Making EuO multiferroic by epitaxial strain engineering


Optical soft mode driven ferroelectric phase transition was discovered in IR spectra of tensile strained ferromagnetic EuO thin films. The phase transition was predicted already ten years ago in films with 4% strain, but we have observed it only now in films with 6.4% strain. As such strain tends to relax after the epitaxial growth of only a few monolayers, we have achieved it in (EuO)2/(BaO)2 superlattices grown epitaxially on LSAT substrates. The observation is supported by a new DFT calculation.

Optical soft mode in (EuO)2/(BaO)2 superlattice
Left: Theoretical strain dependence of the Eu ferroelectric soft mode frequency and of the spontaneous polarization Ps in (EuO)2/(BaO)2 superlattice obtained from the DFT calculations. Insets show schematic eigenvectors of the Eu and A2u symmetry polar phonons.
Rigth: Temperature dependence of the static permittivity of the EuO films and EuO layers in the (EuO)x/(BaO)y superlattices with various tensile strain.

Contact person: Stanislav Kamba