Ferromagnetic and Charge-Ordered Phases in (Nd, Na)-Mn-O Compounds

Polycrystalline Nd1-x Na (x) MnO3 (x=0.05 - 0.20) compounds were prepared in single-phase form with a Pbnm space group. Paramagnetic to ferromagnetic transitions were observed up to a doping concentration of 15% with a maximum T (C) of 113 K. The x=0.20 sample exhibits a charge order transition at 180 K, with a distinct behavior in magnetization versus field curve. The magnetization versus temperature plot of all these materials exhibits an anomaly at around 40 K, with a signature of spin-glass like behavior. The x=0.10 sample is found to exhibit a maximum spontaneous magnetization value of 3.1 mu (B) at 20 K. The magnetization data could be analyzed based on the Brillouin function model, by accounting for the ferromagnetic interaction. The effective spin contribution of 3d electrons for the double-exchange ferromagnetic interaction and the value of magnetic spin-canting angles were estimated. The measured magnetization is explained on the basis of competing magnetic interaction due to spin-canting. The charge order quenching and the first-order transition from the charge-ordered to ferromagnetic phase are observed for a threshold field of 3 T at 12 K. The electrical resistivity of the above samples exhibits insulating behavior.