R. Morales

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

Abstract 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°.

Magneto-optics applied to the analysis of magnetization processes in amorphorus ferri/ferro magnetic bilayers

Abstract We study the magnetization processes in the amorphous ferri—ferro magnetic bilayer of GdCo 2 /YCo 2 by means of the transverse magneto-optic Kerr effect (MOKE). The cycles M cos θ − M sin θ (θ refers to the angle between the magnetization M and the applied field H ) indicate that the irreversible magnetization processes arising at both the coercivity and the transition field do not occur by a coherent-rotation mechanism. MOKE allows one to follow the creation and the extinction of Bloch walls in the bilayer as a function of the applied field. First-order magnetization processes are observed in this macroscopic ferrimagnet when H is applied perpendicularly to the in-plane easy axis of uniaxial anisotropy. In fact, sharp transitions in the magnetic-moment structure are observed at H = 8.5 Oe and H = 17 Oe.

Periodical magnetic effects in FexSi1−x/Si multilayers, depending upon the modulation length

Magnetic properties of compositionally modulated Fe x Si 1-x /Si amorphous and crystalline multilayers are reported. From SQUID magnetometry and transverse magneto-optic Kerr effect measurements, we detected noticeable λ-related structure in both magnetization and relative reflectivity. A systematic oscillation is found for λ < 16 A. On the contrary, in samples with definite multilayered structure (λ ≥ 16 A), a significant reduction in magnetization is found as λ decreases.

Influence of the film inhomogeneity on local magnetization processes in amorphous thin films having perpendicular anisotropy

Abstract Thin films prepared by co-sputtering present slight inhomogeneities in composition and thickness. In this work we analyze the effect of this lack of uniformity on local magnetization processes in amorphous thin films (Fe x Si 1 − x ) having perpendicular anisotropy. Local magnetization processes have been studied by transverse Kerr effect. Variations in the coercive field H c -suggest that the reversal of magnetization occurs locally.