Evolution of charge ordering in Ca1-xSmxMnO3 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
Published online: 15 March 1999
Charge ordering phenomena in the manganites Ca1-xSmxMnO3 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 Tpeak 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 TCO coincides with the temperature Tpeak 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.
PACS: 61.14.-x – Electron diffraction and scattering / 75.30.-m – Intrinsic properties of magnetically ordered materials / 72.20.My – Galvanomagnetic and other magnetotransport effects
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999