A new theory developed by Northwestern Engineering’s James Rondinelli could lead to faster, more energy-efficient technologies, such as computers, smartphones, and data centers, by showing how electric fields can permanently control magnetic states in materials. These magnetic states are the basis for storing and processing information in many electronic devices.

The findings reveal how an electric field can switch a magnetic state that remains stable without continuous power—an advance that could support ultra-low-power memory and logic technologies in future electronics.

“This research is a step towards more powerful, faster, and vastly more energy-efficient electronic devices,” Rondinelli said. 

The study explains how applying an electric field can permanently turn on or reverse a material’s magnetization—and it stays that way even after the power is switched off. Previously, scientists had only seen this kind of lasting control in a few special materials, and there was no general theory to explain how it worked.

“For decades, achieving nonvolatile control of magnetism via an electric field has been a core goal in the fields of spintronics and multiferroic devices,” Rondinelli said.

“The traditional linear magnetoelectric effect is volatile, meaning the reversal of magnetization disappears once the electric field is removed. Our theory identifies how symmetry in multiferroic materials can enable a truly nonvolatile version of this effect.”

The Walter Dill Scott Professor of Materials Science and Engineering at the McCormick School of Engineering, Rondinelli leads the Materials Theory and Design Group. He presented this work in “Design and Theory of Switchable Linear Magnetoelectricity by Ferroelectricity in Type-I Multiferroics,” published last month in Physical Review Letters.

Rondinelli discovered that these materials can reverse their internal electric state in two distinct ways, each leading to a different effect. In one case, the electric field influences how the spin-polarized electrons organize themselves inside the material. In the other, flipping the electric polarization directly changes the magnetic response, creating a stable magnetic state that remains even after the field is removed.

Only one of these two behaviors can occur in a single material, depending on which process requires less energy. This finding gives scientists a clear framework for predicting which materials are more likely to show one effect or the other, allowing them to target and design materials best suited for energy-efficient memory and logic technologies.

The work also highlights the importance of altermagnetism, a newly recognized magnetic phase. The researchers found that this phase supplies the right symmetry conditions for achieving switchable and stable magnetoelectric effects.

“Altermagnetism reveals a hidden symmetry-driven spin-splitting mechanism in these materials that is key to achieving switchable magnetoelectric coefficients,” Rondinelli said.

To build his theory, Rondinelli analyzed how the magnetic and electric properties of materials are linked by symmetry—the mathematical rules that describe how a structure remains unchanged when transformed in specific ways. They included effects from spin-orbit coupling, which ties the motion of electrons to their magnetic orientation, and a key energy term that stays constant when the material’s electric polarization flips. Together, these elements created a framework that can predict when and how electric fields can control magnetism. 

Rondinelli tested his theory across 17 known materials that combine both electric and magnetic order. The results showed that the theory can consistently describe magnetoelectric behavior across all these systems.

They also expanded the model to ferrimagnetic materials—systems that can be engineered from altermagnetic ones by adjusting the arrangement of metal ions. This extension broadens the range of materials that could be designed for electric-field control of magnetism.

Next, Rondinelli plans to work with experimental collaborators to test his predictions in real samples. The goal is to find materials that maintain strong electric and magnetic properties at high temperatures, an essential requirement for use in future energy-efficient electronic devices.