High frequency response of a magneto-optical readout head

In magneto-optical (MO) readout of magnetically printed stripe domains in magnetic bubble film in contact with a recorded sheet, the dynamic response of the printed domains, called the signal domains, has been investigated using a video playback apparatus with a flexible circular magnetic sheet. The dynamic response was evaluated by measuring the S/N of magnetooptically detected signals with a spectrum analyzer. The data show that the critical velocity vcat which the signal domain motion breaks down varies from 25 to 35 m/s, corresponding to signal wavelengths from 10 to 50 μm. The signal domain (plane wall) motion is treated using Slonczewski´s equations of motion. Reasonable quantitative agreement is found between the numerical and the experimental results. The calculation suggests that vchas a maximum at a certain signal field. The vccomes from a formation of holizontal Bloch lines in the wall except for wavelengths in the vicinity of which static magnetic printing becomes impossible. It is pointed out that a thin Bi-substituted garnet film with orthorhombic anisotropy is suitable for both high S/N and high-frequency responsive MO head.