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

Abstract

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.

Enhanced Cycle Stability of Low‐Cost Na‐Rich Metallic NaCl Electrode for Advanced Na‐Ion Batteries

“…The intensities of the peaks decreased at discharged States 2 and 4, indicating the coverage of the bare surface of the NC electrode by the formed interphase layer. [ 10,25,33,34 ] The reappearance of these peaks for State 3*: 2C‐4.5 V confirms again that the interphase layer dissolves at high voltage during charge, and reversibly reforms during the subsequent discharge.…”