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This work describes the preparation of ternary nanoparticles based on the Heusler compound Co2FeGa. Nanoparticles with sizes of about 20 nm were synthesized by reducing a methanol impregnated mixture of CoCl2 · 6H2O, Fe(NO3)3 · 9H2O and Ga(NO3)3 · xH2O after loading on fumed silica. The dried samples were heated under pure H2 gas at 900 °C. The obtained nanoparticles—embedded in silica—were investigated by means of x-ray diffraction (XRD), transmission electron microscopy, temperature dependent magnetometry and Mößbauer spectroscopy. All methods clearly revealed the Heusler-type L21 structure of the nanoparticles. In particular, anomalous XRD data demonstrate the correct composition in addition to the occurrence of the L21 structure. The magnetic moment of the particles is about 5μB at low temperature in good agreement with the value of bulk material. This suggests that the half-metallic properties are conserved even in particles on the 10 nm scale.

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Electron emission from Ag and Au nanoparticle films was studied under excitation with femtosecond-laser pulses with photon energies of 1.55 and 3.1 eV. Films were grown on a glass substrate with particle sizes from the nanometer range to a continuous layer. The transition from a continuous film to a nanoparticle film is accompanied by an increase in photoemission current by more than an order of magnitude. Pump-and-probe experiments with variable delay gave information on the lifetime of the intermediate states. At a fixed pulse power, the emission yield increases as the temporal width of the laser pulses is decreased. Experimental results are interpreted in terms of two different electron emission mechanisms, i.e., multiphoton photoemission and thermionic emission or thermally assisted multiphoton photoemission. The first mechanism prevails for continuous films and larger particles with sizes above several tens of nanometers; the second one prevails for smaller nanoparticles with sizes of a few nanometers.