When a strong laser pulse hits a steel alloy, the material briefly melts where it is irradiated, forming a small magnetic region.Credit: HZDR / Sander Munster
The research team has shown that ultrashort laser pulses can magnetize iron alloys. This discovery has great potential for applications in magnetic sensor technology, data storage, and spintronics.
To magnetize a steel nail, simply stroke its surface several times with a bar magnet. But there is a more unusual method. it is, Helmholtz – Zentrum Dresden – Rossendorf (HZDR) Some time ago, a certain iron was discovered. alloy It can be magnetized with ultrashort laser pulses. The researchers are currently working with the Laser Institute of Mitweida University (LHM) to further investigate this process. They found that this phenomenon also occurs in different classes of materials. This greatly expands the range of potential applications.The working group will publish its results in a scientific journal Advanced functional materials.
Groundbreaking discovery in magnetization
An unexpected discovery was made in 2018. When the HZDR team bombarded a thin layer of iron and aluminum alloy with ultrashort laser pulses, the nonmagnetic material suddenly became magnetic. Explanation: Laser pulses rearrange the atoms in the crystal so that the iron atoms are closer to each other, forming a magnet. The researchers were then able to demagnetize the layer again using a series of weaker laser pulses. This allowed them to discover how to create and erase tiny “magnetic spots” on surfaces.
However, the pilot experiment still left some questions unanswered. “It was unclear whether the effect only occurs in iron-aluminum alloys or in other materials,” explains HZDR physicist Dr. Rantei Bali. “We also wanted to track the process over time.” For further investigation, he collaborated with his Dr. Theo Pflug at LHM and colleagues at the University of Zaragoza in Spain.
Flipbook using laser pulse
Experts especially focused on iron-vanadium alloys. Unlike iron-aluminum alloys, which have a regular crystal lattice, the atoms in iron-vanadium alloys are more randomly arranged, forming an amorphous glass-like structure. To observe what happens during laser irradiation, physicists used a special method called the pump-probe method.
“First, we bombard the alloy with powerful laser pulses to magnetize the material,” explains Theo Pflug. “At the same time, he uses a second, weaker pulse that is reflected off the material surface.”
Analysis of reflected laser pulses reveals the physical properties of the material. This process is repeated several times to continually lengthen the time interval between the first “pump” pulse and subsequent “probe” pulses.
As a result, time-series reflection data are obtained, which can characterize the processes induced by laser excitation. “The whole procedure is similar to creating a flipbook,” he says Pflug. “Similarly, a series of individual images that animate when viewed in succession.”
rapid dissolution
Results: Although they have a different atomic structure than iron-aluminum compounds, iron-vanadium alloys can also be magnetized by lasers. “In both cases, the material melts for a short time at the point of irradiation,” he explains Rantej Bali. “This causes the laser to erase the previous structure and create small magnetic regions in both alloys.”
Promising results: Apparently, this phenomenon is not limited to a particular material structure and can be observed in a variety of atomic arrangements.
The team also tracks the temporal dynamics of the process. “At least we know on what time scale something will happen,” explains Theo Pflug. “Within femtoseconds, a laser pulse excites electrons in the material. After a few picoseconds, the excited electrons transfer their energy to the nucleus.”
Consequently, this energy transfer causes a rearrangement into a magnetic structure, which is then stabilized by rapid cooling. In follow-up experiments, the researchers aim to observe exactly how the atoms rearrange by examining the magnetization process with powerful X-rays.
Perspectives towards applications
Although still in its early stages, this research already provides a first idea of possible applications. For example, one could place small magnets on the chip surface via a laser. “This could be useful in producing highly sensitive magnetic sensors such as those used in vehicles,” he speculates Rantej Bali. “It could also have applications in magnetic data storage.”
Moreover, this phenomenon seems to be related to a new type of electronics: spintronics. Here, instead of electrons passing through transistors as usual, magnetic signals must be used for digital computing processes, providing a possible approach to future computer technology.
Reference: “Laser-Induced Positional and Chemical Lattice Reordering Generating Ferromagnetism” by Theo Pflug, Javier Pablo-Navarro, Md. Chabad Anwar, Markus Olbrich, César Magén, Manuel Ricardo Ibarra, Kay Potzger, Jürgen Faßbender, Jürgen Lindner, Alexander Horn. Lantei Bali, November 21, 2023, Advanced functional materials.
DOI: 10.1002/adfm.202311951
Source: scitechdaily.com
