| 摘要 |
PROBLEM TO BE SOLVED: To obtain such a recording medium that rewriting is impossible after signals are recorded and that the output level decreases after a predetermined effective period to render reproducing impossible by incorporating as a magnetic powder, one or more kinds of magnetic powder selected from among γ-iron oxide magnetic powder, Co-contg. γ-iron oxide magnetic powder and Ba-ferrite magnetic powder, and a MnBi alloy magnetic powder by 90/10 to 60/40 weight ratio into a magnetic layer. SOLUTION: This magnetic recording medium has a magnetic layer containing as a magnetic powder, one or more kinds of magnetic powder selected from among γ-iron oxide magnetic powder, Co-contg. γ-iron oxide magnetic powder and Ba-ferrite magnetic powder, and a MnBi alloy magnetic powder by 90/10 to 60/40 weight ratio. In this medium, reproducing is impossible after signals are recorded and the output level decreases after a predetermined effective period, so that reproducing is impossible. |
