QSSeS Qf eadback Efficiency for in-Film Inductive €€ea

Magnetic recording measurements on a rigid disk are used to derive the readback efficiency of thin film inductive heads as a function of frequency. The technique re- lies on a pseudo-contact air bearing system which keeps the transducer in contact with the disk over a range of vdoeities. It is found that the readback efficiency decreases monotoni- cally with frequency, showing a 3dB loss at 40MHz, for the heads used in this experiment. A four section transmission line model has been developed to include the geometry vari- ations in different areas of the head. Domain wall motion and rotational contributions to flux transmission have been included. The calculated efficiency and impedance values are found to be in good agreement with measured values. I. INTRODUCTION Inductive heads are being used in increasingly higher data rate applications in which maintaining the head per- formance at high frequencies becomes an important issue. Direct measurement of readback efficiency as a function of frequency has been difficult due to the interaction of write, read, flying height and electronics effects. Head fields have been measured at various frequencies by using a micro-loop sensor by other workers (l) . This method excites the head coil and measures the gap field. With increasingly narrow head gaps, the resolution and positioning of the micro-loop structures becomes important. It would be much more satisfying to extract the frequency dependence of readback efficiency directly from magnetic recording measurements. We failed to find any frequency-dependent efficiency mea- surements based on magnetic recording methods in pre- viously published literature. The recent introduction of the advanced thin-film inductive heads fabricated with the pseudo-contact air bearing system (Tripad) has made it possible for us to eliminate flying height effects and mea- sure the frequency dependent efficiency through magnetic recording directly. A Tripad head stays in pseudo-contact with the disk, making its ''flying height" equal to the disk avalanche glide height, which is a constant. Taking advan- tage of the constant 'lying height", we propose a method where the frequency response of the head can be obtained by reading back the recorded data at different linear ve- locities without rewriting. Since there is no rewriting in- volved, we can study the head readback performance inde- pendently. In this paper, we report a technique for measuring the readback efficiency using a magnetic recording method.