MAGNETIC INSTABILITY OF THIN-FILM RECORDING-HEADS

Two forms of magnetic head instability are investigated: Write and rea d instability. Write instability generates noise directly after writin g which impairs sector-servo performance. This noise peaks at write cu rrents saturating the apex or backgap. The noise amplitude is exponent ially distributed. The noise is caused by cooling off of the yoke afte r write as well as by thermally activated domain wall jumps in the upp er yoke. Read instability produces read pulse distortion, predominantl y on the signal's trailing edges. The only form of instability in dedi cated-servo drives, read instability is best characterized by pulsewid th measurements. The degree of instability changes with intermediate w rites. Read instability is caused by hysteretic domain wall motion in the pole tips in response to signal excitation and/or stray magnetic f ields.