Improvement of microwave magnetic properties by inserting nonmagnetic layer

Co/NM (nonmagnetic Ag and SiO2)/Co sandwich structure films with different thicknesses of NM were fabricated on Si(111) substrate via oblique radio frequency sputtering. With increasing thickness of nonmagnetic Ag (t(Ag)), in-plane magnetic anisotropy field H-k initially increased from 100 Oe of t(Ag) = 0 nm to 220 Oe of t(Ag) = 1.5 nm, and then decreased when t(Ag) > 1.5 nm. Resonance frequency showed the same tendency with maximum 5.2 GHz when t(Ag) = 1.5 nm. Damp factor increased from 0.02 for t(Ag) = 0-0.08 for t(Ag) = 2.0 nm. The same result was observed in inserting oxide nonmagnetic SiO2 layer. This can be attributed to the competition between interface energy and exchange coupling energy.