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Antiferromagnetic spintronics

Tomas Jungwirth (Institute of Physics, Academy of Sciences of the Czech Republic School of Physics and Astronomy, University of Nottingham)

Abstract esteso

The field of spintronics is tightly related to magnetic recording, the history of which started from the recording of sound and later included video and data. The first magnetic recording instrument - the magnetic wire recorder was invented at the end of the 19th century in parallel to the gramophone. It had to rely on the 19th century physics, namely on electromagnetic coils, for writing and reading. While other recording technologies like gramophone and CDs have or are becoming obsolete, magnetic recording is a keeper. Hard drives and magnetic tapes provide the virtually unlimited data storage space on the internet. Magnetic computer memory chips are among the leading candidate technologies for the ”More than Moore” era that we have now entered after the official end in 2016 of the Moore’s Law driven International Technology Roadmap for Semiconductors. However, the 19th century electromagnetic coils would not allow for keeping magnetic recording competitive with semiconductor storage and memory devices. In hard drives, the coils were removed from the readout and replaced by the 20th century spintronic elements and the development of the magnetic memory-logic chips would have been unthinkable without spintronics.

The most advanced principles of quantum-relativistic spintronics developed in the 21st century have brought another, unexpected turn in the research of magnetic memory and logic devices. They allowed for including antiferromagnets as candidate materials for these devices. There are two basic types of magnetic materials: ferromagnets that have been utilized so far in all magnetic memory technologies and antiferromagnets which did not seem to have any practical application.  The alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization made antiferromagnetic order notoriously difficult to control and utilize. Within the realms of the 19th century physics, one would need to wind a microscopic electromagnetic coil individually around each magnetic atom to allow for the control of their up and down alternating magnetic moments. The 21st century spintronics makes this seemingly science-fiction scenario possible to realize by a quantum-relativistic trick without physically manufacturing the atomic coils.  This opens the possibility to unlock a multitude of known and newly identified unique features of antiferromagnets for spintronic devices. Among these is the three-orders of magnitude higher speed of writing information in antiferromagnets than in ferromagnets, opening the route from the current gigahertz operation speeds to terahertz memory-logic devices. We will give a taste in the lecture of both the quantum-relativistic tricks and of how far or close we are with antiferromagnets on the route to the ultra-fast magnetic recording.

P. Wadley et al. Science 351, 587 (2016)