3D-XY critical behavior of CsMnF3 from static and dynamic thermal properties

摘要

Static and dynamic critical behavior of the easyplane antiferromagnet CsMnF3 have been studied by means of a highresolution ac photopyroelectric calorimeter.Thermal diffusivity,thermal conductivity and specific heat have been carefully measured in the near vicinity of the antiferromagnetic to paramagnetic transition (51.1 K).Specific heat and thermal diffusivity show singularities at the Néel temperature while thermal conductivity does not.Both the static and dynamic critical parameters agree with the standard 3DXY universality class (α=-0.014,A~+=A~- =1.06): for specific heat α=0.016,A~+=A~- =1.09 and for thermal diffusivity b=-0.010,U~+=U~- =1.09.As the dynamic critical behavior of thermal diffusivity has not yet been theoretically established for the 3DXY universality class,an approximate equation relating static and dynamic critical parameters has been obtained for it,leading to b≈and A~+=A~-≈U~+=U~- by studying the asymptotic behavior of the functions.This equation has also been experimentally verified for another XY antiferromagnet.SmMnO_3.As an easyplane antiferromagnet with a hexagonal structure,CsMnF_3 could have been expected to comply with the 3DXY chiral class (α=+0.34,A~+=A~- =0.36) (as is the case of CsMnBr_3),but the experimental results rule out that possibility.This is attributed to the presence of a small inplane anisotropy of the spins in CsMnF_3,which breaks the chiral degeneracy of the 120° spin structure.