Symmetry analysis for the RuddlesdenPopper systems Ca_{3}Mn_{2}O_{7} and Ca_{3}Ti_{2}O_{7}
Abstract
We perform a symmetry analysis of the zerotemperature instabilities of the tetragonal phase of Ca_{3}Mn_{2}O_{7} and Ca_{3}Ti_{2}O_{7} which is stable at high temperature. We introduce order parameters to characterize each of the possible lattice distortions to construct a Landau free energy which elucidates the proposed groupsubgroup relations for structural transitions in these systems. We include the coupling between the unstable distortion modes and the macroscopic strain tensor. We also analyze the symmetry of the dominantly antiferromagnetic ordering which allows weak ferromagnetism. We show that in this phase the weak ferromagnetic moment and the spontaneous ferroelectric polarization are coupled, so that by rotating one of these orderings by applying an external electric or magnetic field one can rotate the other ordering. We discuss the number of different domains (including phase domains) which exist in each of the phases and indicate how these may be observed. Firstprinciples calculations of Yildirim corroborate our assertion that domain walls in the nonferroelectric phase are narrow.
 Publication:

Physical Review B
 Pub Date:
 August 2011
 DOI:
 10.1103/PhysRevB.84.064116
 arXiv:
 arXiv:1101.2593
 Bibcode:
 2011PhRvB..84f4116H
 Keywords:

 61.66.Fn;
 61.50.Ks;
 75.85.+t;
 Inorganic compounds;
 Crystallographic aspects of phase transformations;
 pressure effects;
 Condensed Matter  Materials Science
 EPrint:
 21 pages, 14 figures