Morphology - composition-and size-related trends in hard magnetic 3d-5d nanoparticles from first principles
Dr. Markus Gruner (Faculty for Physics and Center for Nanointegration, CeNIDE, University of Duisburg-Essen, Duisburg)

Nanometer-sized binary 3d-5d transition metal nanoparticles have become a popular target for fundamental as well as applied research with respect to biomedical applications, catalysis or functional devices. For instance, arrays of L10 ordered nanoparticles of near-stoichiometric Fe-Pt and Co-Pt with diameters down to 4 nm have been discussed as promising material for future ultra-high density recording media due to the large magneto-crystalline anisotropy (MCA) in their bulk alloys. Multiply twinned structures which compromise the required MCA are frequently encountered in gas phase experiments. These morphologies have been confirmed as potential ground state structures in recent large scale density functional theory calculations of 3d-5d transition metal nanoparticles of up to 1415 atoms.
For diameters below 4 nm, the favored L1₀-type layering is energetically superseded by an icosahedral structure with onion-shell alternation of Fe and Pt atoms in the particle core. The preference for multiply twinned structures can be systematically tuned by the exchange of the 3d component, whereas similar clear trends are not encountered upon the exchange of the 5d component. After deposition, significant modifications of the electronic properties arise from the interface to the substrate or a possible embedding matrix. The investigation of nanometer-sized Fe-Pt particles decorated with organic and inorganic elements as, e.g., Au, Cu, Al, Si or C allows predictions concerning the influence of the surrounding matrix on structural and magnetic properties of Fe-Pt nanoparticles. The comparison of calculated orbital moments and MAE with experimental trends finally leads to concrete guidelines for the design of ultrahard nanomagnets.