RESPONSE OF MAGNETIZATION TO HIGH-FREQUENCY EXCITATION IN INDUCTIVE THIN-FILM RECORDING-HEADS

A scanning magneto-optic photometer system was used to study the high frequency response of magnetization in inductive thin-film recording heads. Measurement at 40 MHz show that most domain walls cease to move at this frequency. At the surface of these motionless walls, the magnetization does not respond to the applied field, forming a "dead" surface layer. On the two sides of these motionless domain walls, magnetic flux conduction is by nonuniform rotation in the sense that both the rotation angle and the phase arc different at different places, forming magnetic flux "ripples". Locked ripple was shown to significantly slow magnetization reversal in thin permalloy films decades ago, and these measurement results indicate it will likely limit high frequency performance of thin-film heads as well.