ORBITAL ORDER AND ORBITAL FLUCTUATIONS IN COLOSSAL MAGNETORESISTIVE MANGANITES. AN INVESTIGATION WITH ~(55)Mn AND ~(139)La NMR

摘要

~(55)Mn and ~(139)La NMR techniques are shown to be an excellent tool for detecting changes in the local electronic properties of colossal magnetoresistance manganites. Based on this we discuss the possibility of detecting orbital ordering in ferromagnetic La_(1-x)Ca_xMnO3 (0.20≤_x<0.5). We also provide evidence about the formation of an unusual kind of phase separation in the low temperature regime of the ferromagnetic conductive regime of the magnetic phase diagram for x≥0.25. Specifically, we show that by lowering temperature, an extra NMR signal is formed in the ferromagnetic conductive phase, which originates from regions with extremely small magnetic anisotropy, possibly produced by strong orbital fluctuations.