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Hou Z.,Tongji University | Liu Y.,Tongji University | Cardoso S.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | Freitas P.P.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | And 2 more authors.
Journal of Applied Physics | Year: 2011

The magnetization orientation of the polarizing reference layer would fluctuate between the parallel and antiparallel states when the reference layer loses stability. In this paper, a combined analytical and simulation study is presented to predict the magnetic dynamics of the spin valve element with single-domain magnets as the free and reference layers. We acquire a complete phase diagram that includes the normal spin-torque switching and random magnetization fluctuations by tuning the spin torque strength between the free and reference layers. The phase dynamics strongly depends on the magnetization state of the reference layer, showing that the instability of the reference layer could be responsible for the random fluctuation events. © 2011 American Institute of Physics.


Moreno J.S.,University of Valencia | Munoz D.R.,University of Valencia | Cardoso S.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | Berga S.C.,University of Valencia | And 2 more authors.
Sensors | Year: 2011

A compensation method for the sensitivity drift of a magnetoresistive (MR) Wheatstone bridge current sensor is proposed. The technique was carried out by placing a ruthenium temperature sensor and the MR sensor to be compensated inside a generalized impedance converter circuit (GIC). No internal modification of the sensor bridge arms is required so that the circuit is capable of compensating practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a microfabricated spin-valve MR current sensor. The temperature compensation has been solved in the interval from 0 °C to 70 °C measuring currents from -10 A to +10 A. © 2011 by the authors; licensee MDPI, Basel, Switzerland.


Sanchez J.,University of Valencia | Ramirez D.,University of Valencia | Ravelo S.I.,University of Valencia | Lopes A.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | And 5 more authors.
IEEE Transactions on Magnetics | Year: 2012

The objective of the work was the design of a Wheatstone bridge current sensor using MTJ as magnetoresistive elements. Each one of the four resistances of the bridge consists on 360 MTJ single elements connected in series for improved electrical robustness. A printed circuit board (PCB) was designed with a U-shaped copper trace placed under the PCB maintaining a 1.1 mm separation distance between sensor and trace. A 160% of tunnel magnetoresistance effect in the single junction and a 120% in its corresponding series elements connection has been achieved with a sensitivity of 9.2 Ω/Oe in a 65 Oe linear range. The DC sensor sensitivity in response to an external DC current sweeps of ±10, ±20, and ±30 A gave an average of 9.8 mV/A. The measured AC sensor response in all the tested cases corresponded to a - 3 dB frequency close to 200 kHz. The sensor was submitted to a DC current excursion under different temperatures showing a TC(S) sensitivity temperature coefficient of 0.031%/°C rather lower compared with the spin-valve technology. The work shows that MTJ sensor technology provides a promising tool in the R + D areas of power management and energy consumption like electric vehicles or energy metering. © 2012 IEEE.


Silva A.V.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | Silva A.V.,University of Lisbon | Leitao D.C.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | Huo Z.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | And 9 more authors.
IEEE Transactions on Magnetics | Year: 2013

The switching field dependence on the size of nanometric magnetic tunnel junctions was studied. CoFe/Ru/CoFeB/MgO/CoFeB nano-pillars were fabricated down to 150,×, 300 nm2 and characterized, revealing a squared transfer curve with a sharp transition between magnetic states. A micromagnetic finite element tool was then used to simulate the magnetic behavior of the studied nanopillar. The simulations indicated a single-domain like state at remanence, also displaying a sharp transition between parallel/antiparallel free-layer configurations. Overall, the experimentally measured switching fields (Hsw) were smaller than those obtained from simulations. Such trend was consistent with the presence of a particular free layer profile, signature of the two angle etching step used for pillar definition. Further decrease of experimental Hsw was attributed to local defects and thermal activated processes. This study was able to validate this particular simulation tool for the control of the nanofabrication process. © 2013 IEEE.


Sanchez J.,University of Valencia | Ramirez D.,University of Valencia | Amaral J.,Institute Sistemas e Computadores Microsistemas e Nanotecnologias INESC MN | Amaral J.,University of Lisbon | And 4 more authors.
Review of Scientific Instruments | Year: 2012

The present work shows an electrical ammeter for laboratory purpose based on a magnetoresistive (MR) spin-valve (SV) sensor. The proposed ammeter measures a 10 A maximum current and offers a maximum frequency response between 150 and 800 kHz depending on the electronics whole gain. These features are due to the use of a new generation MR-SV current sensor and a conditioning electronics that compensates in frequency and temperature the sensor response. With little adjustments in the electronics and changing the position of the sensor with respect to current carrying conductor, the designed instrument is able to measure higher current levels. The work shows the proposed ammeter with its different subsystems and describes the procedure used to test the instrument. Also a discussion of the obtained experimental results is included. © 2012 American Institute of Physics.

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