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Ferreira R.,International Iberian Nanotechnology Laboratory | Paz E.,International Iberian Nanotechnology Laboratory | Freitas P.P.,International Iberian Nanotechnology Laboratory | Freitas P.P.,Institute for Nanosciences and Nanotechnologies | And 3 more authors.
IEEE Transactions on Magnetics | Year: 2012

Full Wheatstone Bridge incorporating a serially connected ensemble of Magnetic tunnel junctions was produced, targeting an application as a magnetic field compass. To that end, MTJs with RxA ∼ 10 kΩ μm 2, TMR ∼ 150-200%, Hf=5Oe and Hf=5 Oe were produced. In order to achieve a full bridge signal, two stacks with an asymmetric SAF reference structure where used to produce MTJs with opposite dR/dH upon annealing in the same substrate. The resulting Bridges exhibit sensitivities between 13.5-32 mV/V/Oe depending on the field range and provide a significantly advantageous alternative to AMR and GMR based bridges. © 1965-2012 IEEE.

Amaral J.,Institute for Nanosciences and Nanotechnologies | Amaral J.,University of Lisbon | Gaspar J.,International Iberian Nanotechnology Laboratory | Pinto V.,University of Minho | And 8 more authors.
Applied Physics A: Materials Science and Processing | Year: 2013

An alternative neuroscience tool for magnetic field detection is described in this work, providing both micrometer-scale spatial resolution and high sensitivity to detect the extremely small magnetic fields (nT range) induced by the ionic currents flowing within electrically active neurons. The system combines an array of magnetoresistive sensors incorporated on micro-machined Si probes capable of being inserted within the brain current sources. The Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. The probe shafts are formed by double-sided deep reactive ion etching on a double-side polished silicon wafer. The shafts typically have the dimensions 1.2 mm × 40 μm × 300 μm and end in chisel-shaped tips with an incorporated magnetoresistive sensor with dimensions of 30 μm × 2 μm. An accompanying interconnect flexible cable is glued and wirebonded enabling precise and flexible positioning of the probes in the neural tissue. Our analyses showed sharply defined probes and probe tips. The electrical and magnetic behavior of the sensors was verified, and a preliminary test with brain slices were performed. © 2013 Springer-Verlag Berlin Heidelberg.

Costa M.,International Iberian Nanotechnology Laboratory | Costa M.,University of Lisbon | Gaspar J.,International Iberian Nanotechnology Laboratory | Ferreira R.,International Iberian Nanotechnology Laboratory | And 7 more authors.
2015 IEEE International Magnetics Conference, INTERMAG 2015 | Year: 2015

Various techniques of scanning magnetoresistance microscopy (SMRM) have been previously developed to enable the simultaneous imaging of surface topography and stray magnetic field distributions in order to overcome limitations of magnetic force microscopy (MFM) technique. GMR read-heads [1], micro-hall devices [2] and TMR sensors integrated on piezoeletric stage [3] have been used but lack of acceptable spatial resolution for imaging. To overcome this, magnetoresistive sensors are here integrated into standard atomic force microscopy (AFM) cantilevers and used to simultaneously map both topography and magnetic fields. © 2015 IEEE.

Ravelo Arias S.I.,University of Valencia | Ramirez Munoz D.,University of Valencia | Cardoso S.,Institute for Nanosciences and Nanotechnologies | Ferreira R.,International Iberian Nanotechnology Laboratory | And 2 more authors.
Review of Scientific Instruments | Year: 2015

The work shows a measurement technique to obtain the correct value of the four elements in a resistive Wheatstone bridge without the need to separate the physical connections existing between them. Two electronic solutions are presented, based on a source-and-measure unit and using discrete electronic components. The proposed technique brings the possibility to know the mismatching or the tolerance between the bridge resistive elements and then to pass or reject it in terms of its related common-mode rejection. Experimental results were taken in various Wheatstone resistive bridges (discrete and magnetoresistive integrated bridges) validating the proposed measurement technique specially when the bridge is micro-fabricated and there is no physical way to separate one resistive element from the others. © 2015 AIP Publishing LLC.

Arias S.I.R.,University of Valencia | Munoz D.R.,University of Valencia | Moreno J.S.,University of Valencia | Cardoso S.,Institute for Nanosciences and Nanotechnologies | And 3 more authors.
Sensors (Switzerland) | Year: 2013

Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function Zt (jf) is obtained considering it as the relationship between sensor output voltage and input sensing current, Zt (jf) = Vo,sensor(jf)/Isensor (jf). The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), spin-valve (GMR-SV) and tunnel magnetoresistance (TMR). The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications. © 2013 by the authors; licensee MDPI, Basel, Switzerland.

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