In-depth study of structural, magnetic and XPS behavior of the double perovskite La2-xCex/2Erx/2NiMnO6

Abstract

Structural, morphological, X-ray photoelectron spectroscopy (XPS) and magnetic details of La2-xCex/2Erx/2NiMnO6 (x = 0.00 and 0.025) prepared by the traditional ceramic method were investigated. X ray-diffraction refinements by Rietveld method indicate that our samples have a monoclinic system with the space group P 21/n No. (14). A small amount of MnNi6O8 impurity was detected in both samples. Morphological analysis reveals that our samples contain grains of different sizes equal to 1.249 µm and 1.260 µm for x = 0.00 and 0.025. Mapping and EDX analysis confirm the existence and homogeneous distribution of elements on the surface of our samples. According to the x-ray photoelectron spectroscopy (XPS) analysis, the presence of a trivalent oxidation state La and RE ions, along with a mixed-valence state of Ni and Mn ions, has been confirmed in the samples. For magnetic analysis, a double transition temperature is detected from the dM/dT variation for the FC curve. The initial transition (T1) occurs at lower temperatures, approximately 105 K and 110 K for x = 0.00 and x = 0.025, respectively. On the other hand, the second transition T2 (Tc) takes place at higher temperatures, around 250 K and 265 K, respectively, for x = 0.00 and x = 0.025. These two magnetic transition temperatures are attributed to distinct spin states of Mn and Ni cations. Thus, the low-temperature transition (T1) can be attributed to a vibronic super-exchange interaction involving trivalent oxidation states, specifically Ni3+–O–Mn3+. The higher temperature transition T2 (Tc) was defined as the Curie temperature when the system undergoes a transition from the ferromagnetic (FM) to the paramagnetic state (PM). The magnetocaloric effect (MCE) exhibits the presence of two prominent peaks. The first one is at low temperature around 80 K. The second is at high temperature around 250 K. A phonemological approach called Landau theory was used to deduce the variation of the magnetic entropy (-ΔSM). Good agreement is obtained between the experimental behavior of (- ΔSM) and that predicted by this theory.