Abstract: A single magnetoresistor TMR magnetic field sensor chip and magnetic currency detector head; the single magnetoresistor TMR magnetic field sensor chip is installed above a magnetic excitation element; the sensing direction of the chip is parallel to the surface of the chip, and the direction of the magnetic excitation field generated at the chip by the magnetic excitation element is perpendicular to the surface of the chip; the chip comprises a substrate, a magnetic biasing structure deposited on the substrate, a magnetoresistive element, and an input/output terminal; the magnetoresistive element consists of MTJs; the sensing directions of the magnetoresistive element and the MTJs are the same as the sensing direction of the chip; and the direction of a bias magnetic field generated on the chip by the magnetic biasing structure is perpendicular to the sensing direction of the chip. The chip features high sensitivity, high signal-to-noise ratio, small size, high temperature stability and high reliability.