The ion beam of the HZDR helium-ion microscope acts as a magnetic pencil. Here, it creates spiral-shaped nanomagnetic structures.
Helmholtz-Zentrum Dresden-Rosendorf (FZDR) physicists work together with colleagues from the Leibniz Institute for Solid State and Materials Research (IFW) Dresden and the University of Glasgow to adjust the magnetic properties of nanostructures. A special microscope is used at the HZDR ion beam center, whose thin beam beam can generate periodically distributed and stable nanomagnets in a sample material of rapidly charged atoms (ions). But it also serves to optimize the magnetic properties of carbon nanotubes.
"Magnetically adjustable materials in the nanometer range have great potential for producing cutting-edge electronic components. We carry out a wide range of approaches to our magnetic nanostructures, but always use ionic rays, "said HCDD scientist Dr Ing. Rantey Bali, dr. Kilian Lenz et al. Gregory Flavacek. If one directs an ion beam onto a non-ferromagnetic iron-aluminum alloy, for example, it causes several hundred atoms to separate. Subsequent redirection of atoms in the alloy strongly increases the number of adjacent magnetic iron atoms in the immediate vicinity of the ion beam impact – so strong that ferromagnetism can form in the material. In this way, for example, it was possible to engrave nano-magnets in dot shape into a thin layer of original non-ferromagnetic material.
The disorder leads to embedded nanomagnets
In their current work, HIFD scientists have now shown that ion-induced disturbance also increases the volume of the basic structure of the bars; but not evenly in all directions of the room. In addition to the expected longitudinal magnetization, which is similar to that of a conventional bar magnet, there is also an increase in transverse magnetization caused by the observed network disturbances. Because of the overlap of both effects, the magnetic fields generated by the ion beam twist or twist. These stable, periodically present magnetic domains can be deployed in flexible rounded shapes, which can be used, for example, in miniature magnetic sensors.
In the HZDR helium-ion microscope, physicists use precious gases to produce extremely thin and therefore highly accurate ion beams. "Our ion beam is only a few atoms in diameter," explains Gregor Flavacek, who coordinates the helium-ion microscope experiments. "Depending on the noble gas used, we can alter the properties of the irradiated material or change its morphology by removing the atoms." Operation of a helium-ion microscope is not limited to the same helium. In the current experiments, neon was heavier than helium and therefore had a stronger influence on the material to be modified. FZDR researchers were also able to use the electron transfer microscope at the Department of Materials and Physics of Solid State in collaboration with the University of Glasgow.
In Rantey Bali's experiments, the ion beam generated by neon ions serves as a point of great energy source: "The ion beam enables the production of magnetic nanostructures of any form embedded in the material and defined exclusively by their magnetic and crystallographic properties," concludes Bali. from his earlier research, which he leads as part of the DFG project at HZDR.
Cutting material with neon ions
In turn, Kilian Lenz uses focused ion beam manipulation to optimize the desired properties of the material through a nanostructured change in geometry. The neon ion beam is only two nanometers in diameter. Where affected, material irregularities or only material edges in the same order shall be removed. "We investigate this with carbon nanotubes, which have an almost cylindrical magnetic iron core and whose structure and geometry are optimized in a helium-ion microscope by cutting," Lenz describes the process.
Using a micro-manipulator, only one of these tubes, 70 nanometers in diameter and 10 micrometers in length, is separated and placed into a microresonant for measurement. "It is an extremely complex process that a team from the Leibniz Institute for Dresden Solid State and Materials Research has developed for us," Lenz explains. Through the unique combination of focused ion beam sections and ferromagnetic resonance measurements of the iron core, Lenz's researchers can clarify and perfect the magnetic structures and properties of the iron core in the nanotube.
Such methods of selective impact on the properties of the nanomagnetic material by means of ultrafine ion beams will also be explored in the future at the Institute for Ion Beam Physics and Materials Research at HCDD. Scientists see the potential for advances in spintronics applications and invent new pink sensors or storage media in their methodology and as a result of tailor made materials.
M. Nord, A. Semisalova, A. Coke, Mr. Flavacek, I. McLaren, W. Liers, OM Volkov, D. Makarov, GV Patterson, K. Pozeger, J. Lindner, J. Jasbender, D. McGrutter, et al. R. Bali; "Anisotropy virus and magnetic domains in embedded nanomagnets"; Small 2019.
K. Lenz, R. Narkowicz, K. Wagner, CF Reiche, J. Körner, T. Schneider, A. Kákay, H. Schultheiss, U. Weissker, D. Wolf, D. Suter, B. Bchchner, J. Fassbender , T. Mühl, J. Lindner; "Magnetization Dynamics of Individual Single Crystalline Carbon Using Fe-filled Carbon"; Small 2019.