Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-ray.
Magneto-chiral dichroism (MχD) is a non-reciprocal, i. e. directional, effect observed in magnetised chiral systems featuring an unbalanced absorption of unpolarised light depending on the direction of the magnetisation. Despite the fundamental interest in a phenomenon breaking both parity and time reversal symmetries, MχD is one of the least investigated aspects of light-matter interaction because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enentiopure crsytals of two isostructural molecular helicoidal chains comprising Cobalt(II) and Manganese (II) ions, respectively. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few percent, has been observed in the Cobalt chain system, while it is practically absent for the Manganese derivative. The spectral features of the XMχD signal differ significantly from the natural and magnetic dichroic contributions and have been here rationalized using the simple multipolar expansion of matter-radiation interaction.
Department of Chemistry 'Ugo Schiff' and INSTM research unit, University of Florence, 50019 Sesto Fiorentino, Italy.
Roberta
R
Sessoli
Department of Chemistry 'Ugo Schiff' and INSTM research unit, University of Florence, 50019 Sesto Fiorentino, Italy.
Marie-Emmanuelle
ME
Boulon
Department of Chemistry 'Ugo Schiff' and INSTM research unit, University of Florence, 50019 Sesto Fiorentino, Italy.
Andrea
A
Caneschi
Department of Chemistry 'Ugo Schiff' and INSTM research unit, University of Florence, 50019 Sesto Fiorentino, Italy.
Matteo
M
Mannini
Department of Chemistry 'Ugo Schiff' and INSTM research unit, University of Florence, 50019 Sesto Fiorentino, Italy.
Lorenzo
L
Poggini
European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France.
Fabrice
F
Wilhelm
European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France.
Andrei
A
Rogalev