Magnetic read-out head using induced RF permeability variation

A highly sensitive magnetic readout principle is proposed[1], which can produce an 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 variation is caused by both ferromagnetic resonance[2] and magnetization rotation. A single-pole magnetic read-out head has been experimentally made, using Ni-Fe film, which operates according to the above novel principle. The manufactured head has been evaluated by sinusoidal signals (0.5-10MHz), which were saturatedly recorded in a longitudinally-oriented magnetic tape with a ferrite ring head (head gap:0.3µm, track width: 100µm). The output level reproduced (0.5-10MHz) from the head was considerably higher than that from the ring head. For example, for a 0.5MHz signal, the head was 35.7-47.5dB 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 (1µm wavelength) was 44-47dB (Δ f:30kHz) and was insensitive to the magnetic-pole film (Ni-Fe) thickness.