Paramagnetic gold in a highly disordered Au-Ni-O alloy

A. Stamatelatos (1) , P. Poulopoulos (1) , A. Goschew (1) , P. Fumagalli (1) , E. Sarigiannidou (2) , L. Rapenne (2) , Christine Opagiste (3) , S. Grammatikopoulos (1) , F. Wilhelm (4) , A Rogalev (4)

1 University of Patras
2 LMGP - Laboratoire des matériaux et du génie physique
3 NEEL - MagSup - Magnétisme et Supraconductivité
4 ESRF - European Synchrotron Radiation Facility

Magnetic materials are usually classified into a distinct category such as diamagnets, paramagnets or ferromagnets. the enormous progress in materials science allows one nowadays, however, to change the magnetic nature of an element in a material. Gold, in bulk form, is traditionally a diamagnet. But in a ferromagnetic environment, it can adopt an induced ferromagnetic moment. Moreover, the growth of gold under certain conditions may lead to a spontaneous ferromagnetic or paramagnetic response. Here, we report on paramagnetic gold in a highly disordered Au–ni–o alloy and focus on the unusual magnetic response. Such materials are mainly considered for plasmonic applications. Thin films containing Au, Ni and NiO are fabricated by co-deposition of Ni and Au in a medium vacuum of 2 × 10−2 mbar. As a result, Au is in a fully disordered state forming in some cases isolated nanocrystallites of up to 4 nm in diameter as revealed by high resolution transmission electron microscopy. The disorder and the environment, which is rich in oxygen, lead to remarkable magnetic properties of Au: an induced ferromagnetic and a paramagnetic state. this can be proven by measuring the x-ray magnetic circular dichroism. our experiments show a way to establish and monitor Au paramagnetism in alloys.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

A. Stamatelatos, P. Poulopoulos, A. Goschew, P. Fumagalli, E. Sarigiannidou, et al.. Paramagnetic gold in a highly disordered Au-Ni-O alloy. Scientific Reports, 2019, 9, pp.13137. ⟨10.1038/s41598-019-49457-7⟩. ⟨hal-02314631⟩