Anomalous nuclear relaxation in the ferromagnetic phase of the bilayered manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$.
ORAL
Abstract
In contrast to ferromagnetic (FM) 3D manganites, $^{55}$Mn NMR spectra obtained for the FM phase of the colossal magnetoresistance bilayer manganite La$_{1.2 }$Sr$_{1.8 }$Mn$_{2}$O$_{7}$ show a broad distribution of hyperfine fields implying a large distribution of local environments at Mn sites. The hyperfine distribution may be linked to orbital ordering effects. $^{55}$Mn spin -- lattice relaxation rates have a surprisingly weak dependence both on temperature and applied magnetic field. Significant departures of the relaxation rate from Korringa temperature dependence below 20 K provide evidence for non-Fermi liquid behavior in this quasi-2D metal. At temperatures approaching $T_{C }$ from below, further anomalous behavior is found consistent with spin polaron formation in the range where colossal magnetoresistance starts to appear.
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