Spin Dynamics near the Critical Point in (CH₃NH₃)₂CuCl₄

Abstract

A dip due to the critical slowing down was observed in the real part of the high frequency susceptibility just at T_c in a quasi-two dimensional ferromagnet (CH₃NH₃)₂CuCl₄. The critical exponent, Δ, of the relaxation time for the magnetization along the easy axis, which is defined as τ∝ε^−Δ (ε=(T−T_c)⁄T_c) was obtained as 1.05±0.05 for 0.003\lesssimε\lesssim0.1. The Cole-Cole plots revealed that the Cole-Cole semi-circle became slightly but definitely depressed as the transition point was deadly approached (ε\lesssim0.008).