Niels Bohr Lecture by Alexey Kimel, Radboud Universiteit

Title: Ultrafast magnetism – terra incognita beyond the conventional approximation

Alexey KimelAbstract: While magnetism is essentially the strongest quantum mechanical phenomenon, modern descriptions of magnetization dynamics and magnetization reversal rely on thermodynamics and the corresponding approximations.

However, recent experiments show that ultrashort (sub-100 ps) stimuli push magnetic media into a strongly non-equilibrium state, where the conventional description of magnetic phenomena in terms of equilibrium thermodynamics is no longer valid and the experimentally observed ultrafast magnetization dynamics challenges existing theories of magnetism.

For instance, while according to thermodynamics and simple intuition, heat can only destroy magnetization, we have observed that an ultrafast (sub-100 ps) heat pulse can cause magnetization reversal without any magnetic fields.

In this lecture, I will cover these recent insights and speculate on the future of ultrafast magnetism — both as a platform for technological innovation and as a frontier in fundamental research. In particular, I will discuss the exciting opportunities emerging from studies of antiferromagnets - the largest, least explored, and arguably most intriguing class of magnetic materials, discovered only in the 20th century.

About the speaker

Alexey Kimel obtained his PhD from the Ioffe Institute (St. Petersburg, Russia) and joined the Institute for Molecules and Materials (IMM) at Radboud University as a postdoctoral researcher in 2002.

He was subsequently appointed Assistant Professor in 2007, Associate Professor in 2013, and Full Professor in 2017.

He pioneered ultrafast spin dynamics in antiferromagnetic materials [PRL89, 287401 (2002), Nature 435 655–657 (2005)] and his works in a large extent defined the development of ultrafast magnetism during the last two decades.

He is a co-inventor of ultrafast all-optical magnetic recording [PRL99, 047601 (2007)] and inertia of spins in antiferromagnets [Nature-Physics5, 727–731 (2009)], as a recognized world-leader in the field he obtained several prestigious research grants (Veni2004, Vidi2006, Vici2017, ERC-SG2010, Russian MegaGrant-2013, ERC-AG2022).

Starting from September 2025, he serves as the Research Director of the Institute for Molecules and Materials.

Coffee, tea and cake will be served outside Margrethe Bohr Salen at 14:30.