Von Nanosäulen, Ferromagneten und Piezoelektrizität : Nanoskalige magnetische Hybridsysteme

Für die Anwendungen magnetischer Nanostrukturen im Alltag (Datenspeicherung, Kontrastmittel in der Kernspinresonanztomographie, Hyperthermie zur Tumorbehandlung, in Ferrofluiden in Lautsprechern) werden ganz unterschiedliche magnetische Eigenschaften benötigt. Heiko Wende untersucht diese in neuen nanoskaligen magnetischen Hybridsystemen.
Nanoscale magnetic hybrid systems exhibit new fascinating properties which pave the way to new applications: ranging from new data storage concepts and magneticallycontrolled shock absorbers in cars to hypothermia cancer treatment. In this article some examples are given of the ways in which these magnetic hybrid systems can be constructed by combination of different building blocks such as magnetic molecules, nanoparticles and ultrathin films. To resolve the interesting magnetic interactions, element-specific measurements are carried out by X-ray absorption spectroscopy at largescale facilities, namely synchrotron radiation sources. These provide an insight into the magnetic behavior of the individual components of the hybrid systems. As the local atomic properties are determined by these experimental techniques, the results can be easily compared to ab initio calculations using density functional theory. Thus, theory-based predictions on the specific magnetic interactions within the hybrid systems can be directly tested in the experiment. Therefore, experiment and theory nicely complement each other. This is discussed here, e.g. for the tailoring of the magnetic coupling of rare earth and transition metal layers in gadolinium/chromium/ iron layered structures. The parallel coupling of the gadolinium and the iron magnetic moments reveal the potential of new magnets high in moments for magnetic data storage devices. Furthermore, the modification of the magnetic anisotropy of magnetic iron-platinum nanoparticles embedded in a metallic film is analyzed. The interplay between experiment and theory enabled the establishment of design rules for the synthesis of nanoparticles with properties required for the individual applications. In addition, the coupling of magnetic molecules to thin ferromagnetic films is presented. This coupling leads to the ordering of the magnetic moments in the molecule even at room temperature with a magnetic memory effect (magnetic hysteresis). As an example of the interplay of a piezoelectric system with a ferrimagnetic material, a multiferroic nanocomposite is investigated that consists of magnetic nano columns embedded in a piezoelectric surrounding. The elementspecific measurements demonstrate that a magneto-electric coupling can indeed be determined for this composite. This may be the starting point for new data storage concepts.
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