Patent ID: 8283184

Claim:
A method for measurement of very small local magnetic fields, comprising: using at least one magnetoresistive element, the at least one magnetoresistive element including a hard-magnetic reference layer and a soft-magnetic sensor layer, a magnetization of the soft-magnetic sensor layer configured to be rotated to a position that is parallel or antiparallel with respect to a magnetization of the hard-magnetic reference layer, wherein a plurality of signals tapped off from the magnetoresistive element are dependent on a position of the magnetization of the sensor layer with respect to a position of the magnetization of the reference layer when the magnetization of the sensor layer is saturated in a direction at a right angle to the magnetization of the reference layer using an external saturation magnetic field; at least one of switching off and reducing, by an external power supply, the external saturation magnetic field such that the magnetization of the sensor layer passes a critical point as the sensor layer comes out of saturation, wherein the critical point is an unstable magnetization state of the sensor layer in which the magnetization of the sensor layer is saturated and the saturated magnetization state of the sensor layer is in thermodynamic equilibrium with at least two other magnetization states of the sensor layer, a direction of rotation of the magnetization of the sensor layer at the critical point is influenced by a local magnetic field, the local magnetic field being one of the very small local magnetic fields that are measured, and the magnetization of the sensor layer attains one of the at least two other magnetization states of the critical point due to the influence of the local magnetic field resulting in a change in a signal tapped off at the critical point, the signal being from the plurality of signals; and recording and evaluating only the signal tapped off at the critical point.