Herstellung und Charakterisierung von gekoppelten IrMn/CoFe Schichtsystemen

An investigation of exchange anisotropy, which is observed in thin magnetic bilayers containing a ferromagnetic film in contact with an antiferromagnetic film is presented in this work. On the one hand the manifold technical application, on the other hand a lack of a deeper scientific understanding of the exchange mechanism causes a exceptional interest in this field of basic research. The influence of the substrate to the exchange mechanism is one of the main aims of the present work. While finding a possibility to influence the exchange bias by the substrate it is desirable to switch the exchange coupling ’on’ or ’off’. A system to create magnetic images or to save binary informations with a specific magnetic signature can be realized by a suitable combination of coupled or uncoupled areas. Applications for security features could therfore be realized. Based on this two types of buffer layers the investigation of the magnetic properties is followed as aim of this work. Evidently the investigation has to be done at the ferromagnetic-antiferromagnetic interface due to Exchange Bias is an interface effect. The metallic Ir$_{20}$Mn$_{80}$ / Co$_{80}$Fe$_{20}$ bilayer forms the base of all investigation done here. The system is characterized by low atomic interdiffusion at the interface, high exchange energy (up to 0,5 erg/cm$^{2}$) and small coercivity ($\approx$ 60 Oe). At the beginning the influence of substrate roughness due to different Cu and Ta buffer layers is discussed with a view of the texture in IrMn, the exchange energy J$_{E}$ and the coercivity H$_{C}$ of the system. The absence of a basic correlation between roughness as well as texture and exchange anisotropy is the result of this investigation. While discussing this behavior in the context of other publications one expects that morphology of the interface grains has an essential influence on exchange bias. In this studies it is observed that the exchange bias system decouples if a few layers of Ta are sputtered ontop of the Cu buffer. This is an effective system to switch exchange bias on or off without changing any other parameters. Samples with and without Ta and the same Ir$_{20}$Mn$_{80}$ / Co$_{80}$Fe$_{20}$ system on top serve as a starting point for the use of X-ray circular dichroism experiments at the Co L$_{3,2}$ and Mn L$_{3,2}$ edges. Among the determination of spin- and orbital moment of the respective sample the element specific magnetic hysteresis are given. The existence of uncompensated Mn Spins at the interface is verified. The amount of uncompensated Mn-Atoms carrying an ferromagnetic moment is estimated to 0,22 monolayers. It is doubled in the case of uncoupled sample. It is shown that the ferromagnetic antiferromagnetic coupling in the Ir$_{20}$Mn$_{80}$ / Co$_{80}$Fe$_{20}$ bilayers is not due to the observed uncompensated spins at the interface