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As some accounts have it, the stones were first noticed in around 2500 BCE by a shepherd in Magnesia, in what is modern-day Turkey. He observed that they clung to the nails in his shoes.
The stones were made of naturally magnetic iron ore. They were probably already familiar to the Chinese, who used lodestones — a form of magnetite — to first tell fortunes and later make navigational compasses. It would take until the 20th century for scientists to uncover a second type of magnetism. Astonishingly, researchers announced last week that they had confirmed discovery of a third.
“The idea that there has been a third type of magnetism and we haven’t noticed it, really captures people’s imaginations,” says Felix Flicker, a Bristol University researcher who studies magnetism and author of The Magick of Matter, which draws parallels between scientific phenomena and wizardry. Other forms, he thinks, may be awaiting discovery.
As well as adding mystique to a phenomenon that has long fascinated humans, this new form, called altermagnetism, could lead to more energy-efficient computation. With data centres thought to account for around one per cent of global electricity consumption, even a modest efficiency improvement could have a large environmental impact.
When we think of magnetism, we usually have ferromagnetism in mind. This is the territory of fridge magnets and bar magnets. As we learnt in school, opposites attract and like repels like.
Those forces of attraction and repulsion are choreographed at the atomic level — thanks to the fact that spinning electrons generate their own miniature magnetic fields. In ferromagnetic materials such as iron, cobalt and nickel, the spins of neighbouring electrons can be induced to line up in the same direction, giving rise to a collective magnetic effect. Ferromagnets are used widely in phones and other devices — but repulsion limits how closely they can be packed together.
A second type of magnetism, discovered in the 1930s, is called antiferromagnetism. In these materials, neighbouring electrons have an alternating, rather than parallel, spin. The opposing spins still generate internal magnetism but cancel each other out on the large scale. Accordingly, antiferromagnets don’t attract or repel like a typical magnet.
Altermagnetism seems to combine the best of both worlds, with its unique brand of magnetic magic hinging on a material’s atomic structure. Its existence was first theorised by scientists in Germany and Czechia several years ago; the term “altermagnetism” was coined by Libor Šmejkal of the Johannes Gutenberg University of Mainz.
Strong experimental hints were subsequently found by teams in Korea and China; confirmation finally came from an international team, including Šmejkal, with results published last week in the journal Nature.
The researchers studied crystals of manganese telluride, a prime altermagnetic suspect. As predicted, the spins of neighbouring electrons alternated — meaning, externally, the opposing spins would cancel each other out, just as in an antiferromagnet. But additional complexity in the crystal structure, namely the orientation of the atoms, produced an internal magnetic field about a thousand times stronger than that of a fridge magnet.
In short, the experimentalists confirmed, altermagnets really do exist — with magnetic specifications seemingly tailor-made for better data storage. There could be as many as 200 compounds with altermagnetic properties.
The discovery also raises the possibility of using the magnetic properties of electrons, rather than their electrical characteristics, to carry out computations. The field is called spintronics, rather than electronics. “Spintronics”, Flicker says, “gets people excited because it is massively more energy-efficient and computers are increasingly one of the major uses of energy in the world.”
Practical advantages aside, everything about magnetism, orchestrated at the quantum level and yet so clearly visible in everyday life, suggests sorcery rather than science. Lodestones, nature’s only permanent magnets and ascribed souls by the Greeks because they could move iron flakes, have a remarkable origin: these are pieces of hematite thought to be magnetised through lightning strikes, because they are only found on or near the Earth’s surface.
Without lodestones to keep compass needles magnetised, early sailors would have found it harder to navigate the unknown seas. Pleasingly, new methods of exploration are now allowing the landscape of magnetism itself to be charted more fully.