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This experimental study focuses on the comparison between two different sensors for vibration signals: a magnetoresistive sensor and an accelerometer as a calibrated reference. The vibrations are collected from a variable speed inductor motor setup, coupled to a ball bearing load with adjustable misalignments. To evaluate the performance of the magnetoresistive sensor against the accelerometer, several vibration measurements are performed in three different axes: axial, horizontal and vertical. Vibration velocity measurements from both sensors were collected and analyzed based on spectral decomposition of the signals. The high cross-correlation coefficient between spectrum vibration signatures in all experimental measurements shows good agreement between the proposed magnetoresistive sensor and the reference accelerometer performances. The results demonstrate the potential of this type of innovative and non-contact approach to vibration data collection and a prospective use of magnetoresistive sensors for predictive maintenance models for inductive motors in Industry 4.0 applications.
Rogerio Dionisio; Pedro Torres; Armando Ramalho; Ricardo Ferreira. Magnetoresistive Sensors and Piezoresistive Accelerometers for Vibration Measurements: A Comparative Study. Journal of Sensor and Actuator Networks 2021, 10, 22 .
AMA StyleRogerio Dionisio, Pedro Torres, Armando Ramalho, Ricardo Ferreira. Magnetoresistive Sensors and Piezoresistive Accelerometers for Vibration Measurements: A Comparative Study. Journal of Sensor and Actuator Networks. 2021; 10 (1):22.
Chicago/Turabian StyleRogerio Dionisio; Pedro Torres; Armando Ramalho; Ricardo Ferreira. 2021. "Magnetoresistive Sensors and Piezoresistive Accelerometers for Vibration Measurements: A Comparative Study." Journal of Sensor and Actuator Networks 10, no. 1: 22.
Magnetomyography (MMG) is the measurement of magnetic signals generated in the skeletal muscle of humans by electrical activities. However, current technologies developed to detect such tiny magnetic field are bulky, costly and require working at the temperature-controlled environment. Developing a miniaturized, low cost and room temperature magnetic sensors provide an avenue to enhance this research field. Herein, we present an integrated tunnelling magnetoresistive (TMR) array for room temperature MMG applications. TMR sensors were developed with low-noise analogue front-end circuitry to detect the MMG signals without and with averaging at a high signal-to-noise ratio. The MMG was achieved by averaging signals using the Electromyography (EMG) signal as a trigger. Amplitudes of 200 pT and 30 pT, corresponding to periods when the hand is tense and relaxed, were observed, which is consistent with muscle simulations based on finite-element method (FEM) considering the effect of distance from the observation point to the magnetic field source.
Siming Zuo; Kianoush Nazarpour; Tim Bohnert; Elvira Paz; Paulo Freitas; Ricardo Ferreira; Hadi Heidari. Integrated Pico-Tesla Resolution Magnetoresistive Sensors for Miniaturised Magnetomyography. 2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) 2020, 2020, 3415 -3419.
AMA StyleSiming Zuo, Kianoush Nazarpour, Tim Bohnert, Elvira Paz, Paulo Freitas, Ricardo Ferreira, Hadi Heidari. Integrated Pico-Tesla Resolution Magnetoresistive Sensors for Miniaturised Magnetomyography. 2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC). 2020; 2020 ():3415-3419.
Chicago/Turabian StyleSiming Zuo; Kianoush Nazarpour; Tim Bohnert; Elvira Paz; Paulo Freitas; Ricardo Ferreira; Hadi Heidari. 2020. "Integrated Pico-Tesla Resolution Magnetoresistive Sensors for Miniaturised Magnetomyography." 2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC) 2020, no. : 3415-3419.
Magnetic tunnel junctions are nanoscale spintronic devices with microwave-generation and -detection capabilities. Here, we use the rectification effect called a “spin diode” in a magnetic tunnel junction to wirelessly detect the microwave emission of another junction in the auto-oscillatory regime. We show that the rectified spin-diode voltage measured at the receiving junction end can be reconstructed from the independently measured auto-oscillation and spin-diode spectra in each junction. Finally, we adapt the auto-oscillator model to the case of the spin-torque oscillator and the spin diode and we show that it accurately reproduces the experimentally observed features. These results will be useful for the design of circuits and chips based on spintronic nanodevices communicating through microwaves.
Danijela Marković; Nathan Leroux; Alice Mizrahi; Juan Trastoy; Vincent Cros; Paolo Bortolotti; Leandro Martins; Alex Jenkins; Ricardo Ferreira; Julie Grollier. Detection of the Microwave Emission from a Spin-Torque Oscillator by a Spin Diode. Physical Review Applied 2020, 13, 044050 .
