Stress effects on exchange coupling field, coercivity, and uniaxial anisotropy field of NiO/NiFe bilayer thin film for spin valves

The effects of uniaxial stress on the exchange coupling field, Hex, coercivity, Hc, and uniaxial anisotropy field, HK, in NiO/NiFe bilayers were experimentally studied. The NiO/NiFe bilayers were deposited onto a Si(100) wafer using radio frequency reactive sputtering. Samples of the bilayers were externally and constantly uniaxial stressed (either tensile or compressed) using a specially designed sample holder with a fixed radius of curvature. The hysteresis loops of the stressed NiO/NiFe bilayer samples were measured in situ along the easy and hard axes of the NiFe films using a vibrating sample magnetometer. The composition of the NiFe film in the NiO/NiFe bilayer was characterized as Ni80.2Fe19.8 using x-ray photoelectron spectroscopy. The Hc and HK of the bilayers were significantly affected by the stress, while the Hex was apparently not changed by the same stress. The large changes in the coercivity in the stressed NiO/NiFe bilayer were produced by the change of the effective uniaxial anisotropy field of the bilayer. We conclude that the control and reduction of both intrinsic and external stress are very important in the fabrication of spin-valve giant magnetoresonance heads and sensors.