Major changes in magnetic properties are expected for ultrathin ferromagnetic films as compared to its natural bulk form. With the decreasing size of the magnetic films, surface contributions to magnetic anisotropy become more and more relevant. One of the major task is to find a way to manipulate them. Yet, to tailor films with specific properties, the knowledge about the correlation between the magnetic, structural, and morphological properties is required.

Study of correlation between structure morphology and magnetic properties :

Thin Fe films, epitaxially deposited on Si(111) and Si(001) via MBE, are investigated by means of STM (scanning tunneling microscopy), low-energy electron diffraction (LEED) as well as photoelectron spectroscopy (XPS, XPD, UPS). The magnetic properties were characterized ex situ by longitudinal magneto-optical Kerr effect, using the recent TBIIST method (Transverse Bias Initial Inverse Susceptibility and Torque).

The morphology of the Fe film strongly depends on the iron beam orientation relative to the sample normal. Oblique evaporation on Si(111) or Si(001) leads to the formation of Fe stripes perpendicular to the Fe beam. This growth mode leads to a specific magnetic uniaxial anisotropy. With help of micromagnetic calculations on STM images, it can be shown that it originates from long-ranged dipolar interactions. In-plane uniaxial magnetic anisotropy can also be induced in Fe films by means of a non-magnetic capping layer (Au,Si). The surface morphology of the bcc Fe(111) layers is strongly influenced by the Si capping layer. In particular, deposition of Si at grazing incidence is found to result in a surface-type uniaxial in-plane magnetic anisotropy contribution induced by a breakdown of the threefold symmetry at the bcc Fe(111) surface. The relevant magnetic easy axis direction depends in a critical way on the azimuth of the Si evaporation flux with respect to the Fe crystal surface directions. A model, based on the change of the Fe surface by inhomogeneous chemical reaction with the capping layer is proposed to interpret the magnetic anisotropy evolution. Quantitative confirmation is obtained by means of simulations and micromagnetic calculations.

Growth and magnetic properties of Co2MnSi Heusler alloy thin films on Si(001) :

Heusler alloys exhibit promising possibility enhancing current magnetoresistive devices. Its theoretically 100 % spin polarization is very interesting from both applicative and fundamental point of view. Its structural properties play a dominant role for the magnetic and the underlying spin polarization properties. We report on structural and magnetic properties of thin Co2MnSi films epitaxially grown on Si(001) at 600 K by MBE. A systematic study of the growth temperature influence on crystal quality and magnetic properties leads to the choice of this optimal deposition temperature. A CoSi2 template is first grown on the Si substrate to allow epitaxy and to prevent interdiffusion of Si into the alloy. X-ray photoelectron diffraction (XPD) as well as electron diffraction (LEED, IMEED) measurements show that a 40 ML Co2MnSi film crystallizes in the expected cubic structure. Magnetic properties are investigated by magneto-optical Kerr Effect (MOKE). Quantitative determination of the various contributions to in-plane magnetic anisotropies are obtained by TBIIST-MOKE method. The Co2MnSi films exhibit a ferromagnetic behaviour at room temperature and the observed magnetocrystalline anisotropy is consistent with the crystallographic symmetry. Moreover, the geometry deposition has a strong influence on both surface morphology and magnetic properties. For example, grazing incidence deposition (» 70°) leads to a strong in-plane uniaxial magnetic anisotropy correlated the deposition direction, as it has already been observed on the Fe/Si system.