Giant magnetocapacitance in cerium sesquioxide

We report structural, magnetic, magnetodielectric, and specific heat properties of hexagonal polymorph of ${\mathrm{Ce}}₂{\mathrm{O}}₃$. The $A$-type hexagonal ${\mathrm{Ce}}₂{\mathrm{O}}₃$ crystallizes in the $P\overline{3}2/m1$ space group and shows antiferromagnetic ordering at ${T}_{\mathrm{N}}\ensuremath{\approx}6.2$ K as detected by magnetic susceptibility measurements. The magnetic ordering is accompanied by a $\ensuremath{\lambda}$-shape specific heat anomaly with a peak maximum at $T\ensuremath{\approx}6.1$ K. An isotropic dielectric constant demonstrates a large magnetocapacitance effect at $T={T}_{\mathrm{N}}$, which saturates at $\ensuremath{\sim}80$ kOe. In the magnetically ordered phase the relaxation rate of the dielectric polarization increases with the magnetic field and shows divergence as the temperature approaches ${T}_{\mathrm{N}}$. The magnetic calculations indicate that ${\mathrm{Ce}}₂{\mathrm{O}}₃$ undergoes ``easy plane'' AFM ordering, which is also supported by the neutron diffraction data.