Flashes of femtosecond laser light have enabled the first observation of new three-dimensional magnetic structures. These flashes, lasting only trillionths of a second, allowed researchers to switch magnetism into previously unseen three-dimensional states at the nanoscale. This discovery was made by a collaboration of Swedish, German, Luxembourg, and Chinese researchers.
Magnetism at very small scales can exhibit complex behaviors. Electron spins, a quantum property, organize into stable patterns within solid materials. The researchers observed magnetic hopfions, which are three-dimensional magnetic structures. In these structures, electron spins display all possible directions within a limited volume of material.
Previous theoretical predictions suggested the existence of magnetic hopfions. However, direct experimental observation proved challenging. The experiments were conducted on thin films of iron germanium (FeGe), measuring about 110–200 nanometers thick. Femtosecond laser pulses were crucial for this breakthrough. These pulses briefly disturb the spin system, pushing it out of equilibrium and allowing new magnetic states to form.
The research team used advanced electron-based microscopy to examine the material's magnetic state after laser exposure. Simultaneously, computer simulations recreated these magnetic structures. These simulations, acting as digital twins, modeled how millions of interacting spins evolve into complex three-dimensional patterns. The observed structures aligned with theoretical models of magnetic hopfions.
Topology, a branch of mathematics, was used to analyze the magnetic states. Philipp Rybakov, a researcher at Uppsala University, led this theoretical and topological work. This analysis identified hopfions as distinct and stable three-dimensional magnetic structures. The study highlights a close collaboration between theoretical and experimental work.
This discovery opens new avenues for spintronics research. Hopfions are stable, three-dimensional magnetic structures. They are relevant for storing and processing information using electron spin instead of electric charge. Laser light now provides a method to switch magnetism into these complex states, enabling exploration of previously inaccessible magnetic phenomena.
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