Antiferromagnetic materials are magnetic inside, however, the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets invisible on the outside. It also implies that if information was stored in antiferromagnetic moments it would be insensitive to disturbing external magnetic fields, and the antiferromagnetic element would not affect magnetically its neighbors no matter how densely the elements were arranged in a device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. The outstanding question is how to efficiently manipulate and detect the magnetic state of an antiferromagnet. In this article we give an overview of recent works addressing this question. We also review studies looking at merits of antiferromagnetic spintronics from a more general perspective of spin-ransport, magnetization dynamics, and materials research, and give a brief outlook of future research and applications of antiferromagnetic spintronics.Interesting and useless -this was the common perception of antiferromagnets expressed quite explicitly, for example, in the 1970 Nobel lecture of Louis Néel.1 Connecting to this traditional notion we can define antiferromagnetic spintronics as a field that makes antiferromagnets useful and spintronics more interesting. Below we give an overview of this emerging field whose aim is to complement or replace ferromagnets in active components of spintronic devices.We recall some key physics roots of the field and first concepts of spintronic devices based on antiferromagnetic counterparts of the non-relativistic giantmagnetoresistance and spin-transfer-torque phenomena.
2We then focus on electrical reading and writing of information, combined with robust storage, that can be realized in antiferromagnetic memories via relativistic magnetoresistance and spin torque effects.3,4 Related to these topics is the research of spintronic devices in which antiferromagnets act as efficient generators, detectors, and transmitters of spin currents. This will lead us to studies exploring fast dynamics in antiferromagnets 5 and different types of antiferromagnetic materials. They range from insulators to superconductors. Here we comment also on the relation between crystal antiferromagents and synthetic antiferromagnets, with the latter ones playing an important role in spintronic sensor and memory devices.6 In concluding remarks we outline some of the envisaged future directions of research and potential applications of antiferromagnetic spintronics.
Equilibrium properties and magnetic storage in antiferromagnetsThe understanding of equilibrium properties of ferromagnets has been guided by the notion of a global molecular field, introduced by Pierre Weiss.1 The theory starts from the Curie law for paramagnets with the inverse susceptibility proportional to temperature, χ −1 ∼ T . It further assumes that the externally ap...