Séminaire du lundi 10 mai 2010 à 10h30

 Salle de conférence, bâtiment 15

Campus Boucicaut, 140 rue de Lourmel, 75015 Paris

Andrea GAUZZI (IMPMC-UMR 7509)

Télécharger le résumé du séminaire (207 KB) (Format PDF)

CRYSTALLOGRAPHIC EVIDENCE OF A COUPLING BETWEEN MAGNETIC AND FERROELECTRIC ORDER PARAMETERS IN BIMN₇O₁₂

Manganese oxides AMn₇O₁₂ (A=Na, Ca, La) with quadruple perovskite structure display charge, spin and magnetic orderings not observed in simple perovskites. Here we study the magnetic structure of the single-valent compounds LaMn₇O₁₂ and BiMn₇O₁₂, the quadruple perovskite counterpart of simple perovskites LaMnO₃ and BiMnO₃, respectively. By means of a neutron diffraction study, we found that in both compounds the A’ and B ions order antiferromagnetically (AFM) at low temperatures in an independent fashion. However, in spite of the common Mn³⁺ properties, the magnetic structures are strikingly different in the two compounds. In particular, in LaMn₇O₁₂ the structure of the B-site is of C-type, which contrasts the A-type structure reported for LaMnO₃. On the other hand, in BiMn₇O₁₂, the AFM structure of the B-site is characterized by two distinct propagation vectors (1/2,0,1/2) and (0,0,0). We discuss the origin of these differences in terms of the polar properties of the Bi 6s² lone pair, which gives a first evidence of coupling between magnetic and ferroelectric order parameters.