We report a broadband H-1 NMR study of the spin dynamics of coated maghemite and goldmaghemite hybrid nanostructures with two different geometries, namely dimers and coreshells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T-B similar to 80 K (maghemite), similar to 105 K (dimer), similar to 150 K (coreshell)), and the magnetization reversal time follows the VogelFulcher law. We observed three different anomalies in H-1 NMR T(1)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 surfacecore spin dynamics (T < 25 K). By fitting the T(1)1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.
Spin Dynamics in Hybrid Iron Oxide–Gold Nanostructures / Orlando, Tomas; Capozzi, A.; Umut, E.; Bordonali, L.; Mariani, M.; Galinetto, P.; Pineider, F.; Innocenti, C.; Masala, P.; Tabak, F.; Scavini, M.; Santini, P.; Corti, M.; Sangregorio, C; Ghigna, P.; Lascialfari, A.. - In: JOURNAL OF PHYSICAL CHEMISTRY. C. - ISSN 1932-7447. - STAMPA. - 119:(2015), pp. 1224-1233. [10.1021/jp509411v]
Spin Dynamics in Hybrid Iron Oxide–Gold Nanostructures
Pineider, F.;Innocenti, C.;Sangregorio, C;
2015
Abstract
We report a broadband H-1 NMR study of the spin dynamics of coated maghemite and goldmaghemite hybrid nanostructures with two different geometries, namely dimers and coreshells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T-B similar to 80 K (maghemite), similar to 105 K (dimer), similar to 150 K (coreshell)), and the magnetization reversal time follows the VogelFulcher law. We observed three different anomalies in H-1 NMR T(1)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 surfacecore spin dynamics (T < 25 K). By fitting the T(1)1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.