16,959 research outputs found

    Hund's-Rule Coupling Effect in Itinerant Ferromagnetism

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    We present a general model which includes the ferromagnetic Kondo lattice and the Hubbard model as special cases. The stability of the ferromagnetic state is investigated variationally. We discuss the mechanism of ferromagnetism in metallic nickel, emphasizing the importance of orbital degeneracy and the effect of the Hund's-rule coupling.Comment: 19 pages, 10 figures, to appear in Prog.Theor.Phy

    Probability-Changing Cluster Algorithm for Potts Models

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    We propose a new effective cluster algorithm of tuning the critical point automatically, which is an extended version of Swendsen-Wang algorithm. We change the probability of connecting spins of the same type, p=1eJ/kBTp = 1 - e^{- J/ k_BT}, in the process of the Monte Carlo spin update. Since we approach the canonical ensemble asymptotically, we can use the finite-size scaling analysis for physical quantities near the critical point. Simulating the two-dimensional Potts models to demonstrate the validity of the algorithm, we have obtained the critical temperatures and critical exponents which are consistent with the exact values; the comparison has been made with the invaded cluster algorithm.Comment: 4 pages including 5 eps figures, RevTeX, to appear in Phys. Rev. Let