POWDER FOR SUBLAYER OF COATING TYPE MAGNETIC RECORDING MEDIUM

A powder for an underlayer of a coating-type magnetic recording medium, which powder comprises flat-acicular iron oxide particles having an average major axis length of 20 - 200 nm, a short axis cross-section taken perpendicularly to the long axis that has a long width and a short width, and a short axis cross-section ratio defined as the ratio of the long width to the short width that is greater than 1.3 and substantially uniform in the long axis direction, the powder having a specific surface area measured by the BET method of 30 - 100 m2/g. The underlayer powder preferably contains 0.1 - 5.0 wt% of P and, optionally, an amount of R (R representing one or more rare earth elements, defined as including Y) such that R/Fe expressed in atomic percentage (at.%) is 0.1 - 10 at.%.