Nanoscaled self-alignment of Fe3O4 nanodiscs in ultrathin rGO films with engineered conductivity for electromagnetic interference shielding.

Ultrathin (∼2 µm) reduced graphene oxide (rGO) film embedded with self-aligned Fe3O4 nanodiscs were successfully fabricated through the filtration-assisted self-assembly method. In the as-fabricated hybrid film, Fe3O4 nanodiscs with thin thickness (26 nm) and high aspect ratio (∼9) were readily self-assembled and aligned in rGO intersheets under the assistance of hydrostatic forces. Compared with spherical Fe3O4 nanoparticles, introducing the Fe3O4 nanodiscs into rGO paper could not only offer high magnetic permeability and magnetic loss in a broad frequency range at the gigahertz level, but also increase the electrical conductivity of rGO film by means of improving the surface roughness without disrupting the conductive network of the rGO layers. Due to the above advantages, the free-standing rGO/Fe3O4 nanodisc magnetic hybrid film (56 wt%) exhibited an EMI shielding effectiveness (SE) of around 11.2 dB in the frequency range of 2-10 GHz, which is about 50% and 72% higher than that of neat rGO film and rGO/Fe3O4 nanosphere hybrid films (with similar particle size and loading weight fraction) prepared under the same conditions, respectively. Furthermore, compared with non-magnetic neat rGO film, the outstanding magnetic properties of the rGO/Fe3O4 nanodisc film paves the way for it to be used as a multifunctional material that can be controlled by magnetic fields. Additionally, the moderate thermal reduction temperature (420 °C) would be meaningful for large scale fabrication. Meanwhile, the strategy of achieving good alignment at the nanoscale could shed light on developing heterogeneous structures with self-aligned two-dimensional (2D) (magnetic or non-magnetic) nano-inclusions for various applications.

Methotrexate-conjugated and hyperbranched polyglycerol-grafted Fe3O4 magnetic nanoparticles for targeted anticancer effects.

Superparamagnetic nanoparticles grafted with hyperbranched polyglycerol (HPG) and conjugated with methotrexate (MTX) (MNP-g-HPG-MTX) were synthesized via a sol-gel reaction followed by thiol-ene click chemistry and esterification reaction. The successful grafting of MTX and HPG onto the nanoparticles was confirmed by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-visible spectroscopy. The HPG-graft layer confers the magnetic nanoparticles with good dispersibility and stability in aqueous medium and macrophage-evasive property while the MTX acts as a chemotherapeutic drug as well as a tumor targeting ligand. The dose-dependent targeting and anticancer effect of the MNP-g-HPG-MTX nanoparticles were evaluated, and the results showed that depending on the amount of conjugated MTX and the concentration of the incubated nanoparticles, the uptake of MNP-g-HPG-MTX nanoparticles by human head and neck cancer (KB) cells can be eight times or more higher than those by 3T3 fibroblasts and RAW macrophages. As a result, the MNP-g-HPG-MTX nanoparticles are capable of killing ∼50% of the KB cells while at the same time exhibiting low cytotoxicity towards 3T3 fibroblasts and RAW macrophages. Thus, such nanoparticles can potentially be used as active targeting anticancer agents.

Magnetic random access memory (MRAM).

The high density and high speed nonvolatile MTJ MRAMs are reviewed from perspective of the reading and writing operation. The reading operation of the MRAM with different sensing schemes and cell array structures is discussed, in particular the reference resistance generating schemes which are introduced to maximize the cell efficiency and reading reliability. The high density, low cost cross-point cell layout structures are analyzed systematically. The writing operation modes ranging from the half-select, toggle mode, guided SAF direct writing, thermally assisted writing, to the spin transfer switching are investigated both theoretically and experimentally. The thermal factor always plays an important role in determine not only the thermal stability but also the reading and writing reliability.