| Apr 27, 2026 |
For the first time, researchers have mapped how the boundaries of magnetic nanostructures behave on extremely short timescales. The work shows that these boundaries are much more stable than previously thought.
(Nanowerk News) Every magnet consists of tiny magnets, known as spins. When a material is magnetic, these spins all point in the same direction. Using ultra-short laser pulses, the spins in magnetic materials can change direction in a very short time.
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This so-called ultrafast nanomagnetism is important for, for example, hard drives, on which information is stored using magnetic bits. To make this storage faster and smaller, it is essential to understand exactly what happens at the nanoscale.
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Domains
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Using a new imaging technique capable of tracking processes down to the nanometre and femtosecond scale, Mentink and colleagues have researched the behaviour of domain boundaries – thin walls of about one nanometre that separate magnetic domains. Multiple spins pointing in the same direction form a domain.
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To understand how these structures behave, a measurement technique is required that combines both extreme spatial resolution and ultrafast temporal precision. Using this new imaging technique, which employs extreme ultraviolet light, Mentink’s colleagues at the Max Planck Institute in Göttingen have, for the first time, been able to track what happens to domain walls at the exact moment a laser pulse strikes a magnetic material.
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The research (Nature Materials, “Sub-wavelength extreme ultraviolet microscopy reveals domain-wall stability during ultrafast demagnetization”) shows that these domain walls are much more stable than previously thought. Even when a material is strongly heated by a laser pulse and partially loses its magnetism, domain walls remain in place and barely change shape. This confirms an important theoretical insight: domains do not move rapidly through the material.
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‘On short timescales, that simply cannot happen,’ says Mentink. ‘There is only a finite speed at which those domains can move.’
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The fact that domain walls remain so stable under the influence of a laser had not been observed before. Mentink explains: ‘This tells us that the laser’s energy acts very locally – it causes demagnetisation that is uniform across the material. As a result, the domain structure – its position, shape and width – remains intact.’
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Chance
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With an even more powerful laser, something else begins to happen: small regions of the material flip randomly as a result of stochastic processes at the nanoscale. The domain boundary remains largely intact, but small domains appear at random locations.
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‘A single powerful pulse actually creates a sort of jumble of domains that are oriented up and down,’ explains Mentink. ‘Only by using multiple pulses can they coalesce into a single large domain.’
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This means that demagnetisation occurs mainly locally, rather than through rapid movement of domain boundaries across the material. This insight is important for how researchers aim to control magnetism, ultimately enabling better, faster and more efficient data storage. ‘What happens ultra-fast is the switching,’ says Mentink. ‘But moving a domain boundary through space is a slow process.’
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