Magnetometry and electron paramagnetic resonance studies of phosphine- and thiol-capped gold nanoparticles

© 2010 American Institute of Physics. This research has been supported by the Spanish MECINN Project Consolider-Ingenio in Molecular Nanoscience, CSD2007-00010 and “Junta de Andalucía” Project Nos. P06-FQM-02254 and P09- FQM-4554, group TEP217. EG thanks the Spanish MEC for financial support and MAMM acknowledges the CSIC I3P program. R. L. thanks CSIC for a PhD grant. ; In the last years, the number of studies performed by wholly independent research groups that confirm the permanent magnetism, first observed in our research lab, for thiol-capped Au nanoparticles (NPs) has rapidly increased. Throughout the years, the initial magnetometry studies have been completed with element-specific magnetization measurements based on, for example, the x-ray magnetic circular dichroism technique that have allowed the identification of gold as the magnetic moment carrier. In the research work here presented, we have focused our efforts in the evaluation of the magnetic behavior and iron impurities content in the synthesized samples by means of superconducting quantum interference device magnetometry and electron paramagnetic resonance spectrometry, respectively. As a result, hysteresis cycles typical of a ferromagnetic material have been measured from nominally iron-free gold NPs protected with thiol, phosphine, and chlorine ligands. It is also observed that for samples containing both, capped gold NPs and highly diluted iron concentrations, the magnetic behavior of the NPs is not affected by the presence of paramagnetic iron impurities. The hysteresis cycles reported for phosphine-chlorine- capped gold NPs confirm that the magnetic behavior is not exclusively for the metal-thiol system. ; Depto. de Física de Materiales ; Fac. de Ciencias Físicas ; TRUE ; Ministerio de Ciencia e Innovación (MICINN) ; Junta de Andalucia ; Spanish MEC ; CSIC ; pub