Nanosized Sodium-Doped Lanthanum Manganites: Role of the Synthetic Route on Their Physical Properties

In this paper we present the results of the synthesis and characterization of nanocrystalline La 1 - x Na x MnO 3+ δ samples. Two synthetic routes were employed: polyacrylamide-based sol−gel and propellant synthesis. Pure, single-phase materials were obtained with grain size around 35 nm for the sol−gel samples and around 55 nm for the propellant samples, which moreover present a broader grain size distribution. For both series a superparamagnetic behavior was evidenced by means of magnetization and EPR measurements with peculiar features ascribable to the different grain sizes and morphology. Preliminary magnetoresistivity measurements show enhanced low-field (<1 T) magnetoresistance values which suggest an interesting applicative use of these manganites.