Determination of frequency-dependent magnetic recording losses

A technique to determine the frequency dependent record losses for contact as well as non-contact interfaces has been devised. Measurement of these losses in contact recording is normally accomplished by the use of two different interface speeds in order to factor out wavelength dependent effects; however, this method is undesirable in non-contact disc recording where flying height variations as a function of interface speed are normally encountered. To overcome this problem, the recording process is linearized by a.c. bias and intermodulation products between different frequencies are observed. The loss can be established from the amount by which the record current is increased as a function of frequency in order to maintain a constant level intermodulation product. Both two and three tone intermodulation techniques were investigated and the latter was found superior. Measurements obtained on a flying head/disc interface show, as expected, that the frequency dependent losses are essentially independent of radius and record level.