Nanocomposite membranes based on thermosensitive, poly(N-isopropylacrylamide)-based nanogels and magnetite nanoparticles have been designed to achieve “on-demand” drug delivery upon the application of an oscillating magnetic field. On−off release of sodium fluorescein over multiple magnetic cycles has been successfully demonstrated using prototype membrane-based devices. The total drug dose delivered was directly proportional to the duration of the “on” pulse. The membranes were noncytotoxic, were biocompatible, and retained their switchable flux properties after 45 days of subcutaneous implantation.

A Magnetically Triggered Composite Membrane for On-Demand Drug Delivery

Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe1–xO|Fe3−δO4 nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of antiphase boundaries. Dark-field transmission electron microscopy and powder X-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe1–xO core is removed but that the antiphase boundaries remain. The antiphase boundaries result in anomalous magnetic behavior, that is, a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic propertie...

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Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures: Topotaxial Oxidation of Fe1–xO|Fe3−δO4 Core|Shell Nanocubes to Single-Phase Particles

We have carried out a systematic experimental investigation to address the question why thin films of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ (magnetite) generally have a very broad Verwey transition with lower transition temperatures as compared to the bulk. We observed using x-ray photoelectron spectroscopy, x-ray diffraction, and resistivity measurements that the Verwey transition in thin films is drastically influenced not only by the oxygen stoichiometry but especially also by the substrate-induced microstructure. In particular, we found (1) that the transition temperature, the resistivity jump, and the conductivity gap of fully stoichiometric films greatly depends on the domain size, which increases gradually with increasing film thickness, (2) that the broadness of the transition scales with the width of the domain size distribution, and (3) that the hysteresis width is affected strongly by the presence of antiphase boundaries. Films grown on MgO (001) substrates showed the highest and sharpest transitions, with a 200 nm film having a ${\mathit{T}}_{V}$ of 122 K, which is close to the bulk value. Films grown on substrates with large lattice constant mismatch revealed very broad transitions, and yet all films show a transition with a hysteresis behavior, indicating that the transition is still first order rather than higher order.

Verwey transition in Fe3O4 thin films: Influence of oxygen stoichiometry and substrate-induced microstructure

Investigation on the structure and physical properties of Fe3O4/RGO nanocomposites and their photocatalytic application

Influence of a metallic or oxide top layer in epitaxial magnetic bilayers containingCoFe2O4(111)tunnel barriers

The giant magnetoresistance (GMR) of multilayers in the current in plane (CIP) geometry can be understood by considering the spin-dependent scattering effects within the magnetic layers and at the non-magnetic/magnetic interfaces In this paper we experimentally put on view the magnetoresistance effect created only by the spin-dependent reflection of electrons at the interfaces Two epitaxial systems were studied, consisting of two ferrimagnetic insulators layers at low temperature (CoFe2O4 and Fe3O4) separated by a non-magnetic metallic layer (M = Au or Pt) The transport properties indicate that conduction of the CoFe2O4/M/Fe3O4 trilayers take place within the thin metallic layer An optimal magnetoresistance up to 5% at 10 K associated to the switching from parallel to anti-parallel configuration of the magnetization of the two ferrite layers has been obtained It is associated to the spin-dependent interfacial scattering contribution of the CIP-GMR The augmentation of the GMR when decreasing the metallic layer thickness or increasing the oxide layers width confirms this GMR is essentially an interfacial phenomenon The Pt-based system shows an additional Anisotropic Magnetoresistance (AMR), which is not evidenced in the Au-based trilayer We suggest that this AMR comes from the polarization of the Pt layer by the ferrimagnetic oxides

Experimental evidence of the spin-dependence of electrons reflections in magnetic multilayers

We study the magnetic behavior of ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(111)$ thin films with thicknesses between $5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $50\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The films are epitaxially grown on $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}(0001)$ single crystals by atomic-oxygen-assisted molecular beam epitaxy. The ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(111)$ thin films exhibit high structural order with sharp interfaces and low roughness and exhibit a Verwey transition for thicknesses above $8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. However, the samples have magnetic properties that deviate from the bulk ones. The magnetic moment varies between $2.4{\ensuremath{\mu}}_{B}$ for $5\text{\ensuremath{-}}\mathrm{nm}$-thick film and $3.2{\ensuremath{\mu}}_{B}$ for $50\text{\ensuremath{-}}\mathrm{nm}$-thick film in a field of $1.2\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, which is lower than that of bulk samples ($4.1{\ensuremath{\mu}}_{B}∕{\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ formula). Still the magnetic saturation is never reached, even in fields as large as $2\phantom{\rule{0.3em}{0ex}}T$. The thinner the film, the slower the approach to saturation. Structural analysis, performed using high-resolution transmission electron microscopy, reveals the presence of antiphase boundaries (APB's), the density of which decreases when the thickness increases. Using a model of ferromagnetic domains separated by antiferromagnetically sharp interfaces, we show that the slow approach to saturation observed in the films as a function of thickness is driven by the APB density.

Thickness dependence of anomalous magnetic behavior in epitaxial Fe 3 O 4 (111) thin films: Effect of density of antiphase boundaries

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Experimental evidence of the spin-dependence of electrons reflections in magnetic multilayers

Thickness dependence of anomalous magnetic behavior in epitaxial Fe 3 O 4 (111) thin films: Effect of density of antiphase boundaries