|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1996 : ¥2,000,000 (Direct Cost : ¥2,000,000)
This research project planed to investigate the relationship between the quantum spin fluctuations and anomalous magnetism in S=1/2 quantum spin systems containing either the ladder or triangular lattice. Furthermore, we addressed the impurity and carrier doping effects into two-leg spin ladder systems.
We listed the following results.
1.Sr_2Cu_3O_5 exhibits the long-range magnetic order below -60 K and is characterized by quantum spin fluctuations above 200 K inherent to three-leg ladder.
2.Two-leg ladder compound LaCuO_<2.5> was suggested from the susceptibility measurement to have seemingly a spin gap as in SrCu_2O_3. From the Cu-NMR study, we, however, found that this compound was magnetically ordered below-120 K.A possible competition takes place between the spin liquid state with a spin gap and the magnetic ordered states.
3.S=1/2 triangular lattice LiNiO_2 exhibis no long-range order at low-T,although the ferromagnetic exchange interaction is expected among Ni spins from the suscept
ibility measurement, meaing no frustration. We proposed that the triangular lattice structure make two degenerated orbital states frustrated, leading to some orbital liquid ground states, which prevents the logn-range spin ordering.
4.In hole-doped two-leg spin ladder systems, Sr_<14-x>Ca_xCu_<24>O_<41>, magnitude of the spin gap, DELTA=510 K for Ca-undoped one decreases to 270 K for the Ca11.5.
5.The spin gap stays constant in going from the Ca9 to the Ca11.5.
6.In DELTA <= T,spin dynamics are well characterized by the one-dimensional quantum critical spin fluctuations, despite two chains are exchange-coupled to one another and holes are doped.
7.hole carrieres are localized at low T associated with quasi one-dimensional conducting channel in the ladder plane.
We have thus clarified novel characteristics of quantum spin fluctuations and anomalous magentism inherent to S=1/2 low-dimesional quantum spin systems. The present reaserch project enabled us to open new frontiers in the field.