Storage elements and computer chips are projected to function as rapidly as possible and save as much energy as possible, simultaneously.
Researchers at Goethe University develop novel materials to minimize power consumption of electronic elements. Image Credit: raigvi/Shutterstock.
Advanced spintronic systems are at an advantage here owing to their high speed and efficiency as there is no lossy electrical current, rather the electrons pair with one another magnetically — same as a series of miniature magnetic needles which interact with virtually no loss of friction.
A team of researchers, involving Goethe University Frankfurt and the Fritz Haber Institute in Berlin, has currently discovered promising properties with crystals developed from rare-earth atoms, which provide hope on the long road toward application as spintronic components.
While contemporary computers are already extremely fast, they also use up massive amounts of electricity.
For quite a few years now, a new technology has been talked about a lot, which, although still in its early stages, could in the near future transform computer technology — spintronics, the term is a portmanteau meaning “spin” and “electronics”, because with these components, electrons no longer have to flow through computer chips, but the spin of the electrons works as the information carrier.
A team of scientists with staff from Goethe University Frankfurt has recently discovered materials that have astonishingly fast properties for spintronics. The results have been reported in the specialist magazine “Nature Materials.”
You have to imagine the electron spins as if they were tiny magnetic needles which are attached to the atoms of a crystal lattice and which communicate with one another.
Cornelius Krellner, Professor for Experimental Physics, Goethe University Frankfurt
How these magnetic needles behave with one another depends on the features of the material. Thus far, ferromagnetic materials have been extensively analyzed in spintronics; with the magnetic needles composed of these materials, which are akin to iron magnets, they point in one direction.
In the last few years, however, the importance has been placed on so-called antiferromagnets to a greater degree, as these materials are believed to allow for even quicker and more efficient switchability than other spintronic materials.
With antiferromagnets, the adjacent magnetic needles point in opposite directions at all times. If an atomic magnetic needle is forced in one direction, the neighboring needle turns to point in the opposite direction. This, in turn, makes the next but one neighbor turn in the same direction as the first needle again.
“As this interplay takes place very quickly and with virtually no friction loss, it offers considerable potential for entirely new forms of electronic componentry,” explains Krellner.
In particular, crystals with atoms from the family of rare earths are seen as interesting contenders for spintronics as these relatively heavy atoms have robust magnetic moments — chemists refer to the equivalent states of the electrons, 4f orbitals.
Among the rare-earth metals — few of which are neither uncommon nor costly — are elements such as neodymium and praseodymium, which are also used in magnet technology. The researchers have presently explored seven materials with different rare-earth atoms in total, from praseodymium to holmium.
The challenge in the development of spintronic materials is that flawlessly designed crystals are necessary for such components as the smallest inconsistencies have a negative effect on the total magnetic order in the material. This is where Frankfurt’s expertise was beneficial.
The rare earths melt at about 1000 degrees Celsius, but the rhodium that is also needed for the crystal does not melt until about 2000 degrees Celsius. This is why customary crystallisation methods do not function here.
Cornelius Krellner, Professor for Experimental Physics, Goethe University Frankfurt
The scientists used hot indium as a solvent. The rare earths, as well as the silicon and rhodium that are necessary, dissolve in this at around 1500 °C. The graphite crucible was maintained at this temperature for approximately a week and then gradually cooled.
Consequently, the anticipated crystals developed in the form of thin disks with an edge length measuring 2 to 3 mm. These were then examined by the scientists with the help of X-Rays formed on the Berlin synchrotron BESSY II and on the Swiss Light Source of the Paul Scherrer Institute in Switzerland.
The most important finding is that in the crystals which we have grown the rare-earth atoms react magnetically with one another very quickly and that the strength of these reactions can be specifically adjusted through the choice of atoms.
Cornelius Krellner, Professor for Experimental Physics, Goethe University Frankfurt
This paves the path for additional optimization — ultimately, spintronics is still only basic research and far from the production of commercial parts.
There are still several issues to be solved on the path to commercial maturity, however. Thus, the crystals — which are formed in blazing heat — only provide convincing magnetic features at temperatures of below minus 170 °C.
We suspect that the operating temperatures can be raised significantly by adding iron atoms or similar elements. But it remains to be seen whether the magnetic properties are then just as positive.
Cornelius Krellner, Professor for Experimental Physics, Goethe University Frankfurt
With the new findings, the scientists have a better grasp of where it makes sense to tweak parameters.
Journal Reference:
Windsor, Y.W., et al. (2022) Exchange scaling of ultrafast angular momentum transfer in 4f antiferromagnets. Nature Materials. doi.org/10.1038/s41563-022-01206-4.