Not Your Ordinary Magnetism

Scientists have identified a new type of magnetism, called “altermagnetism.” The discovery will constitute an important step forward for fundamental physics, with the potential to have a significant impact on spintronic technology. The study, published in Nature, adds a third to the two already-known basic magnetic phases known as “ferromagnetism” and “antiferromagnetism”.

Spintronics, or “spin-based electronics,” is also known as magnetoelectronics. It may be considered an emerging technology based on utilising the quantum properties of electrons to exploit their spin and charge states.

Let’s take a look at magnetism. Magnetism is a deeper concept than the magnets we use in our daily lives. Basic magnetic phases are defined by the spontaneous arrangement of magnetic moments (electron spins) in the crystal structures of materials and the atoms that carry these moments. In ferromagnetic materials, the spins (the orientation of electron) align and form a clear macroscopic magnetic field. In antiferromagnets, the spins alternately face different directions and cancel the overall field. These do not show the properties of ordinary magnets.

Altermagnets, similar to antiferromagnets, do not exhibit clear macroscopic magnetisation. However, they form a unique electronic structure with spin arrangement and crystal symmetries. Instead of simply cancelling each other out, the symmetries create an electronic band structure with strong spin polarisation that changes direction when you pass through the material’s energy bands. This creates some properties that are more similar to ferromagnets, but without the disadvantages associated with their evident magnetisation.

Spintronics uses both electron charge and spin data to store information. Despite its significant potential, it faces some challenges. Ferromagnets, while usable due to their strong spin effects, face scalability limitations due to their net magnetisation. Antiferromagnets, on the other hand, are scalable but lack strong spin effects.

At this point, altermagnets offer a potential solution by combining the advantages of both: zero net magnetisation and the ability to develop the next generation of spintronic devices with the desired spin-dependent properties.

Theories of altermagnetism emerged in 2019, followed by predictions for many potential altermagnetised materials. Experimental confirmation finally came in 2024 using photoemission spectroscopy at the Swiss Light Source. The discovery is likely to open the door for further research in the fields of spintronics, unconventional superconductivity, and condensed matter physics.

The researchers emphasize the unexpected simplicity of altermagnetism, noting that it already exists in many previously studied materials. This accessibility could offer the potential for a wide range of scientific and technological advances.