Effect of strontium substitution on the structural and magnetic properties of La1.8Sr0.2MMnO6(M=Ni,Co) layered manganites

Abstract

Sr doped perovskite La1.8Sr0.2MMnO6 (M = Ni, Co) have been synthesized using conventional solid state reaction technique to present a systematic study on their morphological, structural and magnetic properties. The surface morphology was characterized by FESEM images and the average grain size of the as-prepared samples are in the range of 0.2~0.7 μm for La1.8Sr0.2NiMnO6 and those for La1.8Sr0.2CoMnO6 manganites are 0.1~2.8 μm, which is significantly less than that of undoped LNMO and LCMO manganites. The X-ray diffraction patterns revealed that undoped La2MMnO6 (M = Ni and Co) manganites of monoclinic structure change to rhombohedral structure of Sr doped La1.8Sr0.2MMnO6manganites. The EDX spectra confirm the presence of all the constituent elements of La1.8Sr0.2MMnO6manganites. The XPS analysis informs about phase purity, binding energy and oxygen vacancy of La1.8Sr0.2MMnO6manganites. XPS measurements indicated the O 1s peak is around 530.42 eV for La1.8Sr0.2NiMnO6 and the O 1s peak is around 531.41 eV for La1.8Sr0.2CoMnO6 which also matchwell with previous investigation. The two Mn 2p peaks at 642.54 eVand 654.26 eV, with a binding energy gap of 11.72 eV, can be assigned to Mn 2p3/2 and Mn 2p1/2, respectively for La1.8Sr0.2NiMnO6 manganites and the two Mn 2p peaks at 641.32 eVand 653.05 eV, with a binding energy gap of 11.73 eV, can be assigned to Mn 2p3/2 and Mn 2p1/2, respectively of La1.8Sr0.2CoMnO6 manganites. Temperature dependent ZFC and FC magnetization curves for Sr doped LNMO exhibit a sharp FM to PM transition at 160±2 K which is about 120 K less than that of parent LNMO. But in case of Sr doped LCMO, a sharp FM to PM transition is observed at 220±2 K which is 8 K less than that of parent LCMO. The transition temperatures suggest that the effect of Sr on the transition temperature of LNMO is more significant than that of LCMO.The unsaturated linear curves without any detectable hysteresis clearly indicate the paramagnetic nature of La1.8Sr0.2MMnO6 manganites at room temperature.