Critical dynamics of the XY system in (CH3NH3)2FeCl4

Abstract

Dynamic critical phenomena on the structural phase transition from the tetragonal high-temperature phase to the orthorhombic room-temperature phase in ${\left(\mathrm{C}{\mathrm{H}}_3\mathrm{N}{\mathrm{H}}_3\right)}_2$Fe${\mathrm{Cl}}_4$ have been studied with ultrasonic attenuation measurements of the symmetry-breaking field ${\sigma }_{\mathrm{xy}}$. The obtained critical exponent $z\nu =1.40\mathrm{}$ for the characteristic relaxation time $\tau ={\tau }_0{t}^{-z\nu }$ confirms Murata's theoretical calculation for the three-dimensional $\mathrm{XY}$ model.