Magnetoresistive reading of information

The anisotropy in the spontaneous magnetoresistance of ferromagnetic metals can be used to monitor the magnetic fields of cylindrical domains and of magnetic recordings. Depending on which application is chosen, either the magnitude of the anisotropy effect must be optimized by itself, or in a suitable combination with the saturation magnetisation and thickness to account for the demagnetizing field and the thickness dependence of the resistivity. Ni(89)Fe(11) and Ni(70)Co(30) films are shown generally to be acceptable for device materials. Various magnetoresistance reading heads (MRH) have been fabricated and investigated. A MRH was built into the gap of a ferrite write head; minima and maxima were noted in the wavelength response that can be explained theoretically. A new source of noise was found to originate from variations of the heat flow between head and contacting tape. Its influence can be reduced by diminishing the excitation current or by increasing the thermal conductivity near the magneto-resistive material. For analog reading, the head is biased with a field of 50-100 Oe, which has a negligible influence on the recorded information. Track sensing and compensation of cross-talk and external noise are shown to be feasible.