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A light scattering investigation of the incommensurate transition in BaMnF4
Authors:KB Lyons  HJ Guggenheim
Institution:Bell Laboratories, Murray Hill, New Jersey 07974, USA
Abstract:The results of a Brillouin scattering investigation of BaMnF4 near its incommensurate structural phase transition at Ti=247 K are reported. We have observed an anomalous dynamic central peak in the polarized (bb) spectrum, with q 6 c. This feature is visible only very near Ti, and possesses a width which is strongly wavevector dependent. The indicated behavior is Λ=Dtq2, with Dt=0.14 ± 0.02 cm2sec-1. It is identified as the result of a coupling between the LA phonon and the soft mode, where the latter contains a relaxing self energy due to a linear coupling to a diffusive process, possibly entropy fluctuations. The narrow central peak is not visible for q 6 a. In addition, we report an anomalous dispersion (~4%), in the LA mode propagating along c (Vcc) near Ti.
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