POWDER FOR THE LOWER LAYER OF A MAGNET RECORDING MEDIUM OF THE TYPE OF COATING

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A sublayer powder comprises flat acicular iron oxide particle having average length of 20-200 nm along major axis. The cross-section of minor axis is perpendicular to major axis, and has a long width (WL) and a short width (WS). The cross-section ratio of long width to short width is 1.3 or more and the powder has specific surface area of 30-100 m2>/g. A sub-layer powder comprises flat acicular iron oxide particle having average length of 20-200 nm along major axis. The cross-section of minor axis is perpendicular to major axis, and has a long width (WL) and a short width (WS). The cross-section ratio of long width to short width is 1.3 or more, which is uniform in the direction of major axis. The powder has a specific surface area of 30-100 m2>/g measured by BET method. The powder contains 0.1-5 wt.% of phosphorus and at least one element chosen from rare group elements including yttrium. The atomic ratio of rare earth element and iron is 0.1-10%.