Tuning of biased domain wall depinning fields at Permalloy nanoconstrictions

The propagation of a transverse domain wall (DW) through single asymmetric nanoconstrictions is investigated in continuous ferromagnetic planar wire structures, by localized magneto-optical Kerr effect magnetometry. Using focused ion beam (FIB) milled planar Permalloy nanowires, we propagate a DW in opposite directions through single asymmetric nanoconstriction. The DW depinning field from an asymmetric nanoconstriction strongly depends on the direction of motion of the DW relative to the trap. A depinning field bias effect is tuned by varying the constriction width from 50to200nm in 300nm wide nanowires. FIB milled nanoconstrictions, with a width as narrow as 50nm, demonstrate a bias effect. Narrowing the width of the constriction enhances the depinning field bias effect.