Effect of bar width on magnetoresistance of nanoscale nickel and cobalt bars

The anisotropic magnetoresistance (AMR) of nickel and cobalt bars of 1 μm length, 35 nm thickness, and width varying from 50 to 500 nm is studied. As the bar width is reduced from 500 to 50 nm, longitudinal MR change decreases from 0.8% to 0.2% and transverse MR change increases from 1.3% to 1.8% for the Ni bars: longitudinal MR change is zero and transverse MR change is constant at 1.6% for the Co bars. The zero longitudinal MR is attributed to a single-domain magnetization. The AMR value indicates that the electron scattering from bar edges has little effect on AMR even in a 50 nm width. Furthermore, strong, repeatable Barkhausen noise is observed in the Co bars with a width larger than 200 nm. which can be explained by a micromagnetic model.