Uniform magnetic excitations in NiO nanoparticles

A sample of isolated disc shaped NiO nanoparticles was studied at the RITA-II triple axis spectrometer at SINQ (PSI) using the newly implemented multi-analyser blade imaging mode. The particles were 13 nm in diameter and had a thickness of about 2.5 nm. A non-dispersive spin excitation was observed at the antiferromagnetic ( 1 2 1 2 1 2 ) reflection at a scattering vector of κ = 1.30 A - 1 , at an energy of 0.51 ± 0.02 meV . This is shown to be due to uniform magnetic excitations in the nanoparticles.