In Frank Herbert’s space opera Dune, a precious natural substance called spice melange grants people the ability to navigate vast expanses of the cosmos to build an intergalactic civilization.
In real life here on Earth, a group of natural metals known as the rare earths has made possible our own technology-powered society. Demand for these crucial components in nearly all modern electronics is skyrocketing.
Rare earths fulfill thousands of different needs — cerium, for instance, is used as a catalyst to refine petroleum, and gadolinium captures neutrons in nuclear reactors. But these elements’ most outstanding capabilities lie in their luminescence and magnetism.
Rare earths make mighty magnets
Society owes this miniaturization of electronic technology in large part to the exceptional magnetic power of the rare earths. Tiny rare earth magnets can do the same job as larger magnets made without rare earths.
It’s f-electrons at play. Rare earths have many orbitals of electrons, but the f-electrons inhabit a specific group of seven orbitals called the 4f-subshell. In any subshell, electrons try to spread themselves out among the orbitals within. Each orbital can house up to two electrons. But since the 4f-subshell contains seven orbitals, and most rare earths contain fewer than 14 f-electrons, the elements tend to have multiple orbitals with just one electron. Neodymium atoms, for instance, possess four of these loners, while dysprosium and samarium have five.
The rare earths have limits. Pure neodymium, for example, readily corrodes and fractures, and its magnetic pull begins to lose strength above 80° Celsius. So manufacturers alloy some rare earths with other metals to make more resilient magnets, says Durga Paudyal, a theoretical physicist at Ames National Laboratory in Iowa. This works well because some rare earths can orchestrate the magnetic fields of other metals, he says. Just as weighted dice will preferentially land on one side, some rare earths like neodymium and samarium exhibit stronger magnetism in certain directions because they contain unevenly filled orbitals in their 4f-subshells. This directionality, called magnetic anisotropy, can be leveraged to coordinate the fields of other metals like iron or cobalt to formulate robust, extremely powerful magnets.
Link to the full story at Science News: How rare earth elements’ hidden properties make modern technology possible