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Abstract: For the CuGeO3 doped with 1% of Fe, the quantum critical behaviour in a wide temperature range 1–40K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: α=0.34 ( B ∥ a and B ∥ c ) and ( B ∥ b ). New effect of the frequency dependence of the critical exponent is discussed. [Copyright &y& Elsevier]

Abstract: High-frequency electron spin resonance (ESR) measurements (60–100GHz) on a high-quality single crystal of EuB6 have been carried out at temperatures down to 1.8K. The ESR spectrum fine structure has been unambiguously determined for the first time in this experiment. In addition to the single resonance observed at high temperatures T>100K in previous reports, splitting of the resonance into two broad lines was detected below T 0≈80K. A decrease of temperature in the range T

Abstract: The results of high frequency (60–315GHz) studies of the electron spin resonance (ESR) in CuGeO3 single crystals containing 0.9% of the Mn impurity are reported. The quantitative ESR line shape analysis shows that the low-temperature (T<40K) magnetic susceptibility of Cu2+ chains diverges as χ∼1/T α with the critical exponent and therefore indicates an onset of a quantum critical (QC) regime. The scenario, in which disorder caused by the Mn impurity in quantum spin chains in CuGeO3 may lead to the co-existence of the QC regime and the spin-Peierls dimerisation, is discussed. [Copyright &y& Elsevier]