Quantitative characterization of sputter-process-induced nano-voids and porous film state in magnetic thin films

The effect of sputter-process-induced nano-voids on transition metal film magnetic properties has been investigated. Sputtering pressure was used as a means to control the sputtering adatom mobility. At high mobility (low pressure), saturation magnetization (M_s*) of the films agrees with the transition metal bulk values, whereas at low mobility M_s* deviates from the bulk values. When measuring saturation moment density (σ_s), however, this value was not affected by different adatom mobility. X-ray diffraction, Auger spectroscopy and Mossbauer analysis suggest that the M_s* decrease is not an intrinsic change. The discrepancy between M_s* and σ_s values is interpreted as a porosity state of the transition metal films (nano-voids). Transmission electron microscopy confirmed that nano-voids had developed during the low mobility sputtering deposition and the ratio of voids to grains increased with decreasing adatom mobility