Effects of Fall Times of Pulse Currents on Output Voltages in Amorphous-Wire-Based Magnetic Sensors

Micro-sized magnetic sensors with ultrahigh sensitivity are required in biomagnetic measuring devices. The gigahertz (GHz) spin rotation sensor, which is a coil-type magnetic sensor, shows high sensitivity while transmitting GHz-pulse currents. Detection magnetic fields are sensed via a pickup coil, which is wrapped around the wire when the GHz-pulse currents are applied. However, the micromechanism in the amorphous wire, which exhibits high sensitivity, has not yet been elucidated. In this study, we investigated how the fall time of the pulse current, which defines the frequency, affects the output peak voltages and the behavior of the magnetization inside the amorphous wire. We found that the shorter the fall time, the higher are the absolute values of the output peak voltage and the external magnetic field detecting those values. At a fall time of 0.385 ns, only the rotations of magnetization in the outer circumference of the amorphous wire contributed to the output voltages, and at a fall time of 5.0 ns, the domain wall motions inside the wire also contributed to the output voltages. This difference was the reason why the output peak voltages increased as the fall time was shortened.