Tag Archives: Universitat Autonoma de Barcelona (UAB)

Memristors as the new standard for electrical resistance

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An October 27, 2025 Polytechnic University of Turin (Politecnico di Torino [PoliTo]) press release announced research into the science of measurement (metrology), Note: Links have been removed,

Tracking electrical resistance is essential to ensure the accuracy and reliability of electrical measurements worldwide. Since 2019, the units of measurement in the International System (SI) are no longer based on standard samples (kilogram, metre, etc.), but are derived from universal constants such as the speed of light. For electrical resistance, reference is therefore made to electrical conductance – which measures the ability of a material to conduct electricity – quantised (G₀) – a combination of Planck’s constant (h) and the elementary charge (e) – typically measured using the quantum Hall effect, a technique that provides accurate and reproducible values but requires expensive cryogenic systems and high-intensity magnetic fields available in only a few national metrology institutes (NMIs).

The study ‘Quantum resistance memristor for International System of Units intrinsically traceable standard’, co-authored by a group of researchers from Politecnico di Torino together with leading European metrology centres and published today in the prestigious journal Nature Nanotechnology, introduces a new standard for the traceability of electrical resistance: memristors, nanometric devices capable of modifying their conductivity in response to external stimuli. This is an innovative discovery: memristors can provide stable resistance values that are intrinsically correlated with the fundamental constants of nature, with the possibility of programming the resistance by modifying the silver nanofilaments that characterise them.

These changes can be adjusted at the atomic level even at room temperature, thus generating quantum leaps – fundamental concepts of quantum mechanics referring to the phenomenon whereby a quantum system passes from one energy level to another in a discontinuous manner, i.e. without passing through intermediate states, as happens with an electron in an atom – discrete, corresponding to G0 (or multiples) that can be measured with conventional reading systems. This approach paves the way for the concept of “NMI-on-a-chip”, i.e. the possibility of integrating the functions of an entire national metrology institute at the microchip level.

In the future, electrical measuring devices such as multimeters – among the most widely used instruments in the industry for measuring electrical quantities – could thus have a memristor as a reference for self-calibration, i.e. to automatically adjust their measurement or operating parameters so as to maintain the accuracy and correctness of results without external human intervention. This will enable the use of simplified calibration procedures in industry and in sectors where the portability of calibrated measurements is a necessity.

“The results obtained and published in the prestigious journal Nature Nanotechnology are the fruit of the European MEMQuD project, where fundamental research by academic institutions such as Politecnico di Torino and the Forschungszentrum Jülich on the phenomenon of “electrochemical polishing” (thanks to which nanofilaments can be “filed” at the atomic level) was coupled with the methodological rigour of the national metrology institutes of Italy, Turkey, Spain, Portugal and Germany”, comment the co-authors of the study Carlo Ricciardi and Fabio Michieletti, respectively professor and post-doctoral researcher at the Department of Applied Science and Technology-DISAT and members of the NaMeS group at Politecnico di Torino.

An October 28, 2025 Universitat Autonoma de Barcelona press release (also on EurekAlert but published November 3, 2025) provides additional insight,

Microchips with a memristor could replace an entire electrical resistance calibration laboratory

An international research collaboration with the involvement of the UAB demonstrates for the first time that memristors, electronic devices at the nanoscale,  can easily calibrate electrical resistance for certain applications without requiring large and complex laboratories working at extreme temperatures and very high magnetic fields. The work, published in Nature Nanotechnology, explores for the first time the metrological applications of these devices in calibration procedures of electronic systems.

Measuring electrical resistance with maximum precision to be used as a standard in metrology requires complex laboratories at temperatures close to the absolute zero and magnetic fields that are more intense than those used in clinical magnetic resonance imaging.

International research under the framework of the European project MEMQuD, which included the involvement of UAB Department of Electronic Engineering professors Enrique Miranda and Jordi Suñé, demonstrates that memristors can provide stable resistance values directly linked to fundamental constants of nature. Thus, they can become a new much simpler standard than current systems for calibrations of this magnitude.

Measurement standards based on constants of nature

Since 2019, all base units of the International System of Units (SI)—including the metre, second, and kilogram—have been based on fundamental natural constants. For example, the kilogram, which was once based on the “prototype kilogram,” is now linked to Planck’s constant h. A metre is defined with respect to the speed of light, and a second by the oscillation of the cesium atom.

Thanks to laser interferometers and atomic clocks, units of length and time can be verified relatively easily worldwide. The situation is quite different for physical quantities such as mass and electrical units. Their metrological traceability is so complex that the measurements are feasible only in a handful of national metrology institutes.

