Researchers from Augsburg and Japan have achieved a breakthrough by writing and reading magnetic information in antiferromagnets using only light. The new method, based on the momentum of laser pulses, could enable faster, low-energy data storage and directly link optical communication with magnetic memory technologies. Their research was recently published in the renowned journal Nature Materials.

Antiferromagnets, that are magnetically ordered crystals with microscopic magnetic moments alternating in space, are attracting significant attention as materials for next-generation magnetic devices. Members of a Japanese-German international joint research group, which has recently received funding from the JSPS and the DFG, successfully demonstrated the optical writing of magnetic information in an antiferromagnet using femtosecond laser pulses. This new information-writing principle represents a breakthrough in optical control of magnets and may lay the foundation for the realization of next-generation magneto-optical memories and all-optical networks. In fact, the laser used in this pioneering study operates in the telecommunication wavelength range, hence this method is compatible with the current platforms of optical communication technology.

This research was published in the scientific journal Nature Materials. The advanced optical experiments, leading to this scientific breakthrough, have been carried out at the Center for Emergent Matter Science (CEMS) of RIKEN in Japan by Dr. Shingo Toyoda, under the supervision of Dr. Naoki Ogawa, Prof. Yoshinori Tokura and Prof. Takahisa Arima. The German partner, Prof. István Kézsmárki (University of Augsburg), is a senior visiting fellow of CEMS and has a long-standing collaboration with the Japanese colleagues on the optical reading of magnetic information in unconventional antiferromagnets. The current work is in the scope of their recently established bilateral consortium focusing on Light-induced states and non-equilibrium phases in antiferromagnets.

Because light can transmit information at high speeds, it is widely used for communication. Currently, in data centers and other facilities, the information transmitted via light is first converted into electrical signals and then written into storage elements such as magnetic memories. If optical information could be recorded directly in magnets without going through electrical signals, faster information processing would be possible, while minimizing energy losses.

Under these circumstances, research has been progressing on the all-optical control of magnetic states, which means the direct writing and reading of magnetic information by light. So far, it has been demonstrated that magnetic recording is possible in ferromagnets and other materials by using circularly polarized light, expanding the possibilities of optical magnetic recording. As the demand for even faster information processing grows, antiferromagnets are beginning to attract attention as magnetic recording materials. This is because antiferromagnets offer advantages such as faster operation compared to ferromagnets and less susceptibility to external disturbances. On the other hand, because antiferromagnets have an equal number of magnetic moments pointing in opposite directions, thus they possess zero net magnetization, it is impossible to record "0" and "1" in their standard state. Only by giving the antiferromagnet a special crystal structure does it become possible to record "0" and "1" therein. For example, if the magnetic moments are arranged in a microscopic ring-like structure, "0" and "1" can be represented by rings with clockwise or counterclockwise rotation (see Fig. 1, left). However, even in such antiferromagnets, a challenge remains: Since the material as a whole does not possess net magnetization, the control of such states using magnetic fields or conventional optical schemes based on circularly polarized light is impossible.

New concept

To overcome these challenges, this study exploits the "momentum" of light rather than its "polarization" for the reading and writing of magnetic information. Light possesses momentum corresponding to the direction in which it travels. Scientist in CEMS and Prof. Kézsmárki have formerly demonstrated the read-out of magnetic states in antiferromagnets based on this principle. Along this line, they hypothesized that it might be possible to also write the magnetic states in antiferromagnets by utilizing the momentum of light, and chose the antiferromagnet LiNiPO4 (lithium nickel phosphate) as a benchmarking material. This substance exhibits the so-called optical diode effect, when light is strongly absorbed in one direction and transmitted in the opposite direction. This property stems from a strong coupling between the propagation direction of light or equivalently the momentum of light and the antiferromagnetic state within the material. Therefore, the optical diode effect can be used to read "0" and "1" states. Dr. Toyoda and colleagues had the idea that by effectively exploiting this characteristic, they could not only read the magnetic state but also write it by reversing the propagation direction of intense light pulses, taking advantage of the inverse optical diode effect (Fig. 1, right). Importantly, this optical control was achieved without the use of external electric or magnetic fields. It was also demonstrated that by alternating the light propagation direction between forward and backward, the magnetic state can be switched repeatedly in a non-volatile manner. Measurements performed with laser pulses with various polarizations revealed that the efficiency of the optical writing process does not depend on the polarization but is determined solely by the momentum of light. This indicates that the propagation direction of light itself acts as a new control parameter for determining the magnetic state, rather than the polarization conventionally used in magneto-optical control.

Based on this approach, the research group successfully wrote antiferromagnetic domain structures of arbitrary shapes by scanning the light across the sample (Fig. 2). In addition, they demonstrated that by using light with low intensities, the written magnetic patterns can be optically read out via the optical diode effect. In other words, this study realized a series of operations—writing, retaining, and reading antiferromagnetic domains using only light, without external electric or magnetic fields, by utilizing the momentum of light. This marks a major step toward all-optical antiferromagnetic memory operations.

Summary and outlook

The achievements of this study demonstrate a new principle capable of controlling an antiferromagnet using only the propagation direction of light, without relying on electric currents or magnetic fields. This showcases a novel control principle in light-matter interactions and reveals that the momentum of light—which has previously received very little attention—can serve as a new tool for manipulating materials. In the future, this could lead to low-energy-consumption, high-speed information technology as a new recording technique that directly encodes information transmitted via optical communication into magnetic information.

The greatest novelty of this research lies in the fact that it enables the state control of antiferromagnets—which was previously difficult—by utilizing the propagation direction of light, a degree of freedom that has rarely been exploited until now. While conventional magneto-optical control required light polarization or external magnetic fields, this method allows information to be written solely by the direction in which the light travels, realizing a fundamentally extremely simple magneto-optical recording scheme.

This concept is expected to lead to the realization of low-power-consumption magnetic memories, that do not use electric currents, magnetic fields, or polarization optics, as well as new information-processing devices that integrate light and magnetism. In particular, since the operation was demonstrated in the telecommunication wavelength band, this approach is anticipated to expand into a new information technology that connects directly with existing optical communication infrastructure, allowing users to "write with light and retain with magnetism." Furthermore, because antiferromagnets exhibit excellent response speeds, they have the potential to enable ultra-high-speed operations and high-density integration that are currently unachievable with existing electronic devices. This is expected to contribute to solving social issues, such as reducing power consumption in data centers and telecommunication equipment.

Publication

Toyoda, S., Kocsis, V., Tokunaga, Y. et al. All-optical control of antiferromagnetic domains via an inverse optical magnetoelectric effect. Nat. Mater. (2026). https://doi.org/10.1038/s41563-026-02608-4