Micromagnetic characteristics of chevron bubble detectors

A Kerr-effect microscope is described for studies of bubble Permalloy elements at frequencies up to 500 kHz with an illumination spot size of approximately 2 micron. This ´micro-Kerr´ apparatus has been generally applied to understanding the dynamics of the chevron sensor. The magnetization cycles of the elements of isolated sensors have been found to conform to a ´head-to-tail´ model. The magnetization cycles of sensors in a chevron expander array show a sharply differing behaviour which is explained by interaction with the expander. This work has been combined with Fourier analysis of the sensor magneto-resistive signal. For a particular design, the bubble-no bubble information is contained in a phase modulation of the 2w component of the signal. It is shown that the observed magnetization cycles account for the major features of the sensor signal.