In situ observation of the strain of Co and Ni deposited on Pd (111) by reflection high energy electron diffraction

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Abstract
Co/Pd(111) and Ni/Pd(111) bilayer films were grown epitaxially on single crystal MgO (111) substrates by ultrahigh vacuum deposition. In situ observation of the strain of Co and Ni deposited on Pd (111) plane was performed by reflection high energy electron diffraction (RHEED) during fabrication. From RHEED patterns it was confirmed that the lattice constant of a Co film of 2 Å in thickness deposited on Pd was about 3.7 Å, which was different from that of Pd (3.89 Å). The strain (εCo) of the Co layer was rapidly released during further Co deposition. The strain εCo of the third Co monatomic layer on Pd is nearly equal to zero. The large strain of the Co layer is localized at about one or two monatomic layers of the interface between Co and Pd. On the other hand, a Ni film deposited on Pd was not strained from the beginning of the deposition. The relationship between the perpendicular magnetic anisotropy of Co/Pd and Ni/Pd compositionally modulated multilayer films and the strain of Co and Ni is discussed.