The present invention relates generally to magnetic data storage systems, and more particularly but not by limitation to a magnetic read element shield used in such systems.
Magnetoresistive (MR) read heads are typically formed of various layers deposited upon a substrate. MR read heads utilize a MR element positioned between a top and a bottom shield to read magnetically-encoded information from a magnetic medium, such as a disc, by detecting magnetic flux stored on the magnetic medium. The read element may be an anisotropic magnetoresistive (AMR) element, a giant magnetoresistive (GMR) stack or other suitable type of transducer. An AMR element is typically fabricated from iron, nickel, or cobalt-based soft ferromagnetic alloys; whereas a GMR stack is a multi-layered structure generally having two separate layers formed from iron, nickel or cobalt-based soft ferromagnetic alloys separated by a spacer layer formed from non-magnetic materials, such as copper, silver, or gold.
During a read operation, the top and bottom shields ensure that the read element reads only the information stored directly beneath it on a specific track of the magnetic medium or disc by absorbing any stray magnetic fields emanating from adjacent tracks and transitions. Accordingly, the shields are formed of materials having relatively high permeability, low magnetostriction and low coercivity.
In the magnetic recording industry, the drive towards increased recording density has led to the requirement for magnetic storage media having narrower data recording tracks, lower track pitch, i.e., more tracks per inch, and greater linear recording density along the data tracks. Greater linear recording density has led to a reduction in shield-to-shield spacing in the heads and reduced head-media spacing (HMS). At very low HMS, temperature-dependent mechanical distortions, such as thermal pole tip recession (TPTR), become more significant. TPTR effectively alters the HMS. TPTR is greater when the thermal coefficient of expansion (TCE) of the shield is substantially different form the TCE of materials used to form the substrate and insulation layers of the head.
Prior art top and bottom shields are each typically formed of a single layer of a magnetic material such as Permalloy or the like. Permalloy possesses favorable magnetic properties, such as relatively high permeability, low magnetostriction and low coercivity. However, Permalloy has a TCE of about 12xc3x9710xe2x88x926 per degree Centigrade (or Celsius) that is substantially higher than the TCE of Al2O3. TiC (about 8xc3x9710xe2x88x926 per degree Centigrade), which is typically used as a substrate material. Therefore, the TPTR of such prior art heads is usually high.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.
A magnetic head for reading information from a magnetic medium is provided. The magnetic head includes a substrate, having a substrate thermal coefficient of expansion, and a read element positioned above the substrate. The head also includes a shield, positioned above the substrate and adjacent the read element, which has a shield thermal coefficient of expansion that substantially matches the substrate thermal coefficient of expansion. The shield absorbs stray magnetic fields from the magnetic medium, which emanate from stored data that is adjacent to a data element that is directly beneath, and being currently read by, the magnetoresistive read element.
Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.