Domain control in magnetic shields using patterned permanent magnet underlayer

Abstract

The domain state of a magnetic shield in a recording head can be controlled by an adjacent patterned permanent magnet layer. A 1.1-μm-thick electroplated Ni80Fe20 (NF) film with slight uniaxial magnetic anisotropy was patterned into rectangular magnetic shields with various dimensions over patterned thin film made from a 0.1-μm-thick CoCrPt permanent magnet (PM). The shape of the adjacent biasing PM layer should be the shape of a desired final domain in NF. Domain structure in the NF layer and the process of magnetic saturation were imaged using wide-field Kerr microscopy. The NF and PM layers are magnetically coupled and, therefore, a magnetic state with parallel magnetization is preferred. The PM direction of magnetization is set in high magnetic field and the final NF domain state is controlled by the shape of PM features. The simplest stable domain structure in a rectangular thin shield is of an “envelope” type. Using a PM underlayer, either clockwise or counterclockwise domain structure is preferred. Various resulting domain structures were studied after saturation in various magnetic fields and a range of directions. While the resulting domain structures in NF are regular and well defined after saturation in a large magnetic field, more complex and irregular structures are generated in NF after magnetization in a smaller field. Domain structures for various field treatments are discussed.