Quantum Criticality and Collective Effects in Low-Dimensional Magnet CuGeO3:Fe Probed by High Frequency EPR

For CuGeO3 single crystals doped with 1% of Fe, the quantum critical behavior in a wide temperature range 1–40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: α = 0.34 (B ‖ a and B ‖ c) and α = 0.31 (B ‖ b). The description of the temperature dependencies of the line width and g-factor could be obtained in the Oshikawa-Affleck theory assuming that staggered component of the magnetic moment is located predominantly along b-axis. Possible arguments favoring the competition between effects of the staggered field and antiferromagnetic ordering are provided.