Enhancement of charge ordered antiferromagnetic phase due to Sr doping in La0.45Ca0.55-xSrxMnO3

The transition from a charge ordered antiferromagnetic (CO AFM) state to an A-type AFM state induced by a substitution of A-site cation has been investigated in the La0.45Ca0.55-xSrxMnO3 system with the Mn4+ content of 0.49. The CO AFM phase transition becomes sharp while the average ionic radius of A-site cations increases with increasing x up to 0.2. At x≥0.4, the A-type AFM metallic phase dominates the magnetic and electronic properties at low temperatures. In the x=0.3 compound, the CO AFM phase coexists with the A-type AFM metallic phase. On cooling, the favorable transfer of eg electrons between Mn sites promotes the sharp CO AFM phase transition at x≤0.2 although the more favorable transfer induces the A-type AFM metallic phase at x≥0.3. In this system, the coexistence of the two phases at x=0.3 results in the largest reduction of resistivity under the magnetic field of 5 kOe near ferromagnetic-to-antiferromagnetic transition temperature