Low-field extension for magnetometers (TinyBee) used for investigations on low-dimensional superconductors withB_c1< 5 G

Abstract

In this article a simple and easy to install low magnetic field extension of the SQUID magnetometer Quantum Design MPMS-7 is described. This has been accomplished by complementing the MPMS-7 magnet control system with a laboratory current supply for the low magnetic field region (B ≤ 200 G). This hard-and software upgrade provides a significant gain in the magnetic field accuracy up to an order of magnitude compared with the standard instrument's setup and is improving the resolution to better than 0.01 G below 40 G. The field control has been integrated into the Quantum Design MultiVu software for a transparent and user-friendly operation of this extension. The improvements achieved are especially useful, when low magnetic field strengths (B < 1 G) are required at high precision. The specific advantages of this application are illustrated by sophisticated magnetic characterisation of lowdimensional superconductors like Sc 3 CoC 4 and SnSe 2 {Co(η-C 5 H 5 ) 2 } x .

Superconductivity at Tc = 44 K in LixFe2Se2(NH3)y

“…The earth magnetic field was compensated during the zfc sequences (down to 2 K) by a procedure described in detail in Ref. [38]. In the subsequent heating run we applied a small magnetic field (B = 0.5 mT) to record the magnetization data up to 55 K. This procedure reflects the complete shielding effect of the sample at low temperature (χ V = -1 in the ideal case), whereas the fc measurements account for the Meissner expulsion.…”

On the nature of superconductivity in the anisotropic dichalcogenide NbSe2{CoCp2}x

“…The temperature dependent magnetic dc-susceptibility (χ V (T )) of NbSe 2 {CoCp 2 } 0.26 is depicted in figure 3 for zero field cooled (ZFC) and field cooled (FC) cycles in a low magnetic field applied perpendicular and parallel to the ab-planes. For the ZFC sequence the sample was first cooled down to 2 K in a zero field, where the earth magnetic field was compensated within an error bar of 1 µT by the so-called TinyBee setup described in detail in [22]. In the subsequent heating run a small magnetic field of µ 0 H = 0.5 mT was applied to record the susceptibility data up to 8 K. For the susceptibility measurements with H perpendicular to the ab-plane (H ⊥ab) a demagnetization factor of N = 0.8 was taken into account.…”

“…The lower critical fields of 2H-NbSe 2 and NbSe 2 {CoCp 2 } 0.26 are estimated from magnetization measurements µ(µ 0 H ) at very low magnetic fields, using the high resolution of µ 0 H = 1 µT increments accomplished by the TinyBee setup [22]. In figure 4(a) the magnetic moment versus magnetic field for 2H-NbSe 2 in the case of H perpendicular to the ab-planes at 2 K is plotted in the range between 0 and 4 mT using minute increments of µ 0 H = 0.025 mT.…”