Stretching and sensing of 1-µm bubbles in ion-implanted contiguous disk devices

A sensor-stretcher designed for use in ion-implanted contiguous disk devices is described. The current activated stretcher forms part of a self-aligned circuit and is defined simultaneously with the propagation structure. The sensor is a thin Permalloy stripe, 100 μm in length, adjacent to the stretch conductor. Detection of 1 μm diameter bubbles has been achieved at frequencies up to 146 kHz, over a 30-Oe (10 percent) bias field margin. The figure of merit, ΔV/V, for the detector was relatively independent of sensor width in the range 2.5- 10 μm and was ∼0.30%; maximum output was ∼10 mV. Noise resulting from imperfect balance of active and dummy detector was found to be a problem in narrow detectors (< 10 μm) due to high coercivity. However, the coercivity may be reduced substantially by in-situ passivation with a 70 Å Si layer. Stroboscopic observation of bubble stretching indicates expansion velocities of 20-90 m/s, (depending on drive) in representative EuTmGaIG/GdYTmGaIG composites. The stretch current pulse for reliable expansion is a function of the magnitude and phase of the in-plane rotating field and is typically 200 mA, 2.5 μs.