Effect of bias voltage and deposition rate on the structure and coercivity of NiFe films

The effect of the bias voltage $U_b$ and the deposition rate $\nu$ on the structure, grain size $D$, and coercivity $H_c$ of NiFe films with a thickness d from 30 to 980 nm, grown on Si/SiO$_2$ substrates by DC magnetron sputtering, has been studied. In the case of $U_b$ = 0, a decrease in $\nu$ from values $\nu\approx$ 27 to $\approx$7 nm/min is accompanied by an increase in the values of the critical film thickness $d_{\operatorname{cr}}$ from $d_{\operatorname{cr}}\approx$ 220 nm to $d_{\operatorname{cr}}\approx$ 270 nm. In this case, $H_c$ in films with $d<d_{\operatorname{cr}}$ is characterized by the dependence $H_c\sim D^6$ and varies from $\sim$ 1 to $\sim$ 20 Oe. For $U_b$ = -100 V, the effect of the deposition rate on the coercivity is much more noticeable. At $\nu$ = 7 and 14 nm/min, the films exhibit soft magnetic properties ($H_c\approx$ 0.15–1.4 Oe) and the absence of $d_{\operatorname{cr}}$ for the entire range of studied thicknesses. The films obtained at $\nu$ = 21 and 27 nm/min pass into the “supercritical” state at $d\ge d_{\operatorname{cr}}\approx$ 520 nm, and in the range $d<d_{\operatorname{cr}}$ they are characterized by the dependence $H_c\sim D^3$ and an increase in the coercivity from $\sim$0.35 to $\sim$10 Oe.