Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3

The dielectric constant of the incipient ferroelectric EuTiO3 exhibits a sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering of the Eu spins simultaneously appears, indicating coupling between the magnetism and dielectric properties. This may be attributed to the modification of the soft-phonon mode, T1μ, which is the main contribution to the large dielectric constant, by the Eu spins(7μB per Eu). By adding the coupling term between the magnetic and electrical subsystems as −g∑ l ∑