A research team has discovered that ultrashort laser pulses can magnetize iron alloys, a finding that has huge potential for applications in magnetic sensor technology, data storage and spintronics. To magnetize an iron nail, simply tap a magnet on its surface a few times. However, there is a more unusual approach: a team led by the Helmholtz Zentrum Dresden Rosendorf (HZDR) recently discovered that a certain iron alloy can be magnetized with ultrashort laser pulses.
The researchers have now teamed up with the Laserinstitut Hochschule Mittweida (LHM) to further study this process. They found that this phenomenon also occurs with different classes of materials, which significantly broadens the potential applications. The working group published its findings in the scientific journal Advanced Functional Materials.
This unexpected discovery was made in 2018. When the HZDR team illuminated thin layers of iron-aluminum alloy with ultrashort laser pulses, the non-magnetic material suddenly became magnetic. The principle is that the laser pulses rearrange the atoms in the crystal, bringing the iron atoms closer together, creating a magnet. The researchers were then able to demagnetize the layer again with a series of weaker laser pulses. This allowed them to discover a way to create and erase tiny "magnetic spots" on surfaces.
However, the pilot experiment still leaves some unanswered questions. HZDR physicist Dr. Rantej Bali explains: "It is not yet clear whether this effect occurs only in iron-aluminum alloys or also in other materials. We also wanted to try to follow the temporal progression of this process."
To investigate further, he collaborated with Dr. Theo Pflug of the LHM and colleagues at the University of Zaragoza in Spain.
Experts are paying particular attention to iron-vanadium alloys. Unlike iron-aluminum alloys with regular crystal lattice, the atomic arrangement in iron-vanadium alloys is more chaotic, forming an amorphous glass-like structure. To see what happens when laser light shines on them, physicists use a special method: the pump-probe method.
"First, we irradiate the alloy with intense laser pulses, which magnetizes the material," explains Theo Pflug. "At the same time, we use a second, weaker pulse that reflects off the surface of the material."
Analysis of reflected laser pulses provides an indication of the material's physical properties. This process is repeated several times, so that the time interval between the first "pump" pulse and the subsequent "probe" pulse is continuously lengthened.
As a result, the researchers obtained time series of reflection data, which enabled the characterization of processes triggered by laser excitation. "The whole process is similar to generating a page-turning book," Pflug said. "Similarly, a series of individual images animates when viewed in rapid succession."
Although the atomic structure of iron-vanadium alloys is different from that of iron-aluminum compounds, iron-vanadium alloys can also be magnetized by laser. "In both cases, the material melts briefly at the point of irradiation," explains Rantej Bali. "This causes the laser to erase the previous structure, creating a small magnetic region in both alloys."
The encouraging result is that this phenomenon is not restricted to a specific material structure, but can be observed in different atomic arrangements.
The team is also tracking the temporal dynamics of the process: "At least we now know on which time scale something happens. Within femtoseconds, a laser pulse excites electrons in the material. After a few picoseconds, the excited electrons transfer energy to the nucleus."
This energy transfer therefore leads to rearrangement into a magnetic structure, which is stabilized by subsequent rapid cooling. In follow-up experiments, the researchers aim to observe exactly how the atoms rearrange themselves by examining the magnetization process using intense X-rays.
Although still in its early stages, the work already provides first ideas for possible applications: for example, placing tiny magnets on the surface of a chip via laser is conceivable. Rantej Bali speculated: "This could be useful for producing sensitive magnetic sensors, such as those used in vehicles. It could also find possible applications in magnetic data storage."
Furthermore, this phenomenon appears to be related to a new type of electronics called spintronics. Here, the magnetic signals should be used in digital computing processes, rather than electrons passing through transistors as usual - providing a possible approach for future computer technology.
Compiled source: ScitechDaily