High-resolution field measurements near ferrite recording heads

The perpendicular magnetic fields near NiZn and MnZn Winchester-type recording heads driven at 1.4 MHz have been measured with a high-resolution system. The data were fitted by least squares to the Karlquist head-field equation convolved with the probe area, with the probe-to-head separation as an adjustable parameter. For the MnZn heads, the fitted height agreed reasonably well with the measured height, as determined by optical interference; but for the NiZn heads, a good fit to the Karlquist equation was obtained only if a significantly larger value for the probe-to-head separation was used. This difference in height is attributed to the presence of magnetically dead layers on the surface of the NiZn heads. The measurements indicate a dead layer thickness which is 0.35 μm greater for the NiZn than for the MnZn heads. The perpendicular components of the side-fringing fields near the gap region were also measured, and were in good agreement with the theory of van Herk.