Effects of the initial stages of film growth on the magnetic anisotropy of obliquely-deposited cobalt thin films

• Published in: Journal of magnetism and magnetic materials 1996-04, Vol.154 (2), p.249-253
• Main Authors: Alameda, J.M., Carmona, F., Salas, F.H., Alvarez-Prado, L.M., Morales, R., Pérez, G.T.
• Format: Article
• Language: English
• ISSN: 0304-8853
• DOI: 10.1016/0304-8853(95)00577-3

We have studied the in-plane magnetic anisotropy in polycrystalline cobalt films, which were obliquely deposited by e-beam evaporation in UHV at T s = 300 K. Three film series were studied, with average film thicknesses t = 15, 45 and 100 nm. For all cases, the incidence angle of the vapor beam with respect to the surface normal was α = 0, 30, 40, 50, 60 and 70°. At normal incidence, the anisotropy and the coercive fields were found to be H K = 15–25 Oe, and H c ⋍ 25 Oe , independent of the film thickness. In all series it has been observed that, as α increases, the easy axis of in-plane anisotropy switches from perpendicular to parallel with respect to the incidence plane of atoms during film deposition. For t = 15 nm, such a transition occurs at α t ⋍ 70° , whereas for larger values of t we found that α t = 60°. At constant film thicknesses, H K and H c increase with increasing α; the lower the film thickness, the sharper this effect, e.g. for α = 40°, and t = 100, 45 and 15 nm, H K ⋍ 15 , 30 and 150 Oe, respectively. We analyzed two possible contributions to this effect: the shape anisotropy and the magnetocrystalline anisotropy (texture). At low film thicknesses the former becomes dominant. In order to understand the effect of oblique incidence on the in-plane easy axis location we studied the polar plot of reduced remanence m r as a function of both the angle α (between the surface normal and the vapor beam) and the angle γ (between the in-plane applied field and the normal to the incidence plane of atoms during deposition). The behavior of m r( α, γ) for α = 10° and 70° is reminiscent of that predicted by the coherent-rotation Stoner and Wohlfarth model, although fallback processes are observed. We found that the films tend to be magnetically isotropic for α = 60°, whereas they are highly anisotropic for α = 10°.