Abstract: The invention concerns a magnetoresistive magnetic field sensor comprising a stack (1) of a reference element (2), a separation element (3) and an element (4) sensitive to the magnetic field, in which the reference element (2) and the sensitive element (4) have respectively a first and a second magnetic anisotropy (5, 6) in a first and a second direction. The sensitive element (4) comprises the superposition of a layer of a ferromagnetic material (FM1) and a layer of an antiferromagnetic material (AF1) which is arranged in order to obtain a magnetic moment (10) whose component oriented in the direction of the field to be measured varies reversibly in relation to the strength of the magnetic field to be measured, and linearly in an adjustable field range. The invention also concerns a use of such a sensor.