Phase Separation in La1-xSrxMnO3+δNanocrystals Studied by Electron Spin Resonance

Nanocrystals of La 1- x Sr x MnO 3+δ (0< x ≤0.51) with a diameter of about 8 nm were synthesized in the pores of the mesoporous silica SBA-15. The crystal structure at all Sr concentrations had a rhombohedral symmetry. The temperature dependence of the magnetization showed ferromagnetic and superparamagnetic behavior, and the magnetization curves indicate the coexistence of a ferromagnetic and an antiferromagnetic component. ESR spectra were observed even at 77 K and were well reproduced by the summation of two absorption lines with either a Gaussian or a Lorentzian profile. The temperature dependence in the ESR spectra suggests the coexistence of two components with two transition temperatures. The magnetic phase of the nanocrystals indicates the coexistence of a ferromagnetic and an antiferromagnetic phase at all Sr concentrations studied (0< x ≤0.51), with a smooth Sr dependence of the two transition temperatures. The experimental results suggest the existence of a phase separation into a ferromagnetic...