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 mag-netoresistance microscopy. The NiFe read flux guides of the channels have been trimmed down from 12 um to widths varying between 5 um 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 um have been written on CoNiO metal evaporated tape and Cogamma 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 um, in agreement with finite-element modeling of the trimmed heads. The severe attenuation in readback voltage observed for flux guides trimmed below 2 um 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.