In an antiferromagnetic single crystal, regions with different orientations of antiferromagnetic order have been created (blue and red regions), separated by a domain wall. The trajectory of the wall can be controlled by structuring the surface, forming the basis for a new data storage concept. Image: Department of Physics, University of Basel.
In an antiferromagnetic single crystal, regions with different orientations of antiferromagnetic order have been created (blue and red regions), separated by a domain wall. The trajectory of the wall can be controlled by structuring the surface, forming the basis for a new data storage concept. Image: Department of Physics, University of Basel.

Using nanoscale quantum sensors, an international research team has succeeded in exploring certain previously uncharted physical properties of an antiferromagnetic material. Based on their results, the researchers developed a concept for a new data storage medium, which they report in a paper in Nature Physics. The project was coordinated by researchers from the Department of Physics and the Swiss Nanoscience Institute at the University of Basel in Switzerland.

Antiferromagnets make up 90% of all magnetically ordered materials. Unlike ferromagnets such as iron, in which the magnetic moments of the atoms are oriented in the same direction, the orientation of the magnetic moments in antiferromagnets alternates between neighboring atoms. Because these alternating magnetic moments cancel each other out, antiferromagnetic materials appear non-magnetic and do not generate an external magnetic field.

Antiferromagnets hold great promise for exciting applications in data processing, as the orientation of their magnetic moments cannot be accidentally overwritten by magnetic fields – in contrast to the ferromagnets used in conventional storage media. In recent years, this potential has given rise to the budding research field of antiferromagnetic spintronics, which is the focus of numerous research groups around the world.

In collaboration with research groups under Denys Makarov (Helmholtz-Zentrum in Dresden, Germany) and Denis Sheka (Taras Sevchenko National University in Kyiv, Ukraine), the Basel researchers, led by Patrick Maletinsky, examined a single crystal of chromium(III) oxide (Cr2O3). This single crystal is an almost perfectly ordered system, in which the atoms are arranged in a regular crystal lattice with very few defects. "We can alter the single crystal in such a way as to create two areas (domains) in which the antiferromagnetic order has different orientations," explains Natascha Hedrich, lead author of the paper.

These two domains are separated by a domain wall. To date, experimental studies of domain walls of this sort in antiferromagnets have only succeeded in isolated cases and with limited detail. "Thanks to the high sensitivity and excellent resolution of our quantum sensors, we were able to experimentally demonstrate that the domain wall exhibits behavior similar to that of a soap bubble," Maletinsky explains.

Like a soap bubble, the domain wall is elastic and has a tendency to minimize its surface energy. Accordingly, its trajectory reflects the crystal's antiferromagnetic material properties and can be predicted with a high degree of precision, as confirmed by simulations performed by the researchers at Helmholtz-Zentrum.

The researchers exploited this fact to manipulate the trajectory of the domain wall, in a process that holds the key to the proposed new storage medium. To this end, Maletinsky's team selectively structured the surface of the crystal at the nanoscale, fabricating tiny, raised squares. These squares allow the trajectory of the domain wall in the crystal to be altered in a controlled manner.

The researchers could use the arrangement of the raised squares to direct the domain wall to one side of the square or the other. This is the fundamental principle behind the new data storage concept: if the domain wall runs to the 'right' of a raised square, this could represent a value of 1, while having the domain wall to the 'left' could represent a value of 0. Through localized heating with a laser, the trajectory of the domain wall can be repeatedly altered, making the storage medium reusable.

"Next, we plan to look at whether the domain walls can also be moved by means of electrical fields," Maletinsky explains. "This would make antiferromagnets suitable as a storage medium that is faster than conventional ferromagnetic systems, while consuming substantially less energy."

This story is adapted from material from the University of Basel, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.