Publication: Permanent magnetism, magnetic anisotropy, and hysteresis of thiol-capped gold nanoparticles
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2004-08-20
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American Physical Society
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Abstract
We report on the experimental observation of magnetic hysteresis up to room temperature in thiol-capped Au nanoparticles with 1.4 nm size. The coercive field ranges from 860 Oe at 5 K to 250 Oe at 300 K. It is estimated that the Au atoms exhibit a magnetic moment of mu=0.036mu(B). However, Au nanoparticles with similar size but stabilized by means of a surfactant, i.e., weak interaction between protective molecules and Au surface atoms, are diamagnetic, as bulk Au samples are. The apparent ferromagnetism is consequently associated with 5d localized holes generated through Au-S bonds. These holes give rise to localized magnetic moments that are frozen in due to the combination of the high spin-orbit coupling (1.5 eV) of gold and the symmetry reduction associated with two types of bonding: Au-Au and Au-S.
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©2004 American Physical Society.
XAS facilities at BM29 in ESRF and the technical support from O. Mathon are acknowledged. The authors thank J. Llopis and I. Rosa for helping with optical measurements and sample preparation, respectively. Financial support from the Spanish MCyT under Projects No. MAT2002-04246-C05-05 and No. BQU2002-03734 is acknowledged.