The Kondo effect in ferromagnetic atomic contacts

Abstract

Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the $s$ and $p$ electrons, whereas the magnetic moments are mostly in the narrow $d$-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature. The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system;this appears as a Fano-Kondo resonance in the conductance characteristics as observed in other artificial nanostructures. The study of hundreds of contacts shows material-dependent lognormal distributions of the resonance width that arise naturally from Kondo theory. These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems. Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.

7 pages, 5 figures

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• Direct observation of heavy quasiparticles in the Kondo lattice CeIn3
• Molecule-assisted ferromagnetic atomic chain formation
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• Conductance fingerprints of non-collinear magnetic states in single atom contacts: a first-principles Wannier functions study
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• Directional bonding explains high conductance values of atomic contacts in bcc metals
• Non-Zeeman splitting for a spin-resolved STM with a Kondo adatom in a spin-polarized two-dimensional electron gas
• Spin locking at the apex of nano-scale platinum tips
• Current-induced phase transition in ballistic Ni nanocontacts
• The strong-coupling limit of a Kondo spin coupled to a mesoscopic quantum dot: effective Hamiltonian in the presence of exchange correlations
• Break-junction experiments on the zero-bias anomaly of non-magnetic and ferromagnetically ordered metals
• Magnetism- and impurity-assisted chain creation in Ir and Pt break junctions
• Dimensionality effects in the LDOS of ferromagnetic hosts probed via STM: spin-polarized quantum beats and spin filtering
• Scanning Tunneling Microscopy in high vectorial magnetic fields