Vortex Induced by DC Current in a Circular Magnetic Spin Valve Nanopillar

We investigate the characteristic of vortex states induced by a dc current in trilayer circular magnetic nanopillars experimentally. Our samples are designed such that both the soft and hard layers can contain a magnetic vortex and the interlayer is thick enough such that only dipolar interaction is important. The relative chiralities between the two layers´ vortex configurations as functions of external field and current are studied with various diameters. We also perform micromagnetic simulation on the magnetization reversals to compare with the magnetoresistance (MR) curves measured at low current and with current induced magnetization states. The current induced magnetization behaviors due to the spin transfer torque effect and the additional Oersted field are clearly identified on the resistance behavior.