Systematic Investigation of Exchange Coupling in Thickness Gradient Fe/Sm-Co and Co/Sm-Co Magnetic Bilayers

ABSTRACTMagnetic bilayers Fe/Sm-Co and Co/Sm-Co have been fabricated with gradient thicknesses of the soft layers in order to systematically study the dependence of exchange coupling on the thickness of the soft layer. The films were deposited in a combinatorial magnetron-sputtering chamber, where the Fe and Co thickness wedges were created by the natural thickness gradient due to the deposition geometry. The soft layer was deposited at two different temperatures (150°C and 300°C) in order to study the effect of deposition temperature on the exchange coupling. The deposition of the Fe layer at the higher temperature (300°C) was found to enhance the interlayer exchange coupling between Fe and Sm-Co. The single-phase-like magnetization reversal critical thickness increases from 12 nm for Fe deposited at 150°C to 24 nm for Fe deposited at 300°C. We attribute the enhanced exchange coupling in Fe/Sm-Co bilayers to the interfacial mixing and the coherent growth of the Fe layer. On the other hand, we found that the exchange coupling between Co and Sm-Co is not sensitive to the growth temperature of the Co layer.