Laser light can serve as a general tool for accessing new magnetic states
For decades, physicists predicted that electron spins inside certain materials could arrange themselves into intricate three-dimensional knots called hopfions — stable, self-contained structures that seemed to exist only in the language of mathematics. Now, a multinational team of researchers has crossed the threshold from theory to observation, using ultrafast flashes of laser light to coax iron germanium crystals into revealing these hidden magnetic states. The achievement belongs to that rare category of scientific moments when the invisible becomes visible, and what was once a prediction becomes a foundation for new possibility.
- For years, the energy barriers inside magnetic materials kept hopfions locked away — theory promised they existed, but no experiment could reach them.
- Femtosecond laser pulses — each lasting mere trillionths of a second — delivered just enough disruption to push spin systems past those barriers and into previously inaccessible configurations.
- Electron microscopy and computer simulations running in parallel gave researchers two independent ways to confirm what they were seeing, turning a fragile observation into a credible discovery.
- The same laser approach simultaneously produced bimerons, the two-dimensional cousins of hopfions, suggesting this method works across dimensions and materials — not just in one narrow case.
- The field of spintronics now has a new frontier: stable three-dimensional magnetic structures that could one day encode information, if researchers can prove the technique scales reliably.
A multinational research team has achieved something long promised by theory but never demonstrated in the laboratory: the creation and direct observation of magnetic hopfions — three-dimensional structures in which electron spins point simultaneously in every possible direction within a tiny volume of solid material. The key was femtosecond laser pulses, flashes of light lasting only trillionths of a second, which briefly knocked magnetic systems out of equilibrium and allowed them to settle into states that ordinary conditions could never reach.
The experiments used thin films of iron germanium, a chiral magnetic crystal whose built-in atomic asymmetry shapes how spins organize. By illuminating the material once per second with laser pulses and then mapping the results with electron microscopy, the team watched new magnetic configurations emerge after each disturbance. Running alongside the experiments, detailed computer simulations using software called Excalibur modeled how millions of interacting spins evolved — and matched what the researchers were seeing in the lab.
Philipp Rybakov of Uppsala University applied topological mathematics to confirm the structures were genuine hopfions: distinct, stable, three-dimensional magnetic objects whose defining properties survive continuous deformation. In a parallel effort at the SECUF facility, the same laser approach produced bimerons, the two-dimensional counterparts to hopfions, reinforcing the idea that femtosecond light can serve as a general tool for controlling magnetism across materials and dimensions.
Published in Nature Physics and involving institutions from Sweden, Germany, Luxembourg, and China, the work points toward spintronics — where electron spin, rather than electric charge, carries and stores information. Hopfions, being stable structures, are natural candidates for encoding data. The immediate next steps involve testing whether light-based magnetic control holds across different materials and whether these structures can be reliably harnessed for technology. The field has moved from prediction to proof, and that crossing rarely goes anywhere but forward.
A team of researchers has done something that theory said was possible but experiments had never managed to prove: they have created and observed magnetic hopfions, three-dimensional structures made of electron spins arranged in all possible directions within a tiny volume of material. The breakthrough came by using femtosecond laser pulses—flashes of light lasting just a few trillionths of a second—to nudge magnetic systems out of their normal state and into configurations that had only existed on paper until now.
Magnetism at the nanoscale is far stranger than the simple north-south polarity most people imagine. Each electron carries a quantum property called spin, which acts like a miniature compass. When millions of these spins interact inside a solid material, they can organize into stable patterns. For years, physicists predicted that one such pattern—the hopfion—should exist in three dimensions, with spins oriented in every conceivable direction within a confined space. But creating one in the lab and actually seeing it proved to be a formidable problem. Under normal conditions, the magnetic system lacks the energy to reach these states; it gets stuck behind energy barriers that prevent the transition.
The experiments focused on thin films of iron germanium, each between 110 and 200 nanometers thick. Iron germanium belongs to a class of materials called chiral magnetic crystals, where the atomic structure comes in two mirror-image forms—like a left hand and a right hand—that cannot be rotated to match each other. This built-in asymmetry shapes how the spins arrange themselves. The researchers illuminated large surfaces of the material with femtosecond laser pulses once per second. Each pulse briefly disturbed the spin system, pushing it far from equilibrium and allowing new magnetic states to form. After each pulse, they examined the material using electron-based microscopy to map what had happened.
What made the work convincing was the parallel effort on the theoretical side. As the experiments unfolded, the same team ran detailed computer simulations using software called Excalibur, which models how millions of interacting spins evolve and organize into complex three-dimensional patterns. These digital twins of the experiments matched what the researchers were actually observing. Philipp Rybakov, a physicist at Uppsala University and a lead author of the study, applied topological mathematics—a branch that describes properties of shapes that survive continuous deformation, like knots or linked loops—to confirm that the observed structures were indeed hopfions: distinct, stable, three-dimensional magnetic objects.
The work, published in Nature Physics, represents a collaboration between Swedish, German, Luxembourg, and Chinese institutions. In parallel, researchers at a facility called SECUF used the same laser-based approach to create and observe bimerons, which are two-dimensional magnetic structures that serve as counterparts to the three-dimensional hopfions. Together, these results suggest that femtosecond laser light can function as a general tool for controlling magnetism across different materials and in both two and three dimensions.
The practical implications point toward spintronics, a field where electron spin replaces electric charge as the basis for storing and processing information. Because hopfions are stable structures, they could serve as reliable units for encoding data. Rybakov notes that having a way to switch magnetism into these complex states opens avenues for exploring magnetic phenomena that were simply inaccessible before. The next phase will likely involve testing whether this light-based control works reliably across different materials and whether hopfions can actually be harnessed for information technology. For now, the field has moved from theory to observation—a threshold that often precedes practical application.
Citas Notables
Hopfions are fascinating because of their structure. They are three-dimensional objects made of spins that form closed and linked loops. Once they appear, they keep their form and are largely unaffected by their surroundings.— Philipp Rybakov, Uppsala University
Using femtosecond laser light, we now have a way to switch magnetism into these complex states. That allows us to explore magnetic phenomena in ways that were not possible before.— Philipp Rybakov, Uppsala University
La Conversación del Hearth Otra perspectiva de la historia
Why was it so hard to create these hopfions in the first place? Theory predicted them, but experiments kept failing.
The magnetic system naturally settles into low-energy states. Hopfions are high-energy configurations, separated by energy barriers. You need to push the system hard enough to cross those barriers, but conventional methods couldn't deliver that push without destroying the material.
And the femtosecond laser solved that?
Not by brute force. The laser pulse is so brief—a few trillionths of a second—that it disturbs the spin system before it can respond. That creates a window where new states can form. It's like nudging a ball over a hill before gravity has time to pull it back.
The simulations seem crucial here. Why not just trust the experiments?
Because you need to know what you're looking at. The simulations act as a reference frame. When the computer model and the microscopy images match, you know the structure is real and stable, not just a fleeting artifact.
So this is really a story about theory and experiment finally meeting?
Exactly. Theory pointed the way. Experiments made it visible. Topology helped us understand what we were seeing. None of it works alone.
What happens next?
The real test is whether this works reliably for storing information. Hopfions are stable, which is promising. But we need to see if we can write them, read them, and erase them on demand. That's the path to spintronics.