Growth process and magnetic properties of iron nanoparticles deposited on Si ₃N ₄/Si(111)-(8×8)

We investigated the growth process and magnetic properties of iron deposited on Si ₃N ₄/Si(111)-(8×8) and clean Si(111)-(7×7) substrates by scanning tunneling microscopy, x-ray magnetic circular dichroism, and the magneto-optical Kerr effect measurements. These experiments reveal that, on clean Si(111)-(7×7), 1.6-monolayer (ML) Fe forms iron silicide with a very small spin magnetic moment of m _spin=0.17 μ _B, whereas 1.6-ML Fe on Si ₃N ₄/Si(111) has a much larger spin magnetic moment of m _spin=2.62 μ _B, which is enhanced compared with that of bcc bulk Fe (2.2 μ _B). The Si ₃N ₄ surface is found to suppress the silicide formation effectively. Because of weak interaction between Fe and Si ₃N ₄ and possibly the mismatch of the lattice constant, Fe deposited on Si ₃N ₄/Si(111) grows as nanoparticles that exhibit superparamagnetism. Above 7.5 ML, most of the nanoparticles locate very closely to each other and become ferromagnetic.