Ferromagnetic Resonance in amine/organic acid caped Au-nanoparticles assisted by rare-earths oxides

G.G. Lesseux, W. Iwamoto, V.H. Rosas, C. Vautier-Giongo, D. Rettori, C. Rettori
Universidade Estadual de campinas, BR

Keywords: Au nanoparticles, ferromagnetic resonance


Amine/organic acid caped Au-nanoparticles (Au-NPs) were prepared by reducing gold tetrachloroaurate (HAuCl4.3H2O) and rare-earth (RE)-oxides (RE = Er and Y and monodisperse samples of caped Au-NPs of ~10 nm in diameter were obtained. The magnetization results show a FM loop with negligible coercive field at 2 K with magnetic saturation value of ~10 emu/g and 0.1 emu/g to Au-NPs assisted by Er2O3 and Y2O3, respectively. Furthermore, at room-T, a paramagnetic behavior was observed and a intense resonance was observed from room-T down to 4.2 K with the following features: i) the field for resonance, Hr, shifts toward low fields; ii) the linewidth, ΔH, broadens: and iii) the resonance intensity remains almost constant within the accuracy of the experiments. These features characterize the observed resonance as a FMR. These results will be discussed in terms of the interactions established between NP-capping ligands and Au atoms that stimulates an effective hybridization of the 5d-6s conduction electrons at the surface of the Au-NPs and, in turn, allows the Au 5d shell to become magnetic due to uncompensated spins.