38 research outputs found
Current-induced Pinwheel Oscillations in Perpendicular Magnetic Anisotropy Spin Valve Nanopillars
Nanopillar spin valve devices are typically comprised of two ferromagnetic
layers: a reference layer and a free layer whose magnetic orientation can be
changed by both an external magnetic field and through the introduction of
spin-polarized electric current. Here we report the continuous repeated
switching behavior of both the reference and free layers of a perpendicular
spin valve made of Co/Pd and Co/Ni multilayers that arises for sufficiently
large DC currents. This periodic switching of the two layers produces an
oscillating signal in the MHz regime but is only observed for one sign of the
applied current. The observed behavior agrees well with micromagnetic
simulations
Influence of interlayer exchange coupling on ultrafast laser-induced magnetization reversal in ferromagnetic spin valves
In this study, we explore the influence of interlayer exchange coupling on
magnetization reversal triggered by femtosecond laser pulses in ferromagnetic
spin valves. Our experiments, focused on femtosecond laser-induced
magnetization reversal, methodically vary the thickness of the copper (Cu)
spacer layer. We identify a critical Cu thickness threshold at 2.32 nm. Above
this threshold, a stable reversed magnetic domain is consistently generated
upon exposure to a single laser pulse. Conversely, with a Cu spacer thinner
than 2.32 nm, the observed magnetization reversal from parallel (P) to
anti-parallel (AP) states occurs only under continuous laser irradiation. Once
the laser is stopped, the magnetic configuration relaxes back to its initial P
state, influenced by ferromagnetic exchange coupling. This research enhances
our understanding of the mechanisms that drive optically induced ultrafast
magnetization reversal in ferromagnetic spin valves.Comment: After resubmission. Supplemetary Materials adde
All-optical control of ferromagnetic thin films and nanostructures
The interplay of light and magnetism has been a topic of interest since the
original observations of Faraday and Kerr where magnetic materials affect the
light polarization. While these effects have historically been exploited to use
light as a probe of magnetic materials there is increasing research on using
polarized light to alter or manipulate magnetism. For instance deterministic
magnetic switching without any applied magnetic fields using laser pulses of
the circular polarized light has been observed for specific ferrimagnetic
materials. Here we demonstrate, for the first time, optical control of
ferromagnetic materials ranging from magnetic thin films to multilayers and
even granular films being explored for ultra-high-density magnetic recording.
Our finding shows that optical control of magnetic materials is a much more
general phenomenon than previously assumed. These results challenge the current
theoretical understanding and will have a major impact on data memory and
storage industries via the integration of optical control of ferromagnetic
bits.Comment: 21 pages, 11 figure
Asymmetric switching behavior in perpendicularly magnetized spin-valve nanopillars due to the polarizer dipole field
We report the free layer switching field distributions of spin-valve
nanopillars with perpendicular magnetization. While the distributions are
consistent with a thermal activation model, they show a strong asymmetry
between the parallel to antiparallel and the reverse transition, with energy
barriers more than 50% higher for the parallel to antiparallel transitions. The
inhomogeneous dipolar field from the polarizer is demonstrated to be at the
origin of this symmetry breaking. Interestingly, the symmetry is restored for
devices with a lithographically defined notch pair removed from the midpoint of
the pillar cross-section along the ellipse long axis. These results have
important implications for the thermal stability of perpendicular magnetized
MRAM bit cells.Comment: Submitted to Applied Physics Letters on November 4, 2011. Consists of
4 pages, 3 figure
Independence of spin-orbit torques from the exchange bias direction in NiFe/IrMn bilayers
We investigated a possible correlation between spin Hall angles and exchange
bias in NiFe/IrMn samples by performing spin torque ferromagnetic
resonance measurements. This correlation is probed by patterning of
NiFe/IrMn bilayers in different relative orientations with
respect to the exchange bias direction. The measured voltage spectra allow a
quantitative determination of spin Hall angles, which are independent of the
orientation around 2.8\pm0.3%.Comment: 10 page
Extending the scope and understanding of all-optical magnetization switching in Gd-based alloys by controlling the underlying temperature transients
We use the thickness of Cu layers to control all-optical switching of
magnetization in adjacent Gd(Fe0Co) films. While
increasing the Cu thickness from 5 to 900nm has no effect on the switching
threshold, it significantly enlarges the fluence and pulse duration at which
multiple domains emerge. Having shown that thermally activated multi-domain
formation limits the maximum fluence and pulse duration for controlled
switching, we demonstrate that continuous magnetization reversal precedes
multi-domain formation in GdDyCo films excited with fluences
slightly larger than the multi-domain threshold
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Immobilized fibrinogen activates human platelets through GPVI
GPVI, a major platelet activation receptor for collagen and fibrin, is considered as a particularly promising safe antithrombotic target. In this study, we show that human GPVI signals upon platelet adhesion to fibrinogen. Full spreading of human platelets on fibrinogen is abolished in platelets from GPVI-deficient patients suggesting that fibrinogen activates platelets through GPVI. While mouse platelets fail to spread on fibrinogen, human-GPVI-transgenic mouse platelets show full spreading and increased Ca2+ signalling through the tyrosine kinase Syk. Direct binding of fibrinogen to human GPVI was shown by surface plasmon resonance and by increased adhesion of human GPVI-transfected Rbl-2H3 cells to fibrinogen relative to mock-transfected cells. Blockade of human GPVI with the Fab of the monoclonal antibody 9O12 impairs platelet aggregation on preformed platelet aggregates in flowing blood independent of collagen and fibrin exposure. These results demonstrate that human GPVI binds to immobilized fibrinogen and show that this contributes to platelet spreading and platelet aggregation under flow
Alzheimers Dement
Introduction: The free and cued selective reminding test is used to identify memory deficits in mild cognitive impairment and demented patients. It allows assessing three processes: encoding, storage, and recollection of verbal episodic memory. Methods: We investigated the neural correlates of these three memory processes in a large cohort study. The Memento cohort enrolled 2323 outpatients presenting either with subjective cognitive decline or mild cognitive impairment who underwent cognitive, structural MRI and, for a subset, fluorodeoxyglucose-positron emission tomography evaluations. Results: Encoding was associated with a network including parietal and temporal cortices; storage was mainly associated with entorhinal and parahippocampal regions, bilaterally; retrieval was associated with a widespread network encompassing frontal regions. Discussion: The neural correlates of episodic memory processes can be assessed in large and standardized cohorts of patients at risk for Alzheimer's disease. Their relation to pathophysiological markers of Alzheimer's disease remains to be studied