AMA StyleDanijela Marković, Nathan Leroux, Alice Mizrahi, Juan Trastoy, Vincent Cros, Paolo Bortolotti, Leandro Martins, Alex Jenkins, Ricardo Ferreira, Julie Grollier. Detection of the Microwave Emission from a Spin-Torque Oscillator by a Spin Diode. Physical Review Applied. 2020; 13 (4):044050.
Chicago/Turabian StyleDanijela Marković; Nathan Leroux; Alice Mizrahi; Juan Trastoy; Vincent Cros; Paolo Bortolotti; Leandro Martins; Alex Jenkins; Ricardo Ferreira; Julie Grollier. 2020. "Detection of the Microwave Emission from a Spin-Torque Oscillator by a Spin Diode." Physical Review Applied 13, no. 4: 044050.
By harnessing the rich dynamics associated with nonhomogeneous magnetization configurations in confined nanostructures, the free layer of a magnetic tunnel junction (MTJ) can be forced, via a localized magnetic field, to transition between two magnetic states: the quasi-uniform and vortex states. Here, we demonstrate that such transitions can be driven back and forth to a dynamic equilibrium by exciting a MTJ with ac magnetic fields close to the resonant modes of the magnetic vortex. The frequency dependence of the dynamic-state transitions leads to a proposal for an alternative type of broadband analogue frequency-to-resistance converter (FRC). In this report, two quasilinear bands of the FRC are demonstrated: a relatively lower frequency converter operating between 200 and 350 MHz with 250-kHz resolution (∼500 channels) and a higher frequency converter operating between 2.5 and 6 GHz with a 2.5-MHz resolution (∼800 channels). The fact that a single CMOS-compatible nanoscale device can perform such a complex function over a multitude of frequency bands, with high-frequency resolution relative to that of conventional CMOS circuits, can enable the next generation of wireless communication circuit topologies.
Alex S. Jenkins; Lara San Emeterio Alvarez; Roberta Dutra; Ruben L. Sommer; Paulo P. Freitas; Ricardo Ferreira. Wideband High-Resolution Frequency-to-Resistance Converter Based on Nonhomogeneous Magnetic-State Transitions. Physical Review Applied 2020, 13, 014046 .
AMA StyleAlex S. Jenkins, Lara San Emeterio Alvarez, Roberta Dutra, Ruben L. Sommer, Paulo P. Freitas, Ricardo Ferreira. Wideband High-Resolution Frequency-to-Resistance Converter Based on Nonhomogeneous Magnetic-State Transitions. Physical Review Applied. 2020; 13 (1):014046.
Chicago/Turabian StyleAlex S. Jenkins; Lara San Emeterio Alvarez; Roberta Dutra; Ruben L. Sommer; Paulo P. Freitas; Ricardo Ferreira. 2020. "Wideband High-Resolution Frequency-to-Resistance Converter Based on Nonhomogeneous Magnetic-State Transitions." Physical Review Applied 13, no. 1: 014046.
Dealing with big data, especially the videos and images, is the biggest challenge of existing Von-Neumann machines while the human brain, benefiting from its massive parallel structure, is capable of processing the images and videos in a fraction of second. The most promising solution, which has been recently researched widely, is brain-inspired computers, so-called neuromorphic computing systems (NCS). The NCS overcomes the limitation of the word-at-a-time thinking of conventional computers benefiting from massive parallelism for data processing, similar to the brain. Recently, spintronic-based NCSs have shown the potential of implementation of low-power high-density NCSs, where neurons are implemented using magnetic tunnel junctions (MTJs) or spin torque nano-oscillators (STNOs) and memristors are used to mimic synaptic functionality. Although using STNOs as neuron requires lower energy in comparison to the MTJs, still there is a huge gap between the power consumption of spintronic-based NCSs and the brain due to high bias current needed for starting the oscillation with a detectable output power. In this manuscript, we propose a spintronic-based NCS (196 × 10) proof-of-concept where the power consumption of the NCS is reduced by assisting the STNO oscillation through a microwatt nanosecond laser pulse. The experimental results show the power consumption of the STNOs in the designed NCS is reduced by 55.3% by heating up the STNOs to 100°C. Moreover, the average power consumption of spintronic layer (STNOs and memristor array) is decreased by 54.9% at 100°C compared with room temperature. The total power consumption of the proposed laser assisted STNO-based NCS (LAO-NCS) at 100°C is improved by 40% in comparison to a typical STNO-based NCS at room temperature. Finally, the energy consumption of the LAO-NCA at 100°C is expected to reduce by 86% compared with a typical STNO-based NCS at the room temperature.
Hooman Farkhani; Tim Böhnert; Mohammad Tarequzzaman; José Diogo Costa; Alex Jenkins; Ricardo Ferreira; Jens Kargaard Madsen; Farshad Moradi. LAO-NCS: Laser Assisted Spin Torque Nano Oscillator-Based Neuromorphic Computing System. Frontiers in Neuroscience 2020, 13, 1429 .
