Nuclear magnetic resonance study of magnetic phase segregation in La1-xCaxMnO3

A Mn-55 nuclear magnetic resonance (NMR) study of the La1-xCaxMnO3 system, 0 < x < 1, is reported. For x < 0.3 and x > 0.5 the spin echo spectra contain resonance lines corresponding to both the microscopic ferromagnetic and antiferromagnetic regions. A resonance line near 380 MHz, which is similar to that of the spectrum of the ferromagnetic and metallic compounds (0.2 < x < 0.5) is observed for all x. This indicates the presence of clusters in which the Mn magnetic moments are double exchange coupled in the whole range of doping. Their hyperfine field exhibits a much weaker temperature dependence than that of the lines of the host. This reveals the greater strength of the magnetic coupling within the clusters than in the antiferromagnetic regions and indicates a weak magnetic coupling of the clusters to the host matrix. A comparison with the NMR results on the hole doped nonstoichiometric compounds, LaMnO3+delta is made. The temperature dependence of the line intensities corresponding to the double exchange clusters and to the host matrix is attributed to the evolution of the magnetic phases in the compounds. (C) 2000 American Institute of Physics. [S0021-8979(00)66908-6].