Disorder and double-exchange spin dynamics in La0.7 Sr0.3 Mn O3 and La0.7 Sr0.3 Co O3 from NMR hyperfine couplings

The hole-doped transition metal oxides La1-x Srx Mn O3 (LSMO) and La1-x Srx Co O3 (LSCO) show certain similarities to each other in their physical properties but also marked differences. In the metallic-ferromagnetic doping range, important properties of these materials, such as nanoscale phase separation, are due to competing double-exchange ordering interactions and disordering Jahn-Teller (JT) distortions. The present experiments have used low magnetic field NMR of the Mn55 and Co59 transition metal ion nuclei in x=0.3 samples to obtain information on changes in hyperfine couplings and spin dynamics as a function of temperature. At low temperatures, anisotropy effects linked to lattice distortions are more important in LSCO than in LSMO. Structural distortions become important in LSMO above 120 K.