Eur. Phys. J. B 8, 31-41 (1999)
https://doi.org/10.1007/s100510050665

Evolution of charge ordering in Ca_1-xSm_xMnO₃ manganites (0.15≤x≤0.60)

Laboratoire CRISMAT (CNRS -UMR 6508) , ISMRA et Université de Caen, 6 Boulevard du Maréchal Juin, 14050 Caen Cedex, France

Received: 17 June 1998
Published online: 15 March 1999

Abstract

Charge ordering phenomena in the manganites Ca1-xSm_xMnO₃ have been studied for 3.15≤x≤0.60, using electron diffraction and lattice imaging, completed by magnetic and transport measurements. Three domains can be distinguished, depending on the nature of the structural transitions with temperature. For 0.15≤x<0.25, the structural transition from a pseudo-tetragonal to a monoclinic form, with decreasing temperature, coincides with the competition between ferromagnetism and antiferromagnetism that is characterized by the temperature T_peak on the M(T) curves; short-range charge ordering is observed for 3.20≤x<0.25 manganites. For the second domain, 3.25≤x≤0.50, a structural transition from an orthorhombic to a long-range charge ordered state is clearly observed with decreasing temperature. The corresponding temperature T_CO coincides with the temperature T_peak deduced from magnetic measurements. This long range charge ordering, which appears along a, is either commensurate or incommensurate depending on the x value, with a modulation qa^* vector, q being close to x. These modulated superstructures correspond to a stacking of single Mn³⁺ stripes with multiple Mn⁴⁺ stripes along a, either in a commensurate or in an incommensurate manner. The third domain 3.50<x≤0.60, is characterized by a transition to a charge ordered state with commensurate superstructure at low temperature. The latter can be described as a "partially" charge ordered state in which single "Mn³⁺" stripes alternate with mixed "Mn³⁺/Mn⁴⁺" stripes.