Magnetization reversal and interlayer coupling in Co50Fe50 nanomagnets

We investigated magnetization reversal mechanism in elliptical shaped nanomagnets made from single layer and pseudospin valve Co50Fe50 films. The structures were fabricated using deep ultraviolet lithography and the lift-off process. We observed that the magnetization reversal process of the single layer elements is strongly dependent on the film thickness. For thickness t(CoFe)=10 nm, the magnetization reversal process is dominated by a systematic coherent rotation, whereas for t(CoFe)=60 nm, the reversal process is mediated by vortex nucleation, displacement, and annihilation. By exploiting the thickness dependence of the magnetization reversal process, pseudospin valve nanomagnets from two Co50Fe50 thicknesses (10 and 60 nm) were fabricated. We also investigated the effect of interlayer exchange coupling in pseudospin valve structures by varying the Cu spacer layer (t(Cu)). For t(Cu)<= 5 nm, the two ferromagnetic layers are found to be strongly coupled by exchange interaction. The strength of the coupling is significantly dependent on temperature. For t(Cu)>= 20 nm, the two Co50Fe50 layers are antiferromagnetically coupled at 300 K. As the temperature is reduced below 50 K, we observed a clear transition from antiferromagnetic to ferromagnetic coupling.