Until now, the quantum Hall effect has served as the standard for electrical resistance. While it provides highly precise and reproducible values, it requires extreme laboratory conditions, i.e. temperatures close to absolute zero and high magnetic fields. The measurements require sophisticated cryogenic systems and strictly controlled facilities.

Memristors as standard resistance measurement systems

Memristors offer a radically different approach. Originally developed as building blocks for novel computing architectures, such as non-volatile memories and neuromorphic circuits emulating computations in the brain, they exhibit a switching behavior that directly follows universal constants.

Functionally, they act as programmable resistors—essentially resistors with memory. This resistance can be changed by applying external voltages or currents. Conductive nanofilaments of individual silver atoms forms inside them. By applying electrical bias, these filaments can be adjusted with atomic precision so that their conductance changes not continuously, but in discrete quantum steps.

“We have confirmed that memristors can reliably generate discrete resistance states that are directly related to universal constants of nature. In 1998, our group already revealed these quantum effects for the first time in the dielectric breakdown of thin insulators. For certain applications, these devices can be used for calibration without the need of complex cooling systems or high magnetic fields”, says UAB professor Enrique Miranda.

A national metrology institute condensed into one microchip

This approach makes it possible to talk about a concept known as “NMI-in-a-chip”: the service of a national metrology institute condensed into a microchip. In the future, this could mean that a measuring device has its resistance reference built-in directly into the chip. Lengthy calibration chains—from measurements in metrology institutes, reference resistors and precision calibrators, to the calibration of end-user devices—would no longer be necessary. Instead of repeatedly sending a multimeter to the calibration laboratory, it could check itself internally, i.e. a built-in calibration standard.

Applications in research and industries

Applications range from simplified calibration procedures in industry to mobile measuring systems and portable standards for research in the field or in space. “We are at the beginning of a paradigm shift—moving away from complex large-scale facilities towards intrinsic, quantum-accurate standards that can be integrated into any chip”, says UAB professor Jordi Suñé.

Quantified electrical conductance

The foundation of this work is the quantized electrical conductance G₀, derived from Planck’s constant h and the elementary charge e. In the experiments, memristors were reproducibly programmed in air at room temperature into stable conductance states of exactly 1·G₀ and 2·G₀, maintained over extended periods of time. Measurements taken at participating research institutes in Italy, Germany, Spain, Turkey, and Portugal revealed a deviation of 3.8 percent for 1·G₀ and 0.6 percent for 2·G₀. The key lies in a process known as “electrochemical polishing”. In this process, unstable atoms are removed from the conducting filament until only a stable quantized conduction channel remains.

The European project MEMQuD, funded by the European Metrology Programme for Innovation and Research (EMPIR) of the EURAMET alliance of metrology organisations, is an international collaboration with the involvement of the UAB, the INRiM (Italy), the Forschungszentrum Jülich, Peter Grünberg Institute (Germany), the Politecnico di Torino (Italy), the IMDEA Nanociencia (Spain), the TUBITAK National Metrology Institute (Turkey), the TOBB University of Economics and Technology (Turkey), the Instituto Português da Qualidade (Portugal), and the Bulgarian Academy of Sciences (Bulgaria).

Here’s a link to and a citation for the paper,

A quantum resistance memristor for an intrinsically traceable International System of Units standard by Gianluca Milano, Xin Zheng, Fabio Michieletti, Giuseppe Leonetti, Gabriel Caballero, Ilker Oztoprak, Luca Boarino, Özgür Bozat, Luca Callegaro, Natascia De Leo, Isabel Godinho, Daniel Granados, Itir Koymen, Mariela Menghini, Enrique Miranda, Luís Ribeiro, Carlo Ricciardi, Jordi Suñe, Vitor Cabral & Ilia Valov. Nature Nanotechnology volume 20, pages 1884–1890 (2025) Published: 27 October 2025 Version of record: 27 October 2025 Issue date: December 2025 DOI: https://doi.org/10.1038/s41565-025-02037-5

This paper is open access.

New magnetic state, ‘Vortion,’ able to mimic neuronal synapses

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A March 3, 2025 news item on phys.org announces a new magnetic state,

Researchers from the Department of Physics [at the Autonomous University of Barcelona] have managed to experimentally develop a new magnetic state: a magneto-ionic vortex or “vortion.” The research, published in Nature Communications, allows for an unprecedented level of control of magnetic properties at the nanoscale and at room temperature, and opens new horizons for the development of advanced magnetic devices.

