Structural and Magnetic Properties of Ultrafine La0.7Ca0.3MnOz Powders Prepared by Mechanical Alloying

✍ Scribed by M. Muroi; R. Street; P.G. McCormick

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 238 KB
• Volume: 152
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2000.8719

✦ Synopsis

z 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, La 2 O 3 , CaO, MnO 2 , and Mn 3 O 4 mixed in the stoichiometric cation ratio, yields single-phase La 0.7 Ca 0.3 MnO z powders having crystallite sizes of about 10 nm and various oxygen content (2.684z43.35), adjustable by changing the MnO 2 /Mn 3 O 4 ratio. Magnetic measurements show that the spontaneous magnetization (M s ) of the as-milled powder depends less on the nominal Mn valence (v Mn ) than in bulk (La, Ca)MnO 3 and that the maximum M s , observed for v Mn &3.3, is much smaller. Annealing in air at temperatures above 5003C increases M s for all the samples, but a marked increase in M s toward the bulk value (&90 emu/g) occurs in a lower temperature range for lower v Mn than for higher v Mn . These observations are discussed in terms of magnetic disorder resulting from defects induced by high-energy milling and surface e4ects dominant in small crystals.