Novel sensor design for torque magnetometry

Abstract

Torque magnetometry is a powerful method to determine a sample's magnetic properties. In a torque magnetometer, the sample under interest is mounted on a suitable sensor, the core part of the instrument. Piezoresistive atomic force microscope tips are proven to be very useful torque sensors and have already been optimized for the specific needs of torque magnetometry. However, this type of sensor did not offer the possibility of measuring torque along two perpendicular directions simultaneously without sacrificing sensitivity. In this article we demonstrate a fundamentally new sensor design based on the piezoresistive readout technique, which offers a large variability of measurement modes. With a symmetric arrangement of the sensor legs, concurrent two-axis measurements are easily possible with two separate readout circuits. Furthermore, the variability can be exploited by fabricating a thermometer on the sample platform to directly measure the sample temperature. Test measurements are in good agreement with elasticity calculations.

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“…The magnetic anisotropy measurements were carried out with a homemade magnetic torque sensor [24]. A tiny Sm 4 Fe 2 As 2 Te 1−x O 4−y F y single crystal (ß100 × 100 × 10 μm 3 ) was fixed on a platform hanging on piezoresistive legs.…”

“…When a static magnetic field was applied to this anisotropic superconductor, a torque proportional to the vector product of magnetization and field appears and bends the piezoresistive legs. The resulting change in resistance can be read out electronically, yielding a signal proportional to the torque [24]. …”

Single crystals of LnFeAsO1−xFx (Ln=La, Pr, Nd, Sm, Gd) and Ba1−xRbxFe2As2: Growth, structure and superconducting properties

“…A home-made piezoresistive torque sensor was used [59]. The crystal was mounted in an Oxford flow cryostat allowing stabilization of temperatures between 10 K and 300 K. A turnable Bruker NMR magnet with a maximum field of 1.4 T was used to vary the field magnitude and its orientation with respect to the crystallographic axes allowing for a full rotation through 360 deg.…”

Anisotropic magnetic order of the Eu sublattice in single crystals of EuFe2−xCoxAs

“…The magnetic torque measurements were carried out using a home-made torque sensor. 37 The sample is mounted on a platform hanging on piezoresistive legs. A magnetic field H applied to the sample having magnetic moment m results in a mechanical torque τ = µ 0 m× H. This torque bends the legs, and thus creats a measurable electric signal proportional to the torque amplitude.…”