Preparation, Growth, and Study of Ultrafine Ferrite Particles

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Abstract
Ultrafine ferrite particles were prepared by a chemical precipitation process below 100°C in an aqueous medium. The resulting materials were grown hydrothermally at moderate temperatures for extended periods of time. Samples were removed at various times during the growing process and their magnetic and physical properties determined. Coercive forces varied from zero to about 800 oe at room temperature for some hydrothermally grown cobalt ferrites. At liquid nitrogen temperature coercive forces to 10 000 oe were measured. Crystallite size measurements were made by x-ray line broadening. An apparatus to measure hysteresis loops in pulsed fields was constructed and used for measuring magnetic properties of samples difficult to saturate, i.e., cobalt ferrite samples at −196°C. Good agreement was obtained between pulsed fields and dc measurements where samples could be measured by both systems.

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