Magnetic properties and X-ray absorption spectra of La0.7Ca0.3MnO3 nanoparticles

The magnetic properties and structural characterization of La0.7Ca0.3MnO3 nanoparticles (NPs) prepared by mechanical milling were investigated. By changing the milling time (tm) from 1 to 24 h, we obtained NPs with average crystallite sizes of 10–40 nm. The magnetic studies reveal that the Curie temperature (TC), magnetization, and maximum magnetic-entropy change of NPs decrease rapidly with increasing tm. Concurrently, there is a transformation of the first-order to second-order magnetic phase transition. The structural analyses based on X-ray absorption (XAS) spectroscopy prove the tm increase leading to a slight shift of the Mn K-shell absorption edge towards lower energies of Mn3+. It means more Mn3+ ions introduced to NPs as increasing tm, making the concentration ratio of Mn3+/Mn4+ in NPs greater than 7/3 if comparing to the as-prepared sample with tm = 0 h. Particularly, in the first region of extended XAS fine structure spectra, there is a shift of a hump towards higher energies. This is different...