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Spin Dynamics in Hybrid Iron Oxide–Gold Nanostructures

2014; American Chemical Society; Volume: 119; Issue: 2 Linguagem: Inglês

10.1021/jp509411v

1932-7455

Tomas Orlando, Andrea Capozzi, Evrim Umut, Lorenzo Bordonali, Manuel Mariani, Pietro Galinetto, Francesco Pineider, Claudia Innocenti, Paolo Masala, F. Tabak, Marco Scavini, P. Santini, M. Corti, Claudio Sangregorio, Paolo Ghigna, A. Lascialfari,

NMR spectroscopy and applications

We report a broadband 1H NMR study of the spin dynamics of coated maghemite and gold–maghemite hybrid nanostructures with two different geometries, namely dimers and core–shells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (TB ∼ 80 K (maghemite), ∼105 K (dimer), ∼150 K (core–shell)), and the magnetization reversal time follows the Vogel–Fulcher law. We observed three different anomalies in 1H NMR T1–1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surface–core spin dynamics (T < 25 K). By fitting the T1–1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.