FMR Study of Co/Ti Bilayer Thin Films

Abstract

We focused on the interaction between two ferromagnetic cobalt layers through a non-magnetic titanium layer. The magnetic properties of the structure were characterized by ferromagnetic resonance technique. The data were collected as a function of non-magnetic titanium layer thickness. Co/Ti multilayer (Ti(50 angstrom)/ Co(45 angstrom)/Ti(2-40 angstrom)/Co(40 angstrom)/Ti(100 angstrom)) films were grown onto naturally oxidized p-type single crystal Si (100) substrate at UHV condition with magnetron sputtering system at room temperature. The thickness of Ti spacer layer ranges from 2 to 40 angstrom with 2 angstrom steps. We did not observe usual optic and acoustic modes; instead we had two broad overlapped peaks for the films ranged from 6 angstrom to 40 angstrom. One interesting result was the high anisotropic resonance field values for these films. Exchange coupling between ferromagnetic layers causes shift on resonance field values but these shifts in our samples were much larger than expected. This large anisotropic behavior is not clear at the moment. Our theoretical model was not able to determine a value for the exchange coupling parameter. One reason can be the close thickness values for Co sublayers. The other reason can be the Ti non-magnetic layer. If titanium did not grow layer by layer on cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a result one cannot observe exchange interaction between ferromagnetic layers through non-magnetic spacer.