The Effect of the Superlattice on the Magnetic and Transport Properties of Epitaxial Magnetite Thin Films

Abstract

The surface structural, transport, and magnetic properties of superlattice films were examined, focusing on the effects of the superlattice periodicity of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO) layers. The superlattice structures of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO)n ultrathin films were fabricated using molecular-beam epitaxy on MgO(001) substrates, where n is the number of layers. It was observed that these oxide films have a single crystalline quality with the same orientation as the substrates for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> as thin as approximately three unit cells. The transport and magnetic results showed that the conductivity and magnetization of the superlattice increase as the number of (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO) layers is increased. Furthermore, a sharp Verwey transition was found in the (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO)n superlattices with thickness layer smaller than seen in an earlier study for a single or superlattice film. These results give the indication that Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> superlattice ultrathin films have better properties than single layers of the same thickness. This artificial growth of superlattice ultrathin films will provide a useful method to realize novel properties for other complex oxide systems.