MAGNETIC READ-OUT HEAD USING INDUCED RF PERMEABILITY VARIATION.

A highly sensitive magnetic readout principle is proposed that can produce excellent output from a high-density recorded signal. This principle utilizes a sharp RF permeability change in a soft magnetic film due to a weak external field. This change is caused by both ferromagnetic resonance and magnetization rotation. A single-pole magnetic readout head has been experimentally made, using Ni-Fe film, which operates according to the above principle. The manufactured head has been evaluated by sinusoidal signals (0. 5-10 MHz), which were recorded in a longitudinally-oriented magnetic tape with a ferrite ring head (head gap: 0. 3 mu m, track width: 100 mu m). The output level reproduced (0. 5-10 MHz) from the head was considerably higher than that from the ring head. For example, for a 0. 5 MHz signal the head was 35. 7-47. 5 dB more sensitive than the ring head, and at 5 MHz the sensitivity was 17. 6-22. 5 dB better. The carrier-to-noise ratio (CNR) for a 5-MHz carrier (1 mu m wavelength) was 44-47 dB ( DELTA f:30 kHz) and was insensitive to the thickness of the magnetic-pole film (Ni-Fe).