Schematic diagram of the RSM setup. A motor outside the VTI connects to the drive shaft, which rotates the sample holder. The signal of the four pick-up coils is preamplified and measured by a lock-in amplifier using the reference signal provided by the motor controller.
3D visualisation of the bottom part of the RSM. All components are inside a stainless steel tube coaxial with the magnetic field of the solenoid. The cylindrical bearings, which support the drive shaft are connected to the RSM tube (only the lowermost is shown). The sample (brown cube) is positioned in the ring-shaped grove of the aluminium sample holder and rotates closely above the coils. Here, the sample holder is shifted to show the bottom titanium tip (black cone) and the pick-up coil system (equal colours refer to equal polarity).
Signal of the pick-up coil system. (a) Four coils with alternating polarity (see Fig. 2) compose the total signal. The graph also shows the contribution of two neighbouring coils positioned at 90° and 180° to the total signal. This arrangement has two effects: first, an external field sweep generates no net signal, second, the individual signals interfere positively and create strong peaks. (b) The period of the system is 180°, i.e., half a rotation. The first harmonic is the principle component and its peaks are shaped by the third harmonic (see also Fig. 4). All higher harmonics are almost negligible.
Dependence of the pick-up coil signal on the outer coil radius. The magnitude of the first harmonic, which is the measurement quantity, does not decrease if the coil cross-section exceeds that of the sample (approximately at r = 2 mm). The derivative of the first harmonic with respect to r 0 still increases at r 0 = 4 mm, which demonstrates that the outermost windings contribute most to the signal.
Comparison of VSM and RSM measurements on a V3Si single crystal after background subtraction. The RSM measurement shows very good agreement with the VSM data up to the maximum field of the VSM (the RSM data is shifted for clarity in this graph only). The lower inset demonstrates the superior resolution of the RSM (the grey area corresponds to the typical VSM noise of ±10−7 Am2). The upper inset shows the determination of the upper critical field B c2 of the superconductor (at this field the magnetic moment of the sample vanishes). Here, the grey area indicates the RSM noise, which is as low as 10−8 Am2 at 15 T. This allows a precise determination of this parameter up to high magnetic fields.
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