Antiferromagnetic structure with strongly reduced ordered moment of p-electron in CsO₂

We have performed a powder neutron diffraction study on CsO2, where the unpaired electron with s = 1/2 in the pi* orbital of the O-2(-) ion is responsible for the magnetism. The magnetic reflections 0 1/2 0 and 0 1/2 1 were observed below the Neel temperature of about 10 K. An antiferromagnetic structure with a propagation vector of (0, 1/2, 0) and magnetic moments parallel to the a-axis is the most plausible. The magnitude of the ordered moment is about 0.2 mu(B), which is considered to be strongly reduced due to the one-dimensionality of the system. We propose a possible pi* orbital order that can explain the obtained magnetic structure, and discuss its relation to the one-dimensionality.