Charge ordering in $L_{1-x}{A}_x\mathrm{Mn}{\mathrm{O}}_3 (L=\mathrm{rare}\mathrm{earth}, A=\mathrm{C}\mathrm{a},\mathrm{S}\mathrm{r})$) depends strongly on the width of the $e_g$ band or on the average radius of the $A$-site cations, $〈r_A〉$. Investigations of ${\mathrm{Nd}}_{0.5}$${\mathrm{Ca}}_{0.5}$Mn${\mathrm{O}}_3$ with a small $〈r_A〉$ show evidence for a first -order transition due to charge ordering around 220 K, accompanied by a large decrease in volume (0.45%). Structural data at different temperatures indicate that the distortions within the structure are a direct result of charge ordering. Valence sum calculations show the presence of two differently charged Mn atoms. Electron transport and magnetic susceptibility measurements have been carried out down to low temperatures to understand the nature of the charge-ordered state. The charge-ordered state melts on the application of a magnetic field.

• Received 13 May 1996

DOI:https://doi.org/10.1103/PhysRevB.54.15303