Stress inevitably introduced into thin films during fabrication is known as a prime limitation to the growth of very thick films, and causes mechanical deformations such as film fracture, which result from excess of tensile stress, and film buckling, which result from excess of compressive stress. Also, the introduction of stress into active regions of thin films can seriously affect their physical properties such as magnetic anisotropy in magnetic films through inverse magnetostriction mechanism.
Perpendicular magnetic anisotropy(PMA) of Co- and Fe- based mutilayers and the enhancement of the magneto-optical Kerr rotation were explained by the positive surface anisotropy due to lowered symmetry at an interface. But, in Ni-based multialyers, negative surface anisotropy was found theoretically. However, quite recently, our group report the room-temperature PMA in Ni/Pt multilayer and revealed that stress-induced magnetoelastic anisotropy was a major origin for the observed PMA. For the case of Ni/Pd multilayer, in 1991, N.K. Flevaris et al. and H. Takahashi et al. observed perpendicular magnetic anisotropy respectively but the origin of PMA in this system was not revealed yet definitely.
Here we have measured in-situ stress of several Ni/Pd multilayer thin films prepared by dc magnetron sputtering technique, using an optical non-contact displacement detector. It was found that the probe used in our study was sensitive enough to measure the stress induced by monoatomic deposition.
We observed PMA in Ni/Pd multialyer which were made under the 30 W, 7 mTorr depositon conditions and PMA in Ni/Pd multilayers varied largely with the deposition conditions. From the stress measurement we obtained the stress of Ni/Pd multilayer and coherent-to-incoherent transition was observed even in the one monolayer of Ni, Pd.