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

• Published in: Scientific reports Vol. 9; no. 1; pp. 13137 - 8
• Main Authors: Stamatelatos, A, Poulopoulos, P, Goschew, A, Fumagalli, P, Sarigiannidou, E, Rapenne, L, Opagiste, C, Grammatikopoulos, S, Wilhelm, F, Rogalev, A
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 11.09.2019; Nature Publishing Group UK
• Subjects: Alloys; Circular dichroism; Condensed Matter; Gold; Magnetic properties; Magnetism; Materials Science; Physics; Transmission electron microscopy; Vacuum
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-49457-7

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 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.