Abstract
This Chapter will describe the main elements generally needed for solid state NMR/NQR experiments such as magnets, cryogenics, probes, and electronics and will specify which setup was used particularly for the measurements done in this work. An overview of the samples used for the measurements will be given. Various experimental problems had to be faced during the experiments. Some of them and their solutions will be presented in Section 5.4.
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Notes
- 1.
The first superconducting coil which was delivered for this magnet had an homogeneity of 18 ppm and a current decay in persistent mode of 18 ppm/h. This coil was exchanged with the better one described in the text some months later.
- 2.
The radiofrequency applied in NMR experiments is shielded by conducting samples. Grounding powders increases the surface area and such the total amount of accessible nuclear spins.
- 3.
For comparison: The residual resistivity of polycrystalline samples of LiFeAs lies in the range of some mΩcm [128]. For single crystals of Ni- or Co-doped BaFe2 As2 the residual resistivity is \( {\rho_0} = 50\mu \Omega .{\rm{cm}} \) [221], and for Ni-doped SrFe2 As2 single crystals it is \( {\rho _0} = 100\mu \Omega \) [222].
- 4.
For comparison: \( \Delta v \approx 220{\rm{kHz}} \) for stoichiometric LaOFeAs [30, 193] and \( \Delta v \approx 480{\rm{kHz}} \) for stoichiometric CaFe2 As2 [224].
- 5.
This was checked e.g. by comparing superconducting or magnetic transition temperatures measured in the NMR magnets and measured in other setups.
- 6.
The NQR measurements could be performed inside the magnet, since it was possible to drive the magnetic field down to zero in an oscillating mode. The good agreement between linewidths and frequencies of the measurements inside the 16T cryostat with \( {H_0} = 0{\rm{T}} \) and other measurements in the NQR setup confirmed the absence of residual magnetic fields in the former case.
- 7.
To minimize possible defects at the sample, it was kept under a helium gas flow atmosphere during the installation of the additional capacitor and everything was done as quickly as possible. A check of the NQR linewidth and frequency at room temperature after the installation of the additional capacitor proved that the sample was still undamaged.
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© 2012 Vieweg+Teubner Verlag | Springer Fachmedien Wiesbaden
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Hammerath, F. (2012). Experimental Setup. In: Magnetism and Superconductivity in Iron-based Superconductors as Probed by Nuclear Magnetic Resonance. Vieweg+Teubner Verlag, Wiesbaden. https://doi.org/10.1007/978-3-8348-2423-3_5
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DOI: https://doi.org/10.1007/978-3-8348-2423-3_5
Publisher Name: Vieweg+Teubner Verlag, Wiesbaden
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