Platelike magnetic powder and a recording medium which uses the platelike magnetic powder

Claim 1

An iron oxide magnetic powder of platelike particles, having a composition expressed by the formula: MFe.sup.II.sub.m-x-2[x]z Fe.sup.III.sub.12+2(m+n)-y A.sup.II.sub.x B.sup.III.sub.y C.sup.IV.sub.z O.sub.p where: M is a metallic element comprising at least one of Ba, Sr, Pb and Ca; A is at least one metallic element selected from the group consisting of Co, Cu, Ni, Zn and Mn; B is at least one metallic element selected from the group consisting of Cr, Al and In; C is at least one metallic element selected from the group consisting of Ti, Zr, Ge and Sn; x is 0.70 to 1.86; y is 0 to 0.11; z is 0.70 to 1.80; p is a number of oxygens satisfying electric neutrality; and each of m and n is a positive number satisfying the relation: 21.30≧12+3m+2n-z≧14.90, wherein each of the particles has a magnetoplumbite and spinel crystal structure, in which layers each comprising R blocks and layers each comprising S blocks are alternately arranged, where: each of the R blocks is defined as a crystal block which contains Fe 3+ ions and has, in parallel with a c plane of the magnetoplumbite structure, three layers in which a layer containing one M 2+ ion and three O 2- ions is arranged between two layers each containing nine O 2- ions; and each of the S blocks is defined as a crystal block which contains Fe 3+ ions and has, in parallel with the c plane, two symmetrical layers each containing four O 2+ ions, and wherein, in each of the particles, part of the R blocks are lacking in M 2+ ions such that said part is replaced by S blocks to reduce the number of the R blocks whereby the number of the S blocks is larger than that of the R blocks.