Abstract
A tunable hydrothermal synthesis of single-crystalline BaMnO3 nanoparticles is reported. The parameters governing the synthesis pathway are carefully evaluated, assessing their influence on both the morphology and size of the as-prepared products. The reactor filling volume is found to have a main influence on the particle shape (predominance of microrods for a filling volume of 70% and particles for ca 40−50 %), whereas the alkalinity is crucial for the control over the size: higher alkalinities lead to a drastic decrease in both final particle size and aspect ratio. Average minimum particle diameters of ca 20 nm are prepared using a KOH concentration of 20 M, metallic salts concentrations of 50 or 100 mM, and a filling volume of 53%. Finally, the temperature and time exert a minor influence on the final structural properties of the resulting products: 200 °C and lower (even 150°C) and times of 24 hours or less (4 hours) are suitable for nanoparticles formation. The ability to synthesize nanoscale manganites with a narrow particle size distribution has allowed the study of the correlation between the nanoparticle average diameter and magnetic properties. An exchange bias phenomenology is observed in nanosized BaMnO3 as a result of ferromagnetic (FM) correlations in coexistence with a dominant antiferromagnetism. The stronger FM correlations in smaller nanoparticles lead to larger remanence and smaller exchange bias fields.
Published Version
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