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INSULATRONICS Report Summary

Project ID: 669442
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - INSULATRONICS (Controlling Electric Signals with Insulating Antiferromagnets and Insulating Ferromagnets)

Reporting period: 2015-12-01 to 2017-05-31

Summary of the context and overall objectives of the project

Conventional electronics- and spintronics-based logic and memory devices, interconnects, and microwave oscillators are based on (spin-polarized) charge transport, which inherently dissipates power due to ohmic losses. The research proposed seeks to determine the extent to which “Insulatronics” has the potential to control the electric and thermal signal generation, transmission, and detection in more power-efficient ways.

Insulatronics may have a potential to become a revolutionary technology in the daily lives of typical consumers of technology. Conventional electronics function by manipulating electrons through voltage differences. When the electrons move, they release energy to their surroundings, and this dissipation increases with the square of the electrical voltage bias. The associated excessive heating in very small devices prevents a further decrease in feature size of integrated circuits, wireless transmitters, and memory devices. The electromagnetic waves, photons, carry signals for radio, TV, and other devices. Insulatronics may be capable of replacing moving charges with low-dissipation spin waves and their quanta, magnons, in (anti-)ferromagnetic insulators in contact with conventional electronic circuits.

The project aims to facilitate a revolution of information and communication technologies by controlling electric signals with antiferromagnetic insulators and ferromagnetic insulators.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Antiferromagnets may exhibit spin superfluidity since the dipole interaction is weak. We seek to establish that this phenomenon occurs in insulators such as NiO, which is a good spin conductor according to previous studies. We investigate nonlocal spin transport in a planar antiferromagnetic insulator with a weak uniaxial anisotropy. The anisotropy hinders spin superfluidity by creating a substantial threshold that the current must overcome. Nevertheless, we show that applying a high magnetic field removes this obstacle near the spin-flop transition of the antiferromagnet. Importantly, the spin superfluidity can then persist across many micrometers, even in dirty samples.

Additionally, we explore routes to realize electrically driven Bose-Einstein condensation of magnons in insulating antiferromagnets. Even in insulating antiferromagnets, the localized spins can strongly couple to itinerant spins in adjacent metals via spin-transfer torque and spin pumping. We describe the formation of steady-state magnon condensates controlled by a spin accumulation polarized along the staggered field in an adjacent normal metal. Two types of magnons, which carry opposite magnetic moments, exist in antiferromagnets. Consequently, and in contrast to ferromagnets, Bose-Einstein condensation can occur for either sign of the spin accumulation. This condensation may occur even at room temperature when the interaction with the normal metal is fast compared to the relaxation processes within the antiferromagnet. In antiferromagnets, the operating frequencies of the condensate are orders of magnitude higher than in ferromagnets.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Insulatronics has the potential to control the electric and thermal signal generation, transmission, and detection in antiferromagnetic insulators and ferromagnetic insulators in more efficient ways. In such devices, the information is transferred via the electron spin. Achieving long-range transport is essential. Antiferromagnets may exhibit spin superfluidity, transport of spins with very little loss. In the first reporting period, we have demonstrated that spin superfluiditiy can persist across many micrometers, even in dirty samples, in insulators such as NiO.
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