Spin Wave Excitations in Honeycomb Antiferromagnet MnTiO3

Abstract

Using inelastic neutron scattering, we investigate the spin wave excitations on the antiferromagnetic MnTiO3 (T-N = 65 K), which has the stacked honeycomb structure. At T = 2 K, the spin wave energy extends up to 10.7 meV with the zone-center anisotropy gap of 0.8 meV. Whereas the dispersion is also strong along the direction perpendicular to the honeycomb planes, the exchange cancellation causes the magnetic interactions to be effectively anisotropic below T-N. While the spin wave spectrum survives at temperatures above T-N, we find that the magnetic interactions become more anisotropic within the paramagnetic phase. These results suggest that the magnetic interaction in MnTiO3 crosses over from being three dimensional to two dimensional above T-N.