Magnetodielectric Coupling in CoSeO$_4$

We investigate the magnetic phase diagram and magnetodielectric properties of CoSeO$_4$, a material which contains chains of edge-sharing octahedral Co(II) connected by tetrahedral SeO$_4$ units. Specific heat measurements in combination with powder neutron diffraction show a transition to long-range magnetic order below 30\,K. Fits to the high temperature susceptibility give a Curie-Weiss temperature of -35\,K, indicating the magnetic ground state has a dominant antiferromagnetic ordering. However, magnetization measurements in a field of 100 Oe also indicate the presence of weak ferromagnetism and a field-induced transition in fields larger than 30 kOe. The zero-field magnetic structure consists of Co moments aligning antiparallel to nearest neighbors down the length of the chains. We also present evidence of a linear magnetoelectric response in the ground state magnetic phase.