In situ measurement of the remanence curve of magnetic recording media

A measurement technique is described that yields a normalized remanence curve of the recording medium under the actual conditions of the write process directly as a function of the write-head current. This could be a more useful result than the standard representation as a function of the applied field. The result, however, could be represented in the standard form if the head field function and the flying height were known. The measurement consists of writing a low-frequency, saturated all-ones pattern and subsequently overwriting an all-ones pattern, at the same frequency but displaced in phase, using the head-current value for which the remanence is to be measured. The head field has the same direction as the original field for the part of the bit cell unaffected. It has the position direction for the remaining part, reducing or partially reversing the magnetization of this part of the bit cell to the corresponding remanence value. On reading this record with a inductive read head, the area under each voltage pulse yields the remanent magnetization for the overwrite current used