By investigating the spin configuration in ferromagnetic multilayer under stress field, the dependence of magnetoresistance （MR） upon the stress field in the ferromagnetic multilayer is discussed. The stress field can induce MR, and the MR strongly depends on both the value and the direction of the stress field. Generally, for the case of J>0, the stress field dependence of MR is closely related with the differences in magnetostriction and magnetocrystalline anisotropy between two ferromagnetic layers. When the stress field deviates from the magnetic easy axis lowards the magnetic hard axis, the MR first increases slowly, and then decreases rapidly. For a given direction of stress field, the MR first increases rapidly, later decreases slowly with stress field increasing. Moreover, when the direction of stress field approaches that of the hard axis, the dependence of MR upon both the value and the direction of the stress field becomes obvious. Especially, if the direction of the stress field is perpendicular to the easy axis, change of MR can double its value with the stress field increasing. When the stress field Hλ meets the condition 8πM/5≤Hλ≤18πM/5, MR increases monotonically, and the giant magnetoresistance （GMR） occurs. In the case of JJ>0.
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