cationic magnetic Fe3O4 particles have been sandwiched between the polar headgroups of arachidate ion monolayers deposited on oxidized silicon substrates. Optical thicknesses of the SiO2 layer on the substrate, the arachidate ion monolayers (A-), and the Fe3O4 particles thereon have been characterized by incident-angle-dependent reflectance measurements, assuming stratified planar structures for these components. The determined values for optical thicknesses (dj) and reflective indexes (nj), dSiO2 = 91.5, 136.2, and 172.5 Å; nSiO2 = 1.46; dA- = 26.7 Å; nA- = 1.52; dFe3O4 = 49.8 Å; and nFe3O4 = 1.976 (in water, system A), agreed well with values predicted by the models used. Similarly, incident-angle-dependent reflective measurements of seven successive units of arachidate ion sandwiched Fe3O4 particles on Langmuir-Blodgett (LB) films have led to an average thickness of 89.2 Å for a single-sandwich unit. Fe3O4 particles were found to be 83.2 Å from each other in the same layer but were located 96.2 Å from each other in neighboring layers. These values indicated that 35% of the substrate had been covered by Fe3O4 particles. Transmission electron micrographs of arachidate ion sandwiched Fe3O4 particles on a cellulose grid gave the average of the center-to-center separation of the particles and the surface coverage 91 ±to 10 Å and 30 ± 15%, respectively. Longitudinal magnetooptical effects for a 12-sandwich unit revealed rod-shaped magnetic domain structures. © 1990 American Chemical Society.