Volume and anisotropic spontaneous striction in layered manganites: Role of charge localization and magnetic interactions

expansion measurements have been performed on single crystals of R2-2xSr1+2 x Mn2O7 (R = Pr, Nd, and Dy) over a wide temperature range (4-900 K). Our a nalysis allows us to give a general explanation for the large lattice anoma lies observed in the layered manganites. Localization of the carriers gives rise to volume and anisotropic anomalies in the paramagnetic regime. The a nisotropic distortion is enhanced with the establishment of long-range anti ferromagnetism,whereas it is quenched by long-range ferromagnetic order.