Strain induced magnetic transitions and spin reorientations in quantum paraelectric EuTiO 3 material

Strain induced magnetic transitions and spin reorientations in quantum paraelectric EuTiO3 material have been investigated using the first-principles calculations based on density functional theory. Four kinds of magnetic configurations and three possible directions of magnetic moments in every configuration are taken into consideration, respectively, in paraelectric and ferroelectric phases induced by the biaxial compressive and tensile strains. The calculated results indicate that the strain, regardless of the compressive or tensile strain, can induce not only the magnetic transitions from G-type antiferromagnetic to ferromagnetic phase, but also the reorientation of spin polarization in EuTiO3. The compressive strain can induce a ferromagnetic phase with spin polarization along a axis while the tensile one make magnetic moments along c axis. The further analysis for the electronic density of states (DOS) discover that the magnetic moment direction of EuTiO3 have intrinsic correlation with these orbitals, where the density of states are the most localized. In addition, Anderson super-exchange model is proposed to explain the changes of exchange coupling properties induced by the biaxial strains.