SPIN DYNAMICS NEAR THE CRITICAL-POINT IN (CH3NH3)2CUCL4

A dip due to the critical slowing down was observed in the real part of the high frequency susceptibility just at Tc 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 - Tc)/Tc) was obtained as 1.05 ±0.05 for 0.003≲ε≲0.1. The Cole-Cole plots revealed that the Cole-Cole semi-circle became slightly but definitely depressed as the transition point was deadly approached (ε≲0.008). © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.