Ring type permalloy detector for bubble domains

This paper describes a ring shape Permalloy magnetoresistive detector for magnetic bubble domains. The advantages over a rectangular detector are a large increase in signal, low noise generated by a rotating field, and no critical limitation of detector location. The optimal design of the ring Permalloy detector was obtained from the calculated distributions of bubble domain stray fields. Typical geometry of the detector is as follows: Permalloy film thickness = 300 Å, width of sensor = 15 μm, and inner diameter of the ring = 100 μm. The resistance of the detector is 600 Ω. This detector yielded 12 mV output signals for a 100μm diameter bubble domain when the rotating in-plane field was 22 Oe and the input current was 5.5 mA.