Surface effects in the magnetic properties of crystalline 3 nm ferrite nanoparticles chemically synthesized

Abstract

Ratchet effect of the domain wall by asymmetric magnetostatic potentials Appl. Phys. Lett. 99, 192512 (2011) Crystallization behavior and high temperature magnetic phase transitions of Nb-substituted FeCoSiBCu nanocomposites Appl. Phys. Lett. 99, 192506 (2011) Room temperature magnetoelectric memory cell using stress-mediated magnetoelastic switching in nanostructured multilayers Appl. Phys. Lett. 99, 192507 (2011) Current-induced domain wall motion in permalloy nanowires with a rectangular cross-section J. Appl. Phys. 110, 093913 (2011) Correlation between symmetry-selective transport and spin-dependent resonant tunneling in fully epitaxial Cr/ultrathin-Fe/MgO/Fe(001) magnetic tunnel junctions Appl. Phys. Lett. 99, 182508 (2011) Additional information on J. Appl. Phys. We have systematically studied the magnetic properties of ferrite nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain size distributions. Samples were prepared by the thermal decomposition of Fe͑acac͒ 3 in the presence of surfactants giving nanoparticles covered by oleic acid. High resolution transmission electron microscopy ͑HRTEM͒ images and XRD diffraction patterns confirms that all samples are composed by crystalline nanoparticles with the spinel structure expected for the iron ferrite. ac and dc magnetization measurements, as well in-field Mössbauer spectroscopy, indicate that the magnetic properties of nanoparticles with 11 and 7 nm are close to those expected for a monodomain, presenting large M S ͑close to the magnetite bulk͒. Despite the crystalline structure observed in HRTEM images, the nanoparticles with 3 nm are composed by a magnetically ordered region ͑core͒ and a surface region that presents a different magnetic order and it contains about 66% of Fe atoms. The high saturation and irreversibility fields in the M͑H͒ loops of the particles with 3 nm together with the misalignment at 120 kOe in the in-field Mössbauer spectrum of surface component indicate a high surface anisotropy for the surface atoms, which is not observed for the core. For T Ͻ 10 K, we observe an increase in the susceptibility and of the magnetization for former sample, indicating that surface moments tend to align with applied field increasing the magnetic core size.

Exceeding natural resonance frequency limit of monodisperse Fe3O4 nanoparticles via superparamagnetic relaxation

“…The two sextets with hyperfine fields ( H hf ), and center shift ( CS ) of one (487.55 kOe and 0.32 mm/s) and the other (456.5 kOe and 0.66 mm/s) suggest the Fe 3+ ions on the tetrahedral sites and Fe 2.5+ (Fe 2+ Fe 3+ ) ions on the octahedral sites, respectively. The results are consistent with the room-temperature results observed for magnetite nanoparticles23. The hyperfine fields are lower than those of the bulk material and the resonance lines are broadened.…”

Magnetic properties study of iron-oxide nanoparticles/PVA ferrogels with potential biomedical applications

“…As it has already been said, it is well known that saturation magnetization of iron-oxide NPs depends on their size (collective excitations) and on their surface magnetic configuration (disorder). These phenomena can reduce the saturation magnetization below the bulk expected value (Lima et al 2010;Laurent et al 2008;Wu et al 2007). One example of this effect has been published in a recent work by Laurent et al (2008).…”

Synthesis, Characterization, and Nanocatalysis Application of Core–Shell Superparamagnetic Nanoparticles of Fe3O4@Pd

“…[45,46] The obtained values are ,D TB . E 6 nm (Fe 3 O 4 ) and 5 nm (Fe 3 O 4 @Pd), which are in good agreement with the TEM results.…”

“…Similar values were reported for bare Fe 3 O 4 NPs and for NPs covered with OA. [45,46] The bulk saturation magnetization of the Fe 3 O 4 is approximately M s bulk E 470 emu cm À3 . To obtain an estimation about the importance of the surface effects when the particle's size is reduced in many ferro-and ferrimagnetic nanocrystalline materials, the ratio between the saturation magnetization of the NPs and the bulk: M s /M s bulk E 0.42 was calculated.…”