US 8,283,184 B2Granted

Method for measurement of very small local magnetic fields, in particular for measurement of local magnetic stray fields produced by magnetic beads, and an associated device for carrying out the method

AssigneeSiemens Aktiengesellschaft

InventorManfred Rührig

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Abstract

In a method for measurement of very small local magnetic fields, in particular of local magnetic stray fields produced by magnetic beads, at least one magnetoresistive element is used. The element includes a hard-magnetic reference layer and a soft-magnetic sensor layer, whose magnetization can be rotated to a parallel position or an antiparallel position with respect to the reference layer magnetization, and whose output signal which can be tapped off is dependent on the position of the sensor layer magnetization with respect to the reference layer magnetization. In this case, the magnetization of the sensor layer is saturated by way of an external saturation magnetic field in a direction at right angles to the reference layer magnetization, after which the magnetic field is switched off or reduced to such an extent that the magnetization of the sensor layer passes through a critical point as it comes out of saturation, at which critical point the rotation direction of the sensor layer magnetization can be influenced via an existing local magnetic field that is to be measured. Magnetoresistive elements are provided in the associated device and, in particular, are connected to form a bridge.

Claims16

Dependent claims

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.

5 more elements

A device that measures very small local magnetic fields, the device comprising:

at least one magnetoresistive element including a hard-magnetic reference layer and a soft-magnetic sensor layer, wherein
a magnetization of the soft-magnetic sensor layer is configured to rotate to a position parallel or antiparallel with respect to a magnetization of the hard-magnetic reference layer, and
the at least one magnetoresistive element is configured to output a plurality of signals dependent on the position of the magnetization of the sensor layer with respect to the magnetization of the reference layer;
and
at least one interconnect adjacent to the at least one magnetoresistive element and configured to couple to an external power supply, wherein
a varying current flowing through the at least one interconnect produces a varying saturation magnetic field, the varying saturation magnetic field being at right angles to the magnetization of the reference layer and saturating the magnetization of the sensor layer,
switching off or reducing the varying saturation magnetic field causes the magnetization of the sensor layer to pass a critical point as the magnetization of the sensor layer comes out of saturation, the critical point being 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,
the magnetization of the sensor layer attains one of the at least two other magnetization states of the critical point due to an influence of a 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
only the signal tapped off at the critical point is recorded and evaluated.

6 more elements

Dependencies are inferred from the claim text.