Samarium is deposited on Si(001) at various temperatures (room temperature to 400 A degrees 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 Sm-0 is found with an increasing amount of Sm2+. Freshly prepared Sm-0 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.