In the thesis, we report a 77Se, 7Li and 1H nuclear magnetic resonance (NMR) study of magnetic, structural and superconducting properties of powdered Lix(C2H8N2)yFe(2−z)Se2 sample in comparison to iron-based superconductor FeSe. The critical superconducting temperature, Tc, of FeSe can be dramatically enhanced by intercalation of layers between FeSe layers. In our sample critical temperature rises from initial Tc = 8 K to nearly optimal Tc = 45 K.
Absence of shift in 7Li and 1H NMR spectra indicates a total decoupling of conducting FeSe layer and insulating Lix(C2H8N2)y layers. Measurements of 7Li and 1H spin-lattice relaxation rates show weak temperature dependence which indicates that there are non-negligible Fe impurities in insulating layer.
Measurements of 77Se NMR spectra and spin-lattice relaxation rates, 1/77T1, show strong temperature dependence which can be attributed to the hole-like bands near Fermi energy. Relaxation rates 1/77T1 show no anisotropy which would indicate the onset of electronic nematic order. Similarly, enhancements in 1/77T1 due to spin fluctuations in normal state are absent. However, a characteristic power-law
1/77T1 ∝ T^(4,5) indicates that Cooper pair bonding is mediated by spin fluctuations.