Spintronics: Innovative crystals for future computer electronics

Date:
February 28, 2022
Source:
Goethe University Frankfurt
Summary:
Computer chips and storage elements are expected to function
as quickly as possible and be energy-saving at the same
time. Innovative spintronic modules are at an advantage here thanks
to their high speed and efficiency, as there is no lossy electrical
current, rather the electrons couple with one another magnetically
-- like a series of tiny magnetic needles which interact with almost
no friction loss. A team of scientists has now found promising
properties with crystals grown from rare-earth atoms, which offer
hope on the long path towards usage as spintronic components.



FULL STORY ========================================================================== While modern computers are already very fast, they also consume vast
amounts of electricity. For some years now a new technology has been
much talked about, which although it is still in its infancy could
one day revolutionise computer technology -- spintronics. The word
is a portmanteau meaning "spin" and "electronics," because with these components electrons no longer flow through computer chips, but the spin
of the electrons serves as the information carrier. A team of researchers
with staff from Goethe University Frankfurt has now identified materials
that have surprisingly fast properties for spintronics. The results have
been published 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," says Cornelius Krellner, Professor for Experimental Physics at Goethe University Frankfurt. How these magnetic
needles react with one another fundamentally depends on the properties
of the material. To date ferromagnetic materials have been examined in spintronics above all; with these materials - - similarly to iron magnets
-- the magnetic needles prefer to point in one direction. In recent
years, however, the focus has been placed on so-called antiferromagnets
to a greater degree, because these materials are said to allow for even
faster and more efficient switchability than other spintronic materials.

With antiferromagnets the neighbouring magnetic needles always point
in opposite directions. If an atomic magnetic needle is pushed in
one direction, the neighbouring needle turns to face in the opposite
direction. This in turn causes the next but one neighbour to point
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.

Above all crystals with atoms from the group of rare earths are regarded
as interesting candidates for spintronics as these comparatively heavy
atoms have strong magnetic moments -- chemists call the corresponding
states of the electrons 4f orbitals. Among the rare-earth metals --
some of which are neither rare nor expensive -- are elements such as praseodymium and neodymium, which are also used in magnet technology. The research team has now studied seven materials with differing rare-earth
atoms in total, from praseodymium to holmium.

The problem in the development of spintronic materials is that perfectly designed crystals are required for such components as the smallest discrepancies immediately have a negative impact on the overall magnetic
order in the material. This is where the expertise in Frankfurt came
into play. "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," says Krellner. "This is why customary crystallisation
methods do not function here." Instead the scientists used hot indium as
a solvent. The rare earths, as well as the rhodium and silicon that are required, dissolve in this at about 1500 degrees Celsius. The graphite
crucible was kept at this temperature for about a week and then gently
cooled. As a result the desired crystals grew in the form of thin disks
with an edge length of two to three millimetres. These were then studied
by the team with the aid of X-rays produced 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," says Krellner. This opens up the path for further optimisation - - ultimately spintronics is still purely fundamental
research and years away from the production of commercial components.

There are still a great many problems to be solved on the path to market maturity, however. Thus, the crystals -- which are produced in blazing
heat - - only deliver convincing magnetic properties at temperatures
of less than minus 170 degrees Celsius. "We suspect that the operating temperatures can be raised significantly by adding iron atoms or similar elements," says Krellner.

"But it remains to be seen whether the magnetic properties are then
just as positive." Thanks to the new results the researchers now have
a better idea of where it makes sense to change parameters, however.

========================================================================== Story Source: Materials provided by Goethe_University_Frankfurt. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Y. W. Windsor, S.-E. Lee, D. Zahn, V. Borisov, D. Thonig,
K. Kliemt, A.

Ernst, C. Schu"ssler-Langeheine, N. Pontius, U. Staub, C. Krellner,
D. V.

Vyalikh, O. Eriksson, L. Rettig. Exchange scaling of ultrafast
angular momentum transfer in 4f antiferromagnets. Nature Materials,
2022; DOI: 10.1038/s41563-022-01206-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220228114356.htm

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