I present the results obtained from elastic scattering of metastable helium 23S atoms (He*) from the CoO(001) surface. Elastic, diffractive scattering of He* atoms revealed a 2 x 1 surface magnetic structure, consistent with a bulk termination. Studies of the temperature-dependence of the magnetic diffraction peak intensity has led to the observation of an anomalous temperature induced component in the antiferromagnetic (AFM) order on the CoO(001) surface.

This experimental technique is based on the fact that the post scattering survival probability of a He*atom depends on the relative orientation of the local surface electron-spin and the spin polarization of the He* atoms. A periodic modulation of the surface electron spin orientation will then result in a diffraction pattern of the scattered He*atoms that manifests this periodicity.

The experimental observations are discussed within the framework of a Bogolyubov-Peierls mean-field study and Monte-Carlo simulations performed for a three-dimensional lattice of interacting spins. They reveal the anomalous behavior to be closely associated with the presence of low lying surface-spin excited states.