Static and dynamic interaction between π and d electrons in organic superconductor β'-(BEDT-TTF)_4[(H_3O)Fe(C_2O_4)3] • C_6H_5Br studied by ~(13)C NMR spectroscopy

摘要

We present the results of ~(13)C NMR experiments in an organic superconductor with localized Fe spins β'-(BEDT-TTF)_4[(H_3O)Fe(C_2O_4)3] • C_6H_5Br. We reveal the antiferromagnetic coupling between Fe d spins and n spins, which creates an exchange field antiparallel to the external field direction at the π electrons. In addition to the static effects of Fe spins, we show from the nuclear spin-lattice relaxation rate measurement that the magnetic fluctuations generated by Fe spins are suppressed at low temperatures and high magnetic fields. These conditions are suitable to stabilize the field-induced superconductivity by the field compensation mechanism. After the suppression of Fe-spin dynamics by a magnetic field of 19 T, we observed the underlying π-electron contribution. We discuss a possible anomaly in the π-electron system.