Formation and investigation of ultrathin layers of Co2FeSi ferromagnetic alloy synthesized on silicon covered with a CaF2 barrier layer

Abstract Ultrathin (∼2 nm) films of Co 2 FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ . Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF 2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3 p and Co 3 p electrons. The study shows that the synthesis of the Co 2 FeSi ferromagnetic alloy occurs in the temperature range of 200–400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF 2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.