Epitaxial ferromagnetic samarium and samarium silicide synthesized on Si(001)

Samarium is deposited on Si(001) at various temperatures (room temperature to 400 °C), and the surface structure, interface reactivity, electron configuration, and magnetic properties are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and magneto-optical Kerr effect (MOKE), respectively. It is found that metal Sm is present on samples prepared at room temperature with an interface layer containing mostly Sm²⁺ and a lower amount of Sm³⁺. When samples are prepared at high temperature, much less Sm⁰ is found with an increasing amount of Sm²⁺. Freshly prepared Sm⁰ and SmSi₂ layers react strongly with oxygen from the residual gas, promoting formation of Sm₂O₃ at the expense of both metal Sm and SmSi₂. Room temperature ferromagnetism is observed for all prepared layers with a decrease of the saturation magnetisation when samples are prepared at high temperature. It is found that ferromagnetism implies mostly Sm³⁺ and Sm metal. In addition to these findings, this work proposes a new assignment of the Sm 3d chemically shifted components. Also, a noticeable variation of the XPS Sm 3d spin-orbit splitting is found as a function of the Sm ionization state.