Local Atomic and Electronic Structure with Magnetism of LaCaMnCuO ( x=0, 0.03, 0.06, 0.1).

Local atomic and electronic structure with magnetic properties, especially Griffiths phase, of polycrystalline samples LaCaMnCuO ( x=0, 0.03, 0.06, 0.1) have been studied. The X-ray absorption spectra (XAS) of Cu 2 p core level prove that the valence state of Cu ions exhibits trivalent state when doping content x≤0.06 and divalent Cu ions begin to show for x=0.1. For the valence states of Mn ions, the X-ray photoelectron spectroscopy data show that they are in mixed states of Mn and Mn, and a shift to lower binding energy is observed, which is not attributed to the variation of valence states of Mn ions but the change of crystallographic surroundings, because there is no obvious change detected by X-ray absorption fine structure spectroscopy (XAFS). The Debye-Waller factor ( σ) of x=0.1 sample is only slightly larger compared to x=0, which may be the origin of enhancement of Griffiths phase observed in the inverse-susceptibility as a function of temperature ( H/ M∼ T). The H/ M∼ T curves of Cu doped samples indicate coexistence of FM, AFM and PM phase above Curie temperature T, which may be related to the strong hybridization of O 2 p and Mn 3 d reflected by O 1 s XAS spectra. [ABSTRACT FROM AUTHOR]