Epitaxial growth and physical properties of Permalloy film deposited on MgO(001) by biased dc plasma sputtering

Permalloy films 5 to about 40 nm thick were deposited on MgO(001) substrate s at 230 degrees C by biased de plasma sputtering at 2.7 kV in pure Ar gas using a Ni0.77Fe0.23 target. A bias voltage V-s between 0 and -150 V was ap plied to the substrate during deposition. The initial growth structure and physical properties of epitaxial films were investigated by x-ray photoelec tron spectroscopy, reflection high energy electron diffraction, transmissio n electron microscopy, and by measuring electrical and magnetic properties. Epitaxial FCC-Ni1-xFex (Permalloy) films, where x is scattered between 0.3 6 and 0.32, could be prepared with NiFe(001)[010]\\MgO(001)[010] in full th ickness independently of V-s. However, films with lower electrical resistiv ity and with higher saturation magnetization having an atomically smooth su rface could be prepared at V-s = -90 V. The film was composed of discrete i slands of at least 5 nm thickness at an initial growth stage. Misfit disloc ations were already formed even in isolated islands along the MgO 100 direc tion with lattice expansion along the same direction. The practical lattice misfit f computed from transmission electron diffraction patterns graduall y increased reaching the theoretical value with an increase in thickness up to 17 nm. Such anf dependence on thickness could be reasonably simulated o n the basis of van der Merwe's model. Thus the epitaxial Permalloy film gro ws forming misfit dislocations as well as expanding the lattice at the MgO interface to keep a balance between the energies of strain and dislocation. Under the application of V-s, the initial discrete island structure on the MgO substrate might be modified not only by accelerated incoming ions but also by charged ions on the insulating substrate. (C) 2000 American Vacuum Society. [S0734-2101(00)02805-0].