Christopher J. Rea

Thermomechanical head performance

Mismatch of thermal expansion of various materials used in the transducer and slider of giant magnetoresistive (GMR) recording heads causes, at higher operating head temperature, mechanical stresses and, in particular, protrusion toward the media [thermal pole tip recession (T-PTR)]. Low T-PTR is necessary for low head-media spacing without mechanical contact. Impact of the magnitude of the Poissons ratio of a photoresist coil insulator on thermal protrusion is shown to be large, due to large variation of the volume compressibility. Three-dimensional FE (3-D FE) thermomechanical modeling shows that the distribution of thermal stress in shields caused by mismatch of coefficient of thermal expansion changes completely close to the air bearing surface due to protruded head surface. During head operation, the primary heat source arises from the writer coil. The maximum temperature and the particular temperature distribution depends on the ability of the head components to dissipate effectively the generated heat. As the transducer continues to scale down in size with increasing areal density and data rate, the power dissipated per unit volume grows due to the larger coil resistance in the core region.

Domain control in magnetic shields using patterned permanent magnet underlayer

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....