A technique exploiting the properties of antiferromagnetic materials shows potential for an innovative new data storage medium. An international research team explored properties that have previously resisted experimental examination by using nanoscale quantum sensors.

Antiferromagnets differ from ferromagnets in how the magnetic moments of atoms are oriented. In ferromagnets, such as iron, the atoms are parallel to each other, while in antiferromagnets the orientation of the magnetic moments alternates between neighboring atoms. Antiferromagnetic materials appear non-magnetic and do not generate an external magnetic field due to the cancelation of the alternating magnetic moments. About 90% of all magnetically ordered materials are composed of antiferromagnets.

Because the orientation of their magnetic moments cannot be accidentally overwritten by magnetic fields, they have significant potential for applications in data processing compared to ferromagnets used in In an antiferromagnetic single crystal, regions with different orientations of the antiferromagnetic order have been created (blue and red regions), separated by a domain wall. Their course can be controlled by structuring the surface. This is the basis for a new storage medium concept. Source: University of Basel (Switzerland)conventional storage media. As a result, antiferromagnetic spintronics has become the focus of research interest.

Here, the researchers studied a single crystal of chromium(III) oxide in which atoms are arranged in a regular crystal lattice with almost no defects. The crystal was altered in such a way as to create two domains in which the antiferromagnetic order has different orientations.

The accompanying video documents how the researchers were able to generate, measure and move domain walls in an anti-ferromagnetic system, and how this technique could be used for a memory device to move a domain wall in order to define a bit (0 or 1). The group developed a technology to measure a domain wall based on a diamond defect, specifically a nitrogen vacancy, which is sensitive to magnetic fields. By bringing the defect close to the antiferromagnetic surface, it is possible to measure the stray magnetic fields that are produced from the domain wall.

The high resolution of quantum sensors enabled the team to demonstrate that the domain wall exhibits behavior similar to that of a soap bubble. The domain wall is elastic, like a soap bubble, and has a tendency to minimize its surface energy. Simulations confirmed that its trajectory reflects the crystal's antiferromagnetic material properties and can be predicted with a high degree of precision.

The surface of the crystal is selectively structured at the nanoscale, leaving tiny raised squares that alter the trajectory of the domain wall in the crystal in a controlled manner. The scientists then use the orientation of the raised squares to direct the domain wall to one side of the square or the other. Running to the right of the square, the domain wall could represent a value of 1, and to the left, a value of 0. Localized heating with a laser can repeatedly alter the trajectory of the domain wall. This is what makes the storage medium reusable.

Future research will determine whether the domain walls can also be moved by means of electrical fields, which would make antiferromagnets suitable as a storage medium that is faster than conventional ferromagnetic systems, while consuming substantially less energy.

A paper on the research conducted by collaborators from the University of Basel (Switzerland), Helmholtz-Zentrum Dresden-Rossendorf e.V. (Germany) and Taras Shevchenko National University of Kyiv (Ukraine) is published in Nature Physics.