| Research Abstract |
The purpose of the present research is to elucidate the quantum spin effects in low dimensional magnets, especially in bond alternating chain and spin ladder systems using molecule-based magnetic complexes. We performed various experiments including nuclear magnetic resonance (NMR), electron spin resonance (ECR), neutron scattering, muon spin relaxation (uSR), high field magnetization as well as susceptibility and specific measurements. We obtained the following results.
1.Study of quantum effects of composite spin systems composed of S=1/2 subelements.
(1) We studied new quantum spin effects in one-dimensional S=1/2 trimer systems, 3CuCl_2・dioxane and A_3Cu_3(PO_4)_4, in which ferromagnetic or antiferromagnetic trimers composed of three S=1/2 spins are respectively, weakly coupled antiferromagnetically in one dimension. We found peculiar magnetic properties characteristic of composite spin systems with nonuniform spatial structure.
(2) We performed the susceptibility, high field magnetiz
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ation and NMR measurements on a S=1/2 alternating linear chain system CuCl_2・2picolin, uniform linear chain systemCuBr_2・2picolin and their mixed compounds CuCl_<281-x)>Br_<2x>・2picolin (0<x<1). We founda systematic change in singlet-ground-state properties as a function of composition as a result of a formation or destruction of the quantum spin gap due to the effects of bond alternation and randomness.
2.Study of singlet-ground-state in antiferromagnetic quantum spin chains.
(1) We performed a systematic study on the impurity effects on the intimately related quantum states in the Haldane and spin-Peierls systems, S=1 NiC_2O_4・2DMIz and S=1/2 CuGeO_3. We found that the SP state is very unstable and the broken SP state results in the appearance of the antiferromagnetic staggered moments, while the Haldane state is stable against nonmagnetic impurity doping up to 20%.
(2) We performed the ESR measurements on the Zn-doped NENP,S=1 Haldane system with nonmagnetic impurities. A new interpretation was proposed that observed signals are due to the S=1/2 broken valence bond which is subjected to the field-induced staggered internal fields produced by the underlying antiferromagnetic lattice.
(3) We studied the S=1 quasi-one dimensional Heisenbergantiferromagnet CsNiCl_3 which undergoes 3D ordering at T_N=4.8K,in order to revel the effect of the interchain coupling on the Haldane state. We found that the Haldane state really exists in the 1D phase above T_N. We confirmed the S=1/2 edge states characteristic of the Haldane state and revealed a crossover from the quantum to classical regimes as a function of both temperature and magnetic field. Less
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