Phase coexistence in manganites: doping and structural dependence

We present a study on the phase coexistence (PC) of paramagnetic insulating (PM-I) and ferromagnetic metallic (FM-M) phases in the La1−y(Ca1−xSrx )yMnO3 system with 0.23 y 0.45. The study was performed by means of magnetization and electron spin resonance (ESR) measurements. At high temperatures the ESR spectrum consists of a single symmetric PM line. At TC, a FM asymmetric line is observed shifted to low fields. In aT temperature range both lines are visible, defining a range of PC. For x = 0, we obtainedT as a function of the carrier concentration y, finding that the largestT corresponds to y = 0.25. For this y value, the extreme compounds are orthorhombic and rhombohedral for x = 0 and 1, respectively. The rhombohedral to orthorhombic temperature transition (TRO) was determined as a function of x. We found thatT � 0 only if TC < TRO. The PM-I/FM-M phase coexistence was only observed in the orthorhombic phase while seems to be incompatible with the more symmetric rhombohedral phase. (Some figures in this article are in colour only in the electronic version)