NMR as a local probe of magnetic anisotropy: The possibility of orbital ordering and orbital liquid states in colossal magnetoresistance manganites

Abstract

${}^{139}\mathrm{La}$ rf enhancement experiments are shown to be an excellent tool for detecting changes of the local magnetic anisotropy in colossal magnetoresistance manganites. Based on this, we discuss the possibility of orbital ordering in ferromagnetic (FM) ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3},$ and provide evidence about the formation of an unusual kind of phase separation in the low temperature regime of the FM conductive (FMC) phase for $0.25l~xl0.5.$ We show that by lowering temperature, an extra NMR signal is formed in the FMC phase, which originates from regions with vanishingly small magnetic anisotropy. We anticipate that this feature is due to the formation of regions with strong orbital fluctuations within an orbitally frozen matrix.