L139aNMR Investigation of Quasistatic Orbital Ordering inLa1−xCaxMnO3

We report ${}^{139}\mathrm{La}$ nuclear magnetic resonance in ferromagnetic and insulating (FMI) ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$, $0.10\le x\le 0.20$, which at low temperatures shows the formation of Mn octants with enhanced Mn-O wave function overlapping and electron-spin alignment. The rapid increase of the relaxation rates and the “wipeout” of the ${}^{139}\mathrm{La}$ NMR signal intensity on heating, imply a quasistatic character for the Mn octant cells in the FMI phase, which freeze below a transition temperature $T_f$.