The effect of stray magnetic fields on thin film record heads

The main effects of a 10-30-Oe vertical stray field on a thin-film head during reproduction are erasure and broadening of one pulse polarity or even-ordered harmonic distortion. When a field is applied during recording, the alternate pulse asymmetry is more pronounced, and an extra pulse is recorded at the trailing pole corner for one polarity of record current. Calculations indicate that the stray vertical field is amplified by more than an order of magnitude near the outer corners of the thin-film head. This corner field and the corner field of the head generated by the record current combine to record the extra pulse and also cause the alternate pulse asymmetry. Numerical estimates of gap and corner fields are given. The effect of vertical fields on the waveforms and 40-KFCI (1575 fc/mm) digital data channel performance are reported. For the 700-Oe coercivity tape and record conditions used, a field larger than 10 Oe adversely affected the channel performance