Ultrathin iron responds more strongly to laser pulses
Researchers at the University of Duisburg-Essen and Helmholtz-Zentrum Berlin have found that reducing the thickness of an iron film can substantially strengthen its ultrafast loss of magnetic order after laser excitation. The work examines a process called ultrafast demagnetization, in which a short laser pulse disrupts a material’s magnetism on an extremely short timescale.
The result is notable because magnetic materials sit at the core of hard-disk storage. Information in those systems is represented by the orientation of tiny magnetic regions. Researchers are investigating whether light-based approaches could eventually help control magnetic states more quickly, and the new study identifies film thickness as a major factor in how iron reacts.
A 75% stronger effect in the thinnest films
The team compared iron layers of different thicknesses while keeping the laser excitation intensity the same. At a thickness of 2 nanometers, the iron showed approximately 75% stronger demagnetization than a 16-nanometer layer.
Two nanometers is two millionths of a millimeter, making the result a measurement of behavior at a scale where interfaces make up a much larger share of the material. The researchers reported their findings in Advanced Science, using ultrafast electron diffraction to investigate the response.
The effect was not simply attributed to a thinner film absorbing light differently, nor to differences in vibrations of the atomic lattice. Instead, the researchers traced the change to the magnetic properties of the material itself.
Why interfaces matter
Iron’s magnetism depends on electron spins: a collective alignment that gives the material its magnetic order. In a very thin film, more of those spins are situated near interfaces rather than deep within the material.
At an interface, a spin has fewer neighboring spins with which to interact magnetically. That reduced local environment makes the collective order easier for a laser pulse to disturb. As the proportion of interface-associated spins rises in thinner films, the overall magnetic response becomes more susceptible to disruption.
Researchers had previously suspected that film thickness could influence ultrafast demagnetization. The new work emphasizes both the scale of the observed difference and the underlying explanation: the stronger response is tied to the altered magnetic environment of spins in ultrathin layers.
What the result does—and does not—establish
The study does not describe a new commercial storage device, and it does not show that thinner films alone will produce a finished ultrafast memory technology. It instead provides a materials-level finding about how iron layers react under the tested optical excitation.
That distinction matters. Moving from a controlled experiment to practical magnetic storage would require additional work on device architectures, writing and reading mechanisms, stability, energy use and integration with existing technologies. But the result gives researchers a clearer variable to consider when designing magnetic structures for fast optical control.
For the team, the central lesson is straightforward: shrinking the iron layer can make laser-driven demagnetization substantially more effective without increasing the stated laser excitation intensity. That relationship could be useful wherever engineers want to tune magnetic responses through nanoscale structure rather than solely through more powerful optical pulses.
A route toward faster magnetic control
Modern data infrastructure relies on enormous volumes of stored information, and magnetic storage remains important in large data centers. Research on ultrafast magnetism is motivated by the prospect of changing magnetic order on timescales beyond those associated with conventional approaches.
The findings offer a physical rationale for why nanoscale engineering may be important in that effort. By changing thickness, researchers also change the balance between interior spins and interface spins. In this experiment, that shift made the iron more vulnerable to the loss of magnetic order induced by a laser pulse.
Future studies will be needed to determine how broadly the effect applies across materials, interfaces and device-relevant structures. Still, the observation in iron films provides a concrete benchmark: at the smallest thickness tested, the demagnetization response was about three-quarters stronger than in the thicker comparison layer under the same excitation conditions.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
