The fluence dependence of exchange bias induced by oxygen ion implantation has been studied in highly textured face centered cubic Co films. These films exhibit a strong magnetocrystalline anisotropy prior to implantation. Upon implantation, the crystalline order is strongly reduced, even for the lowest implantation fluence, as shown by an isotropic magnetic behavior. Detailed analysis of the structural changes shows that the crystallite size remains basically unaltered upon implantation, suggesting that CoxOy is formed at the Co grain boundaries. A large suppression of the magnetocrystalline anisotropy is observed after implantation. This anisotropy has no influence on the unidirectional anisotropy associated to the exchange bias effect. Our study identifies a narrow implantation fluence window in which exchange bias by oxygen ion implantation is established. With increasing oxygen fluence, an increase in the magnitude of the exchange bias effect for higher fluences and, finally, a saturation of the exchange bias effect is observed in the studied fluence window. Moreover, the particular shape of the measured hysteresis loop is ascribed to a distribution of switching fields, which results from the implantation depth profile of oxygen throughout the Co film.

Oxygen implantation in ferromagnetic Co thin films is shown to be an advantageous route to improving the magnetic properties of Co−CoO systems by forming multiple nanoscaled ferromagnetic/antiferromagnetic interfaces homogeneously distributed throughout the layer. By properly designing the implantation conditions (energy and fluence) and the structure of the films (capping, buffer, and Co layer thickness), relatively uniform O profiles across the Co layer can be achieved using a single-energy ion implantation approach. This optimized configuration results in enhanced exchange bias loop shifts, improved loop homogeneity, increased blocking temperature, reduced relative training effects and increased retained remanence in the trained state with respect to both Co/CoO bilayers and Oimplanted Co films with a Gaussian-like O depth profile. This underlines the great potential of ion implantation to tailor the magnetic properties by controllably modifying the local microstructure through tailored implantation profiles.

Exchange bias (EB) is induced by oxygen implantation in three different ferromagnetic materials: polycrystalline Co, highly textured Co and polycrystalline Ni. These systems are compared in order to study the influence of the grain boundary density and the intrinsic ferromagnet/antiferromagnet coupling strength on the implantation-induced EB. Special emphasis is given to the role of the implantation profile in the EB properties. The implantation profile is thoroughly characterized and its correlation with the magnetic depth profile, i.e. the magnetization as a function of depth, for different magnetic states is studied. This is achieved by modelling the implanted system as a layered system. In the three systems, the magnetization reversal mechanism is studied. In this way the effect of the implantation process on the reversal mechanism is unraveled. Irrespective of the particular system, the magnetization reverses solely by domain wall nucleation and motion, as opposed to Co/CoO bilayer systems, where a change in the reversal mechanism is observed upon the first reversal.

An original approach for the formation of an exchange bias system is presented. Alternative to surface oxidation or deposition for the formation of Co/CoO bilayer exchange bias systems, implantation of oxygen ions into Co films is applied. The implantation results in the formation of CoxOy embedded in a Co matrix. Comparison with noble gas implantation unambiguously demonstrates that the observed exchange bias effect is induced by the implanted oxygen. Opposed to bilayers formed by surface oxidation, the implantation results in a different morphology of the interface between Co and CoxOy and also gives rise to a radically different magnetization reversal mechanism.

We studied the exchange-spring behavior in FePt-Fe hard-soft magnetic heterostructures. We present a study of the spin structure of the soft Fe layer of Fe-FePt bilayers by nuclear forward scattering of synchrotron radiation. The orientation of the Fe moments close to the top of the soft layer was determined quantitatively as a function of the soft-layer thickness. We show that for a few monolayers of Fe, the magnetically hard FePt layer pins the magnetization in the soft Fe layer to the out-of-plane direction. With increasing Fe-layer thickness, the influence of the FePt diminishes and the magnetization cants toward the in-plane Fe͓001͔ direction. The significance of the exchange coupling constant as the relevant parameter for the exchange-spring behavior is demonstrated by one-dimensional micromagnetic simulations.