60 research outputs found
An Aminopeptidase Acting as a Potential Factor in Host Adaptation of Mycoplasma Gallinarum
Unlike most other host-specific mycoplasmas, Mycoplasma gallinarum exists as a commensal with a host range including most poultry as well as some mammals. This property of M. gallinarum may reflect unique mechanisms for its colonization and persistence in hosts. Whereas M. gallinarum shows leucine and arginine aminopeptidase activity, the genes encoding the enzymes had not been cloned and characterized. We identified an aminopeptidase gene (APN) by oligonucleotide hybridization to a genomic library of M. gallinarum in lambda ZAPII bacteriophage. Nucleotide sequence analysis of overlapping phage clones identified a 1,362 bp open reading frame (ORF) encoding a putative leucine aminopeptidase gene. Database searches indicate that this ORF has 68% nucleotide identity and 51% amino acid identity with the M. salivarium leucine aminopeptidase gene. The active sites of the leucine aminopeptidases in other eukaryotes and prokaryotes were conserved in the cloned aminopeptidase gene. Northern-blot hybridization analysis showed that this ORF is expressed as a 1.5 kb transcript. Southern-blot hybridization analysis demonstrated this gene was present as a single copy in M. gallinarum. Characterization of the leucine aminopeptidase demonstrated that it is a metallo-aminopeptidase (EC 3.4.11.1) and is located in the cytoplasm with a weak interaction with the cell membrane. The subcellular location was further confirmed by immunoblotting with polyclonal anti-recombinant APN serum and M. gallinarum Triton-114 partitions. Immunoblotting results with sera from three chickens experimentally infected with M. gallinarum showed that there were very few proteins in M. gallinarum exposed to the host immune responses and that leucine aminopeptidase was not able to stimulate production of specific humoral antibody. Our results suggest that this leucine aminopeptidase play a role in nutrition supply for the host adaptation of M. gallinarum and that the enzyme was not strongly immunogenic
Threshold current of field-free perpendicular magnetization switching using anomalous spin-orbit torque
Spin-orbit torque (SOT) is a candidate technique in next generation magnetic
random-access memory (MRAM). Recently, experiments show that some material with
low-symmetric crystalline or magnetic structures can generate anomalous SOT
that has an out-of-plane component, which is crucial in switching perpendicular
magnetization of adjacent ferromagnetic (FM) layer in the field-free condition.
In this work, we analytically derive the threshold current of field-free
perpendicular magnetization switching using the anomalous SOT. And we
numerically calculate the track of the magnetic moment in a FM free layer when
an applied current is smaller and greater than the threshold current. After
that, we study the applied current dependence of the switching time and the
switching energy consumption, which shows the minimum energy consumption
decreases as out-of-plane torque proportion increases. Then we study the
dependences of the threshold current on anisotropy strength, out-of-plane
torque proportion, FM free layer thickness and Gilbert damping constant, and
the threshold current shows negative correlation with the out-of-plane torque
proportion and positive correlation with the other three parameters. Finally,
we demonstrate that when the applied current is smaller than the threshold
current, although it cannot switch the magnetization of FM free layer, it can
still equivalently add an effective exchange bias field H_{bias} on the FM free
layer. The H_{bias} is proportional to the applied current J_{SOT}, which
facilitates the determination of the anomalous SOT efficiency. This work helps
us to design new spintronic devices that favor field-free switching
perpendicular magnetization using the anomalous SOT, and provides a way to
adjust the exchange bias field, which is helpful in controlling FM layer
magnetization depinning
Perinatal COVID vaccination and breastfeeding during a pandemic : influences on decision making
"When the COVID-19 vaccine was first offered to pregnant individuals, little research was available on the effects of the vaccine on mom and baby (Sutton et. al, 2020; Fisher et. Al, 2021). Due to misinformation and other factors, low vaccine confidence (and vaccine hesitancy/skepticism) has been observed in Missouri and throughout the Midwest Ecological characteristics of a community, such as higher income and perceived community support, can have a significant impact on local breastfeeding practices. (Isherwood et. al, 2019). The purpose of this study was to examine how habitus influenced women’s health behavior regarding breastfeeding and COVID-19 vaccination. Habitus = The reflection of deeply ingrained habits, skills, and beliefs that shape an individual's perception of the world (Power, 1999)"--Background
Magnon-mediated interlayer coupling in an all-antiferromagnetic junction
The interlayer coupling mediated by fermions in ferromagnets brings about
parallel and anti-parallel magnetization orientations of two magnetic layers,
resulting in the giant magnetoresistance, which forms the foundation in
spintronics and accelerates the development of information technology. However,
the interlayer coupling mediated by another kind of quasi-particle, boson, is
still lacking. Here we demonstrate such a static interlayer coupling at room
temperature in an antiferromagnetic junction Fe2O3/Cr2O3/Fe2O3, where the two
antiferromagnetic Fe2O3 layers are functional materials and the
antiferromagnetic Cr2O3 layer serves as a spacer. The N\'eel vectors in the top
and bottom Fe2O3 are strongly orthogonally coupled, which is bridged by a
typical bosonic excitation (magnon) in the Cr2O3 spacer. Such an orthogonally
coupling exceeds the category of traditional collinear interlayer coupling via
fermions in ground state, reflecting the fluctuating nature of the magnons, as
supported by our magnon quantum well model. Besides the fundamental
significance on the quasi-particle-mediated interaction, the strong coupling in
an antiferromagnetic magnon junction makes it a realistic candidate for
practical antiferromagnetic spintronics and magnonics with ultrahigh-density
