Mossbauer Study of Temperature-Dependent Cycloidal Ordering in BiFeO3 Nanoparticles

To study the effects of different temperatures and particle sizes on the anharmonic cycloidal spin structure in BiFeO3 nanoparticles, Mossbauer spectroscopy was applied to three sets of particles with different mean diameters in the range of 54 nm to 1.6 mu m at temperatures between 4.2 and 800 K. The paramagnetic transition showed a distinct broadening upon decreasing particle size with Neel temperatures decreasing from 652 to 631 K. The anharmonicity of the long-range cycloidal structure, calculated from experimental Mossbauer spectra, is revealed to decrease upon rising temperature, starting at 150200 K and reaching the harmonic state at about 400 K.