Discovery of a Novel Magnetic Phenomenon Holds Potential for Enhanced Memory Devices

Recent study has shown the existence of three distinct forms of magnetism, rather than just two. This newly discovered kind of magnetism has the potential to be highly sought after.

The first users of compasses likely saw magnets as a kind of sorcery. Upon gaining a comprehensive understanding of the conventional phenomenon called ferromagnetism, a novel form known as antiferromagnetism was unexpectedly uncovered. Our current descriptions of that phenomenon seem to be insufficient, given the evidence of a third form known as altermagnetism. When questioned about the functioning of magnets, scientists have not been dishonest, but their responses have been inadequate.

Magnetism, in the absence of macroscopic electric currents or varying fields, arises from the alignment of electron spins. The term “spin” in this context does not imply actual rotation of electrons like planets, but rather describes a subatomic phenomenon that is labeled with the same term. Electrons in orbit possess magnetic moments due to their spins, however they are often grouped in a random manner. Due to the immense quantity of electrons present in even the tiniest object, their effects nullify each other or become negligible.

Nevertheless, magnetic moments sometimes align to a significant extent, resulting in the creation of a magnetic field on a vast scale. This phenomenon, known as magnetism, is mostly seen in a limited number of elements, with iron being the most well-known example. When magnetism occurs, it enables the lodestone to be drawn towards the magnetic north pole or a magnet to stick to a refrigerator.

Antiferromagnets, which were first found in 1933, often need low temperatures and exhibit patterns in which atoms possess magnetic spins that are opposed to those of their neighboring atoms. Antiferromagnets exhibit similar behavior to other materials in the absence of an external magnetic field. Upon exposure to a magnetic field, the magnetic moments of the atoms align in an antiparallel manner with their neighboring atoms, rather than aligning randomly or in a parallel manner as seen in ferromagnets. While the material does not provide a significant overall contribution to the field, it does exhibit notable variations in conductivity under different conditions, which may be useful in practical applications.

If materials may synchronize their movement with the instructions of magnetic fields, either by rejecting them by changing direction or by completely disregarding them, what other possibilities remain?

Remarkably, altermagnets provide a solution. At first glance, altermagnets may seem like another variant of antiferromagnets. Their internal spins exhibit an opposite orientation compared to their neighboring spins, resulting in a lack of overall impact. The patterns exhibit rotational symmetry rather than translational symmetry. This implies that instead of nearby atoms nullifying each other, they generate a spin polarization that may result in the formation of alternating bands.

The resultant characteristics may provide a compromise between the two previously recognized types of magnets, and have the potential to significantly enhance the performance of magnetic memory recorders beyond the capabilities of current ones.

This phenomenon is referred to as spintronics, which involves using both the spin states and charges of electrons to transmit information. Spintronics, using ferromagnets, has been the subject of research and sometimes exaggeration for many years. Nevertheless, the substantial magnetism exhibited by ferromagnets poses a challenge in the upscaling of spintronic devices due to the interference of the bulk magnetic field with the spin of its own components and neighboring ones. Antiferromagnets circumvent this issue, but their absence of spin-dependent phenomena hinders the manifestation of some desired behaviors.

Physicists were intrigued by theories suggesting the existence of altermagnets as a potential sweet spot for spintronics. Consequently, they embarked on a quest to validate their existence.

With the confirmation now established, several individuals are sufficiently enthusiastic to use an alternative term beginning with the letter M. “The remarkable aspect of altermagnets,” said Professor Tomáš Jungwirth of the Czech Academy of Sciences. “Something that was previously deemed impossible until recent theoretical predictions has now been proven to be feasible.”

In 2019, Jungwirth contributed to the identification of a group of magnetic materials that deviated from the established classifications. These materials had internal electric currents even in the absence of an external magnetic field. After three years, he became a member of a team that discovered over 200 potential instances of altermagnetism in various types of materials. However, there exists a significant disparity between suspicion and evidence, and at that moment, there was no confirmation of altermagnetism.

Upon subjecting manganese telluride crystals, formerly classified as antiferromagnets, to X-ray irradiation, Jungwirth and his colleagues have shown that the crystals had electronic bands with alternating spin states, which is a defining trait of an altermagnet.

According to the X-ray analysis, it was determined that manganese telluride exhibits “Lifted Kramers Spin Degeneracy” due to its magnetic order. Although it may resemble the levitation practice of a pseudo-Medieval cult, this phenomenon is really a well-researched property of ferromagnets that was predicted in altermagnets but does not manifest in antiferromagnets.

In addition to enhancing our comprehension of magnetism and the possible ramifications it may have, Jungwirth and his colleagues believe that their research might provide novel perspectives on superconductivity.

“Altermagnetism is not excessively complex.” “It is a profoundly fundamental aspect that has been in plain sight for decades yet remained unnoticed,” states Jungwirth. “Furthermore, it is not limited to a handful of obscure substances.” It is present in several crystals that individuals conveniently store in their drawers. By shedding light on this issue, it will now be possible for several individuals worldwide to address it, creating the opportunity for a significant and far-reaching influence.

The work is published in the open access journal Nature.