Critical Relaxation Studied by High Frequency Magnetic Susceptibility in Mn(COOCH₃)₂·4H₂O

Abstract

The critical relaxation of the uniform mode in Mn(COOCH₃)₂·4H₂O near the phase transition point was studied by using the high frequency susceptibility technique (up to 450 MHz). A dip was found in χ′(ω) just at T_N in the frequency range higher than 180 MHz. This is a clear evidence of the critical slowing down. The dispersion is found to be monodispersive except the immediate vicinity of the transition point, where it changes to slightly polydispersive. The relaxation time is expressed as τ∝ε^−Δ, Δ=1.30±0.03 for 3×10⁻²\lesssimε\lesssim1 (ε=|1−T⁄T_N|). The exponent Δ is smaller than that of the static susceptibility, γ=1.53±0.03 for 6×10⁻²\lesssimε\lesssim1.