MR head response from arrays of lithographically patterned perpendicular nickel columns

We report, for the first time, the MR head response from lithographically patterned perpendicular nickel columns. Electron-beam lithography is used to fabricate arrays of Ni columns, 400 nm tall and 150 nm in diameter spaced 2.1 μm apart, embedded in SiO₂. The sample surface is planarized with a chemical mechanical polish. The technique of Scanning Magnetoresistance Microscopy (SMRM), in which a magnetoresistive (MR) head is raster-scanned in contact with a sample, is used to investigate the MR head response from the Ni columns. Single columns can be “read” with a 0-peak MR voltage of 60-70 μV. Unexpectedly, we find that the magnetic field due to the bias current in the MR head is enough to switch the columns during scanning, which results in a “dibit-like” MR response, By scanning in the presence of a small (~21 Oe) external magnetic bias field, the columns can be imaged in either their “up” or “down” magnetic states