In-Situ Magnetooptical Probing for High-Frequency Current in Magnetic Heads

We developed a magnetooptical probe system for measurement of high-frequency current in magnetic heads. The key technique of the system is magnetooptical probing using a Bi-YIG field sensor. This technique enables nondestructive and noninvasive measurement of the device under test. The system bandwidth is more than 6 GHz. The insertion impedance is negligibly small for magnetic heads. The minimum detectable current is less than 0.3 mA peak-to-peak. Therefore we can perform precise measurements of current waveforms which correspond to real currents in hard disk drives.