X-ray Magnetic Circular Dichroism of Size-Selected, Thiolated Gold Clusters

Abstract

We report herein the X-ray magnetic circular dichroism (XMCD) at the Au L2,3 edges of a series of Au clusters protected by glutathione (GSH). The samples used here included AuN(SG)M with (N, M) = (10, 10), (15, 13), (18, 14), (22, 16), (25, 18), (29, 20), (39, 24) and a sodium gold(I) thiomalate (SGT) as a reference. Magnetic moments per cluster were found to be increased with size, whereas those per Au-S bond were nearly constant. This finding suggests that a localized hole created by Au-S bonding at the gold/glutathione interface, rather than the quantum size effect, is responsible for the spin polarization of gold clusters.

Toward an Atomic-Level Understanding of Size-Specific Properties of Protected and Stabilized Gold Clusters

“…111 To address this issue, we measured the magnetic moments of a series of Au n (SG) m (Ref. 113) by Xray magnetic circular dichroism (XMCD) which is an elementselective magnetic probe. Figure 9c shows an X-ray absorption spectrum (XAS) and an XMCD spectrum at the Au L 3 edge (2p 3/2 ¼ 5d 5/2 , 6s 1/2 ) of Au 25 (SG) 18 at 2.7 K under a field of 10 T. 113 The XMCD amplitudes were of the order of a thousandth of the XAS step height.…”

“…113) by Xray magnetic circular dichroism (XMCD) which is an elementselective magnetic probe. Figure 9c shows an X-ray absorption spectrum (XAS) and an XMCD spectrum at the Au L 3 edge (2p 3/2 ¼ 5d 5/2 , 6s 1/2 ) of Au 25 (SG) 18 at 2.7 K under a field of 10 T. 113 The XMCD amplitudes were of the order of a thousandth of the XAS step height. The sign of the XMCD signal reversed when the magnetic field was switched to ¹10 T. These observations verify that the Au atoms in Au n (SG) m are inherently spin polarized.…”

Electronic structure, magnetic properties, and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

“…Despite all the efforts in this field, the permanent magnetism shown by these systems is not yet understood (Vager and Naaman, 2004;Hernando and García, 2006;Hernando et al, 2006a;Crespo et al, 2006). On this matter, studies regarding the origins of the ferromagnetic-like behaviour (Yamamoto et al, 2004;Negishi et al, 2006) were performed by means of x-ray magnetic circular dichroism (XMCD); unfortunately, in spite of having two research works trying to discern the origins of such a particular magnetic behaviour, the reason behind it still remains unclear. Recently, a set of new experiments was performed in our research group that studied the influence of the particle diameter in the magnetic behaviour of thiol-capped gold NPs (Guerrero et al, 2007).…”

Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles

“…In addition, the hysteresis cycle measured in iron-free samples reinforces the previous experimental works that claimed ferromagneticlike behavior in systems that are diamagnetic as bulklike materials. [7][8][9] Moreover, the ferromagneticlike behavior is verified for gold NPs protected with phosphine ligands.…”

“…5,6 Permanent magnetism in thiol-capped gold NPs has already been confirmed by wholly independent research groups throughout the world using different experimental techniques. [7][8][9][10][11] Some of these works are based on element-specific techniques such as x-ray magnetic circular dichroism ͑XMCD͒ on the gold L-edge 8,9 and, the most recent study by Garitaonandia et al 11 has combined XMCD measurements with 197 Au Mössbauer spectroscopy to study the magnetic behavior of gold NPs, which are identical to the synthesized thiolcapped NPs studied in the research work presented here. As a result of the research carried out with element-specific techniques, it has been univoquely determined that the gold atoms in the nanoparticle surface are carriers of the magnetic moment.…”