Researchers from the Universitat Autònoma de Barcelona (UAB) 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.

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 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.