AMA StyleHooman Farkhani, Tim Böhnert, Mohammad Tarequzzaman, José Diogo Costa, Alex Jenkins, Ricardo Ferreira, Jens Kargaard Madsen, Farshad Moradi. LAO-NCS: Laser Assisted Spin Torque Nano Oscillator-Based Neuromorphic Computing System. Frontiers in Neuroscience. 2020; 13 ():1429.
Chicago/Turabian StyleHooman Farkhani; Tim Böhnert; Mohammad Tarequzzaman; José Diogo Costa; Alex Jenkins; Ricardo Ferreira; Jens Kargaard Madsen; Farshad Moradi. 2020. "LAO-NCS: Laser Assisted Spin Torque Nano Oscillator-Based Neuromorphic Computing System." Frontiers in Neuroscience 13, no. : 1429.
We present an investigation into the in-plane field induced free layer state transitions found in magnetic tunnel junctions. By applying an ac current into an integrated field antenna, the magnetisation of the free layer can be switched between the magnetic vortex state and the quasi-uniform anti-parallel state. When in the magnetic vortex state, the vortex core gyrates a discrete number of times, and at certain frequencies there is a 50% chance of the core gyrating n or n − 1 times, leading to the proposal of a novel nanoscale continuous digital true random bit generator.
Alex S. Jenkins; Lara San Emeterio Alvarez; Paulo P. Freitas; Ricardo Ferreira. Nanoscale true random bit generator based on magnetic state transitions in magnetic tunnel junctions. Scientific Reports 2019, 9, 1 -6.
AMA StyleAlex S. Jenkins, Lara San Emeterio Alvarez, Paulo P. Freitas, Ricardo Ferreira. Nanoscale true random bit generator based on magnetic state transitions in magnetic tunnel junctions. Scientific Reports. 2019; 9 (1):1-6.
Chicago/Turabian StyleAlex S. Jenkins; Lara San Emeterio Alvarez; Paulo P. Freitas; Ricardo Ferreira. 2019. "Nanoscale true random bit generator based on magnetic state transitions in magnetic tunnel junctions." Scientific Reports 9, no. 1: 1-6.
We demonstrate field and current controlled magnetodynamics in nanocontact spin-torque nano-oscillators based on orthogonal magnetic tunnel junctions. We systematically analyze the microwave properties (frequency f, linewidth Δf, power P, and frequency tunability df/dI) with their physical origins—perpendicular magnetic anisotropy, dampinglike and fieldlike spin transfer torque (STT), and voltage-controlled magnetic anisotropy (VCMA). These devices present several advantageous characteristics: high emission frequencies (f>20 GHz), high frequency tunability (df/dI=0.25 GHz/mA), and zero-field operation (f∼4 GHz). Furthermore, detailed investigation of f(H, I) reveals that df/dI is mostly governed by the large VCMA [287 fJ/(V m)], while STT plays a negligible role.
S. Jiang; M. Ahlberg; S. Chung; A. Houshang; R. Ferreira; P. P. Freitas; J. Åkerman. Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions. Applied Physics Letters 2019, 115, 152402 .
AMA StyleS. Jiang, M. Ahlberg, S. Chung, A. Houshang, R. Ferreira, P. P. Freitas, J. Åkerman. Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions. Applied Physics Letters. 2019; 115 (15):152402.
Chicago/Turabian StyleS. Jiang; M. Ahlberg; S. Chung; A. Houshang; R. Ferreira; P. P. Freitas; J. Åkerman. 2019. "Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions." Applied Physics Letters 115, no. 15: 152402.
Microcystins are the most worldwide extended and common toxins produced by cyanobacteria in freshwater. Microcystin-leucine arginine (MC-LR), associated with the most toxic incidents involving microcystins, are within the cyanobacteria (intracellular) until released into the surrounding waters (extracellular) during cell lysis. Therefore, the relationship between intracellular and extracellular cyanotoxins will allow a comprehensive risk of cyanobacteria-containing waters, preventing disease and improving human safety. In this work, we present the development of a novel portable microfluidic sensing platform for the simultaneous detection of free (extracellular) and total MC-LR (intracellular and extracellular). The integrated system contains the sample processing and detection modules capable of performing the chemical lysis, filtration, sample mixing with antibodies, and electrochemical detection of MC-LR based on an indirect strategy. The performance of the immunosensors was evaluated by electrochemical impedance spectroscopy, showing a linear dynamic range between 3.3 × 10-4 and 10-7 g L-1 and a limit of detection of 5.7 × 10-10 g L-1. The results demonstrate the potential of the developed portable biosensor platform and its suitable application for the analysis of MC-LR at regulated levels for drinking water. Finally, the integrated system was able to simultaneously detect the free and total MC-LR on a Microcystis aeruginosa culture. To the best of our knowledge this is the first described system that can differentiate between intracellular and extracellular concentration of MC-LR. This novel electrochemical sensing platform avoids the multiple processing steps typically needed for standard MC-LR analysis in the laboratory and provides an early warning system for MC-LR remote monitoring in water.
