Direct Observation of the High Frequency Write Response of Recording Heads Using the Magnetic Force Microscope (Abstract)

A direct measure of the high frequency (HF) response of recording heads is becoming increasingly important as storage densities head toward 10 Gb/in.2. One of the quantities for characterizing head response is the value of the magnetic field at high write frequencies. Typical, HF testing of heads has been mostly indirect; the recording head is used to write data to a disk and the head performance is evaluated based on the readback signal. The results of the testing depend on the test media and the readback system in addition to the actual HF performance of the recording head. To our knowledge, the only direct testing of HF head response was done with a scanning magneto-optic photometer which images the dynamic domain structure of the recording head.1 Unlike these other techniques, the magnetic force microscope (MFM) responds directly to the magnetic field above the recording head. Normally, the MFM response time is limited by the resonant frequency of the cantilever, typically 60–80 kHz in our system. However, by either AM or FM modulation of the HF drive of the recording head, vibrations were excited in the MFM cantilever and the response of the head was characterized at head drive frequencies in excess of 50 MHz.2 In this work, we have measured the response of a metal-in-gap recording head from a commercially available disk drive (Seagate, Inc., Bloomington, MN). As expected, we found that the head had a single pole rolloff at roughly 1 MHz. The effects of dc and ac biasing were also studied.