Study of exotic superconductivity in the iron-family-based intermetallic compounds

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This project performed studies of exotic superconductivity and geometrical frustration effects in several iron-family-based compounds. And remarkable research results were obtained especially in the study of exotic superconductivity in the iron silicide Lu_2Fe_3Si_5, and the study of geometrical frustration effects in The spinel cobaltite GeCo_2O_4.The iron silicide superconductor Lu_2Fe_3Si_5 has three-dimensional multiband structure which is demarcated from the multiband structure in the iron arsenide superconductors. This project performed study of non-magnetic impurity effects on the superconductivity, and magneto-thermal transport experiments in Lu_2Fe_3Si_5. And we obtained research results which strongly suggest the sign-reversed multigap superconductivity.The spinel cobaltite GeCo_2O_4 is a geometrically-frustrated magnet with orbital degrees of freedom, where an antiferromagnetic transition occurs despite the dominance of ferromagnetic exchange interactions. Inelastic neutron scattering experimets in GeCo_2O_4 observed a typical frustration effect of molecular spin excitations. Furthermore, ultrasound velocity measuremets in GeCo_2O_4 observed elastic anomalies driven by the molecular spin excitations, and elastic anomalies which strongly suggest the occurrence of magnetic-field induced orbital order-order transitions.