Marília Barreiros dos Santos; Raquel Queirós; Alvaro Geraldes; Carlos Marques; Vânia Vilas-Boas; Lorena Diéguez; Elvira Paz; Ricardo Ferreira; João Morais; Vitor Vasconcelos; João Piteira; Paulo P. Freitas; Begoña Espiña. Portable sensing system based on electrochemical impedance spectroscopy for the simultaneous quantification of free and total microcystin-LR in freshwaters. Biosensors and Bioelectronics 2019, 142, 111550 .
AMA StyleMarília Barreiros dos Santos, Raquel Queirós, Alvaro Geraldes, Carlos Marques, Vânia Vilas-Boas, Lorena Diéguez, Elvira Paz, Ricardo Ferreira, João Morais, Vitor Vasconcelos, João Piteira, Paulo P. Freitas, Begoña Espiña. Portable sensing system based on electrochemical impedance spectroscopy for the simultaneous quantification of free and total microcystin-LR in freshwaters. Biosensors and Bioelectronics. 2019; 142 ():111550.
Chicago/Turabian StyleMarília Barreiros dos Santos; Raquel Queirós; Alvaro Geraldes; Carlos Marques; Vânia Vilas-Boas; Lorena Diéguez; Elvira Paz; Ricardo Ferreira; João Morais; Vitor Vasconcelos; João Piteira; Paulo P. Freitas; Begoña Espiña. 2019. "Portable sensing system based on electrochemical impedance spectroscopy for the simultaneous quantification of free and total microcystin-LR in freshwaters." Biosensors and Bioelectronics 142, no. : 111550.
In this work we are going to present the ability to tune the linear range of magnetic sensors based on magnetic tunnel junctions (MTJs) from 20 Oe to 400 Oe. Controlling the linear range we control the sensitivity, the lower the linear range is the higher is the sensitivity of the sensor but in a smaller field range. To control the linear range it is fundamental to tune all the thicknesses of MTJ stack and to control all its anisotropies. The MTJ stack under study is composed of: buffer / 20 PtMn / 2 CoFe30 / 0.7 Ru / 2.6 CoFe40B20 / MgO / 2 CoFe40B20 / 0.21 Ta / tNiFe / tCoFe / tRu / tIrMn / Top Contact. The free layer is softly pinned to an anti-ferromagnet (AFM) that allows to have the pinned layer and the free layer anisotropies independent to each other. To have a good linearity we need to have the pinned and the free layers to be perpendicular. By changing any of the free layer and the top AFM thicknesses we are able to change in a control way the linear range of the sensors. [1] We achieve a linear response with the magnetic field performing two annealing in the double pinned MTJs, one to define the direction of the bottom AFM and a second one perpendicular to the first to rotate the top AFM direction. The signal is not completely centred in zero field because the free layer crystalline anisotropy is along the first annealing, perpendicular to the top AFM. In order to improve this we develop a three-step annealing process instead of only two annealing that controls the three anisotropies present in the sample (bottom and top AFM and crystalline anisotropy). [2] [1] R. Ferreira, E. Paz, P. P. Freitas, J. Wang, and S. Xue, IEEE Trans. Magn., vol. 48, no. 11, pp. 3719–3722, Nov. 2012. [2] E. Paz, R. Ferreira, and P. P. Freitas, IEEE Trans. Magn., vol. 52, no. 7, p. 4002104, 2016.
Elvira Paz; Ricardo Ferreira; Paulo P. Freitas. Tuning the linear range of magnetic sensors based on MTJs (Conference Presentation). Spintronics XII 2019, 11090, 110903N .
AMA StyleElvira Paz, Ricardo Ferreira, Paulo P. Freitas. Tuning the linear range of magnetic sensors based on MTJs (Conference Presentation). Spintronics XII. 2019; 11090 ():110903N.
Chicago/Turabian StyleElvira Paz; Ricardo Ferreira; Paulo P. Freitas. 2019. "Tuning the linear range of magnetic sensors based on MTJs (Conference Presentation)." Spintronics XII 11090, no. : 110903N.
