Totally NEW type of magnetism has been discovered

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There is now a new addition to the magnetic family: thanks to experiments at the Swiss Light Source SLS, researchers have proved the existence of altermagnetism. The experimental discovery of this new branch of magnetism is reported in Nature and signifies new fundamental physics, with major implications for spintronics.

Magnetism is a lot more than just things that stick to the fridge. This understanding came with the discovery of antiferromagnets nearly a century ago. Since then, the family of magnetic materials has been divided into two fundamental phases: the ferromagnetic branch known for several millennia and the antiferromagnetic branch.

The experimental proof of a third branch of magnetism, termed altermagnetism, was made at the Swiss Light Source SLS, by an international collaboration led by the Czech Academy of Sciences together with Paul Scherrer Institute PSI.

The fundamental magnetic phases are defined by the specific spontaneous arrangements of magnetic moments — or electron spins — and of atoms that carry the moments in crystals. Ferromagnets are the type of magnets that stick to the fridge: here spins point in the same direction, giving macroscopic magnetism. In antiferromagnetic materials, spins point in alternating directions, with the result that the materials possess no macroscopic net magnetisation — and thus don’t stick to the fridge. Although other types of magnetism, such as diamagnetism and paramagnetism have been categorised, these describe specific responses to externally applied magnetic fields rather than spontaneous magnetic orderings in materials.

Altermagnets have a special combination of the arrangement of spins and crystal symmetries. The spins alternate, as in antiferromagnets, resulting in no net magnetisation. Yet, rather than simply cancelling out, the symmetries give an electronic band structure with strong spin polarization that flips in direction as you pass through the material’s energy bands — hence the name altermagnets. This results in highly useful properties more resemblant of ferromagnets, as well as some completely new properties.

A new and useful sibling

This third magnetic sibling offers distinct advantages for the developing field of next-generation magnetic memory technology, known as spintronics. Whereas electronics makes use only of the charge of the electrons, spintronics also exploits the spin-state of electrons to carry information.

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hey guys…. this looking even more weird than I realized! take a look!

Altermagnets are an emerging elementary class of collinear magnets. Unlike ferromagnets, their distinct crystal symmetries inhibit magnetization while, unlike antiferromagnets, they promote strong spin polarization in the band structure.

The corresponding unconventional mechanism of time-reversal symmetry breaking without magnetization in the electronic spectra has been regarded as a primary signature of altermagnetism but has not been experimentally visualized to date.

We directly observe strong time-reversal symmetry breaking in the band structure of altermagnetic RuO2 by detecting magnetic circular dichroism in angle-resolved photoemission spectra.

Our experimental results, supported by ab initio calculations, establish the microscopic electronic structure basis for a family of interesting phenomena and functionalities in fields ranging from topological matter to spintronics, which are based on the unconventional time-reversal symmetry breaking in altermagnets.

Recently, a nonrelativistic spin-symmetry classification and description, focusing within the hierarchy of interactions on the strong Coulomb (exchange) interaction, has divided all collinear magnets into three mutually exclusive spin-group classes:

(i) conventional ferromagnetic with strong (exchange)
reversal symmetry breaking in the electronic band structure and net magnetization,

(ii) conventional antiferromagnetic with, at least in the nonrelativistic limit,
reversal symmetric electronic band structure and zero net magnetization, and

(iii) a third class dubbed altermagnetic with strong (exchange)
reversal symmetry breaking in the electronic band structure and with, at least in the nonrelativistic limit, zero net magnetization (13, 14).

We note that the strong altermagnetic symmetry breaking in the electronic structure is distinct from the previously studied relativistic spin-orbit coupling mechanism in conventional antiferromagnetic crystals with a symmetry combining and crystal inversion transformations (15), from weak ferromagnetism (16, 17), or from noncollinear magnetism (3).

Figure 1 illustrates the spin-symmetry protected compensated antiparallel magnetic order in altermagnets that generates an unconventional alternating spin polarization and the symmetry breaking in the band structure without magnetization (13, 14, 18).

A new kind of magnetism has been measured for the first time. Altermagnets, which contain a blend of properties from different classes of existing magnets, could be used to make high capacity and fast memory devices or new kinds of magnetic computers.

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Until the 20th century, there was thought to be only one kind of permanent magnet, a ferromagnet, the effects of which can be seen in objects with relatively strong external magnetic fields like fridge magnets or compass needles.

… 2019, researchers predicted a perplexing electric current in the crystal structure of certain antiferromagnets, called the anomalous Hall effect, which couldn’t be explained by the conventional theory of alternating spins. The current was moving without any external magnetic field.

It seemed, when looking at a crystal in terms of sheets of spins, that a third kind of permanent magnetism might be responsible, which has been called altermagnetism. Altermagnets would look like antiferromagnets, but the sheets of spins would look the same when rotated from any angle. This would explain the Hall effect, but no one had seen the electronic signature of this structure itself, so scientists were unsure whether it was definitely a new kind of magnetism.

Now, Juraj Krempaský at the Paul Scherrer Institute in Villigen, Switzerland, and his colleagues have confirmed the existence of an altermagnet by measuring the electron structure in a crystal, manganese telluride, that was previously thought to be antiferromagnetic.

New magnetism type confirmed experimentally opens the way to more #EnergyEfficiency in #DataCenter via #spintronics
-Named altermagnetism is 1000x stronger than normal magnets.
-Found in manganese telluride crystals, potentially in 200+ other compounds.

h/t Digital mix guy Spock

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