Magnetic properties of face-centered cubic Co films

Abstract

We deposited face-centered cubic (FCC) Co films on glass substrates by sputtering. From Auger-depth profile analysis, we found that there is one CoO layer, about 13 /spl Aring/ thick, lying on the top surface of the Co film, and another CoO layer, about 37 /spl Aring/ thick, lying within the Co/glass interface. At room temperature, the thin CoO film is supposed to be paramagnetic. However, because of the proximity effect between CoO and Co, the CoO layer may become ferromagnetic, with saturation magnetization M/sub o/. By fitting the saturation magnetization (M/sub s/) data of the whole Co/CoO film as a function of (1/t/sub f/), where t/sub f/ is the Co thickness, we can prove that the last conjecture is correct, and the M/sub o/ of the CoO layer is indeed not zero. Both the t/sub f/ dependence of the magnetostriction constant (/spl lambda//sub s/) and the t/sub f/ dependence of the coercive field (H/sub c/) show a two-region characteristic. The dividing line for the former quantity is at t/sub f/ = 88 /spl Aring/, and for the latter it is at t/sub f/ = 120 /spl Aring/. When crossing such a dividing line, there is a discontinuous jump in /spl lambda//sub s/ (or H/sub c/). These phenomena occur because the lattice-strain and magnetoelastic effects within the CoO layer dominate the /spl lambda//sub s/ and the H/sub c/ behavior in ultra-thin (t/sub f/ < 88 /spl Aring/) Co films. In this region, the roughness-to-thickness ratio (S/sub q//t/sub f/) may also affect /spl lambda//sub s/. Finally, there seems to be no connection between the grain size (D) and H/sub c/.