Evidence for Griffiths phase in multiferroic BiMnO₃ and BiFe₀.₅Mn₀.₅O₃ films

Abstract

Microstructure and magnetic properties of the BiMnO₃ and BiFe₀.₅Mn₀.₅O₃ films, prepared by the rf magnetron sputtering on LaAlO₃ (001) single-crystalline substrate, have been investigated. The selected-area electron diffraction analysis allows us to indentify the crystal structure of the BiMnO₃ film as an orthorhombic one while the BiFe₀.₅Mn₀.₅O₃ film has a hexagonal lattice symmetry. The high-resolution electron microscopy study reveals the presence of strip-domain phase with a periodic spacing of about 3c in both films. The magnetic measurements show that in addition to the basic paramagnetic phase, the films manifest the Griffiths phase behavior in a wide temperature range. We argue that the observed weak ferromagnetism is provided by an appearance of the strip-domain layered inclusions rather than the intrinsic physical origin of the films.