| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥300,000)
Fiscal Year 2007: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2006: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
Main emphasis of the research has been put on the pyrochlore magnet, a typical system showing geometrical frustration. Progress has been achieved on the following three topics, 1) vortex order in the triangular-lattice Heisenberg antiferromagnet, 2) the ordering of the Heisenberg pyrochlore antiferromagnet with the ferromagnetic second-neighbor interaction, and 3) the ordering of the Ising pyrochlore magnet with the long-range RKKY interaction. Concerning the subject 1), by means of extensive Monte Carlo simulation, we estimate the correlation length and the correlation time of the classical triangular-lattice Heisenberg antiferromagnet, revealing that the topological ordered state of the model is a peculiar "spin-gel" state which accompanies large and slow spin fluctuations. Concerning the subject 2), by means of extensive Monte Carlo simulations, it was established that the model exhibited a first-order transition into the peculiar ordered state in which a sharp Bragg peak characteri
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zed by an incommensurate wavevector appeared in the spin structure factor, yet the spin remained largely fluctuating. Concerning the subject 3), motivated by the recent interest in the ordering of "spin-ice" magnets, we have studied the ordering of the <111> Ising magnet with the long-range RKKY interaction, which is intended to model metallic "spin-ice" magnets such as Pr_2Ir_2O_7. We performed extensive Monte Carlo simulation by using the Ewald sum technique to fully take account of the long-range nature of the interaction. Depending on the parameter k_F. representing the Fermi wavevector, the model has turned out to exhibit rich ordering behaviors. In particular, we have found that the RKKY model corresponding to the experimental system takes "2-in 2-out" local spin structure at low temperatures under the antiferromagnetic Curie-Weiss constant, consistently with the experiment. By contrast, the model always exhibits a thermodynamic phase transition into the magnetic long-range ordered state, a spin-liquid-like behavior being never realized. Less
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