Magnetic storage systems and magnetically actuated devices are ultimately controlled by magnetic fields generated using electric currents. This involves significant power dissipation by Joule heating effect. Manipulating magnetism with electric voltage has an enormous potential to boost energy efficiency since this allows writing of magnetic data with minimized currents (i.e., with reduced heating effects). Here, new materials concepts to enhance magnetoelectric effects (i.e., control of magnetism with voltage) will be presented. Among various types of magnetoelectric materials, porous alloys and oxides have gained considerable attention due to their very large surface-area-to-volume ratio which allows for large electric surface charge accumulation and eventual electrochemical reactions. First, I will show that a drastic reduction of coercivity at room temperature can be obtained with voltage in a variety of thick nanoporous films, including Cu-Ni, Cu-Fe or Co-Pt alloys (thereby reducing the magnetic field –and electric currents– needed to write information on them). In some materials, an applied electric field can even induce a transition from magnetic to non-magnetic states (i.e., ON-OFF switching of ferromagnetism with voltage). This is the case of materials exhibiting voltage-driven ion transport capabilities, which has traditionally relied on O2- motion in metal oxide systems (e.g., FeOx, Co3O4). I will show that voltage-driven transport of nitrogen ions can be also triggered at room temperature in transition metal nitride (CoN, FeN) films via liquid electrolyte gating. Nitrogen magneto-ionics can induce reversible ON-OFF transitions of ferromagnetic states at faster rates and lower threshold voltages than oxygen magneto-ionics. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. Furthermore, nitrogen magneto-ionics can be used to emulate some important neuromorphic functionalities. By cumulative effects of DC and pulsed voltage actuation (at frequencies in the range 1 – 100 Hz), learning, memory retention, forgetting and self-learning by maturity (post-stimulated learning) can be mimicked. Finally, I will show how voltage can be used to tune the magnetization reversal mode of ferromagnetic disks or the interactions between ferromagnetic and antiferromagnetic layers grown onto ferroelectric substrates. In both cases (which can be considered as multiferroic heterostructures), voltage effects are mediated by strain and precise control of the crystal orientation and voltage protocol is essential to maximize the effects. In the future, both strain and magneto-ionics might be used to hide magnetic information with voltage. Using magnetoelectricity for data security applications is a whole new research area to be explored and it constitutes the topic of my ERC Advanced Grant which I will describe in some detail during my talk.
Jordi Sort leads the Group of Smart Nanoengineered Materials, Nanomechanics and Nanomagnetism (Gnm3) at the Universitat Autonoma de Barcelona (UAB). He received his PhD Degree in Materials Science from UAB in 2002 (Extraordinary Award). The topic of his PhD dissertation was the study of magnetic exchange interactions in ferromagnetic-antiferromagnetic systems. He worked for two years as Postdoctoral Researcher at the SPINTEC Laboratory (Grenoble) and subsequently stayed several months at Argonne National Laboratory (USA). He also performed long-term secondments at the Grenoble High Magnetic Fields Laboratory and at Los Alamos National Laboratory. His group focuses its research activities on the synthesis of a wide variety of functional materials (electrodeposited films, lithographed structures, porous materials, bulk metallic glasses, nanocomposites) and the study of their structural, mechanical, magnetic and thermal properties. This research aims at enhancing the performance of these materials in new technological applications that go beyond the state-of-the-art. Prof. Sort’s research activity was awarded by the Catalan Physical Society (Jordi Porta i Jué’s Prize, 2000), as well as by the Spanish Royal Physical Society (Young Researcher Award in Experimental Physics, 2003), the Federation of Materials Societies (FEMS Prize in Materials Science & Technology, 2015) and UPC/Naturgy (Duran Farell Award for Technological Research, 2020). Prof. Sort has supervised 16 PhD Theses and is currently co-supervising the work of 5 more PhD students. So far, Prof. Sort has published around 350 articles that have received approximately 11300 citations (h = 53) in ISI Web of Science. He has issued 6 patents and has managed 33 national/international research projects. Prof. Sort has been personally appointed as Invited/Plenary Speaker in more than 80 conferences. In 2014 Prof. Jordi Sort was awarded a Consolidator Grant from the European Research Council (ERC). His project, entitled «Merging Nanoporous Materials with Energy-Efficient Spintronics (SPIN-PORICS)», aimed to integrate engineered nanoporous materials into novel spintronic applications. He is also the Coordinator of the “BeMAGIC” Marie Sklodowska-Curie Innovative Training Network (ITN-ETN), whose aim is to use magnetoelectric effects for memory and biomedical applications. Recently he has been awarded an Advanced Grant from the ERC with title “Voltage-Reconfigurable Magnetic Invisibility: A New Concept for Data Security Based on Engineered Magnetoelectric Materials (REMINDS)”, which focuses on the use of magnetoelectric materials for data security applications.