Particle size dependence of magnetization and noncentrosymmetry in nanoscale BiFeO3

The saturation magnetization (M-S), antiferromagnetic transition point (T-N), and the off-center displacements of Bi and Fe ions have been measured as a function of particle size in nanoscale BiFeO3. TN decreases down to similar to 550 K for particles of size similar to 5 nm from similar to 653 K in bulk, while MS rises by more than an order of magnitude. Analysis of crystallographic structure from Rietveld refinement of x-ray diffraction patterns shows significant rise in off-center displacements of Bi (delta(Bi)) and Fe (delta(Fe)) ions within a unit cell with the decrease in particle size. The net unit-cell polarization PS too, is found to be larger in nanoscale regime. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3567038]