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A March 3, 2025 Universitat Autonoma de Barcelona [Autonomous University of Barcelona] press release on EurekAlert, which originated the news item, describes the impetus for this research,

The use of Big Data has multiplied the energy demand in information technologies. Generally, to store information, systems utilize electric currents to write data, which dissipates power by heating the devices. Controlling magnetic memories with voltage, instead of electric currents, can minimise this energy expenditure. One way to achieve this is by using magneto-ionic materials, which allow for the manipulation of their magnetic properties by adding or removing ions through changes in the polarity of the applied voltage. So far, most studies in this area have focused on continuous films, rather than on controlling properties at the nanometric scale in discrete “bits”, essential for high-density data storage. Moreover, it is known that new magnetic phenomena can emerge at the sub-micrometre scale, that do not exist at the macroscopic level, such as magnetic vortices – small swirl-like magnetic structures. These vortices have applications in the way magnetic data are currently recorded and read, as well as in biomedicine. Nevertheless, changing the vortex state in already prepared materials is often impossible or requires large amounts of energy.

Researchers from the UAB Department of Physics, in collaboration with scientists from the ICMAB-CSIC, the ALBA Synchrotron and research institutions in Italy and the United States, propose a new solution that combines magneto-ionics and magnetic vortices. Researchers experimentally developed a new magnetic state that they have named magneto-ionic vortex, or “vortion”. This new object allows “on-demand” control of the magnetic properties of a nanodot (a dot of nanometric dimensions) with high precision. This is achieved by extracting nitrogen ions through the application of voltage, thus allowing for efficient control with very low energy consumption.

“This is a so far unexplored object at the nanoscale,” explains ICREA [Catalan Institution for Research and Advanced Studies] researcher in the UAB Department of Physics Jordi Sort, director of the research. “There is a great demand for controlling magnetic states at the nanoscale but, surprisingly, most of the research in magneto-ionics has so far focused on the study of films of continuous materials. If we look at the effects of ion displacement in discrete structures of nanometre dimensions, the ‘nanodots’ we have analysed, we see that very interesting dynamically evolving spin configurations appear, which are unique to these types of structures”. These spin configurations and the magnetic properties of the vortices vary as a function of the duration of the applied voltage. Thus, different magnetic states (e.g., vortices with different properties or states with uniform magnetic orientation) can be generated from nanodots of an initially non-magnetic material by the gradual extraction of ions through the application of voltage.

“With the ‘vortions’ we developed, we can have unprecedented control of magnetic properties such as magnetisation, coercivity, remanence, anisotropy or the critical fields at which vortions are formed or annihilated. These are fundamental properties for storing information in magnetic memories, which we are now able to control and tune in an analogue and reversible manner by a voltage-activated process with very low energy consumption,” explains Irena Spasojević, postdoctoral researcher in the UAB Department of Physics and first author of the paper. “The voltage actuation procedure, instead of using electric current, prevents heating in devices such as laptops, servers and data centres, and it drastically reduces energy loss.”

Researchers have shown that by precisely controlling the thickness of the voltage-generated magnetic layer, the magnetic state of the material can be varied at will, in a controlled and reversible manner, between a non-magnetic state, a state with a uniform magnetic orientation (such as that found in a magnet), and the new magneto-ionic vortex state.

Ability to mimic the behaviour of neuronal synapses

This unprecedented level of control of magnetic properties at the nanoscale and at room temperature opens new horizons for the development of advanced magnetic devices with functionalities that can be tailored once the material has been synthesised. This provides greater flexibility which is needed to meet specific technological demands. “We envision, for example, the integration of reconfigurable magneto-ionic vortices in neural networks as dynamic synapses, capable of mimicking the behaviour of biological synapses”, says Jordi Sort. In the brain, the connections between neurons, the synapses, have different weights (intensities) that adapt dynamically according to the activity and learning process. Similarly, “vortions” could provide tuneable neuronal synaptic weights, reflected in reconfigurable magnetisation or anisotropy values, for neuromorphic (brain-inspired) spintronic devices. In fact, “the activity of biological neurons and synapses is also controlled by electrical signals and ion migration, analogous to our magneto-ionic units,” comments Irena Spasojević.

Researchers believe that, besides their impact in brain-inspired devices, analogue computing or multi-state data storage systems, vortions may have other potential applications, including medical therapy techniques such as theragnostics, data security, magnetic spin computing devices (spin logics), and the generation of spin waves (magnonics).

The research, led by ICREA professor of the UAB Department of Physics Jordi Sort, and postdoctoral researcher of the UAB Department of Physics Irena Spasojević as the first author of the publication, also included Zheng Ma, from the same department, Aleix Barrera and Anna Palau, from the Institute of Materials Science of Barcelona (ICMAB-CSIC), and researchers from the ALBA Synchrotron, the Istituto Nazionale di Ricerca Metrologica (INRiM) of Turin, Italy, and Colorado State University, USA. The study was published in the latest issue of the journal Nature Communications. This study was financed by the REMINDS project from the European Research Council.

