Toroidicity as a route towards non-volatile quaternary memory in antiferromagnets

Why four-state memory matters

Our phones, laptops, and data centers rely on a simple language of zeros and ones to store information, but this binary code is beginning to strain under growing demands for speed and capacity. This study explores a new way to store information using a material that can naturally remember not just two, but four distinct states. By harnessing a subtle kind of magnetism called toroidicity in an antiferromagnet, the researchers outline a path toward denser, more stable memory devices that could help push computing beyond the limits of today’s silicon technology.

The limits of traditional electronics

For decades, the electronics industry has followed Moore’s law, steadily packing more and more transistors onto chips to boost performance. That trend is now slowing as components shrink to scales where quantum effects undermine reliability. In response, a field known as spintronics has emerged, seeking to use the spin of electrons, and the tiny magnets associated with them, rather than just their electric charge. One especially attractive class of materials are magnetoelectrics, in which electric and magnetic properties are coupled so that electric fields can write magnetic information faster and with less energy than magnetic fields alone.

Beyond two-state bits

Most existing memory technologies encode data in two states, like up or down magnetization, forming the basis of binary bits. However, magnetoelectric materials open the possibility of more than two stable states controlled by external fields. Previous demonstrations of four-state, or quaternary, memory have typically relied on composite structures made from several layers and have included ferromagnets that are vulnerable to stray fields. The present work instead focuses on a single, bulk crystal that is antiferromagnetic, meaning its internal magnetic moments cancel out overall, making it naturally resistant to disturbances from external magnetic noise.

A special crystal with four magnetic patterns

The researchers study a compound called LiNi0.8Fe0.2PO4, a slightly modified version of a known magnetoelectric material. In this crystal, tiny magnetic moments on nickel and iron atoms line up in an alternating, head-to-tail pattern. As the crystal is cooled, these moments first align along one direction in the crystal, then gradually tilt within a plane. This rotation, combined with the underlying symmetry of the crystal, leads to the existence of four distinct magnetic “domains” that are all equally possible in the absence of external influences. Each domain corresponds to a different arrangement of the internal spins and a different direction of a toroidal moment, a doughnut-like pattern that ties together space and time asymmetry in the material.

Writing four states with crossed fields

To determine whether these four domains can be individually selected and read, the team uses spherical neutron polarimetry, a technique in which a beam of polarized neutrons probes the sample and the spins of the neutrons are tracked before and after scattering. Because the neutron spin responds sensitively to the internal magnetism, the pattern of rotation of the neutron spins serves as a fingerprint for each magnetic domain. By cooling the crystal while applying an electric field in one direction and a magnetic field at right angles to it, the researchers show that they can favor one specific domain at a time. At an intermediate temperature, the crossed fields control which of two toroidal domains dominates, while at lower temperatures, fine-tuning the direction of the magnetic field selects between two orientation variants within each toroidal domain, yielding four distinct, non-volatile states.

How the material remembers without power

A key observation is that once the sample has been cooled under the chosen combination of electric and magnetic fields, those fields can be removed and the domain pattern remains stable. Follow-up neutron measurements confirm that the selected domain persists over a range of low temperatures, even though the probing is performed in the complete absence of external fields. The authors connect this behavior to a subtle interaction known as the Dzyaloshinskii–Moriya effect, which gently twists neighboring spins and helps lock in the preferred domain depending on how the fields were applied during cooling. This mechanism explains why electric and magnetic fields act as two independent “handles” to choose among the four possibilities.

What this means for future memory devices

Although LiNi0.8Fe0.2PO4 itself operates only at very low temperatures and is not a ready-made device material, it serves as a clean model that demonstrates quaternary, non-volatile memory in a single-phase antiferromagnet. The work shows that toroidicity can be used to encode four robust states that are resistant to stray fields and, in principle, compatible with ultrafast spin dynamics. By clarifying how electric and magnetic fields can be used together to control toroidal domains, this study provides a roadmap for searching for related materials, possibly in thin films and at room temperature, where such four-state elements could dramatically increase storage density and expand the design space for future spintronic technologies.

Citation: Qureshi, N., Painganoor, A., Larsen, M.C. et al. Toroidicity as a route towards non-volatile quaternary memory in antiferromagnets. Nat Commun 17, 4033 (2026). https://doi.org/10.1038/s41467-026-70767-8

Keywords: antiferromagnetic memory, toroidic order, magnetoelectric materials, spintronics, quaternary logic