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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FAST (Fast electronics with Antiferromagnetic SpinTronics)

Teaser

Summary

The past few decades have seen Information and Communication Technology (ICT) dramatically changing the lives of individuals and organisations. Innovative plans for long-term economic prosperity are no longer imaginable without ICT. However, the current electronic industry, based on both conventional semiconductor logic and ferromagnet based data storage technologies, face major challenges. The energy consumption of information and communication technologies is critical as it represents a continuously increasing part of the electrical energy generated in the world. The von-Neumann bottleneck, arising when memory and processors are separated, increases this energy consumption and limits the speed of ICT devices while the scalability of state of the art computer chips slow down. The upcoming years will be crucial in finding new paths towards smaller, faster, energy efficient and more robust electronic devices.
Spin-based electronics, or spintronics, in which information writing, storage and readout relies on the spin rather than the charge of electrons, is seen as one of the most promising routes for developing the next generation of ICT devices. Classically, spintronics exploits the exchange interaction between conduction electrons and local spins in magnetic materials to create spin-polarized currents and then to manipulate the magnetization of components by spin transfer torques from these currents. Spintronic based devices are already exploited in the read head of all hard disk drives. Device prototypes, exploiting the effect of spin-orbit torques, are anticipated to enhance the functionalities of Boolean logic circuits by integrating logic and memory functions. However, the ferromagnetic materials used in spintronic devices have a number of drawbacks due to their parasitic magnetic stray fields and intrinsically low characteristic frequencies that respectively limit their density integration and operation speed.
Recently, the combination of spintronic effects and the unforeseen and intriguing class of antiferromagnetic materials has opened many promising perspectives. In an antiferromagnet, electron spins on adjacent atoms cancel each other out. An antiferromagnet has thus no associated magnetic field meaning that individual devices can encode information and be more densely packed without interacting with one another. The strong antiparallel exchange interaction between adjacent spins leads to characteristic frequencies on the order of THz as required for ultrafast devices. Writing spin information would then only be limited by the circuitry time scales (of 10 ps) required to generate electrical pulses.
The FAST project focused on manipulating and monitoring antiferromagnets through electrical currents. By fully understanding and maximizing the efficiency of the effects, this would lead to possible technologies for designing energy efficient and ultra fast electronic devices.

Work performed

A key objective of the project was to identify new spin-orbit effects in order to electrically control the static and dynamic properties of antiferromagnetic materials. The first step of the project was to establish â€œgold standardâ€ methods to access the antiferromagnetic order. We thus demonstrated that depositing heavy metals with strong spin-orbit coupling on top of an antiferromagnet generates a magnetoresistance effect. Correlated with optical magnetic measurements, we highlighted that this surface sensitive technique permits one to electrically detect the antiferromagnetic order, and determine the magnetic anisotropies, in both antiferromagnetic single crystals and ultra-thin films. During the project, we have found that spin-orbit torques arise at the interface between heavy metals and antiferromagnetic insulators. Interestingly, these torques can lead to antiferromagnetic domain wall motion, as required for memory devices, and to the generation of propagating antiferromagnetic spin-waves, as required for spin-logic and microwave nanoscale devices. A key result was to measure the transport properties of antiferromagnetic spin-waves in antiferromagnetic iron oxide, more commonly known as rust. In this ubiquitous material, spin-waves can carry spin-information and propagate over long-distances, in excess of tens of micrometres, three orders of magnitude larger than in previous reports. This promising result opens the way towards the development of ultra-fast nanoelectronic spintronic devices based on antiferromagnets. As a result of this research, a number of papers were published in high impact journals and the results were disseminated at national and international conferences.

Final results

In spintronics, the means to manipulate magnetization in order to design efficient magnetic memory and microwave devices is a crucial task. Especially the present method of manipulating the magnetization of components has severe efficiency limitations, and the operating frequency is limited to the characteristic GHz frequencies of ferromagnetic materials. New concepts of utilizing the spin-orbit effects and antiferromagnetic materials has arisen for designing efficient spintronic devices, which operate in the THz regime. The research results have led us to a better understanding of spin-orbit effects and antiferromagnetic materials. An efficient electrical control of the ultra-fast dynamics of antiferromagnets will assist in ICT industries developing emitters and detectors in the THz frequency gap. Higher efficiency will also result in a reduction in energy consumption leading to new ICT applications.