Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing temperature they become static and form a charge ordered (CO) phase below TCO=210 K. In the static regime, superlattice reflections are observed through neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l). Crystallographic analysis of the CO state demonstrates that the degree of charge and orbital ordering in this manganite is weaker than the charge ordering in three dimensional perovskite manganites. A TN=170K a type-A antiferromagnetism (AF) develops and competes with the charge ordering, that eventually melts below T*=100K. High resolution diffraction measurements suggest that that CO- and AF-states do not coincide within the same region in the material but rather co-exist as separate phases. The transition to type-A antiferromagnetism at lower temperatures is characterized by the competition between these two phases.
@article{arxiv.cond-mat/9912017,
title = {Charge Ordering and Phase Competition in the Layered Perovskite Lasr2mn2o7},
author = {D. N Argyriou and H. N. Bordallo1 and B. J. Campbell and A. K. Cheetham and D. E. Cox and J. S. Gardner and K. Hanif and A. dos Santos and G. F. Strouse},
journal= {arXiv preprint arXiv:cond-mat/9912017},
year = {2009}
}