  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. T_N decreases down to ~550 K for
particles of size ~5 nm from ~653 K in bulk while M_s 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 (del_Bi) and Fe (del_Fe) ions within a unit cell with the
decrease in particle size. The net unit-cell polarization P_S too, is found to
be larger in nanoscale regime.
