Eur. Phys. J. B 25, 431-438 (2002)
https://doi.org/10.1140/epjb/e20020049

Polarization-flip transition under electric field in BCCD

¹ Laboratoire Léon Brillouin, CEA de Saclay, 91191 Gif-sur-Yvette, France
² Departamento de Física de la Matería Condensada, Facultad de Ciencias, Universidad del País Vasco, Apdo. 644, 48013 Bilbao, Spain
³ Departamento de Física Aplicada I, ETSIIT, Universidad del País Vasco, Apdo. 644, 48013 Bilbao, Spain
⁴ UMR 6511 du CNRS-Université de Rennes 1, Institut de Chimie de Rennes, Bâtiment 10B, Campus Beaulieu, Avenue du Général Leclerc, 35042 Rennes, France

Corresponding author: ^a kilik@llb.saclay.cea.fr

Received: 20 September 2001
Published online: 15 February 2002

Abstract

Three-axes elastic neutron scattering measurements demonstrate that the five-fold modulated phase (phase 1/5) of BCCD exhibits under electric field a phase transition without change of superlattice periodicity. Through the monitoring of high-order satellite diffraction peaks as a function of electric field and temperature, the competition between this phase and neighboring polar phases with other periods has been characterized. At a threshold electric field of about 20 kV/cm, a rather abrupt redistribution of the satellite intensities of phase 1/5 is observed, without change of the corresponding primary modulation wave vector (). A quantitative analysis of these intensity variations confirms the earlier conjecture based on dielectric experiments that the modulation essentially changes from a non-polar sequence 5up5down () of polarized z-perpendicular layers of basic semicells, to a polar sequence 6up4down (). The transition is caused by the flip of the average polarization of one of the interface layers, and can then be described as a bounded discrete motion of the wall separating positive and negative microdomains within the five-fold unit cell. This type of polarization-flip phase transition had been detected and characterized in one-dimensional theoretical models as generalized Frenkel-Kontorova models or spin chains with elastic couplings, but had not been anticipated in theoretical analyses of BCCD, for which other phenomenological or microscopic models (as the ANNNI model) have been considered adequate. Only recently and in view of the experimental results reported here, we demonstrated, using a general phenomenological displacive model, the possibility of this type of transition in systems as BCCD [Phys. Rev. B 62, 11418 (2000)]. Phase diagrams with spin-flip phase transitions yield very peculiar phase diagrams with a checkerboard topological structure and self-similar features. In particular, they may present special critical points as the so-called upsilon points [J. Statistical Phys. 62, 45 (1991)]. BCCD may be then the first experimental system where they could be observed.