Performance of focused ion beam trimmed yoke-type magnetoresistive heads for magnetic microscopy

Thin-film yoke-type magnetoresistive (MR) tape heads with eight channels have been used for scanning magnetoresistance microscopy. The NiFe read flux guides of the channels have been trimmed down from 12 μm to widths varying between 5 μm and 100 nm by focused ion-beam milling with Ga⁺ ions. The tape-bearing surface of the milled regions has been reconstructed in situ by the local deposition of Pt. Tracks with a minimum bit length of 1 μm have been written on Co-Ni-O metal evaporated tape and Co-γ-Fe₂O₃ particulate tape with trimmed and untrimmed write channels and have been successfully imaged with all the trimmed read channels. A linear decrease in readback voltage across the MR sensor is observed for channels possessing flux guides trimmed down to 2 μm, in agreement with finite-element modeling of the trimmed heads. The severe attenuation in readback voltage observed for flux guides trimmed below 2 μm is attributed to a combination of micromagnetic effects. Additionally, damage to the NiFe from Ga⁺ ion implantation may make a minor contribution to the loss in sensor performance. A 65% drop in readback voltage is observed for a channel possessing a flux guide that was trimmed by 98.3% to 200 nm