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Ferromagnetism Exhibited by Nanoparticles of Noble Metals
Author(s) -
Maitra Urmimala,
Das Barun,
Kumar Nitesh,
Sundaresan Athinarayanan,
Rao C. N. R.
Publication year - 2011
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100121
Subject(s) - ferromagnetism , nanoparticle , magnetization , metal , noble metal , alkane , aqueous solution , chemistry , inorganic chemistry , hydroxymethyl , materials science , nanotechnology , organic chemistry , catalysis , condensed matter physics , physics , quantum mechanics , magnetic field
Gold nanoparticles with average diameters in the range 2.5–15 nm, prepared at the organic/aqueous interface by using tetrakis(hydroxymethyl)phosphonium chloride (THPC) as reducing agent, exhibit ferromagnetism whereby the saturation magnetization M S increases with decreasing diameter and varies linearly with the fraction of surface atoms. The value of M S is higher when the particles are present as a film instead of as a sol. Capping with strongly interacting ligands such as alkane thiols results in a higher M S value, which varies with the strength of the metal–sulfur bond. Ferromagnetism is also found in Pt and Ag nanoparticles prepared as sols, and the M S values vary as Pt>Au>Ag. A careful study of the temperature variation of the magnetization of Au nanoparticles, along with certain other observations, suggests that small bare nanoparticles of noble metals could indeed possess ferromagnetism, albeit weak, which is accentuated in the presence of capping agents, specially alkane thiols which form strong metal–sulfur bonds.