integration.Comment: 19 pages, 4 figure
Field-free spin-orbit torque switching enabled by interlayer Dzyaloshinskii-Moriya interaction
Perpendicularly magnetized structures that are switchable using a spin
current under field-free conditions can potentially be applied in spin-orbit
torque magnetic random-access memory(SOT-MRAM).Several structures have been
developed;however,new structures with a simple stack structure and MRAM
compatibility are urgently needed.Herein,a typical structure in a perpendicular
spin-transfer torque MRAM,the Pt/Co multilayer and its synthetic
antiferromagnetic counterpart with perpendicular magnetic anisotropy, was
observed to possess an intrinsic interlayer chiral interaction between
neighboring magnetic layers,namely the interlayer Dzyaloshinskii-Moriya
interaction (DMI) effect. Furthermore, using a current parallel to the
eigenvector of the interlayer DMI, we switched the perpendicular magnetization
of both structures without a magnetic field, owing to the additional
symmetry-breaking introduced by the interlayer DMI. This SOT switching scheme
realized in the Pt/Co multilayer and its synthetic antiferromagnet structure
may open a new avenue toward practical perpendicular SOT-MRAM and other SOT
devices
Observation of Fluctuation Spin Hall Effect in Antiferromagnet
The spin Hall effect (SHE) can generate a pure spin current by an electric
current, which is promisingly used to electrically control magnetization. To
reduce power consumption of this control, a giant spin Hall angle (SHA) in the
SHE is desired in low-resistivity systems for practical applications. Here,
critical spin fluctuation near the antiferromagnetic (AFM) phase-transition is
proved as an effective mechanism to create an additional part of SHE, named as
fluctuation spin Hall effect (FSHE). This FSHE enhances the SHA due to the AFM
spin fluctuation between conduction electrons and local spins. We detect the
FSHE with the inverse and direct spin Hall effect (ISHE and DSHE) set-up and
their temperature (T) dependences in the Cr/MgO/Fe magnetic tunnel junctions
(MTJs). The SHA is significantly enhanced when temperature is approached to the
N\'eel temperature (T_N) and has a peak value of -0.34 at 200 K near T_N. This
value is higher than the room-temperature value by 240% and comparable to that
of heavy metals Ta and W. Furthermore, the spin Hall resistivity of Cr well
fits the modeled T-dependence when T approaches T_N from low temperatures,
implying the AFM spin fluctuation nature of strong SHA enhancement. Thus, this
study demonstrates the critical spin fluctuation as a prospective way of
increasing SHA and enriches the AFM material candidates for spin-orbitronic
devices.Comment: 27 pages, 9 figure
N\'eel-type skyrmion in WTe2/Fe3GeTe2 van der Waals heterostructure
The promise of high-density and low-energy-consumption devices motivates the
search for layered structures that stabilize chiral spin textures such as
topologically protected skyrmions. At the same time, layered structures provide
a new platform for the discovery of new physics and effects. Recently
discovered long-range intrinsic magnetic orders in the two-dimensional van der
Waals materials offer new opportunities. Here we demonstrate the
Dzyaloshinskii-Moriya interaction and N\'eel-type skyrmions are induced at the
WTe2/Fe3GeTe2 interface. Fe3GeTe2 is a ferromagnetic material with strong
perpendicular magnetic anisotropy. We demonstrate that the strong spin orbit
interaction in 1T'-WTe2 does induce a large interfacial Dzyaloshinskii-Moriya
interaction at the interface with Fe3GeTe2 due to the inversion symmetry
breaking to stabilize skyrmions. Transport measurements show the topological
Hall effect in this heterostructure for temperatures below 100 K. Furthermore,
Lorentz transmission electron microscopy is used to directly image N\'eel-type
skyrmions along with aligned and stripe-like domain structure. This interfacial
coupling induced Dzyaloshinskii-Moriya interaction is estimated to have a large
energy of 1.0 mJ/m^2, which can stabilize the N\'eel-type skyrmions in this
heterostructure. This work paves a path towards the skyrmionic devices based on
van der Waals heterostructures.Comment: 32 pages, 4 figures in the main tex
Record thermopower found in an IrMn-based spintronic stack
The Seebeck effect converts thermal gradients into electricity. As an approach to power technologies in the current Internet-of-Things era, on-chip energy harvesting is highly attractive, and to be effective, demands thin film materials with large Seebeck coefficients. In spintronics, the antiferromagnetic metal IrMn has been used as the pinning layer in magnetic tunnel junctions that form building blocks for magnetic random access memories and magnetic sensors. Spin pumping experiments revealed that IrMn Néel temperature is thickness-dependent and approaches room temperature when the layer is thin. Here, we report that the Seebeck coefficient is maximum at the Néel temperature of IrMn of 0.6 to 4.0 nm in thickness in IrMn-based half magnetic tunnel junctions. We obtain a record Seebeck coefficient 390 (±10) μV K-1 at room temperature. Our results demonstrate that IrMn-based magnetic devices could harvest the heat dissipation for magnetic sensors, thus contributing to the Power-of-Things paradigm
Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2
The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals
(vdW) materials holds promises for novel spintronic devices with exceptional
performances. However, in order to utilize 2D vdW magnets for building
spintronic nanodevices such as magnetic memories, key challenges remain in
terms of effectively switching the magnetization from one state to the other
electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the
magnetization of few-layered Fe3GeTe2 can be effectively switched by the
spin-orbit torques (SOTs) originated from the current flowing in the Pt layer.
The effective magnetic fields corresponding to the SOTs are further
quantitatively characterized using harmonic measurements. Our demonstration of
the SOT-driven magnetization switching in a 2D vdW magnet could pave the way
for implementing low-dimensional materials in the next-generation spintronic
applications
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