Hydrothermal synthesis and magnetic properties of RMn2O5 (R=La, Pr, Nd, Tb, Bi) and LaMn2O5+δ

RMn2O5 (R=La, Pr, Nd, Tb, Bi) crystallites were prepared by a mild hydrothermal method and characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and magnetic measurement. The formation of manganates was sensitive to the alkalinities and Mn-containing precursors of the reaction mixtures. This family of manganates is isostructural and has a space group of Pbam. The magnetic measurements for RMn2O5 showed an antiferromagnetic transition. The strong irreversibility between the ZFC and FC curves indicated a helicoidally magnetic structure below 40 K. The max d.c. susceptibilities of LaMn2O5+δ (δ=0.01, 0.06, 0.08, 0.16, 0.17) were found to be variable and the excess oxygen (δ) in the compounds was influenced by the alkalinity used in the hydrothermal synthesis. - Graphical abstract: Several RMn2O5 (R=La, Pr, Nd, Tb, Bi) and LaMn2O5+δ crystallites were prepared by the mild hydrothermal treatment of mixtures of rare-earth oxides, K-birnessite gel and KOH. The magnetic susceptibility measurements show an antiferromagnetic transition in RMn2O5 (R=Pr, Nd, Bi). Magnetic susceptibility of the LaMn2O5+δ was variable at low temperature due to the different oxygen excess in the compound, which is dominated by the different KOH concentration used in the hydrothermal synthesis