"Topological orbital magnetic moments"

Who: Manuel dos Santos Dias

Place: CFM Auditorium

Date: Wednesday, 26 September 2018, 12:00

Host: Julen Ibaņez (CFM)

The magnetic moment carried by electrons in a condensed matter system has two components: the one originating from its spin and the one originating from its orbital motion. The spin magnetic moment arises from the first of Hund?s rule in most cases, which is also partially satisfied in magnetic solids. There are two well-known mechanisms for the formation of the orbital magnetic moment: the second of Hund?s rules, which applies only to atomic-like electron orbitals, and spin-orbit coupling, which lifts the quenching of the orbital moment in a magnetic solid.

Here we discuss a third mechanism that leads to the formation of orbital magnetic moments: magnetic structures with a special topology, where the spin magnetic moments do not all lie in the same plane [1]. We illustrate the basic aspects considering magnetic trimers as model systems, e.g. Fe3 on the Cu(111) surface. The symmetry of the effect is established, showing how to distinguish the topological and the spin-orbit contributions. We then focus on the implications of the topological orbital moments for single magnetic skyrmions formed in Pd/Fe/Ir(111), using first-principles electronic structure calculations and a simplified tight-binding model. We propose that the topological orbital moments could enable detecting and distinguishing skyrmions from anti-skyrmions by soft x-ray spectroscopy [2], as an alternative and complementary technique to transport measurements of the topological Hall effect, magnetic force microscopy or scanning tunneling microscopy.

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