In-situ scanning tunneling microscopy observation of surfaces exhibiting ferromagnetic dipolar coupling

We have investigated a number of surfaces that exhibit dipolar coupling using in-situ STM. Co and Cu layers were characterized for their roughness and the resulting parameters were used to calculate a value for the interlayer coupling from a theoretical expression. The films were grown on Pt on Al2O3 to facilitate transport measurements. Using the hysteresis loops from spin valves made from these layers, the actual coupling could be compared to the theoretical value when the surfaces were modeled as sinusoidal. The results give an order-of-magnitude agreement. The sign of the coupling is also found to vary with the deposition technique: ferromagnetic for ion-beam sputtering and antiferromagnetic for DC magnetron sputtering.