ASIQS · Antiferromagnetic spintronics investigated by quantum sensing techniques

Antiferromagnetic spintronics investigated by quantum sensing techniques

An increasing interest in the antiferromagnets was boosted in 2016 by the discovery of electric Néel vector manipulation, which is of a great promise for data storage technologies. In antiferromagnets, information can be stored within antiferromagnetic domains, which can be controlled by spin-orbit torques and read by magnetoresistance effect. Since this pioneering discovery, a plethora of materials controlled by different mechanisms based on electric current have been proposed and demonstrated. Interestingly, due to the difficulty to directly image the antiferromagnetic state, some of the strongest reported effects remain controversial. However, while many laboratories focused on the development of these materials and schemes for data storage, research on synthetic antiferromagnets for computational purposes stayed out of the spotlight. This is caused mainly by the fact that such a functionality was not demonstrated even in the conventional ferromagnets. The discovery of chiral coupling in thin ferromagnetic films with tailored anisotropies obtained in the course of this project opened avenues to antiferromagnetically couple neighboring out-of-plane magnetic regions via the interfacial Dzyaloshinskii-Moriya interaction and realize all-electric magnetic logic devices. At the start of this project, we identified the possibility to build logic gates employing the chiral coupling effect in antiferromagnetically coupled regions of ferromagnetic films, which in combination with the spin-orbit-torques offer a unique way of all-electric control. The core of our logic-circuits is a NOT gate, which comprises two out-of-plane magnetized regions, which serve also as domain wall conduits, which are chirally antiferromagnetically coupled via a narrow in-plane magnetized region. The polarity of a domain wall (e.g. up-down) electrically driven across such a region can be therefore inverted (to down-up). This concept has been extended towards more complex logic circuits and functionalities. While the domain wall logic has been shown in prototypical films based on Co, other attractive materials would enable further functionalities such as reduced electric currents or higher domain wall mobilities or their facilitated implementation into existing industrial processes. In the second part of the project, we have therefore developed a scheme based on asymmetric domain wall motion, which can be used to quantify the coupling in any material. We have shown that an equally efficient coupling mechanism can be realized in CoB or GdCoB thin films. In the third part of the project, we have explored the possibility to establish a strong coupling in out-of-plane magnetized ferrimagnets. These are especially interesting near their compensation temperature where they become effectively antiferromagnetic and thus offer similar attractive properties as antiferromagnets. Crucially, they can be imaged by conventional laboratory techniques. Similarly to the spatially patterned anisotropies in the ferromagnets, we have spatially patterned material properties by means of ion irradiation so that regions with compensation temperatures below and above room temperatures were created. This, so far, revealed a strong novel coupling mechanism allowing to antiferromagnetically couple neighboring ferrimagnetic regions, which can be embedded into logic circuits. This work can potentially offer unprecedented functionalities.

Data: CORDIS, © European Union