Diameter dependence of ferromagnetic spin moment in Au nanocrystals

Abstract

Au nanoparticles exhibit ferromagnetic spin polarization and show diameter dependence in magnetization. The magnetic moment per Au atom in the particle attains its maximum value at a diameter of about 3 nanometer (nm) in the Magnetization-Diameter curve. Because Au metal is a typical diamagnetic material, its ferromagnetic polarization mechanism is thought to be quite different from the ferromagnetism observed in transition metals. The size effect strongly suggests the existence of some spin correlation effect at the nanoscale. The so-called "Fermi hole effect" is the most probable one given in the free electron gas system. Ferromagnetism in Au nanoparticles is discussed using this model.

Unexpected magnetism in gold nanostructures: making gold even more attractive

“…However, this analysis of the size dependence, in particular of the surface magnetization, has recently come under criticism [70]. A re-interpretation by He shows an increasing and leveling of surface magnetization [70], instead of the declining surface magnetization with increasing particle diameter reported by Hori [55]. Hori and co-workers also investigated dodecanethiol (CH 3 (CH 2 ) 11 SH)-capped Au nanoparticles, but found greatly reduced saturation magnetizations compared to Au-PVP.…”

“…In addition to polymer-encapsulated [19,54,55,60,61,78] and alkanethiol-coated nanoparticles [24,40,[44][45][46][47][48][49][51][52][53], magnetism has now been observed in Au nanoparticles coated with ligands such as thiolated sugars [41,42] and biomolecules [48,51], thiolated azobenzenes [58,59], phosphine [53], and oleic acid and/or oleic amine [43,57]. The behaviors range from permanent, ferromagneticlike at room temperature, to superparamagnetic, to paramagnetic.…”

“…This work pointedly highlighted the remarkable difference nanoscale gold may have with the bulk state, most noticeably by highlighting the presence of unpaired coupled magnetic moments. Further early studies of the Au-polyvinyl pyrrolidone (PVP) system looked at the size dependence of the saturation magnetization [55], which showed a maximal value around 3 nm over the 1-8-nm diameter range. However, this analysis of the size dependence, in particular of the surface magnetization, has recently come under criticism [70].…”

Correlated d ferromagnetism and photoluminescence in undoped ZnO nanowires

“…The diamagnetic backgrounds of the Si substrates were subtracted from the raw data. Considering that nanoscale Au, Ag may induce weak ferromagnetism, 18,19 we first investigated the magnetic characteristics of the silicon substrates coated with Au or Ag thin films. All substrates without NWs growth showed only diamagnetic behaviors.…”

Structural and magnetic characterization of oleic acid and oleylamine-capped gold nanoparticles

“…Superparamagnetic behavior has been reported in Pd and Au nanoparticles embedded in poly͑N-vinyl-2-pyrrolidone͒ at low temperatures with a mean diameter of 3 nm, 8 and recently Hori et al 9 have also reported ferromagnetic behavior in Au NPs with protective agents polyacrylonitrile and polyallyl amine hydrochloride ͑PAAHC-Au͒. Ferromagnetic spin polarization of Au nanoparticles protected by PAAHC with a mean diameter of 1.9 nm has been measured by x-ray magnetic circular dichroism.…”