Electric fields can reliably reverse magnetization in nanoscale structures made from the multiferroic material BiFe₀.₁Co₀.₁O₃ (BFCO), according to new research from Institute of Science Tokyo (Science Tokyo). Multiferroic materials display coupled electric and magnetic order, making them attractive candidates for low-power memory devices, and the team’s findings offer a concrete experimental foundation for building them.

With the rapid spread of cloud computing, artificial intelligence, and data centers, global energy consumption is climbing fast. One promising way to ease that burden is to develop memory devices that store information magnetically but are written using electric fields rather than electric currents. Magnetic memories are non-volatile, meaning stored information survives without a continuous power supply. The trouble is that conventional magnetic memory is written using the magnetic field induced by electric currents, which inevitably dissipates energy as heat. Switching the magnetic state with an electric field instead could open the door to significantly more energy-efficient devices.

Watching a Nanodot Flip

Multiferroic materials, which simultaneously display both electric and magnetic order, are a promising route toward that goal, since applying an electric field to them can cause their magnetic state to flip. But for these materials to find their way into real memory devices, their behavior at nanometer scales has to be demonstrated — and at those dimensions, materials can develop complex polarization patterns called topological domain structures whose relationship to magnetic behavior is much less clear.

To close that gap, a research team led by Assistant Professor Kei Shigematsu, along with JSPS Postdoctoral Fellow Koomok Lee and Professor Masaki Azuma of Science Tokyo, working with the Sumitomo Chemical Next-Generation Eco-Friendly Devices Collaborative Research Cluster and the Kanagawa Institute of Industrial Science and Technology (KISTEC), fabricated arrays of BFCO nanodots roughly 190 nanometers in diameter. Using two complementary imaging techniques — piezoresponse force microscopy to map electric polarization and scanning nitrogen-vacancy center magnetometry to detect magnetic fields — they visualized both the electric and magnetic domain structures of the nanodots before and after applying an electric field.

Each nanodot originally showed a “center-convergent” electric polarization structure, with polarization vectors all pointing inward toward the center. Applying an electric field transformed this into a “center-divergent” structure, with the vectors pointing outward instead — and that restructuring was accompanied by a reversal of magnetization in both the in-plane and out-of-plane directions within each nanodot.

Not a Simple Flip

Notably, this reversal doesn’t happen through a simple flip of individual electron spins. Instead, the magnetic moment rotates within the easy plane — the preferred orientation for magnetization in the material — in response to the polarization switching, driving the magnetization into a reversed configuration. That gives the approach a degree of controllability the researchers say is promising for practical applications. “This mechanism enables complex yet controllable magnetic configurations at nanoscale dimensions relevant to semiconductor devices,” Shigematsu explains.

The findings could have real implications for next-generation memory technologies. By enabling magnetic information to be written electrically and read magnetically, such devices could combine low energy consumption with non-volatile operation. “Compared to current-based technologies such as spin-transfer torque magnetic RAM, this approach could significantly reduce energy consumption,” Shigematsu says. He adds that the complex domain structure of a single nanodot could, in principle, encode multiple magnetic states, opening a path to higher-density memory architectures that go beyond simple binary values.

The study was published in Science Advances (DOI: 10.1126/sciadv.aec2861) and was supported by the Japan Society for the Promotion of Science, the Japan Science and Technology Agency, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and the Army Research Office under the ETHOS MURI program.