Applied Physics Letters · 2007 · 84 citations · 18 references
Natural SciencesMaterials SciencePhysicsCondensed Matter PhysicsMagnetic MaterialsNanomaterialsFerromagnetismMagnetic NanomaterialsMagnetic Properties Of SolidsMagnetism In SolidsNanomaterial CharacterizationNanoparticle CharacterizationBlocking TemperatureCoercivityExchange BiasMagnetic CoercivityMagnetic NanoparticlesNanoparticlesSaturation MagnetizationSuperparamagnetism
In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB≃50K in D≃5nm NPs but only diamagnetism in 12nm NPs. For T<TB=50K, the strong temperature dependence of coercivity Hc, saturation magnetization Ms, and exchange bias He (in the field-cooled sample) confirm the blocked state resembling ferromagnetism with Hc≃250Oe, He≃−40Oe, and Ms≃10−2emu∕g at 5K. The observed electron magnetic resonance line shows expected shift, broadening, and reduced intensity below TB. A magnetic moment μ≃0.006μB per Au atom attached to DT is determined using a model which yields Ms varying as 1∕D, with its source being holes in the 5d band of Au produced by charge transfer from Au to S atoms in DT.
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