Magnetic properties of metallic AuPdO nanoparticles confined in ordered mesoporous silica SBA-15 channels

W. Iwamoto, G.G. Lesseux, B.F. Dias, A.A. Teixeira-Neto, E. Teixeira-Neto, R.R. Urbano, C. Rettori
Universidade Estadual de Campinas (UNICAMP), BR

Keywords: magnetism, nanoparticles, electron spin resonance, magnetization, SBA-15


Materials consisting of metallic AuPdO nanoparticles (AuPdO-NPs) supported on mesoporous silica SBA-15 channels (AuPdO-NPs/SBA15, Figure 1) have become composite compounds of great interest due to their catalytic applications [1]. In this work we report on magnetization and Electron Spin Resonance experiments in the AuPdO-NPs/SBA15 composites. The magnetization results displayed in Figure 2 show a ferromagnetic (FM) loop with saturation magnetic moment MS ~ 0.5 emu/gAuPdO (~ 0.03 µB/AuPdO) and negligible coercive field at 300 K. The value of MS was estimated knowing that our AuPdO-NPs/SBA15 contains about 1.5 % of AuPdO-NPs determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). We observed no evidence of superparamagnetic behavior for the zero-field cooling (ZFC) and field cooling (FC) magnetic susceptibility data within the range of 2 K < T < 300 K and an applied magnetic field of H = 500 Oe. Moreover, a single magnetic resonance line was observed from room-T down to 50 K. The normalized integrated resonance intensity remains nearly constant in the entire T-range (Figure 3). This behavior characterizes a ferromagnetic resonance (FMR), in contrast to the scenario of active ESR paramagnetic defect centers suggested by E. Rombi, et. al. [2] in Au/SBA15 samples.