Size-induced changes of structural and ferromagnetic properties in La1-xSrxMnO3 nanoparticles

La1-xSrxMnO3 nanocrystals were grown using a microemulsion approach with different water-to-surfactant ratios Rw resulting in diameters between 20 and 40 nm. The variation of Rw entails a variation in the Sr concentrations between x = 0.35 and 0.50. This technique allows the controlled growth of structurally well-defined nanoparticles using the same calcination conditions. With decreasing particle size, the unit-cell volume increases together with the Mn–O bond length, while the Mn–O–Mn bond angle was found to decrease. The size-dependent change of structural properties is possibly related to surface effects or disorder. With the decrease in particle size, the ferromagnetic ordering temperature TC decreases significantly by up to 20%. The reduction of TC can be well understood with respect to the structural changes: the increase of Mn–O bond length and the decrease of Mn–O–Mn bond angle weaken the double-exchange coupling and hence reduce T C. In addition the intrinsic finite-size effect reduces T C. The ...