Investigations of new field induced quantum phenomena in magnetic systems by high field ESR and neutron diffraction measurements

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New model substances for diamond chain, delta chain and zig-zag chain systems are found, and following new field induced quantum phenomena have been investigated.1) The model substance of diamond chain Cu_3(CO_3)_2(OH)_2 has been found for the first time. The magnetic susceptibility result shows two peaks and it suggests that two kinds of short range order exist in the system. Low temperature magnetization measurements show 1/3 magnetization plateau, which has been observed in the diamond chain model substance for the first time. The exchange interactions of Cu_3(CO_3)_2(OH)_2 are determined by analyzing the magnetization curve by the theory. High field ESR measurements of shows the dynamics of the system and the direct transition which changes at the magnetization plateau.2) The breather mode up to the saturation magnetization, the decrease of the field induce gap under the high field and the cross-over effect of the excited mode above the saturation field have been observed in the on … More e dimensional antiferromagnet Cu-benzoate. The breather mode is also observed in the one dimensional mixed crystal system BaCu_2(Si_<1-x>Gex)_2O_7.3) Two-triplet bound state is investigated in details for two dimensional dimer system SrCu_2(BO_3)_2.4) The magnetization plateau has been observed in the giant magnetic molecule for the first time, and the frustration effect in the system is discussed.5) High field ESR system under high pressure has been developed. The suppression of the spin gap under pressure at 4.2 K has been observed directly in the dimer system KCuCl_3 by observing the direct transition using our new high field ESR system under pressure up to 10 kbar.6) The fine energy structure of the finite Haldane chain system has been investigated by high field ESR. Owing to the high spectral resolution by high fields and high frequencies, observed ESR signals can be separated into the contributions of the finite chains with various chain length. The chain length dependence of the interaction has been obtained experimentally for the first time, and the correlation length in the real system is discussed. Less