Local structural variation as source of magnetic moment reduction in BaFe₂As₂

We report time-of-flight neutron powder diffraction results on stoichiometric BaFe₂As₂. Pair distribution function analysis shows that the orthorhombic distortion in the a-b plane at short distances are significantly different from the average lattice distortion, indicating local variations in the lattice at short range. We propose that this local variation reflects a high density of nanotwins, short-ranged structures which locally affect the magnetic alignment. This result suggests that the discrepancies between the observed and calculated magnetic moments in BaFe ₂As₂ arise partly from short-ranged variation of the lattice in the a-b plane.