Direct Observation of Coherent Exchange Scattering by Low-Energy Electron Diffraction from Antiferromagnetic NiO

Coherent exchange scattering has been observed in low-energy electron diffraction from antiferromagnetic NiO. Half-order diffraction beams which correspond to the translational symmetry of the magnetic cell occur below the Néel temperature, $T_{\mathrm{N}}=525\mathrm{}$°K, and disappear at $T_{\mathrm{N}}$. These beams are attributed entirely to exchange scattering because of their intensity, which is much too great to be accounted for by direct dipole-dipole and spin-orbit interactions.