Physicists predict ‘parallel circuits’ of spin currents in antiferromagnets

June 08, 2023

(Nanowerk News) A team of physicists, spearheaded by Professor SHAO Dingfu of the Hefei Institutes of Physical Science (HFIPS), have theoretically predicted the existence of a “parallel circuit” of spin currents in antiferromagnets. This prediction, they believe, has the potential to substantially accelerate the development of spintronics.

This research was peer-reviewed and has been published in Physical Review Letter (“Néel Spin Currents in Antiferromagnets”).

Spintronics represents the ultimate frontier in data storage and processing technology. It makes use of the spin of electrons in a magnetic substance to encode data. An important component of spintronics is the spin-polarized electric current, which orders and distinguishes the orientation of the magnetic moments, thereby facilitating the writing and reading of binary data – 1s and 0s.

Today, most spintronic devices are based on ferromagnets due to their ability to effectively rotate polarizing electric currents thanks to their net magnetization. Antiferromagnets, although having alternately aligned opposite magnetic moments, have been relatively under-explored. However, these materials could pave the way for more efficient and compact spintronic devices.

One of the main obstacles to antiferromagnets is their net zero magnetization, leading to the general belief that they can only carry spin-neutral currents, which is ostensibly irrelevant for spintronics. Antiferromagnets consist of two aligned antiparallel magnetic sublattices. Conventionally, the properties of these sub-lattices are considered to be “averaged”, causing them to rotate independently.

Challenging this common notion, Professor SHAO put forward a hypothesis showing that collinear antiferromagnets could operate as “electric circuits”. This circuit will consist of two magnetic sub-lattices functioning in parallel, given the strong coupling between the magnetic atoms in each sub-lattice. Acting on this intuition, Professor SHAO and his team provided a theoretical framework predicting that the magnetic sublattices within these antiferromagnets could locally polarize electric currents. This will, in turn, generate a staggered spin current hidden within the global spin-neutral current.

These staggered spin currents are referred to as “neel spin currents”, a tribute to Nobel laureate Louis Néel, who won the prestigious award for his groundbreaking work and breakthroughs in the field of antiferromagnetism.

“The Néel spin current represents a unique property of antiferromagnetism that, until now, remained largely unrecognized,” says Professor SHAO. “These currents have the potential to produce beneficial spin-dependent characteristics hitherto considered incompatible with antiferromagnets. For example, they can generate spin-transfer torque and tunneling magnetoresistance at antiferromagnetic tunnel junctions, which are important for electrical encoding and retrieval of information in antiferromagnetic spintronics.”

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