Magnetic and plasmonic Au/Fe oxide composite NPs: compilation

1) Exchange bias effect in Au-Fe3O4 nanocomposites.
Sayan Chandra, N A Frey Huls, M H Phan, S Srinath, M A Garcia, Youngmin Lee, Chao Wang, Shouheng Sun, Òscar Iglesias and H Srikanth

Nanotechnology 25, 055702 (2014)

Low temperature hysteresis loops simulated after a cooling in a magnetic field h_FC = 100 K as computed by MC simulations of individual nanoparticles with cluster (a) and dimer (b) geometries. The non-magnetic metal is simulated as a hole in the middle for the cluster geometry and a sharp facet for the cluster. Panels (a) and (b) show hysteresis loops of a particle with cluster and dimer geometry, respectively, for two different values of the surface anisotropy constant: k_S = 0.01 (blue squares) equal to the core value k_C = 0.01, and increased surface anisotropy k_S = 30 (red circles). The dashed lines in (b) stand for a spherical particle of the same size as the dimer. The inset displays the contribution of the surface (yellow circles) and core (green squares) spins of a dimer particle to the hysteresis loop for k_s = 30. Snapshots of the spin configurations for cluster ((c) and (d) panels) and dimer ((e) and (f) panels) particles for k_S = 30 obtained at the end of the FC process ((c) and (e) panels) and at the coercive field point of the decreasing field branch ((d) and (f) panels) of the hysteresis loops displayed in figures (a) and (b). For clarity, only a slice of width 4a along the applied field direction and through the central plane of the particles is shown. Surface spins have darker colors and core spins have been colored lighter.

2) Chemically synthesized Au–Fe3O4 nanostructures with controlled optical and magnetic properties. Victor Velasco, Laura Muñoz, Eva Mazarío, Nieves Menéndez, Pilar Herrasti, Antonio Hernando and Patricia Crespo

J. Phys. D: Appl. Phys. 48, 035502 (2015)

(a) ZFC-FC magnetization curves of Fe₃O₄ and Au–Fe₃O₄ NPs measured under an applied field of 25 Oe. (b) Hysteresis loops of Fe₃O₄ and Au–Fe₃O₄ NPs with Au : Fe initial molar ratios of 1 : 1 and 1 : 3 measured at 5 K applying a maximum field of 50.000 Oe. The ferromagnetic behaviour is highlighted in the inset.

3) Spin Dynamics in Hybrid Iron Oxide-Gold Nanostructures.

Tomas Orlando,A. Capozzi, E. Umut, L. Bordonali, M. Mariani, P. Galinetto, F. Pineider, C. Innocenti,  P. Masala,  F. Tabak,  M. Scavini, P. Santini, M. Corti, C . Sangregorio, P. Ghigna, and A. Lascialfari

Journal of Physical Chemistry C 119, 1224 (2015) 

 

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 (T_B ∼ 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.

 

4) Superparamagnetic Au-Fe3O4 nanoparticles: one-pot synthesis, biofunctionalization and toxicity evaluation.

A Pariti, P Desai, S K Y Maddirala, N Ercal, K V Katti, X Liang and M Nath

Materials Research Express 1, 035023 (2014)
5) Spin-Polarization Transfer in Colloidal Magnetic-Plasmonic Au/Iron Oxide Hetero-nanocrystals.
Francesco Pineider, César de Julián Fernández, Valeria Videtta, Elvio Carlino, Awni al Hourani,Fabrice Wilhelm, Andrei Rogalev, P. Davide Cozzoli, Paolo Ghigna, and Claudio Sangregorio

ACS Nano 7, 857 (2013)

We report on the unprecedented direct observation of spin-polarization transfer across colloidal magneto-plasmonic Au@Fe-oxide core@shell nanocrystal heterostructures. A magnetic moment is induced into the Au domain when the magnetic shell contains a reduced Fe-oxide phase in direct contact with the noble metal. An increased hole density in the Au states suggested occurrence of a charge-transfer process concomitant to the magnetization transfer. The angular to spin magnetic moment ratio, m_orb/m_spin, for the Au 5d states, which was found to be equal to 0.38, appeared to be unusually large when compared to previous findings. A mechanism relying on direct hybridization between the Au and Fe states at the core/shell interface is proposed to account for the observed transfer of the magnetic moment.