Abstract:
Single crystals of double manganites $R$BaMn$_2$O$_6$ ($R$ = Pr$_{0.5}$Nd$_{0.5}$, Nd$_{0.5}$Sm$_{0.5}$, Sm) were grown and the magnetic and optical properties in the near-IR range were studied. From the analysis of structural data, partial ordering of the R and Ba ions (A-site ordering) $\sim$50% was confirmed. According to magnetic data, the ferromagnetic contribution decreases and the coercive force increases as the average radius of the rare-earth ion decreases in the series Pr$_{0.5}$Nd$_{0.5}$$\to$ Nd$_{0.5}$Sm$_{0.5}$$\to$ Sm. From measurements of the temperature dependences of light transmission a change in the conductivity character from “semiconductor” to “metallic” at cooling was discovered: for manganite with Pr$_{0.5}$Nd$_{0.5}$ the conductivity change temperature $T_{\mathrm{MI}}$ is close to the magnetic phase transition temperature $T_c$, and for manganites with Nd$_{0.5}$Sm$_{0.5}$ or Sm the $T_{\mathrm{MI}}$ value is higher than $T_c$. Near $T_{\mathrm{MI}}$ in the manganites under consideration, the influence of the magnetic field on the transmission of light and the magnetotransmission effect were found. The highest magnetotransmission of 5% is observed in manganite with $R$ = Pr$_{0.5}$Nd$_{0.5}$.