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

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Abstract
The effects of stress on the exchange coupling field, Hex, and coercivity, Hc, 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 Hc of the bilayers were significantly affected by the stress, while the Hex 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, HK, 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.