11 Nov. Rotating instead of magnetizing: data storage with light
Information is generally stored digitally as binary data in the form of zeros and ones. Consequently, any physical system that can reliably switch between two stable states could serve as a medium for digital data storage.
Ferroaxial materials are a recently discovered addition to the ferroic family. They consist of rotating arrangements of electric dipoles that can be aligned in two opposite directions – clockwise and counterclockwise – without generating magnetization or electric polarization. This makes these materials very stable and unaffected by external fields. For the same reason, however, they are also very difficult to manipulate, which has limited their research to date.
Ferroic materials are solids that can be switched between two such stable states. The best-known examples are ferromagnets, which can be magnetized in opposite directions, and ferroelectrics. These can accommodate opposite electrical polarizations. Since these states can be easily switched by magnetic or electric fields, these ferroic materials are now commonly used in data storage and electronics. However, these systems are susceptible to external influences, such as strong magnetic fields near a hard drive, and tend to lose data over time.
Terahertz light controls dipoles
Researchers at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) and the University of Oxford used circularly polarized terahertz pulses to switch between clockwise and counterclockwise ferroaxial domains in the material rubidium iron dimolybdate (RbFe(MoO₄)₂). „We generate a synthetic effective field that arises when a terahertz pulse causes ions in the crystal lattice to rotate,“ says researcher Zhiyang Zeng, who was involved in the project. „By adjusting the helicity or direction of rotation of the circularly polarized light pulses, we can selectively stabilize the alignment of the electric dipoles in a clockwise or counterclockwise direction,“ continues his colleague Michael Först, „thus enabling the storage of information in the two ferroaxial states.“ Since ferroaxial materials are free of depolarizing electrical or magnetic stray fields, they are among the most promising candidates for stable and durable data storage in the future, Först summarizes.
Original publication:
[Z. Zeng, M. Först, M. Fechner, D. Prabhakaran, P. G. Radaelli, A. Cavalleri; Photo-induced nonvolatile rewritable ferroaxial switching, Science 390 (6769), 195-198 (2025), https://dx.doi.org/10.1126/science.adz5230]
Source: www.mpsd.mpg.de
Image: Jörg Harms / MPSD