The effects of magnetic properties and thickness of Co-Cr/Ni-Fe double-layered medium on perpendicular magnetic recording are investigated. Experiments are performed using a single-pole-type head for recording and a ring-type head for reproducing. Our experiments show that: (1) Thickness of the Ni-Fe layer is required to be greater than half of thickness of the head pole to obtain the maximum reproduced voltage. (2) Reproduced voltage Ep is proportional Hc0.6 (Hc: coercive force of the Co-Cr layer in the film normal direction). (3) Ep/Hc0.6 to (≡Ep′) is independent of saturation magnetization of the Co-Cr layer. (4) Ep′ increases with thickness of the Co-Cr layer δp at long recording wavelength. (5) Ep′ is independentof δp when the recording wavelength is short. The relationships (2) to (4) are close to those suggested by calculation based on magnetization model of the medium and a reciprocal theorem. But the relationship (5) a does not agree with the result of our calculation probably because of the incorrectness of the magnetization model for short recording wavelength. The calculation shows that magnetic interaction between the ring head and the medium has an important effect on the reproducing characteristics.
