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The authors studied the magnetoresistive effect, effective anisotropy field, domain patterns and reading abilities of an improved sensor structure made of highly magnetoresistive Ni-Co films with an auxiliary Ni-Fe film pole. The demagnetizing field in the improved sensors having the same Ni-Co stripe width as conventional sensors was reduced to half that of the latter. With angular changes in applied field or application of low bias fields, the magnetoresistive effect in conventional sensors was weakened due to the existence of domain walls. The improved sensors, on the other hand, consist of a single domain; thus the magnetoresistive effect is not decreased under the same field conditions. The read output using the magnetoresistive effect of the improved sensors is roughly 1.6 to 1.8 times greater than for conventional sensors. The ratio of the stripe width of the sensors to the recording bit length was found to be an important factor in enabling greater distances from medium to sensor.