Ultrafine La0.7Ca0.3MnOz powders with controlled oxygen stoichiometry have been synthesized by mechanical alloying at ambient temperature. It is found that high-energy ball milling of the starting materials, La2O3, CaO, MnO2, and Mn3O4 mixed in the stoichiometric cation ratio, yields single-phase La0.7Ca0.3MnOz powders having crystallite sizes of about 10 nm and various oxygen content (2.68 less than or equal to z less than or equal to 3.35), adjustable by changing the MnO2/Mn3O4 ratio, Magnetic measurements show that the spontaneous magnetization (M-s) of the as-milled powder depends less on the nominal Mn valence (nu(Mn)) than in bulk (La,Ca)MnO3 and that the maximum M-s, observed for nu(Mn) similar to 3.3, is much smaller. Annealing in air at temperatures above 500 degrees C increases M-s for all the samples, but a marked increase in M, toward the bulk value (similar to 90 emu/g) occurs in a lower temperature range for lower nu(Mn) than for higher nu(Mn). These observations are discussed in terms of magnetic disorder resulting from defects induced by high-energy milling and surface effects dominant in small crystals. (C) 2000 Academic Press.
Muroi, M., Street, R., & Mccormick, P. (2000). Structural and Magnetic Properties of Ultrafine La0.7Ca0.3MnOz Powders Prepared by Mechanical Alloying. Journal of Solid State Chemistry, 152, 503-510. https://doi.org/10.1006/jssc.2000.8719