78 research outputs found
Magnetic Tunneling Junctions for biosensors: From the growth to the detection
In the last ten years, magnetoelectronics has emerged as a promising new platform technology for biosensor and biochip development. In particular, magnetoresistive-based sensors, conventionally used as read heads in hard disk drives, have been used in combination with biologically functionalized magnetic labels to demonstrate the detection of molecular recognition. In this paper, the growth and fabrication of spintronic transducers based on the magnetoresistance of tunneling magnetic junctions are described. Moreover the detection of 250 nm streptavidin magnetic beads is presented
Domain wall engineering through exchange bias
The control of the structure and position of magnetic domain walls is at the basis of the development of different magnetic devices and architectures. Several nanofabrication techniques have been proposed to geometrically confine and shape domain wall structures; however, a fine tuning of the position and micromagnetic configuration is hardly achieved, especially in continuous films. This work shows that, by controlling the unidirectional anisotropy of a continuous ferromagnetic film through exchange bias, domainwalls whose spin arrangement is generally not favored by dipolar and exchange interactions can be created. Micromagnetic simulations reveal that the domain wall width, position and profile can be tuned by establishing an abrupt change in the direction and magnitude of the exchange bias field set in the system
Da resistência ao poder: Governos da vida, sofrimento social e a violência da remoção
The urban transformations witnessed by the city of Rio de Janeiro in the last years multiplied the governing of life mechanisms, producing and reinventing technologies of population control and conduct regulation. I understand the evictions of favelas as a dispositive of life possibilities management in the city, composed by discourses and practices which mark relations and conflicts among several agents in the margins of the state. From an ethnographical point of view, the paper starts by analyzing the ways of resisting to the evidtions, aiming to comprehend how life is produced in a context of precarity and destruction.As transformações urbanas pelas quais passou o Rio de Janeiro nos últimos anos multiplicaram mecanismos de governo da vida dos sujeitos na cidade, produzindo e reinventando tecnologias de controle de populações e regulação de condutas. Entendo a remoção de favelas como dispositivo de gestão das possibilidades de vida na cidade, composto por diversos discursos e práticas que enredam relações e conflitos entre diversos agentes nas margens do Estado. Parto, de um ponto de vista etnográfico, das formas de resistência às remoções para compreender como se produz a vida em meio à precariedade e à destruição
Biocompatibility of a Magnetic Tunnel Junction Sensor Array for the Detection of Neuronal Signals in Culture
Magnetoencephalography has been established nowadays as a crucial in vivo technique for clinical and diagnostic applications due to its unprecedented spatial and temporal resolution and its non-invasive methods. However, the innate nature of the biomagnetic signals derived from active biological tissue is still largely unknown. One alternative possibility for in vitro analysis is the use of magnetic sensor arrays based on Magnetoresistance. However, these sensors have never been used to perform long-term in vitro studies mainly due to critical biocompatibility issues with neurons in culture. In this study, we present the first biomagnetic chip based on magnetic tunnel junction (MTJ) technology for cell culture studies and show the biocompatibility of these sensors. We obtained a full biocompatibility of the system through the planarization of the sensors and the use of a three-layer capping of SiO2/Si3N4/SiO2. We grew primary neurons up to 20 days on the top of our devices and obtained proper functionality and viability of the overlying neuronal networks. At the same time, MTJ sensors kept their performances unchanged for several weeks in contact with neurons and neuronal medium. These results pave the way to the development of high performing biomagnetic sensing technology for the electrophysiology of in vitro systems, in analogy with Multi Electrode Arrays
Nanopatterning spin-textures: A route to reconfigurable magnonics
Magnonics is envisioned to enable highly efficient data transport and processing, by exploiting propagating perturbations in the spin-texture of magnetic materials. Despite the demonstrations of a plethora of proof-of-principle devices, the efficient excitation, transport and manipulation of spin-waves at the nanoscale is still an open challenge. Recently, we demonstrated that the spin-wave excitation and propagation can be controlled by nanopatterning reconfigurable spin-textures in a continuous exchange biased ferromagnetic film. Here, we show that by patterning 90° stripe-shaped magnetic domains, we spatially modulate the spin-wave excitation in a continuous film, and that by applying an external magnetic field we can reversibly â\u80\u9cswitch-offâ\u80\u9d the spin-wave excitation. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits
Three-dimensional spin-wave dynamics, localization and interference in a synthetic antiferromagnet
Spin waves are collective perturbations in the orientation of the magnetic
moments in magnetically ordered materials. Their rich phenomenology is
intrinsically three dimensional, from the trajectory of the spin precession
during their propagation, to the profiles of the spin-wave mode throughout the
volume of the magnetic system. This gives rise to novel complex phenomena with
high potential for applications in the field of magnonics. However, the
three-dimensional imaging of spin waves, key to understanding and harnessing
these phenomena, has so far not been possible. Here, we image the
three-dimensional dynamics of spin waves excited in a synthetic
antiferromagnet, with nanoscale spatial resolution and sub-ns temporal
resolution, using time-resolved magnetic laminography. In this way, we map the
distribution of the spin-wave modes throughout the volume of the structure,
revealing unexpected depth-dependent profiles originating from the interlayer
dipolar interaction. We experimentally demonstrate the existence of complex
three-dimensional interference patterns, and analyze them via micromagnetic
modelling. We find that these patterns are generated by the superposition of
spin waves with non-uniform amplitude profiles, and that their features can be
controlled by tuning the composition and structure of the magnetic system. Our
results open unforeseen possibilities for the study of complex spin-wave modes
and their interaction within nanostructures, and for the generation and
manipulation of three-dimensional spin-wave landscapes for the design of novel
functions in magnonic devices.Comment: 15 pages, 4 figure
Plasmon-enhanced second harmonic sensing
It has been recently suggested that the nonlinear optical processes in
plasmonic nanoantennas allow for a substantial boost in the sensitivity of
plasmonic sensing platforms. Here we present a sensing device based on an array
of non-centrosymmetric plasmonic nanoantennas featuring enhanced second
harmonic generation (SHG) integrated in a microfluidic chip. We evaluate its
sensitivity both in the linear and nonlinear regime using a figure of merit
(FOM = ) that accounts for the relative change in the
measured intensity, \textit{I}, against the variation of the environmental
refractive index \textit{n}. While the signal-to-noise ratio achieved in both
regimes allows the detection of a minimum refractive index variation , the platform operation in the nonlinear regime
features a sensitivity (i.e. the FOM) that is at least 3 times higher than the
linear one. Thanks to the surface sensitivity of plasmon-enhanced SHG, our
results show that the development of such SHG sensing platforms with
sensitivity performances exceeding those of their linear counterparts is within
reach.Comment: 19 Pages, 5 Figure
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