Magnetic field sensor and instrument comprising such a sensor

An instrument for measuring a magnetic field, comprising:

• a Wheatstone bridge having at least four layered magnetoresistive elements on a substrate, each element including at least three layers, comprising successively a first ferromagnetic layer, a non-magnetic layer and a second ferromagnetic layer, wherein each of the magnetoresistive elements comprises one or more strip-shaped portions which extend in mutually parallel directions, the first ferromagnetic layer exhibits uni-axial anisotropy in one plane and the second ferromagnetic layer exhibits uni-axial or uni-directional anisotropy in one further plane, the magnetization of the second ferromagnetic layer being determined by exchange interaction with an antiferromagnetic layer provided on the second ferromagnetic layer, and wherein magnetoresistive elements arranged in two adjacent branches of the bridge circuit have approximately opposite magnetization directions of the second ferromagnetic layers.

A method of manufacturing a sensor formed of magnetoresistive elements which are arranged in a bridge on a substrate, which magnetoresistive elements each comprise at least two strip-shaped elements in parallel and with first and second ferromagnetic layers which exhibit uni-axial anisotropy in one plane and which are separated by a non-ferromagnetic layer, and a current conductor near each strip-shaped element and with its longitudinal direction extending parallel to the longitudinal direction of the strip-shaped portion of the magnetoresistive element, the magnetization direction of the second ferromagnetic layer of the associated magnetoresistive elements extending substantially perpendicular to the longitudinal direction of the current conductors, the magnetization of the second ferromagnetic layer being determined by exchange interaction with an antiferromagnetic layer provided on the second ferromagnetic layer, said method comprising:

• exposing the second ferromagnetic layer and the antiferromagnetic layer, at a temperature higher than a blocking temperature, to a magnetic field which is generated by an electric current flowing in the current conductors, subsequently lowering the temperature of said layers to a value below the blocking temperature while sustaining the magnetic field.