Understanding Magnetic Field Reversal Mechanisms in Mesoscopic Magnetic Multilayer Ring Structures

Patterned pseudo spin-valve rings show great promise for device applications due to their non-volatility and variety of stable magnetic states. However, the magnetic reversal of these elements under an applied field is complex due to the magnetostatic coupling between the two ferromagnetic layers. Elliptical rings are electrically probed using highly symmetric Wheatstone bridges in conjunction with traditional four-point electrical measurements and micromagnetic simulations. New insight into domain wall nucleation and propagation events are elucidated. The resulting behavior is found to yield large signals at very low fields, making these devices ideal for device applications in data storage and computer logic. 3600 domain walls are found to be extremely stable until fields as high as 10000e, but are positionally uncontrollable in elliptical rings. Rhombic rings were investi-gated as a geometry that can nucleate, propagate and pin domain walls more easily. Measurements and simulations confirm that the same reversal mechanisms exist and domain walls are more systematically positioned. The control over 360 ' domain wall