In-situ TEM Analysis and Transport in Manganites La$_{5/8-y}$Pr$_{y}$Ca$_{3/8}$MnO$_{3}$ Exhibiting Phase Separation below Metal-Insulator Transition

Epitaxial films of doped La$_{5/8-y}$Pr$_{y}$Ca$_{3/8}$MnO$_{3}$ (LPCMO: y = 0.275-0.375) manganites were examined by \textit{in-situ} Lorentz microscopy and other TEM methods below the metal-insulator transition point T$_{MI}\sim $164 K. Such films are known for colossal magneto-resistance effect (CMR). Clear evidences were obtained for mesoscale two-phase separation process involving antiferromagnetic charge-ordered (AFM/CO) and ferromagnetic (FM) phases, coexisting below T$_{MI}$ in LPCMO films. The first-order CO-FM phase transition is accompanied by partial magnetic melting of the CO phase at CO/FM interfaces thereby creating charge-disordered spin-glass metastates. In contrast, FM phase shows specific ``zig-zag'' magnetic domains coupled with dense (101) crystal twins. This allows refining relations for charge-orbital and spin-ordering vectors in films. Transport resistance data show that T$_{MI}$ point is decreased with Pr$_{y}$ growth in LPCMO. On cooling films below T$_{MI}$ their resistance drops by several orders in magnitude. The observed M-I transition shows striking linear relation for log-conductance curve versus FM fraction measured by TEM, which does not follow typical percolation equations, suggesting that percolation transport model in manganites needs further revisions.