Magnetic structure of CoO studied by neutron and synchrotron x-ray diffraction

Below T_N=289 K, the antiferromagnet CoO exhibits magnetic long-range order described by a propagation vector along the trigonal axis, whereas the lattice is distorted monoclinicly along both the tetragonal and the trigonal axes. In order to elucidate this inconsistency, we performed neutron and synchrotron x-ray diffraction experiments on single crystals of CoO, and found a series of magnetic reflections represented by a propagation vector along the tetragonal axis below T_N. These results suggest an altered magnetic structure of CoO, which includes both the trigonal and the tetragonal propagation vectors, has a monoclinic symmetry, and which is in accordance with the distorted lattice symmetry.