Exchange coupling in FeCoB/Ru, Mo/FeCoB trilayer structures

Abstract

In this work, bilinear (J1) and biquadratic (J2) coupling between two FeCoB layers across Ru and Mo spacer layers is studied. The investigated structures are FM1/Ru and Mo(d)/FM2, where FM1 is Fe/FeCoB, FM2 is FeCoB/NiFe, and d is the thickness of the Ru and Mo spacer layers where d is varied from 0.3 to 1.5 nm. Using a ferromagnetic resonance(FMR) model, we are able to determine J1–2J2 of all as-deposited samples and those annealed at 200 and 300 °C. FMR measurements are also used to extract Gilbert damping of the magnetic films. We also use a micromagnetic model to fit magnetization as a function of field to determine J1 and J2 independently for antiferromagnetically coupled samples. This study shows that the spacer layer thickness range, for which antiferromagnetic coupling between FeCoB layer can be achieved, is reduced with increasing annealing temperature. Antiferromagnetic coupling is not realized in samples annealed at 300 °C. The damping of magnetic layers first rapidly increases and then gradually decreases with an increase in the spacer layer thickness. The exchange coupling and spin pumping in the studied structures are responsible for this trend.