Effect of stress on exchange coupling field, coercivity, and uniaxial anisotropy field of NiFe/NiO bilayer thin films

The effects of stress on the exchange coupling field, H-ex, and coercivity, H-c, in NiFe/NiO bilayers deposited onto a Si wafer using rf-reactive sputtering were experimentally studied. Samples of the bilayers were externally and constantly uniaxial strained (either tensile or compressive) using a specially designed sample holder. The hysteresis loops of the stressed NiFe/NiO bilayer samples were measured in situ along the easy and hard axis of the NiFe films using a vibrating sample magnetometer. The composition of the NiFe film was characterized to be Ni80.2Fe19.8 using x-ray photoelectron spectroscopy. The H-c of the bilayers were significantly affected by the stress, while the H-ex was not apparently changed by the same stress. The large changes in the coercivity in the stressed NiFe/NiO bilayer were produced by the large change of the effective uniaxial anisotropy field, H-K, of the bilayer. The control and reduction of both intrinsic and external stresses are important in the fabrication of spin-valve giant magnetoresistance heads and sensors. (C) 1997 American Institute of Physics.