Bias sputtering effect on ultra-thin SmCo5 films exhibiting large perpendicular coercivity

This paper reports the deposition and characterization of ultra-thin SmCo5 films exhibiting large perpendicular coercivity under different bias sputtering conditions. The films were deposited onto a Cu (20 nm)/Ti (5 nm) bilayer at 300 degrees C and 0.5 Pa argon pressure at substrate biases in the range 0 to - 100 V. The effect of a negative substrate bias on the stoichiometric ratio of Sm/Co, surface morphology, structure and magnetic properties of the SmCo5 films is investigated using inductively coupled plasma atomic emission spectroscopy, atomic force microscopy, X-ray diffractometry and vibrating sample magnetometry. An intrinsic coercivity of 1050 kA/m and unity squareness ratio in the direction perpendicular to the film plane are achieved at a substrate bias voltage of - 60 V. The ideal stoichiometric ratio of Co/Sm, relatively smaller grain sizes, and preferred crystallographic orientation of the easy axis are found to be strong functions of the bias voltage applied. These studies show that the magnetic properties of ultra-thin SmCo5 films can be significantly improved by using bias sputtering. (C) 2008 Elsevier B.V. All rights reserved