Magnetic properties, electronic structure and morphology of PtCo and PtCo/Au dumbbell nanoparticles

M. MIZRAHI; GIOVANETTI, L. J.; RAMALLO-LÓPEZ, J. M.; BERON, F.; PIROTA, K. R.; SHEVCHENKO, E. V.; REQUEJO, F. G.

Campinas

Congreso; LNLS 23th ANNUAL USERS MEETING; 2013

Brazilian Synchrotron Light Laboratory

Multicomponent nanocrystals (MNCs) became an important class of materials due to their abilities to carry multiple functions that can be utilized simultaneously[1-3]. Recent progress in synthesis of MNCs allows obtaining di®erent types of nanoparticles such as core-shells [1], dumbbells, or other geometries [3]. Characterization of PtCo and PtCo/Au alloys was performed using electron microscopy (TEM), X-ray absorption (XAS), X-ray scattering at low angle (SAXS), global magnetic measurements (MM) and magnetic circular dichroism measurements (XMCD). Combination of TEM and SAXS results show spherical particles with a size dispersion of about 5% for Pt 3Co system. SAXS reveals that the addition of Au modifies the stability of MNCs in solution producing NPs agglomerates. XAFS measurements at the Pt L2;3 edges and Co K reveal changes in the oxidation state of Co after Au deposition. XAFS previous results [3] have shown that the Au addition removes the Co atoms from the surface of the PtCo NP. XANES at the Pt L2;3 edges show a charge transfer from Pt 5d level after Au deposition respect to the Pt con¯guration in the MNCs used as seed. From MM is observed that all samples exhibit superparamagnetic behavior at RT with a blocking temperature which decreases in smaller Pt 3Co MNCs. XMCD at the Pt-L2;3 edges measurements show that there is a transfer of magnetic moment from Co atoms to Pt and also reveals that addition of Au does not a®ect the magnetic behavior for the Pt atoms. The variation of the XMCD intensity signal with temperature is in accordance with changes in the magnetization of the PtCo alloy. This shows that the Co atoms in the alloy are main responsible for the appearance of the XMCD signal, but can not rule out a contribution to this e®ect from the size of NPs. References 1. For example see: M. Casavola, et. al., Nano Lett. 2007,7, 1386.; R. Buonsanti, et al., J. Am. Chem. Soc. 2006, 128, 16 953; J. Gao, et al., J. Am. Chem. Soc. 2007, 129, 1428. 2. J.-H. Lee, et al., J. Cheon, Nat. Med. 2006,13, 95. 3. Krylova, G.; Giovanetti, L.; Requejo, F.; Dimitrijevic, N.; Prakapenka, A.; Shevchenko, E. Journal of the American Chemical Society, Manuscript ID: ja-2011-11459p.R1