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11 december 2018

Approved FOM programme

Number 158.
Exciting exchange (EEX)
Executive organisational unit BUW
Programme management Prof.dr. Th.H.M. Rasing
Duration 2015-2020
Cost estimate M€ 2.2

The objectives
The goal of Exciting Exchange is to understand the physics of magnetism in the regime where the exchange interaction parameters are time-dependent and strongly non-local. To achieve this goal we have formulated the following objectives:
1. To probe the dynamics and spatial dependence of the exchange parameters, as well as the emergence of magnetic ordering on nm length and fs timescales.
2. To achieve a microscopic understanding and description of strongly non-equilibrium and nonlocal spin dynamics beyond the thermodynamic limit.
3. To control and manipulate the exchange interactions by light, electric field pulses and/or nanostructuring to find novel ways to manipulate magnetic order.

Background, relevance and implementation
Excitation by femtosecond lasers has revealed extraordinary spin dynamics in magnetic materials in recent years that cannot be explained by equilibrium descriptions of magnetism. The main reason is that all theories of magnetic phenomena substantially rely on the adiabatic approximation, assuming that all relevant processes are very slow in comparison with characteristic electron hopping/scattering times (typically femtoseconds) and that different parts of a magnetic system are in equilibrium with each other. But, exciting a magnet with a stimulus like a femtosecond laser pulse, much shorter than the time of thermal equilibration in solids (~1-10 ps) and comparable to the characteristic time of the exchange interaction (exchange fields of 100-1000 Tesla correspond to precessional frequencies of 3-30 THz or periods of 300-30 femtoseconds ), brings the medium into a strongly non-equilibrium state where the conventional description of magnetic phenomena is no longer valid. Only very recently has it become clear that these internal magnetic fields can be efficiently exploited when exciting magnetic systems by ultrashort optical laser pulses or by tailoring systems at the nanoscale as, for example, demonstrated by the femtosecond all-optical exchange-mediated magnetic switching in ferrimagnetic alloys and the observation of exotic chiral domain textures in sub-nm magnetic films.

Exploring magnetism at the time scale of the exchange interaction is not only of fundamental interest: ultrafast and energy efficient manipulation of magnetic states by optical or electrical fields may have dramatic impacts on future magnetic devices, storage and possibly logic, and may lead to the development of novel magnetic materials. The programme will therefore focus on metallic magnetic multilayer systems that not only have been shown to give rise to a rich variety of novel magnetic non-equilibrium phenomena, but are potentially also the most useful for future applications.
To achieve these objectives we will combine the complimentary expertise and infrastructure of researchers from Nijmegen, Eindhoven and Twente. The programme is organized in six joint projects that jointly contribute to the three objectives. Each project will be supervised by two project leaders of our team of seven researchers who are key players worldwide in the fields of ultrafast magnetization dynamics, ab-initio and first-principles theory of magnetism and magnetization dynamics, as well as atomic and nanoscale engineering of magnetic materials.

The final evaluation will be based on the self-evaluation report initiated by the programme leader and is foreseen for 2020.