R. Mégy

Effect of submonolayer coverage on magnetic anisotropy of ultrathin cobalt films M/Co/Au(111) with M=Au, Cu, Pd

Using in situ polar magneto‐optical Kerr‐effect measurements, the variation of the Kerr rotation and magnetic anisotropy of a (0001)Co ultrathin film on a (111)Au substrate has been precisely recorded, during the first stages of the growth of an overlayer of metal M=Au, Cu, and Pd. As reported earlier, a drastic increase of the magnetic anisotropy was observed, with a peak around 1 monolayer of overlayer thickness. From a careful study of the variation of the remanent Kerr rotation, it could be shown that only the interface contribution to the anisotropy changes with the overlayer thickness, while the bulk contribution remains mostly constant. The overall behavior can be interpreted in terms of electronic effects in the metal overlayer, acting on the interface anisotropy via band hybridization at the interface.

MAGNETIZATION REVERSAL IN PATTERNED CO(0001) ULTRATHIN FILMS WITH PERPENDICULAR MAGNETIC ANISOTROPY

Using x‐ray lithography we have patterned dot arrays in Au/Co/Au(111) sandwiches based on ultrathin Co layers with perpendicular anisotropy. Large area arrays of dots with diameters of 1 and 2 μm have been obtained, keeping mostly undamaged the ultrathin Co layer. Hysteresis loops of the arrays depend drastically on the dot diameter. Magneto‐optical domain visualization experiments confirm a magnetization reversal mechanism based on a large distribution of nucleation fields in the film, with complete reversal of the magnetization of one dot through the domain wall propagation after a local nucleation process. This could give information on the magnetization reversal processes in Au/Co/Au(111) continuous films.

Light diffraction effects in the magneto-optical properties of 2D arrays of magnetic dots of Au/Co/Au(111) films with perpendicular magnetic anisotropy

Using X-ray lithography and ion beam etching we have patterned micrometer-sized square lattices of round dots, out of Au/Co/Au(111) films with perpendicular easy magnetization axes. The magneto-optical Kerr rotation shows strong variations versus the diffraction order, the light polarization direction and the ratio of film to background reflectance, particularly when the lattice spacing is high compared with the dot size. This reveals an important interplay between diffraction and magneto-optics.

Domains and magnetization reversal dynamics in Au/Co/Au (1 1 1) ultrathin films: Co and Au thickness dependence

Abstract The magnetic anisotropy of epitaxial ultrathin Co-films on Au(1 1 1) depends drastically on Co- or Au-overlayer thickness. We have used polar magneto-optical Kerr effect on stepped-wedge samples to perform ex situ domain imaging, together with in situ and ex situ magnetic aftereffect measurements. Domains configurations and magnetization reversal dynamics were thus investigated versus perpendicular magnetic anisotropy strength. Large changes with Co thickness in Au/Co/Au(1 1 1) sandwiches are observed; they can be interpreted using existing theories. The drastic evolution of the dynamics of the magnetization reversal process with submonolayer Au coverage is attributed to a structural reorganization of the Co-layer with Au deposition, due to surfactant effect.

Inverse giant magnetoresistance (invited)

Inverse giant magnetoresistance (GMR) is obtained in multilayers alternating two ferromagnetic layers F1 and F2 with different asymmetry of spin scattering, α1≳1 and α2<1. This is clearly demonstrated in the simple spin‐valve system with perpendicular magnetization Fe1−xVx/Au/Co. With respect to Fe, the FeV alloys with x=0.18 and 0.29 exhibit an inversion of the spin scattering coefficients (αFe≳1, αFeV<1) due to the change of the densities of states at the Fermi level. The inverse MR of FeV/Au/Co is studied as a function of FeV layer thickness and temperature and compared to calculations based on the Camley–Barnas model. The data show that the inverse GMR is due to the bulk scattering within the FeV layer, which coexists with a substantial interface scattering favoring normal GMR.

Magnetic anisotropy and interlayer exchange coupling in Fe(110) / Au(111) ultrathin films

Abstract By using in situ polar Kerr effect measurements on stepped wedge samples, we have investigated experimentally the magnetic anisotrophy at room temperature of a bcc Fe(110) ultrathin film on Au(111), during the first stages of the deposition of an Au overlayer. We observe a maximum in the perpendicular anisotropy around 1 AL of Au coverage, in surprising similarity with previous observations on Co ultrathin films. We have then measured the interlayer exchange coupling through Au(111) on Au/Fe/Au/Co/Au(111) trilayers. We find evidence for oscillating coupling, with about the same period as in Co/Au(111)/Co structures, but a very different phase.

Magnetization, coercive forces and magnetoresistance in simple and double Co films with perpendicular magnetization

Abstract Our Au(111)/Co/Au samples show perpendicular spontaneous magnetization for Co thicknesses t below t ∗ = 1.2 nm. Recent RHEED results are in favour of the existence of an important “strain-induced” anisotropy, helping to overcome the shape anisotropy. From the measured parameters of anisotropy and roughness, we propose a quantitative model that explains the fast variation of the perpendicular coercive force with t below t c . Finally, disymmetric Au/Co( t 1 )/Au/Co( t 2 )/Au bilayers ( t 1 and t 2 t c ) show enhanced magnetoresistance (5%) in the field range whe re the layers are magnetized antiparallel.

Magnetic interface anisotropy in ultrathin cobalt films Au/Co/M/Au, with M = Au, Cu, Pd or Pt

We have measured the bulk and interface contributions to magnetic anisotropy on mainly hcp (0001) cobalt ultrathin films grown on polycrystalline textured Au(111) substrate, and covered with different metals. We have studied magnetic anisotropies versus nature of coverage metal M=Au, Cu, Pd or Pt. Large interface anisotropy constants K s were found for Co/Pd and Co/Pt interfaces in which occurs strong band hybridization and large spin-orbit coupling. A (1.2±0.6 μ B ) induced magnetic moment per interface atom was found in Co/Pd interface

Elaboration and magneto-optical study of submicron magnetic structures in Au/Co/Au ultrathin films

Abstract X-ray lithography and ion beam etching processes have been optimized to realize large areas of dots patterned in ultrathin Au/Co/Au/SiO 2 /Si(100) sandwiches. The coercive force increases dramatically as the dot diameter is reduced. Spectroscopic polar magneto-optical Kerr effect measurements show a change in the sign of the Kerr rotation with magnetic dots to non-magnetic background surface ratio.

Kerr rotation and perpendicular magnetic anisotropy oscillations versus Cu(111) coverage thickness in Cu(111)/Co/Au trilayers

Abstract We report here the observation of polar magneto-optical Kerr rotation and coercive force oscillations versus Cu overlayer thickness on Cu/Co/Au(111) UHV deposited trilayers with different Co and Cu thicknesses and perpendicular easy magnetization axis. The coercive force oscillation is attributed to an oscillatory behavior of the perpendicular magnetic anisotropy due to a spin-dependent electron confinement effect in the Cu(111) overlayer.