Figure 1. Magnetic ordering of substrate (Ni) and organic adsorbate (CoTPP) with respect to the NO-induced switching.

In all spectra, 'a.u.' represents arbitrary units. (a) Chemical structure of the CoTPP molecule (top) and schematic view of the XMCD experiment (bottom). (b) Chemical identification of Co and Ni: L-edges X-ray absorption spectra of Co (CoTPP, photon energy range: 765–815 eV) and Ni (substrate, photon energy range: 835–885 eV) acquired with circularly polarized X-ray light from a synchrotron source with opposite helicities (μ⁺ and μ⁻). The difference in X-ray absorption for the opposite helicities (dichroism) reveals the magnetization of the observed chemical species. (c) Spin-switching sequence from left to right as indicated by arrows: L-edges XMCD spectra of Co (top panels) and Ni (bottom panels) recorded on the CoTPP/Ni(001) system after the initial preparation of molecular adlayers (left), after NO addition (centre) and on temperature-induced NO desorption (right). The directions of the remanent substrate magnetization M are indicated by grey arrows to the left of each spectrum. Ferromagnetic ordering of molecular spins with respect to the substrate is observed initially. Reversible 'off–on' switching of Co magnetization is observed with progressing NO addition and temperature-induced NO desorption.