Industry 4.0 paradigm is a reality in the digitization of industrial processes and physical assets, as well as their integration into digital ecosystems with several suppliers of the value chain. In particular, Industry 4.0 is the technological evolution of embedded systems applied to Cyber-Physical Systems (CPSs). With this, a shift from the current paradigm of centralization to a more decentralized production, supported by Industrial Internet of Things (IIoT), is implied. The work reported in this paper focuses on the development of smart devices (SmartBoxes), based on low-cost hardware such as Raspberry Pi and also platforms certified for industrial applications, such as NI CompactRIO. Both platforms adopted the OPC-UA architecture to collect data from the shop-floor and convert it into OPC-UA Data Access standard for further integration in the proposed CPPS. Tests were also performed with the MQTT protocol for monitorization. Each SmartBox is capable of real-time applications that run on OPC-UA and MQTT, allowing easy interaction between supervisory systems and physical assets.
Pedro Torres; Rogerio Dionisio; Sérgio Malhão; Luis Neto; Ricardo Ferreira; Helena Gouveia; Hélder Castro. Cyber-Physical Production Systems supported by Intelligent Devices (SmartBoxes) for Industrial Processes Digitalization. 2019 IEEE 5th International forum on Research and Technology for Society and Industry (RTSI) 2019, 73 -78.
AMA StylePedro Torres, Rogerio Dionisio, Sérgio Malhão, Luis Neto, Ricardo Ferreira, Helena Gouveia, Hélder Castro. Cyber-Physical Production Systems supported by Intelligent Devices (SmartBoxes) for Industrial Processes Digitalization. 2019 IEEE 5th International forum on Research and Technology for Society and Industry (RTSI). 2019; ():73-78.
Chicago/Turabian StylePedro Torres; Rogerio Dionisio; Sérgio Malhão; Luis Neto; Ricardo Ferreira; Helena Gouveia; Hélder Castro. 2019. "Cyber-Physical Production Systems supported by Intelligent Devices (SmartBoxes) for Industrial Processes Digitalization." 2019 IEEE 5th International forum on Research and Technology for Society and Industry (RTSI) , no. : 73-78.
In spintronic-based neuromorphic computing systems (NCSs), the switching of magnetic moment in a magnetic tunnel junction (MTJ) or magnetic oscillation in spin torque nano-oscillator (STNO) is used to mimic biological neuron firing. Although using STNO reduces the power consumption significantly, still there is a huge gap between the power consumption of spintronic-based NCS and brain due to the high bias current. In this paper, the power consumption of the proposed STNO-based NCS is reduced by thermally assisting the STNO oscillation through a microwatt nanosecond laser pulse. The experimental results show the power consumption of STNOs in NCS reduces by 56% by heating them up to 100°C. The total power consumption of the proposed laser assisted oscillation-based NCS (LAO-NCS) is reduced by 46% at 100°C compared with a typical STNO-based NCS at room temperature.
Hooman Farkhani; Tim Böhnert; Mohammad Tarequzzaman; Diogo Costa; Alex Jenkins; Ricardo Ferreira; Farshad Moradi. Spin-Torque-Nano-Oscillator based neuromorphic computing assisted by laser. 2019 14th International Conference on Design & Technology of Integrated Systems In Nanoscale Era (DTIS) 2019, 1 -5.
AMA StyleHooman Farkhani, Tim Böhnert, Mohammad Tarequzzaman, Diogo Costa, Alex Jenkins, Ricardo Ferreira, Farshad Moradi. Spin-Torque-Nano-Oscillator based neuromorphic computing assisted by laser. 2019 14th International Conference on Design & Technology of Integrated Systems In Nanoscale Era (DTIS). 2019; ():1-5.
Chicago/Turabian StyleHooman Farkhani; Tim Böhnert; Mohammad Tarequzzaman; Diogo Costa; Alex Jenkins; Ricardo Ferreira; Farshad Moradi. 2019. "Spin-Torque-Nano-Oscillator based neuromorphic computing assisted by laser." 2019 14th International Conference on Design & Technology of Integrated Systems In Nanoscale Era (DTIS) , no. : 1-5.
Spin-transfer torque nano-oscillators (STNO) are important candidates for several applications based on ultra-tunable microwave generation and detection. The microwave dynamics in these STNOs are induced by spin currents that are typically generated either by spin polarization in an adjacent ferromagnetic layer or through the spin Hall effect. In this paper, a 3-terminal STNO based on a magnetic tunnel junction is excited by both of these spin injection mechanisms. The combination of these two mechanisms excites the free layer into dynamic regimes beyond what can be achieved by each excitation mechanism individually, resulting in enhanced output powers, a key figures of merit for device performance. The system response can be coherently quantified as a function of the total injected spin current density. The experimental data shows an excellent consistency with this simple model and a critical spin current density of 4.52 ± 0.18 × 109ħ/2 e−1 Am−2.
