A possible coupling mechanism between magnetism and dielectric properties in EuTiO3

The dielectric constant of an incipient ferroelectric EuTiO3 exhibits a sharp decrease at about 5.5K, at which the antiferromagnetic ordering of the Eu spins simultaneously appears. This fact indicates the existence of a coupling between the magnetism and dielectric properties of EuTiO3. We propose a possible coupling mechanism between the magnetic and electrical subsystems as -g\dsuml \dsum〈i,j〉q2l\vec Si·\vec Sj. In the framework of soft-mode theory, we have obtained analytically a dielectric constant expression related to the spin correlation of nearest neighbours of Eu ions.