57 research outputs found
Magnetoresistive sensors based on the elasticity of domain walls
Magnetic sensors based on the magnetoresistance effects have a promising
application prospect due to their excellent sensitivity and advantages in terms
of the integration. However, competition between higher sensitivity and larger
measuring range remains a problem. Here, we propose a novel mechanism for the
design of magnetoresistive sensors: probing the perpendicular field by
detecting the expansion of the elastic magnetic Domain Wall (DW) in the free
layer of a spin valve or a magnetic tunnel junction. Performances of devices
based on this mechanism, such as the sensitivity and the measuring range can be
tuned by manipulating the geometry of the device, without changing the
intrinsic properties of the material, thus promising a higher integration level
and a better performance. The mechanism is theoretically explained based on the
experimental results. Two examples are proposed and their functionality and
performances are verified via micromagnetic simulation.Comment: 4 figures, 13 page
All-optical switching of magnetic domains in Co/Gd heterostructures with Dzyaloshinskii-Moriya Interaction
Given the development of hybrid spintronic-photonic devices and chiral
magnetic structures, a combined interest in all-optical switching (AOS) of
magnetization and current-induced domain wall motion in synthetic ferrimagnetic
structures with strong Dzyaloshinskii-Moriya Interaction (DMI) is emerging. In
this study, we report a study on single-pulse all-optical toggle switching and
asymmetric bubble expansion in specially engineered Co/Gd-based multilayer
structures. In the absence of any external magnetic fields, we look into the
AOS properties and the potential role of the DMI on the AOS process as well as
the stability of optically written micro-magnetic domains. Particularly,
interesting dynamics are observed in moon-shaped structures written by two
successive laser pulses. The stability of domains resulting from an interplay
of the dipolar interaction and domain-wall energy are compared to simple
analytical models and micromagnetic simulations
Tuning the Dzyaloshinskii-Moriya Interaction in Pt/Co/MgO heterostructures through MgO thickness
The interfacial Dzyaloshinskii-Moriya interaction (DMI) in the
ferromagnetic/heavy metal ultra-thin film structures , has attracted a lot of
attention thanks to its capability to stabilize Neel-type domain walls (DWs)
and magnetic skyrmions for the realization of non-volatile memory and logic
devices. In this study, we demonstrate that magnetic properties in
perpendicularly magnetized Ta/Pt/Co/MgO/Pt heterostructures, such as
magnetization and DMI, can be significantly influenced through both the MgO and
the Co ultrathin film thickness. By using a field-driven creep regime domain
expansion technique, we find that non-monotonic tendencies of DMI field appear
when changing the thickness of MgO and the MgO thickness corresponding to the
largest DMI field varies as a function of the Co thicknesses. We interpret this
efficient control of DMI as subtle changes of both Pt/Co and Co/MgO interfaces,
which provide a method to investigate ultra-thin structures design to achieve
skyrmion electronics.Comment: 18 pages, 11 figure
Enhanced Interfacial Dzyaloshinskii-Moriya Interaction in annealed Pt/Co/MgO structures
The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is attracting great
interests for spintronics. An iDMI constant larger than 3 mJ/m^2 is expected to
minimize the size of skyrmions and to optimize the DW dynamics. In this study,
we experimentally demonstrate an enhanced iDMI in Pt/Co/X/MgO ultra-thin film
structures with perpendicular magnetization. The iDMI constants were measured
using a field-driven creep regime domain expansion method. The enhancement of
iDMI with an atomically thin insertion of Ta and Mg is comprehensively
understood with the help of ab-initio calculations. Thermal annealing has been
used to crystallize the MgO thin layer for improving tunneling
magneto-resistance (TMR), but interestingly it also provides a further increase
of the iDMI constant. An increase of the iDMI constant up to 3.3 mJ/m^2 is
shown, which could be promising for the scaling down of skyrmion electronics
Elevated Levels of Cell-Free Circulating DNA in Patients with Acute Dengue Virus Infection
BACKGROUND: Apoptosis is thought to play a role in the pathogenesis of severe dengue and the release of cell-free DNA into the circulatory system in several medical conditions. Therefore, we investigated circulating DNA as a potential biomarker for severe dengue. METHODS AND FINDINGS: A direct fluorometric degradation assay using PicoGreen was performed to quantify cell-free DNA from patient plasma. Circulating DNA levels were significantly higher in patients with dengue virus infection than with other febrile illnesses and healthy controls. Remarkably, the increase of DNA levels correlated with the severity of dengue. Additionally, multivariate logistic regression analysis showed that circulating DNA levels independently correlated with dengue shock syndrome. CONCLUSIONS: Circulating DNA levels were increased in dengue patients and correlated with dengue severity. Additional studies are required to show the benefits of this biomarker in early dengue diagnosis and for the prognosis of shock complication
Semiconductor Quantum Dots in Chemical Sensors and Biosensors
Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical transduction scheme. Representative examples of quantum dot-based optical sensors from this fast-moving field have been selected and are discussed towards the most promising directions for future research
Unprecedented random lasing in 2D organolead halide single-crystalline perovskite microrods
Three-dimensional organic–inorganic hybrid halide perovskites have been demonstrated as great materials for applications in optoelectronics and photonics. However, their inherent instabilities in the presence of moisture, light, and heat may hinder their commercialization. Alternatively, emerging two-dimensional (2D) organic–inorganic hybrid perovskites have recently attracted increasing attention owing to their great environmental stability and inherent natural quantum-well structure. In this work, we have synthesized a high-quality long-chain organic diammonium spacer assisted 2D hybrid perovskite FA-(N-MPDA)PbBr4 (FA = formamidinium and N-MPDA = N-methylpropane-1,3-diammonium) by the slow evaporation at constant temperature method. The millimeter-sized single-crystalline microrods demonstrate low threshold random lasing behavior at room temperature. The single-crystalline 2D hybrid perovskite random laser achieved a very narrow linewidth (∼0.1 nm) with a low threshold (∼0.5 μJ cm−2) and a high quality factor (∼5350). Furthermore, the 2D hybrid microrod laser shows stable lasing emission with no measurable degradation after at least 2 h under continuous illumination, which substantially proves the stability of 2D perovskites. Our results demonstrate the promise of 2D organic–inorganic microrod-shaped perovskites and provide an important step toward the realization of high-performance optoelectronic devices
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