Surface vacancy mediated pinning in maghemite NP

Surface vacancy mediated pinning of the magnetization in γ−Fe2O3 nanoparticles: A micromagnetic simulation study

Bassel Alkadour, J. I. Mercer, J. P. Whitehead, J. van Lierop, and B. W. Southern

Phys. Rev. B 93, 140411(R) (2016)

The energy landscape for a nanoparticle selected at random from the K10 enemble. Each point on the surface of the sphere represents the energy associated with the alignment of the magnetic moment. The energy is calculated using a mean field approximation based on the distribution of surface vacancies and the average angular distribution of the energy per spins at T=0 shown in Fig. 4. The energy scale associated with the color map shown on the right is given in K.

Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles - IOPscience

Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles.
Mikael Svante Andersson, Roland Mathieu, Peter S Normile, Su Seong Lee, Gurvinder Singh, Per Nordblad and Jose Angel De Toro
Materials Research Express 3, 045015 (2016)

 Temperature-dependent (normalized to the maximum of near the onset of dissipation) data replotted as a function of reduced temperature , where the denominator is the temperature of maximum slope of for each sample (h = 80 A m⁻¹, f = 10 Hz).

Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles.

Hafsa Khurshid, Paula Lampen-Kelley, Òscar Iglesias, Javier Alonso, Manh-Huong Phan, Cheng-Jun Sun, Marie-Louise Saboungi & Hariharan Srikanth

Scientific Reports 5, 15054 (2015) 

Snapshots of the outer and inner surface spin configurations subject to varying magnetic fields (a) h = 100 (the maximum positive applied field), (b) h = 0 (remanence at the upper branch), (c) h = −25 (near the negative coercive field), and (d) h = −100 (the maximum negative applied field). Spins have been colored with a gradient from dark-red/dark-blue (outer/inner surface) for spins along the field direction to yellow/green (outer/inner surface) for spins transverse to the field direction. Only a slice of the spin configurations of a hollow nanoparticle close to the central plane and perpendicular to the field direction is shown.

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes : Nature Communications : Nature Publishing Group

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes.

Yoann Prado, Niéli Daffé, Aude Michel, Thomas Georgelin, Nader Yaacoub, Jean-Marc Grenèche, Fadi Choueikani, Edwige Otero, Philippe Ohresser, Marie-Anne Arrio, Christophe Cartier-dit-Moulin, Philippe Sainctavit, Benoit Fleury, Vincent Dupuis, Laurent Lisnard, Jérôme Fresnais

Nature Communications 6, 10139 (2015)

(a) Field-cooled and zero-field-cooled (FC/ZFC) magnetization curves measured in the 5–80 K temperature range under an applied field of 50 Oe and (b) magnetization vs field curves measured at 5 K for 0b and 1 in diluted solutions.

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes : Nature Communications : Nature Publishing Group

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes.

Yoann Prado, Niéli Daffé, Aude Michel, Thomas Georgelin, Nader Yaacoub, Jean-Marc Grenèche, Fadi Choueikani, Edwige Otero, Philippe Ohresser, Marie-Anne Arrio, Christophe Cartier-dit-Moulin, Philippe Sainctavit, Benoit Fleury, Vincent Dupuis, Laurent Lisnard; Jérôme Fresnais

Nature Communications 6, 10139 (2015)

(a) Representation of the [Co(TPMA)Cl₂] complex used to enhance the magnetic anisotropy of the γ-Fe₂O₃ nanoparticles. (b) TEM image of the γ-Fe₂O₃ nanoparticles functionalized with the cobalt(II) complex: 1 (5.0 nm, σ=0.09) and (c) schematic view of the coordination of the complex with the iron ions. (d) Synthesis scheme with measured pH values, hydrodynamic diameters (Z_av), sizes (D) and distributions (σ).

Tuning the magnetic anisotropy in coordination nanoparticles: random distribution versus core–shell architecture.

Yoann Prado, Nada Dia, Laurent Lisnard, Guillaume Rogez, François Brisset, Laure Catala and   Talal Mallah

Chem. Commun. 48, 11455 (2012)

Core–shell magnetic coordination nanoparticles made of a soft core and a hard magnetic shell, containing anisotropic Co(II) ions, display a dramatic increase in their average blocking temperature with a coercive field value 25 times larger than that of the soft core, due to a large enhancement of the magnetic anisotropy.

From core/shell to hollow Fe/γ-Fe2O3 NPs

From core/shell to hollow Fe/γ-Fe2O3 nanoparticles: evolution of the magnetic behavior.

Z Nemati, H Khurshid, J Alonso, M H Phan, P Mukherjee and H Srikanth

Nanotechnology 26, 405705 (2015)

Bright-field TEM images of the 12 nm Fe/γ-Fe₂O₃ (a) core/shell, (b) core/void/shell, and (c) hollow nanoparticles