Structural, magnetic properties and steep magnetoresistance change with low saturation magnetic fields in Co/Ni multilayer thin films

We have fabricated Co/Ni multilayer thin films with a constant Co thickness of 2.2 nm, Ni thickness changing from 0.5 to 5.0 nm, and a total of 20 bilayers using dc magnetron sputtering. The magnetic measurements show that these multilayers have an in-plane uniaxial anisotropic properties. These multilayers show a steep magnetoresistance change with low saturation magnetic field, an especially large magnetoresistance change between magnetic field H applied parallel and perpendicular to the in-plane easy axis. For H parallel to the multilayer easy axis and H at 45° to the current I, a magnetoresistance ratio of 15.0% with a FWHM of 13 Oe was obtained. While for H perpendicular to the multilayer easy axis and H at 45° to the current I, a magnetoresistance ratio of 19.1% with a FWHM of 34 Oe was obtained. The former implies a magnetoresistance sensitivity of 1.15%/Oe, while the sensitivity of the latter is just 0.56 %/Oe. All the peaks of the magnetoresistance curve appeared at the coercive field H _c of the multilayers. The most important characteristic of the magnetoresistance change were a sharp increase in resistance followed by a very steep decrease with increasing H