Ferromagnetism induced by lattice volume expansion and amorphization in EuTiO[3] thin films

Abstract

Lattice volume expansion or amorphization renders EuTiO[3] ferromagnetic, although the stable phase of crystalline EuTiO[3] is an antiferromagnet. The lattice volume expansion is induced into the crystalline EuTiO[3] thin film by utilizing the lattice mismatch between the thin film and a substrate. The magnetization at low temperatures monotonically increases with an increase in lattice volume for the crystalline EuTiO3 thin film, coincident with the results of calculations based on the hybrid Hartree–Fock density functional approach. The ferromagnetic interaction between Eu[2+] ions is enhanced by the amorphization as well; the amorphous EuTiO[3] thin film becomes a ferromagnet, and the Curie temperature is higher for amorphous Eu[2]TiO[4] than for its crystalline counterpart. The phenomenon, that is, the volume expansion- and amophization-induced ferromagnetism, is explained in terms of the competition between ferromagnetic and antiferromagnetic interactions among Eu[2+] ions.