Ultrasonic Attenuation Study of the Order-Parameter Relaxation below the Néel Temperature in Rb₂CoF₄

抄録

Ultrasonic attenuation in Rb₂CoF₄ has been measured at frequencies ranging from 10 to 150 MHz below and above the Néel temperature T_N. The critical attenuation has been separated into the relaxation and fluctuation contributions. The relaxation contribution α_R takes a maximum below T_N and the temperature at which the maximum appears decreases as the frequency increases. Below T_N it is found that α_R is described by a scaling function, α_R∝ω^1+y′ f_R(ωτ′), where τ′=τ′_0mt^−x′ and t=1−T⁄T_N with the results x′=1.20±0.03 and y′=0.15±0.05. The scaling function f_R(ωτ′) takes such a form as 2ωτ′⁄[1+(ωτ′)²].