Magnetic Readout Head Using Induced RF Permeability Variation in Ni-Fe Film

A novel principle of magnetic readout is proposed which can extract a high-quality output from high-density recorded signals. The principle utilizes sharp RF permeability changes in a soft magnetic film due to a weak external field. This variation is caused by both magnetization rotation and ferromagnetic resonance. A magnetic readout head which operates on this novel principle has been trial-fabricated. The prototype head was evaluated using sinusoidal signals (0.5 to 10 MHz) which were saturation-recorded on a magnetic tape with a ferrite ring head (head gap 0.3 μm, track width 100 μm). The signal level reproduced at 0.5 MHz by the prototype head was at least 35.7 dB higher than that from a ring head, and for 5-MHz signals the output was from 17.6 to 22.5 dB higher. The carrier-to-noise ratio for a 5 MHz carrier (1 μm wavelength) was from 44 to 47 dB, and was independent of the Ni-Fe film thickness.