ORBITAL GLASS INDUCED BY 2D ANTIFERROMAGNETIC FLUCTUATIONS IN EU2CUO4

A low-frequency dispersion of the permittivity which is characteristic of structural glasses [E. Courtens, Phys. Rev. B 33, 2975 (1986)] has been observed in an insulating single crystal of Eu2CuO4 in the tempe rature range 120-300 K. A model in which the glassy behavior arises in the orbital magnetic system of Jahn-Teller Cu2+ ions is proposed. Thi s behavior arises because the interaction of tetragonal magnetic doubl ets through the 2D AFM spin subsystem is a variable-sign long-range in teraction. It is suggested that this interaction leads, by virtue of a transition to chaos, to a glassy behavior even in an ordered system.