M. Tarequzzaman; Tim Böhnert; M. Decker; J. D. Costa; Jérôme Borme; Bertrand Lacoste; Elvira Paz; A. S. Jenkins; S. Serrano-Guisan; C. H. Back; Ricardo Ferreira; P. P. Freitas. Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current. Communications Physics 2019, 2, 20 .
AMA StyleM. Tarequzzaman, Tim Böhnert, M. Decker, J. D. Costa, Jérôme Borme, Bertrand Lacoste, Elvira Paz, A. S. Jenkins, S. Serrano-Guisan, C. H. Back, Ricardo Ferreira, P. P. Freitas. Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current. Communications Physics. 2019; 2 (1):20.
Chicago/Turabian StyleM. Tarequzzaman; Tim Böhnert; M. Decker; J. D. Costa; Jérôme Borme; Bertrand Lacoste; Elvira Paz; A. S. Jenkins; S. Serrano-Guisan; C. H. Back; Ricardo Ferreira; P. P. Freitas. 2019. "Spin torque nano-oscillator driven by combined spin injection from tunneling and spin Hall current." Communications Physics 2, no. 1: 20.
H. F. Yang; X. K. Hu; S. Sievers; T. Böhnert; M. Tarequzzaman; J. D. Costa; Ricardo Ferreira; M. Bieler; H. W. Schumacher. The magnetic tunnel junction as a temperature sensor for buried nanostructures. Journal of Applied Physics 2018, 124, 174501 .
AMA StyleH. F. Yang, X. K. Hu, S. Sievers, T. Böhnert, M. Tarequzzaman, J. D. Costa, Ricardo Ferreira, M. Bieler, H. W. Schumacher. The magnetic tunnel junction as a temperature sensor for buried nanostructures. Journal of Applied Physics. 2018; 124 (17):174501.
Chicago/Turabian StyleH. F. Yang; X. K. Hu; S. Sievers; T. Böhnert; M. Tarequzzaman; J. D. Costa; Ricardo Ferreira; M. Bieler; H. W. Schumacher. 2018. "The magnetic tunnel junction as a temperature sensor for buried nanostructures." Journal of Applied Physics 124, no. 17: 174501.
Short wavelength exchange-dominated propagating spin waves will enable magnonic devices to operate at higher frequencies and higher data transmission rates. While giant magnetoresistance (GMR)-based magnetic nanocontacts are efficient injectors of propagating spin waves, the generated wavelengths are 2.6 times the nano-contact diameter, and the electrical signal strength remains too weak for applications. Here we demonstrate nano-contact-based spin wave generation in magnetic tunnel junctions and observe large-frequency steps consistent with the hitherto ignored possibility of second- and third-order propagating spin waves with wavelengths of 120 and 74 nm, i.e., much smaller than the 150-nm nanocontact. Mutual synchronization is also observed on all three propagating modes. These higher-order propagating spin waves will enable magnonic devices to operate at much higher frequencies and greatly increase their transmission rates and spin wave propagating lengths, both proportional to the much higher group velocity. Nano-contact-based spin wave generation may enable high-frequency magnonic devices but has been limited to long wavelengths and weak signal strengths. Here the authors demonstrate high-order short-wavelength propagating spin waves with increased transmission rates and propagation lengths in magnetic tunnel junction stacks.
A. Houshang; R. Khymyn; Himanshu Fulara; A. Gangwar; Mohammad Haidar; Seyyed Ruhollah Etesami; Ricardo Ferreira; P. P. Freitas; M. Dvornik; R. K. Dumas; J. Åkerman. Spin transfer torque driven higher-order propagating spin waves in nano-contact magnetic tunnel junctions. Nature Communications 2018, 9, 1 -6.
AMA StyleA. Houshang, R. Khymyn, Himanshu Fulara, A. Gangwar, Mohammad Haidar, Seyyed Ruhollah Etesami, Ricardo Ferreira, P. P. Freitas, M. Dvornik, R. K. Dumas, J. Åkerman. Spin transfer torque driven higher-order propagating spin waves in nano-contact magnetic tunnel junctions. Nature Communications. 2018; 9 (1):1-6.
Chicago/Turabian StyleA. Houshang; R. Khymyn; Himanshu Fulara; A. Gangwar; Mohammad Haidar; Seyyed Ruhollah Etesami; Ricardo Ferreira; P. P. Freitas; M. Dvornik; R. K. Dumas; J. Åkerman. 2018. "Spin transfer torque driven higher-order propagating spin waves in nano-contact magnetic tunnel junctions." Nature Communications 9, no. 1: 1-6.
