Researchers from the Swiss Light Source (SLS), an international collaboration between the Czech Academy of Sciences and the Swiss Paul Scherrer Institute (PSI), have just provided the first concrete evidence of the existence of a new type of magnetism! In an article in the scientific journal Nature, the researchers explain how they found something previously predicted only in theory, which now opens the door to the exploration of spintronics, a technology that is still in its infancy but promises to revolutionize many fields.
“Strange” materials
The story of this research begins a few years ago, in 2019, when Tomas Jungwirth of the Institute of Physics of the Czech Academy of Sciences and principal investigator of the study together with his colleagues identified a new class of materials that behaved “strangely » from a magnetic point of view. “Strange” in the sense that they did not fit into the classical descriptions of ferromagnetism or antiferromagnetism known until then.
Czech physicists named the phenomenon Altermagnetism and continued their research. By 2022, more than 200 potential alteromagnetic materials of all kinds have been discovered: from insulators to semiconductors, from metals to superconductors. Curiously, many of these materials were known and widely studied in the past, without, however, anyone noticing their alteromagnetic nature.
Czech physicists and their collaborators confirmed the existence of an alterromagnet by studying the crystal structure of manganese telluride, which was previously thought to be antiferromagnetic. Thanks to the high precision and sensitivity of their measurements, they were able to show that manganese telluride is neither an antiferromagnet nor a conventional ferromagnet, but belongs to the new class of magnetic materials.
It is certain that the discovery of the Czech and Swiss scientists will lead to the rewriting of school and university textbooks, while also opening up enormous new research possibilities. In fact, the discovery enriches our understanding of the physics of matter, offering a promising platform for exploring unconventional superconductivity (through new insights into the superconducting states that can arise in different magnetic materials).
New research fields
But perhaps the most immediate benefit is the technological applications. Suffice it to say that, without external magnetic fields like ferromagnets, ferromagnets could be used to create magnetic devices that don’t interfere with each other, perhaps offering the possibility of increasing the storage capacity of hard drives. Commercial devices contain ferromagnetic materials so tightly packed that the magnetic fields create interference, while alternative magnets could be packed even more densely without suffering from this problem.
Perhaps a little later in the future there is the promise of spintronics, electronics based on the spin of the electron, which, being able to adopt only two configurations, lends itself to binary encoding. In this case, the hope is to make spintronic devices a reality through a new generation of microprocessors that are much faster than today’s and with lower power consumption, combining memories and microchips in a single device.
«Alteromagnetism is actually not something extremely complicatedThomas Ugirth said. “It’s something completely fundamental that has been right in front of our eyes for decades without us noticing. And it’s not something that only exists in a few dark materials. It’s in a lot of crystals that people just had in their drawers. In this sense, now that we have brought it to light, many people around the world will be able to work on it, allowing for a wide impact».
Discovering the secrets of magnets
We are all familiar with refrigerator magnets, a typical example of ferromagnetism which until the 20th century was thought to be the only type of magnetism that existed. It was then shown that the magnetic properties of a macroscopic object are the result of what happens at the microscopic or, better, atomic level. In particular, it was understood that the rotational motion of (electrically charged) electrons creates the magnetic moment, spin. That is, a charged particle in circular motion can be thought of as a tiny coil of electric current. And according to the laws of electromagnetism, this creates a magnetic moment with a specific direction (with respect to the axis of rotation of the particle) and intensity (which depends on the characteristics of the material).
The magnetism of a material is therefore due to the orientation of the magnetic moments of the atoms that make it up. In the case of ferromagnetic materials, the magnetic moments all point in the same direction, thus causing the kind of macroscopic magnetism that causes the magnet to stick to the fridge.
In the 1930s, the French physicist Louis Neel discovered another type of magnetism called antiferromagnetism because in this case the magnetic moments have alternating directions, resulting in the macroscopic net magnetic field in these materials being zero (and therefore a “magnet” made of antiferromagnetic material would never stick to the fridge).
In 2019, a disturbing behavior of the electric current in the crystal structure of some antiferromagnetic materials (the Hall effect) was found that could not be explained by alternating spins. In practice the current appeared to move without an external magnetic field. Then researchers begin to think about the existence of a third type of permanent magnetism, precisely, Alteromagnetism.
However, no one had experimentally confirmed the existence of this Alteromagnetism, which was recently done by the Czechoswiss research team.
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