Ferroelectricity and ferromagnetism in EuTiO₃ nanowires

Анотація

We predicted the ferroelectric–ferromagnetic multiferroic properties of EuTiO₃ nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first-principles calculations. Since bulk EuTiO₃ is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the possibility of inducing the ferroelectric and ferromagnetic properties of EuTiO₃ by reducing the bulk to nanosystems. Our results indicate that ferroelectric spontaneous polarization of ∼0.1–0.5 C/m² is induced in EuTiO₃ nanowires due to the intrinsic surface stress, which is inversely proportional to the nanowire radius. Spontaneous polarization exists at temperatures lower than 300 K for wire diameter of ∼4 lattice constants with 10 N/m surface stress coefficient. Due to the strong biquadratic magnetoelectric coupling, the spontaneous polarization in turn induces the ferromagnetic phase at temperatures lower than 30 K for 2-nm nanowire and at temperatures lower than 10 K for 4-nm nanowire in EuTiO₃. Thus, we predicted that the EuTiO₃ nanowires can be the new ferroelectric–ferromagnetic multiferroic.