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Magnetite particles of 2–4 nm were synthesized by an economic, biocompatible chemical coprecipitation route, with their size tuned by the reaction temperature. The microstructure and morphology of the nanoparticles were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), whereas the magnetic properties were investigated by vibrating sample magnetometry (VSM) and superconducting quantum interference device (SQUID). It is found that the nanoparticles demonstrate well-defined superparamagnetic behavior as prepared and after annealing. Distinct lattices were observed which manifest the high crystallinity of such ultrasmall particles and the finite-size effect was revealed by analyzing the corresponding microstructure and magnetism.

International audience; Two-dimensional materials have outstanding scalability due to their structural and electrical properties for the logic devices. Here, we report the current fluctuation in multilayer WSe2 field effect transistors (FETs). In order to demonstrate the impact on carrier types, n-type and p-type WSe2 FETs are fabricated with different work function metals. Each device has similar electrical characteristics except for the threshold voltage. In the low frequency noise analysis, drain current power spectral density (SI) is inversely proportional to frequency, indicating typical 1/f noise behaviors. The curves of the normalized drain current power spectral density (NSI) as a function of drain current at the 10 Hz of frequency indicate that our devices follow the carrier number fluctuation with correlated mobility fluctuation model. This means that current fluctuation depends on the trapping-detrapping motion of the charge carriers near the channel interface. No significant difference is observed in the current fluctuation according to the charge carrier type, electrons and holes that occurred in the junction and channel region.

Cobalt nanowires were fabricated by DC electrodeposition onto anodic aluminium oxide (AAO) templates. The effects of AAO pore diameter, current density, pH, annealing and deposition under external magnetic fields on the structure and magnetic properties of the nanowire arrays were studied. It is found that the smaller pore size produces high crystallinity, resulting in improved magnetic performance at low current density. The pH can transform fcc-Co phase to hcp-Co phase, with the easy axis along the nanowire axis switched over to the perpendicular direction. Annealing demonstrates excellent thermal stability of the magnetic nanowire arrays at high temperature. The application of external magnetic field during deposition influences the growth habit of the nanowires, leading to the change in the magnetic properties.

Polyvinylpyrrolidone (PVP)-coated sub-5 nm monosize Fe 3 O 4 nanoparticles were synthesized by reduction of Fe(III) acetylacetonate in the presence of PVP polymer as surfactant in one-pot polyol process. Their microstructure and magnetic properties were characterized by XRD, TEM/HRTEM and VSM. It is found that the nanoparticles have high crystallinity with distinct lattices and the magnetic measurements reveal their well-defined superparamagnetic behavior at room temperature. Such Fe 3 O 4 nanoparticles with tailorable size and tunable magnetic properties are promising for biomedical applications.

Double-barrier magnetic tunnel junctions (DMTJs) comprising Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO x /free layer (CoFe 4/NiFeSiB 2/CoFe 4, CoFe 10, or NiFeSiB 10)/AlO x /CoFe 7/IrMn 10/Ru 60 (nm) have been examined with an emphasis given on understanding the interfacial mixing effects. The DMTJ, consisted of NiFeSiB, shows low switching field and low bias voltage dependence because the amorphous NiFeSiB has lower M S (=800 emu/cm 3 ) and offers smoother interfaces than polycrystalline CoFe. An interesting feature observed in the CoFe/NiFeSiB/CoFe sandwich free layered DMTJ is the presence of a wavy MR transfer curve at high-resistance region. Because the polycrystalline CoFe usually grows into a columnar structure, diamagnetic CoSi, paramagnetic FeSi, and/or diamagnetic CoB might have been formed during the sputter-deposition process. By employing electron energy loss spectrometry (EELS) and Auger electron spectroscopy (AES), we were able to confirm that Si and B atoms were arranged evenly in the top and bottom portions of AlO x /CoFe interfaces. This means that the interfacial mixing resulted in a distorted magnetization reversal process.

The Co and multilayered Co/Cu nanowire arrays were fabricated by pulsed DC electrodeposition using anodized aluminum oxide (AAO) templates. Each nanowire has the length of 20 μm and the diameter of 200 nm. The layer thickness of Co layer was slightly decreased even if the deposition time was fixed as Cu deposition time increased due to the metal exchange. Unlike the Co nanowire array case, multilayered Co/Cu nanowire array exhibited an easy magnetization direction perpendicular to the nanowire axis due to the separation of Co layers.

Ferromagnetic amorphous Ni 16 Fe 62 Si 8 B 14 layer have been studied as free layers for magnetic tunnel junctions (MTJs) to enhance cell switching performance. Traditional MTJ free layer materials such as NiFe and CoFe were also prepared for switching comparison purposes. Both NiFeSiB and NiFe resulted in an order of magnitude smaller switching fields compared to the CoFe. The switching field was further reduced for the synthetic antiferromagnetic NiFeSiB free layered structure.

A double-barrier magnetic tunnel junction (DMTJ) comprising an amorphous ferromagnetic NiFeSiB was investigated to reduce bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The typical DMTJ structures were Ta45∕Ru9.5∕IrMn10∕CoFe7∕AlOx∕free layer7∕AlOx∕CoFe7∕IrMn10∕Ru60 (in nanometers). Various free layers such as CoFe 7, NiFeSiB 7, CoFe3.5∕NiFeSiB3.5, and NiFeSiB3.5∕CoFe3.5 were prepared and compared. The NiFeSiB-used DMTJ shows a low root-mean-square surface roughness of 0.17 nm, a resistance of about 860Ω, a Vh (voltage where the TMR ratio becomes half of its nonbiased value) of 1.1 V, and a high junction breakdown voltage of 2.0 V. The DMTJ with an amorphous NiFeSiB free layer offers smooth surface roughness resulting in reduced interlayer coupling field and bias voltage dependence.