Spin-Excitation Spectroscopy: Probing Magnetic Nanostructures at the Atomic Scale

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• Cyrus Hirjibehedin, University College London
• Wednesday 25 February 2009, 11:15-12:15
• Mott Seminar Room, Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Michael Sutherland.

The spectroscopic capabilities of a scanning tunneling microscope (STM) can be used to measure the low energy excitation spectrum of individual nanostructures on surfaces with atomic-scale detail. Originally used to probe the vibrations of single molecules, inelastic electron tunneling spectroscopy can also measure magnetic excitations. We discuss recent studies in which we have used STM -based spin-excitation spectroscopy to determine the orientation and strength of the anisotropies for individual atomic spins on a copper nitride surface, as well as the interplay between magnetic anisotropy and Kondo screening. In structures containing more than one magnetic atom, we observe excitations of the coupled spin system that can change both the total spin and its orientation. We are able to describe the mechanisms that drive these inelastic spin excitations using a simple exchange coupling between the tunneling electron and the electrons that comprise the atomic spin. This description predicts the existence of a sum rule that includes a previously unnoticed type of spin-dependent elastic scattering, and evidence of both are seen in the observed spectra. We discuss the key factors that determine the relative strength of the inelastic tunneling, providing insight on when such processes can be observed and potentially how they might be enhanced.

This talk is part of the Quantum Matter Seminar series.

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