The Fe3Si(24 nm)/CaF2(2 nm)/Fe3Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF2/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe3Si underlayer was grown epitaxially on CaF2/Si(111) at approximately 400 degrees C; however, the surface of the Fe3Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF2 barrier layer. The average roughness (Ra) of the CaF2 barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 degrees C on CaF2/Si(111), followed by annealing at 250 degrees C for 30 min to form the Fe3Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field H-c of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT). (c) 2007 Elsevier B.V. All rights reserved.