Correlating X-ray absorption spectra and ultraviolet photoelectron spectra to understand magnetic and transport properties of charge-ordered perovskite manganites

Abstract X-ray absorption spectra and ultraviolet photoelectron spectra have been used to compare the electronic structures of (La0.6Pr0.4)0.65Ca0.35MnO3 and (La0.4Pr0.6)0.65Ca0.35MnO3 systems to understand their magnetic and transport properties. Structural analysis showed that increased Pr-substitution triggers expansion in apical Mn-O bond lengths, which eventually causes narrowing of the eg band width. (La0.6Pr0.4)0.65Ca0.35MnO3 exhibits ferromagnetic ordering below 215 K and shows semiconductor to metal transition around 212 K, while (La0.4Pr0.6)0.65Ca0.35MnO3 exhibit complex magnetic behaviour and also show local semiconductor to metal transition around 95 K before re-entering into semiconducting region again below 80 K. A slight change in the slope of resistivity around 220 K and four orders increase in resistivity indicates presence of charge-ordering in (La0.4Pr0.6)0.65Ca0.35MnO3. Moreover, (La0.4Pr0.6)0.65Ca0.35MnO3 exhibits ~ 100% magneto-resistance. X-ray absorption studies of Mn-L2,3 edge and O-K edge reveal the onset of Mn3+-Mn4+ charge-ordering in (La0.4Pr0.6)0.65Ca0.35MnO3 at room temperature. O-K edge spectra exhibits an increased spectral intensity of O2p-Mn3d(eg) states near Fermi-level for (La0.4Pr0.6)0.65Ca0.35MnO3, which reflects the number of unoccupied eg states. Valence band ultraviolet photoemission spectroscopy study revealed that Mn3d(eg) states of (La0.6Pr0.4)0.65Ca0.35MnO3 extends into conduction band by crossing-over the Fermi-level. On the other hand, (La0.4Pr0.6)0.65Ca0.35MnO3 exhibits no electronic state at Fermi-level explaining stronger semiconducting nature of x = 0.6 system than x = 0.4 near room temperature.