We experimentally study magnetization dynamics in magnetic tunnel junctions driven by femtosecond-laser-induced surface acoustic waves. The acoustic pulses induce a magnetization precession in the free layer of the magnetic tunnel junction through magnetoelastic coupling. The frequency and amplitude of the precession show a pronounced dependence on the applied magnetic field and the laser excitation position. Comparing the acoustic-wave-induced precession frequencies with precession induced by charge currents and with micromagnetic simulations, we identify spatially non-uniform magnetization modes localized close to the edge regions as being responsible for the optically induced magnetization dynamics. The experimental scheme even allows us to coherently control the magnetization precession using two acoustic pulses. This might prove important for future applications requiring ultrafast spin manipulation. Additionally, our results directly pinpoint the importance of acoustic pulses since they could be relevant when investigating optically induced temperature effects in magnetic structures.
H. F. Yang; F. Garcia-Sanchez; X. K. Hu; S. Sievers; T. Böhnert; J. D. Costa; M. Tarequzzaman; Ricardo Ferreira; M. Bieler; H. W. Schumacher. Excitation and coherent control of magnetization dynamics in magnetic tunnel junctions using acoustic pulses. Applied Physics Letters 2018, 113, 072403 .
AMA StyleH. F. Yang, F. Garcia-Sanchez, X. K. Hu, S. Sievers, T. Böhnert, J. D. Costa, M. Tarequzzaman, Ricardo Ferreira, M. Bieler, H. W. Schumacher. Excitation and coherent control of magnetization dynamics in magnetic tunnel junctions using acoustic pulses. Applied Physics Letters. 2018; 113 (7):072403.
Chicago/Turabian StyleH. F. Yang; F. Garcia-Sanchez; X. K. Hu; S. Sievers; T. Böhnert; J. D. Costa; M. Tarequzzaman; Ricardo Ferreira; M. Bieler; H. W. Schumacher. 2018. "Excitation and coherent control of magnetization dynamics in magnetic tunnel junctions using acoustic pulses." Applied Physics Letters 113, no. 7: 072403.
We report time-domain measurements of acoustic-wave-induced magnetization dynamics in magnetic tunnel junctions. The acoustic pulses are generated by femtosecond laser excitation and interact with the magnetization through magnetoelastic coupling. The induced magnetization precession is not only dependent on the externally applied magnetic field, but also on the laser excitation position. The presented method even allows us to coherently control the precession using two laser pulses at various magnetic fields and excitation positions.
H. F. Yang; X. K. Hu; S. Sievers; Tim Böhnert; J. D. Costa; M. Tarcquzzaman; Ricardo Ferreira; M. Bieler; H. W. Schumacher. Coherent Control of Acoustic-Wave-Induced Magnetization Dynamics in Magnetic Tunnel Junctions. 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) 2018, 1 -2.
AMA StyleH. F. Yang, X. K. Hu, S. Sievers, Tim Böhnert, J. D. Costa, M. Tarcquzzaman, Ricardo Ferreira, M. Bieler, H. W. Schumacher. Coherent Control of Acoustic-Wave-Induced Magnetization Dynamics in Magnetic Tunnel Junctions. 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). 2018; ():1-2.
Chicago/Turabian StyleH. F. Yang; X. K. Hu; S. Sievers; Tim Böhnert; J. D. Costa; M. Tarcquzzaman; Ricardo Ferreira; M. Bieler; H. W. Schumacher. 2018. "Coherent Control of Acoustic-Wave-Induced Magnetization Dynamics in Magnetic Tunnel Junctions." 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) , no. : 1-2.
In this paper, perpendicular magnetic anisotropy (PMA) is tailored by changing the thickness of the free layer with the objective of producing MTJ nanopillars with a smooth linear resistance dependence with both the in-plane magnetic field and DC bias. We furthermore demonstrate how this linear bias dependence can be used to create a zero-threshold broadband voltage rectifier, a feature which is important for rectification in wireless charging and energy harvesting applications. By carefully balancing the amount of PMA acting in the free layer, the measured RF to DC voltage conversion efficiency can be made as large as 11%.
M. Tarequzzaman; Alex Jenkins; T. Bohnert; J. Borme; L. Martins; Elvira Paz; Ricardo Ferreira; P. P. Freitas. Broadband voltage rectifier induced by linear bias dependence in CoFeB/MgO magnetic tunnel junctions. Applied Physics Letters 2018, 112, 252401 .
AMA StyleM. Tarequzzaman, Alex Jenkins, T. Bohnert, J. Borme, L. Martins, Elvira Paz, Ricardo Ferreira, P. P. Freitas. Broadband voltage rectifier induced by linear bias dependence in CoFeB/MgO magnetic tunnel junctions. Applied Physics Letters. 2018; 112 (25):252401.
Chicago/Turabian StyleM. Tarequzzaman; Alex Jenkins; T. Bohnert; J. Borme; L. Martins; Elvira Paz; Ricardo Ferreira; P. P. Freitas. 2018. "Broadband voltage rectifier induced by linear bias dependence in CoFeB/MgO magnetic tunnel junctions." Applied Physics Letters 112, no. 25: 252401.
