Electronic Structure and Magnetism of Correlated Nanosystems

Magnetic nanostructures based on transition metals represent a main building block of standard memory devices. Their unique electronic properties are related to a complex multiplet structure of the partially filled d-shell with strong Coulomb interactions. Starting from a general formulation of the effective multi-orbital impurity problem for a transition metal atom in a fermionic bath of conduction electrons, the exact Quantum Monte Carlo solution is discussed. The concept of Hund’s impurities to describe the electronic structure and magnetism of transition metal adatoms becomes very useful for the interpretation of numerous experimental data.