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講演者：Dr. J.E. Gubernatis (Theoretical Division, Los Alamos National Laboratory)

日時： １１月５日（月）　午後４時半から [いつもと曜日が異なります]
場所： 青山学院大学　理工学部（世田谷キャンパス）　一号館　５階　１５３８号室

講演題目： Basic Mechanism and Models for Itinerant Ferromagnetism
要旨：While itinerant ferromagnetism is a familiar and well-studied quantum phenomena, the microscopic mechanism driving this collective state is largely unknown. Part of the difficulty is the absence of controlled theories and simple models that produce the phenomena for the proper reasons. Mean field theories, for example, tend to estimate the energy of fully polarized states well but often underestimate the energy of non-magnetic states badly. In many models, itinerant ferromagnetism is thus predicted too favorably. This favorable situation contrasts that of more rigorous treatments of some models, like the one-band Hubbard model, that displays itinerant ferromagnetism only under unphysical circumstances. In this talk, I will present a simple mechanism for itinerant ferromagnetism that emerges from a simple two-band model, like the periodic Anderson model (PAM). I will show that the PAM supports the mechanism by demonstrating the consistency of an analytic derived effective Hamiltonian and the predictions of quantum Monte Carlo simulations of the PAM. I will also show how this mechanism supports the familiar ferromagnetism in the iron group and the anomalous ferromagnetism observed in certain ternary boride and actinide monochalcogenide compounds.