IRON NITRIDE-BASED MAGNETIC POWDER, PROCESS FOR PRODUCING THE SAME, AND MAGNETIC RECORDING MEDIUM

摘要

An iron nitride-based magnetic powder comprising magnetic particles which each has a core consisting mainly of an Fe<SUB>16</SUB>N<SUB>2</SUB> phase and further has, outside the core, an oxide phase derived from an iron metal phase resulting from reduction of the iron nitride and which have an average particle diameter of 20 nm or smaller. The iron nitride-based magnetic powder has a weatherability index ?ss and a saturation magnetization ss which satisfy the relationship ?ss=0.8×ss-30. In the relationship, ?ss is (ss-ss<SUB>1</SUB>)/ss×100, provided that ss<SUB>1</SUB> represents the saturation magnetization of the magnetic powder as measured after one-week standing in an atmosphere of 60°C and 90 %RH. This powder can be obtained by exposing powder particles consisting mainly of an Fe<SUB>16</SUB>N<SUB>2</SUB> phase to a reducing gas to convert a surface region of each particle to an iron metal phase (gradual reduction treatment) and then exposing them to an oxidizing gas to convert a surface region of the iron metal phase to an oxide phase (gradual oxidation treatment).