Three-dimensional dispersion of spin waves measured in NiO by resonant inelastic x-ray scattering

The authors have investigated the dispersion of magnetic excitations in thin films of antiferromagnetic NiO using resonant inelastic x-ray scattering (RIXS) at the ${L}_{3}$ edge of nickel. They demonstrate here that, thanks to the recent improvements in energy resolution and scattering geometry, soft x-ray RIXS is a valid complement to inelastic neutron scattering in this field because it allows a clear identification of the spin-wave peaks not only in bulk crystals but also in thin films and heterostructures too small for neutron studies. Moreover, the spin-wave dispersion measured along three high-symmetry directions of the 3D fcc Brillouin zone allows an accurate determination of the main super-exchange integral ${J}^{\ensuremath{'}}$ that establishes the antiferromagnetic structure of NiO. This report demonstrates definitively that RIXS is not confined to 2D materials such as cuprates and can be a useful tool for the study of magnetic interaction in a wide class of 3$d$ transition metal systems.