A magnetic field vector sensor includes a substrate parallel to a plane, a support mobile relative to it and rotatable about a vertical rotation axis perpendicular to it, a magnetic field source generating a field having a moment in a non-perpendicular direction, the source being fixed to the support with no degree-of-freedom to exert torque on the support when a field to be measured is present, the field being non-collinear with the moment, a transducer to convert torque exerted on the support into a field amplitude of a component of the field along a measurement axis in the plane, wherein the source comprises a magnetostrictive permanent magnet for generating the field having a moment whose direction varies with stress on the magnet, and wherein the sensor further comprises a controllable device to reversibly modify the moment direction, and a stress generator to vary stress and hence moment direction.