Condensed Matter Physics Seminar

A-Site Disorder and Phase Separation of Manganites

Prof. J.–M. Liu
Laboratory of Solid State Microstructures, Nanjing University
International Center for Materials Physics, Chinese Academy of Sciences
Tuesday, December 5, 2006
Higgins 235, 3pm

Manganites, typical strongly correlated electron systems, have been extensively studied over the last decade not only because of their colossal magnetoresistance (CMR) effect. While a huge number of interesting phenomena associated with manganites have been revealed, a comprehensive understanding of the underlying physics remains to be a challenging issue. Conventionally, the scenario of electronic phase separation and percolation at various microscopic scales seems to be attractive, and it does shed some light on the microscopic origin of CMR effect. In this talk, I shall highlight our experiments on some intrinsic aspects associated with the phase separation sequences in manganites.

We study the effect of A-site cational size disorder on the magnetotransport behaviors of manganites. It is revealed that for the manganites of ferromagnetic metallic ground state, the ground state transits from ferromagnetic metal to cluster-glass insulator upon increasing disorder. The A-site disorder is believed to enhance the random local radial distortion of MnO6 octahedra and suppress the ferromagnetic long-range order. In the case of high A-site disorder, the long-range ferromagnetic ordering is completely melted into the short-range magnetically ordered clusters, which become frustrated at the frustrating point, below which a cluster-glass transition occurs due to the weak intercluster interaction. The above physical scenario can be further extended to manganites of charge (oribital) ordered (CO-OO) ground state and ferromagnetic ground state. The induced A-site disorder will destabilize the CO-OO state and ferromagnetic state, respectively, and bring the system into cluster-glass state. It seems that the disorder-induced phase separation represents an essential ingredient of CMR physics in manganites.