Authors: G.G. Lesseux, W. Iwamoto, V.H. Rosas, C. Vautier-Giongo, D. Rettori, R.R. Urbano, C. Rettori
Affilation: Universidade Estadual de Campinas (UNICAMP), Brazil
Pages: 71 - 74
Keywords: Au nanoparticles, ferromagnetic resonance
In this work we report on the enhancement of the ferromagnetism of amine/organic acid capped Au nanoparticles (AuNPs) by incorporation of yttrium-oxide (Y2O3). The magnetization measurements displayed a ferromagnetic (FM) loop with a coercive field Hc ~ 490 Oe and magnetic saturation moment Msat ~ 4 x10-4 µB/Au at 2 K. The latter is a lower limit estimated from the mass of Au left over after performing thermogravimetric analysis (TGA). These values are suppressed to Hc ~ 80 Oe and Msat ~ 0.7 x 10-4 µB/Au at room-T. The T-dependent magnetization showed superparamagnetic behavior with a blocking temperature TB ~ 13 K. Furthermore, an intense FM resonance (FMR) line was observed from 370 K down to 90 K. As the temperature is lowered, the field for resonance, Hr, slightly shifts toward lower fields and the linewidth, ΔH, broadens, although the normalized integrated intensity remains almost constant within the entire investigated range of temperature. These results are discussed in terms of covalent-like bonds between the NP-capping ligands, Y2O3 and the Au atoms, which create an effective hybridization of the 5d-6s conduction electrons at the surface of the AuNPs.