We describe the design and construction of a sensitive dc torque magnetometer suitable for liquid as well as solid state samples. It can be used from room temperature down to very low temperatures (mK range) in magnetic fields produced either by superconducting or resistive magnets, in particular in the high fields (B≈30 T) produced by Bitter and hybrid magnets. The highest resolution that we have attained so far is about 0.3 pNm, which is mainly the result of a symmetric design. In typical laboratory conditions (at B=10 T) this corresponds to a magnetization resolution of about 3×10−11 emu. Other features include modularity, linearity, feedback and forward bias capabilities, and an in situ calibration of the signal.
We have investigated the distribution of the Hall current in a Corbino geometry two-dimensional electron gas ͑2DEG͒ under quantum Hall effect conditions by measuring the induced magnetic moment. The magnetic moment near integer filling factor shows oscillations around the quantized value, which reflect a spatial redistribution of the Hall current density. The results show that at integer filling factor the local Hall conductivity in a high mobility sample is not quantized. Between integer filling factor the normal Hall current with the expected magnitude V r e 2 /h is measured, showing the reliability of the technique.
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