Magnetic tunnel junction nanopillar devices were patterned into three-terminal spin Hall nano-oscillators starting from a 200 mm wafer with an MgO barrier wedge with a nominal thickness variation between 0.72 and 1.36 nm. The resulting devices, with R x A values in the range between 1 and 110 Ω · μm², were characterized in the frequency domain in an attempt to optimize the MgO barrier thickness with respect to the nano-oscillators output power. While all the devices exhibit oscillations, the integrated matched output power reaches a maximum of 12.5 nW for an R x A of 34 Ω · μm² with a nominal MgO thickness of 1.2 nm.
M. Tarequzzaman; T. Bohnert; Alex Jenkins; J. Borme; Elvira Paz; Ricardo Ferreira; P. P. Freitas. Influence of MgO Tunnel Barrier Thickness on the Output Power of Three-Terminal Spin Hall Nano-Oscillators. IEEE Transactions on Magnetics 2018, 54, 1 -4.
AMA StyleM. Tarequzzaman, T. Bohnert, Alex Jenkins, J. Borme, Elvira Paz, Ricardo Ferreira, P. P. Freitas. Influence of MgO Tunnel Barrier Thickness on the Output Power of Three-Terminal Spin Hall Nano-Oscillators. IEEE Transactions on Magnetics. 2018; 54 (11):1-4.
Chicago/Turabian StyleM. Tarequzzaman; T. Bohnert; Alex Jenkins; J. Borme; Elvira Paz; Ricardo Ferreira; P. P. Freitas. 2018. "Influence of MgO Tunnel Barrier Thickness on the Output Power of Three-Terminal Spin Hall Nano-Oscillators." IEEE Transactions on Magnetics 54, no. 11: 1-4.
Information storage and monitoring relies on sensitive transducers with high robustness and reliability. This paper shows a methodology enabling the qualification of magnetic sensors for magnetic pattern readout, in applications different than hard disk magnetic recording. A magnetic tunnel junction MTJ sensor was incorporated in a reader setup for recognition of the magnetization of patterned arrays made of CoCrPt thin films and magnetic ink. The geometry of the sensor (in particular, the footprint and vertical distance to the media) was evaluated for two sensor configurations. The readout conditions were optimized to cope for variable media field intensity, resulting from CoCrPt film or magnetic ink thickness, with fixed reading distance and dimensions of the pattern. The calibration of the ink magnetic signal could be inferred from the analytical calculations carried out to validate the CoCrPt results.
K. J. Merazzo; T. Costa; F. Franco; Ricardo Ferreira; M. Zander; M. Türr; T. Becker; P. P. Freitas; S. Cardoso. Reading magnetic ink patterns with magnetoresistive sensors. AIP Advances 2018, 8, 056633 .
AMA StyleK. J. Merazzo, T. Costa, F. Franco, Ricardo Ferreira, M. Zander, M. Türr, T. Becker, P. P. Freitas, S. Cardoso. Reading magnetic ink patterns with magnetoresistive sensors. AIP Advances. 2018; 8 (5):056633.
Chicago/Turabian StyleK. J. Merazzo; T. Costa; F. Franco; Ricardo Ferreira; M. Zander; M. Türr; T. Becker; P. P. Freitas; S. Cardoso. 2018. "Reading magnetic ink patterns with magnetoresistive sensors." AIP Advances 8, no. 5: 056633.
The thermoelectric power generated in magnetic tunnel junctions (MTJs) is determined as a function of the tunnel barrier thickness for a matched electric circuit. This study suggests that lower resistance area product and higher tunnel magnetoresistance will maximize the thermoelectric power output of the MTJ structures. Further, the thermoelectric behavior of a series of two MTJs, a MTJ thermocouple, is investigated as a function of its magnetic configurations. In an alternating magnetic configurations the thermovoltages cancel each other, while the magnetic contribution remains. A large array of MTJ thermocouples could amplify the magnetic thermovoltage signal significantly.
Tim Böhnert; Elvira Paz; Ricardo Ferreira; P.P. Freitas. Magnetic tunnel junction thermocouple for thermoelectric power harvesting. Physics Letters A 2018, 382, 1437 -1440.
AMA StyleTim Böhnert, Elvira Paz, Ricardo Ferreira, P.P. Freitas. Magnetic tunnel junction thermocouple for thermoelectric power harvesting. Physics Letters A. 2018; 382 (21):1437-1440.
Chicago/Turabian StyleTim Böhnert; Elvira Paz; Ricardo Ferreira; P.P. Freitas. 2018. "Magnetic tunnel junction thermocouple for thermoelectric power harvesting." Physics Letters A 382, no. 21: 1437-1440.