The fluctuation of charge/orbital/spin ordering structure in Sm$_{1-x}$Sr$_{x}$MnO$_{3}$ (x = 0.55 and 0.6)

In over-doped Sm$_{1-x}$Sr$_{x}$MnO$_{3 }(x \quad >$ 0.5), the disorder due to ionic size mismatch of Sm and Sr cations is very large. A large disorder decreases the electronic correlation length and induces the electronic structure competition and hence the spatial phase fluctuation. In this study, the charge/orbital ordering (CO/OO) structure and magnetic domain structure in Sm$_{1-x}$Sr$_{x}$MnO$_{3}$ with doping levels of 0.55 and 0.6 have been examined by transmisstion electronic microscopy (TEM). For $x$ = 0.55, the CO/OO structure with commensurate modulation vector \textbf{\textit{Q}} = (0, 1/3, 0) is seen above the A-type transition temperature ($T_{NA} \quad \sim $ 180 K) and that with the incommensurate one below $T_{NA}$. For $x$ = 0.6, typical 180-degree magnetic domains were observed in the (110) plane below 50 K, indicating the canted AFM structure. This AFM structure locally collapses because of the existence of short-range CO.