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Miniature Torque Magnetometer

IP.com Disclosure Number: IPCOM000116996D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Bauer, P: AUTHOR [+3]

Abstract

The ever decreasing size of the samples to be investigated generate an increasing demand for high-sensitivity methods for magnetic measurements. Single crystals are essential for investigating intrinsic magnetic anisotropy but the preparation of macroscopic samples is not always straightforward. Often only very small crystals of high purity and without defects can be obtained. Therefore, herein it is proposed to build a very sensitive and miniaturized torque magnetometer based on the concept of active micro-levers (with piezo-resistive, piezo-electric or capacitive deflection detection). This magnetometer can be used for samples as small as a few microns.

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Miniature Torque Magnetometer

      The ever decreasing size of the samples to be investigated
generate an increasing demand for high-sensitivity methods for
magnetic measurements.  Single crystals are essential for
investigating intrinsic magnetic anisotropy but the preparation of
macroscopic samples is not always straightforward.  Often only very
small crystals of high purity and without defects can be obtained.
Therefore, herein it is proposed to build a very sensitive and
miniaturized torque magnetometer based on the concept of active
micro-levers (with piezo-resistive, piezo-electric or capacitive
deflection detection).  This magnetometer can be used for samples as
small as a few microns.

      The levers are commercially available or could be custom made.
The sample is fixed to the end of the cantilever beam and the
deflection in an externally applied magnetic field is measured for
example through resistance changes in the piezo-resistive path (doped
Si layer) using a simple Wheatstone bridge and lock-in amplifier
technique or a dc-amplifier.  The proven deflection resolution of the
AFM cantilever is around 0.01 nm.

      This tiny device with the attached sample can easily be
implemented in the small chamber of a cryostat (conventional or
dilution refrigerator) or in a high pressure cell (when measuring
magnetization under pressure).  The external magnetic field is
generated either by a normal electromagnet or by a superconducting
magnet.  Rotating this field allows to perform anisotropy
measurements.  Hybrid systems could also be design by combining for
example torque and specific heat measurement or torque and
resistivity.  The device can be used for measurement of time
dependent effects like the relaxation of M(t).

      The highest sensitivity with minimal level of noise and no
influence of the magnetoresistance and temperature drifts of the
cantilever can be achieved by differential measurement, i.e.,
applying two similar cantilevers in parallel (Figure), one of which
holding the sample with the other one providing a reference signal.
This technique allows also to measure the torque continuously as a
function of temperature without the need for additional calibration
at each t...