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TT: Tiefe Temperaturen

TT 25: Correlated Electrons - Poster Session

TT 25.106: Poster

Wednesday, March 29, 2006, 14:30–18:30, P1

Novel mean-field theory for strongly disordered non-frustrated antiferromagnets — •Heidrun Weber and Matthias Vojta — Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, 76128 Karlsruhe, Germany

Quantum paramagnets with elementary spin-1 excitations show magnetic ordering upon introducing non-magnetic impurities: the vacancies produce free spins 1/2 which order antiferromagnetically at low temperatures. We have developed a novel mean-field theory for the impurity degrees of freedom, taking into account the random distribution of coupling constants. In particular, we demonstrate that the conventional first-order spin-flop transition is split into two transitions at low temperatures, associated with seperate order parameters along and perpendicular to the easy axis. We apply our results to impurity-induced order in spin-gap magnets like TlCuCl₃.