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

We used resonant inelastic x-ray scattering (RIXS) at the Ni L3 edge to measure the dispersion of spin waves in NiO thin films along the [101], [001], and [111] directions. Samples with tensile and compressive in-plane strain show identical dispersion within the experimental uncertainty. The fitting of the data with a linear spin wave model applied to a three-dimensional Heisenberg antiferromagnetic lattice provides a leading superexchange parameter J?=18meV. The magnon energy at the Brillouin zone boundary and the value of J? are 5% smaller than those determined by inelastic neutron scattering on bulk single crystals. This discrepancy is likely induced by the strain or other structural differences between bulk and epitaxially grown samples. These results demonstrate the capabilities of high-resolution RIXS in the study of the magnetic structure of thin films and heterostructures for which neutron scattering is not sensitive enough.