Interface magnetization of ultrathin epitaxial Co2FeSi(110)/Al2O3 films

Element-specific magnetic properties of ultrathin epitaxial Co2FeSi( 110) films were measured using x-ray magnetic circular dichroism ( XMCD). The epitaxial Heusler films were grown by RF magnetron sputtering on Al2O3( 1120) substrates. The magnetization of thicker films as determined by XMCD is smaller than expected for a half-metallic material. In addition, the magnetization decreases considerably for films thinner than 10 nm. The thickness dependence of the magnetic moment can be described by introducing a certain number of dead layers representing a deficiency of magnetization at the interfaces. Quantitative evaluation results in a dead layer thickness of 0.8 nm at room temperature, consisting of a temperature induced size effect of 0.1 nm and a surface effect of 0.15 nm at the top and 0.55 nm at the bottom interface.