Improving ferrite MIG head read-back distortions caused by domain walls and granularity (abstract)

Abstract

Ferrite MiG heads intended for narrow track (≲10 μm) digital recording were recently investigated in the critical pole-tip region at the air-bearing-surface using micro-ellipsometry, Kerr microscopy, and electron back-scatter diffraction from individual grains,1 and using magnetic force microscopy to detect air-gap remanent fields.2 Comparison of these direct observations with readback-after-write waveforms from written test tracks, and consideration of granularity influences on bulk permeability and domain size, indicate that waveform instability and asymmetry from polycrystalline ferrite (PCF) heads would be diminished by suitable size and orientation of the grains.1 The use of single-crystal ferrite3 (SCF) for advanced laser enhanced etch definition3 of narrow pole MiGs can avoid this type of distortion. However, secondary signals4 often appear as weak pulses separated in time from the main gap pulse. We have associated this effect with a zig-zag shaped wall seen nucleated and propagated from the pole tips by a write pulse.4 This wall and its underlying domains lie remanent in the stressed ABS material and evidently react to the bit fields during the read cycle. The secondary read-back response, though similar to the pseudo-gap effect, differs in origin. Its timing depends on the distance of the zig-zag wall to the gap, not the fixed position of the sendust-ferrite interface. Our results indicate that suitable grain oriented ferrite would reduce PCF MiG head read-back asymmetry and instability. For SCF heads, a method for electrically removing zig-zag walls is possible and secondary pulse removal has now been demonstrated on a spin test strand.