Background:

The technology is named for the giant magnetoresistive effect, first discovered by two European researchers -- Peter Gruenberg and Albert Fert -- in the late 1980s. While working with large magnetic fields and thin layers of magnetic materials, Gruenberg and Fert noticed very large resistance changes when these materials were subjected to magnetic fields.

GMR - Head Technology:

Giant magneto resistance (GMR) is a rapidly growing area of interest because researchers study new methods for increasing the memory capacity (gigabytes) of a hard-drive within a small area. This ground-breaking technology will enable individual 2.5" hard-drive units to have capacities in the range of 160 to 360 gigabytes (GB), with commercial introduction of the new read-head technology expected within two to four years.

Characteristics of a GMR Head:

GMR heads are made up of four layers of thin material that combine into a single structure: Free layer - The sensing layer. The free layer is passed over the surface of the data bits to be read. It is free to rotate in response to the magnetic patterns on the disk. Spacer - Typically made from copper, this is a nonmagnetic layer that separates the magnetization of the free and pinned layers. Pinned layer - A layer of cobalt material that is held in a fixed magnetic orientation by its proximity to the exchange layer. Exchange layer - A layer of anti ferromagnetic material that fixes the pinned layer's magnetic orientation.

GMR Head Structure:

Merged read/write head:

The head design consists of a thin film inductive write element and a read element (look at the GMR Schematic above). The read element consists of an MR or GMR sensor between two magnetic shields. The magnetic shields greatly reduce unwanted magnetic fields coming from the disk; the MR or GMR sensor essentially "sees" only the magnetic field from the recorded data bit to be read. In a merged head the second magnetic shield also functions as one pole of the inductive write head.

The advantage of separate read and write elements is both elements can be individually optimized. A merged head has additional advantages. This head is less expensive to produce, because it requires fewer process steps; and, it performs better in a drive, because the distance between the read and write elements is less.