Effect of High Permeability Film in Magneto-Optical Readout Head

A new type of magnetic head, called a domain-modulation type optical reproduction head, which uses a magneto-optical effect for signal reproduction, is proposed. The prototype head consists of a high-permeability magnetic film and a magnetic garnet film with a reflex mirror. The high-permeability magnetic film works as a magnetic flux guide to transfer the fringing magnetic flux from the recorded bits in the magnetic recording medium to a magnetic garnet film, and modulates the width of the magnetic domains sufficiently to enable reproduction by a laser beam. Thus high-resolution reproduction with regard to both track density and bit density is anticipated. To investigate the feasibility of use of such a head, a prototype head was placed on recorded magnetic tape, and the modulated domains in the magnetic garnet film were observed through a polarization microscope. We found that the change in domain width reached vaiues greater than 1 ¿m for magnetic garnet film with a natural domain width of 2.5 ¿m. According to an analytical reproduction model, this value is sufficient to enable a high signal-to-noise ratio (of approximately 75 dB) in reproducing recorded bits by a 2-¿m laser beam.