Improved bias and stability in dual-exchange-biased unshielded magnetoresistive heads

Data are presented on dual-exchange-biased NiFe-TbCo UMR (unshielded magnetoresistive) tape heads with improved signal response and process stability. It was found that a Si₃N₄ passivation layer offered better stability of the exchange bias through head processing than SiO₂. In order to improve sensor sensitivity, the longitudinal component of the exchange bias was reduced by increasing the exchange angle to 75° from the sense current direction. This resulted in a +6-dB improvement in signal over previous heads without sacrificing Barkhausen-noise-free operation in narrow trackwidths. Heads with trackwidths as narrow as 8 μm were shown to operate at linear densities of up to 50 kFCI with excellent signal-to-noise ratios (>45 dB). Investigations of different passivation materials showed Si₃N₄ to provide the best protection against environmental corrosion and thermally induced oxidation of the TbCo layer