Dynamical Aspect of Critical Fluctuation of a Quasi One-Dimensional Ising-like Ferromagnet (CH3)3NHCoCl3·2H2O

Abstract

The complex susceptibilities of (CH 3 ) 3 NHCoCl 3 ·2H 2 O along the a - and c -axes, χ a * (ω) and χ c * (ω), are measured in the frequency range from 50 Hz to 100 MHz. These quantities reflect the dynamical features of the staggered and the uniform mode fluctuations along the easy ( c ) axis, respectively, in this three-dimensionally antiferromagnetic system. χ a * (ω) shows the Debye type dispersion above T N . A dip in the χ a * (ω)- T curve is observed just at T N at the frequencies above 2 MHz, indicating the critical slowing down of the staggered mode. The characteristic time constant τ a diverges at T N as ε - Δ ( ε = T / T N -1) with the critical index Δ =1.20 ±0.05, which is the same as the index γ=1.21 ±0.05 of the static susceptibility χ a . While, χ c * (ω) shows the non-Debye type dispersion (Cole-Cole arc). The time constant τ c increases as T N is approached from high temperature side but it does not diverge at T N .