Iron oxide powder for undercoat layer of coat-type magnetic recording medium having multilayer structure and a process of producing the same

摘要

Iron oxide powder for an undercoat layer of a coat-type magnetic recording medium having a multilayer structure which comprises cobalt-doped iron oxide particles having an average length of 0.02 to 0.3 mum, an aspect ratio (length to width ratio) of 2 to 13, and a BET specific surface area of 40 to 100 m²/g, containing a cobalt compound in an amount of 0.2 to 10 atom % in terms of cobalt based on total iron, and having a pH of 6 to 8, a soluble cation content of 50 ppm or less, and a soluble anion content of 50 ppm or less.