Structural And Physical Properties Of Rare Earth Manganites Nd_1-xNa_xMnO₃(0.05≤x≤0.40)

We investigated the crystal structure, electrical transport, magnetic andmicro-magnetic properties of Na-doped neodymium manganites Nd1- NaxMnO3 x(0.05≤x≤0.40) prepared by Pechini process. X-ray powder diffraction and inductivecoupled plasma emission spectroscopy results indicate that the compounds arehomogenous and show single orthorhombic distorted perovskite structure. With theincreasing Na content, the unit-cell volume decreases and the structure becomescubic. The prepared compounds Nd1- NaxMnO3 (0.05≤x≤0.25) are insulating at xtemperatures ranging from 77 K to 300 K. The low- temperature resistivity decreasesbelow a certain Na concentration and increases above it. A ferromagnetic-to-paramagnetic phase transition was observed in the composition range of0.05≤x≤0.15 and higher Na doping (0.20≤x≤0.40) induces a charge orderingtransition at paramagnetic insulating state. In order to obtain further information on micro-magnetism of Nd1- NaxMnO3 x(0.15≤x≤0.30), electron spin resonance (ESR) was performed in the temperaturerange of 77-300 K. Temperature dependence of ESR parameters of typical x=0.15and 0.20 samples shows that all Mn spins (both Mn3+and Mn4+) contribute to theESR lines. The line width broadens with increasing temperature above 150 K forNd0.85Na0.15MnO3, which can be explained by spin-lattice relaxation model. A"knee" arising from charge disordering-ordering transition was observed at chargeordering transition temperature in the line width versus temperature curve for - ii -天津大学硕士学位论文Nd0.80Na0.20MnO3 sample. In addition, magnetic phase separation phenomenon was also observed. Below130 K, the distortions of resonance line are visible for x=0.20, which indicates theappearance of ferromagnetic phase. In other words, the ferromagnetic cluster andparamagnetic state coexist in the compounds. Finally, based on the experimentalresults mentioned above, a compositional phase diagram for Nd1- NaxMnO3 x(0.05≤x≤0.40) compounds is also presented.