Here’s a link to and a citation for the paper,

Magneto-ionic vortices: voltage-reconfigurable swirling-spin analog-memory nanomagnets by Irena Spasojevic, Zheng Ma, Aleix Barrera, Federica Celegato, Alessandro Magni, Sandra Ruiz-Gómez, Michael Foerster, Anna Palau, Paola Tiberto, Kristen S. Buchanan & Jordi Sort. Nature Communications volume 16, Article number: 1990 (2025) DOI: https://doi.org/10.1038/s41467-025-57321-8 Published: 26 February 2025

This paper is open access.

EGNITE, a derivative of graphene, improves performance of neuroprostheses

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A July 10,2024 news item on ScienceDaily announces work on a new material for use in neuroprostheses could help people who are paralyzed or have amputated limbs, Note: This research involves use of animal models,

Neuroprostheses allow the nervous system of a patient who has suffered an injury to connect with mechanical devices that replace paralyzed or amputated limbs. A study coordinated by the UAB Institut de Neurociències, in collaboration with the l’Institut Català de Nanociència i Nanotecnologia (ICN2), demonstrates in animal models how EGNITE, a derivative of graphene, allows the creation of smaller electrodes, which can interact more selectively with the nerves they stimulate, thus improving the efficacy of the prostheses. The study also demonstrated that EGNITE is biocompatible, showing that its implantation is safe.

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A July 10,2024 Universitat Autonoma de Barcelona press release (also on EurekAlert) provides more detail,

After an amputation or a severe nerve injury, patients lose to a greater or lesser extent the ability to move and feel a lost limb, which limits their autonomy in activities of daily living. Currently, the only strategy that allows to recover the lost functions consists of neuroprostheses: electrodes capable of stimulating the nerves, to induce specific sensations, and of recording motor signals that, once decoded, can be sent to a bionic prosthesis.

In the design of neuroprostheses, it is important that the electrodes are small enough that they are selective and interact electrically only with a reduced number of axons in the nerve. Therefore, although they have commonly been constructed from metals such as gold, platinum or iridium oxide, it is necessary to find other materials that have enhanced conductive capacity and allow the creation of even smaller electrode contacts. This is where graphene and its derivatives come into play; their excellent electrical properties have allowed the development of a new generation of microelectrodes.

A research coordinated by the UAB Institut de Neurociències (INc-UAB) has studied the capacity of a new material derived from graphene, EGNITE, to stimulate and record from the peripheral nerve. Furthermore, its biocompatibility has been validated, which is key for preserving the function of the interface over time. The research was carried out in the Neuroplasticity and Regeneration group of the INc-UAB, led by professor Xavier Navarro of the UAB Department of Cell Biology, Physiology and Immunology, in collaboration with Jose Garrido’s research group at the Institut Català de Nanociència i Nanotecnologia (ICN2), which was in charge of developing the EGNITE together with the neural interfaces.

These electrodes, implanted in rat sciatic nerve, were shown to be capable of producing selective muscle activation for up to a maximum of 60 days. “The reduction in the electrical current necessary to produce this muscle activation is notable in comparison to other larger metal microelectrodes”, explains Bruno Rodríguez-Meana, postdoctoral researcher at the INc-UAB and first author of the article. Furthermore, the electrodes with EGNITE demonstrated to be biocompatible, since none of the functional tests showed significant alterations produced by the implanted interfaces nor was exacerbated inflammation observed.

“The next steps will consist of the optimization of the EGNITE-based technology and its application in pre-clinical studies for vagus nerve or spinal cord stimulation systems. In parallel, progress is being made towards its clinical translation in bioelectronic medicine approaches”, explains Professor Navarro.

Together, these results indicate the potential of the material derived from graphene to be part of neuroprostheses that allow patients to recover lost functions, thus improving their capacity and quality of life.

Here’s a link to and a citation for the paper,

Engineered Graphene Material Improves the Performance of Intraneural Peripheral Nerve Electrodes by Bruno Rodríguez-Meana, Jaume del Valle, Damià Viana, Steven T. Walston, Nicola Ria, Eduard Masvidal-Codina, Jose A. Garrido, Xavier Navarro. Advanced Science Volume 11, Issue 29 August 7, 2024 2308689 DOI: https://doi.org/10.1002/advs.202308689 First published: 11 June 2024

This paper is open access.