in frank herbert’s space opera duneA precious natural substance called spice melange gives people the ability to sail in the vast universe to build an interstellar civilization.
In real life on Earth, a group of naturally occurring metals known as rare earths make our own technology-driven society possible. Demand for these critical components is soaring in almost all modern electronics.
Rare earths fill thousands of different needs—cerium, for example, is used as a catalyst in refining petroleum, while gadolinium captures neutrons in nuclear reactors. But the most outstanding abilities of these elements are their luminescence and magnetism.
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We rely on rare earths to color our smartphone screens, to fluoresce to signal the authenticity of euro banknotes, and to relay signals through fiber optic cables under the sea. They are also essential to making some of the strongest and most reliable magnets in the world. They generate sound waves in your headphones that augment digital information through space and alter the trajectory of heat-seeking missiles. Rare earths are also driving green technologies such as wind power and electric vehicles, and may even lead to new components for quantum computers.
“The list goes on and on,” says synthetic chemist and independent consultant Stephen Boyd. “They’re everywhere.”
Rare earths’ superpowers come from their electrons
The rare earths are the lanthanides — lutetium and all 14 elements on the periodic table between lanthanum and ytterbium — plus scandium and yttrium, which tend to occur in the same deposits and have similar chemical properties to the lanthanides. These gray to silvery metals usually have high melting and boiling points and are malleable.
Their secret power lies in their electrons. All atoms have a nucleus surrounded by electrons, which reside in regions called orbitals. The electrons in the orbitals furthest from the nucleus are valence electrons, which participate in chemical reactions and form bonds with other atoms.
Most lanthanides possess another important set of electrons, called “f electrons,” which are located in the Goldilocks region close to the valence electrons but slightly closer to the nucleus. “It’s these f electrons that determine the magnetic and luminescent properties of rare earth elements,” says Ana de Bettencourt-Dias, an inorganic chemist at the University of Nevada, Reno.
Rare earth adds color and luster
Along some shores, the night sea occasionally glows turquoise as glowing plankton crash in the waves. Rare earth metals also glow when stimulated. The trick, says de Bettencourt-Dias, is to excite their f electrons.
Using an energy source such as a laser or lamp, scientists and engineers can jolt one of the rare earth’s f electrons into an excited state and then send it back to a lethargic or ground state. “When the lanthanides return to their ground state,” she said, “they emit light.”
Each rare earth reliably emits light at a precise wavelength when excited, de Bettencourt-Dias said. This reliable precision allows engineers to carefully tune electromagnetic emissions in many electronic products. Terbium, for example, emits light at a wavelength of about 545 nanometers, making it ideal for building green phosphors in TV, computer and smartphone screens. There are two common forms of europium used to make red and blue phosphors. Together, these phosphors can paint most shades of the rainbow on your screen.
Rare earths also radiate useful invisible light. Yttrium is a key component of yttrium aluminum garnet, or YAG, a synthetic crystal that forms the heart of many high-power lasers. Engineers tune the wavelength of these lasers by combining YAG crystals with another rare earth. The most popular variety is the neodymium-doped YAG laser, which is used for everything from cutting steel to removing tattoos to laser ranging. Erbium YAG laser beams are a good choice for minimally invasive procedures because they are easily absorbed by the moisture in the flesh and therefore do not cut too deeply.
In addition to lasers, lanthanum is critical to making the infrared-absorbing glass used in night-vision goggles. “Erbium powers our internet,” says Zhong Tian, a molecular engineer at the University of Chicago. Most of our digital information travels through optical fibers in the form of light with a wavelength of about 1,550 nanometers—the same wavelength that erbium emits. Signals in fiber optic cables dim as they move away from the source. Since these cables can extend thousands of kilometers under the sea, erbium is added to the fiber to enhance the signal.
Rare earths make powerful magnets
[In1945scientistsbuilttheworld’sfirstprogrammablegeneral-purposedigitalcomputerENIAC([1945年，科學家建造了世界上第一台可編程的通用數字計算機ENIAC（SN: 2/23/46, p. 118). Nicknamed “The Giant Brain,” ENIAC weighs more than four elephants and occupies about two-thirds the size of a tennis court.
Less than 80 years later, the ubiquitous smartphone — with far more computing power than ENIAC has ever seen — fits in the palm of our hands. Society attributes this miniaturization of electronics in large part to the special magnetic power of rare earths. Tiny rare earth magnets can do the same job as larger magnets without rare earths.
It’s those f electrons that do the work. Rare earths have many electron orbitals, but the f electrons reside in a specific set of seven orbitals, called the 4f subshell. In any subshell, electrons try to spread out in the inner orbitals. Each orbital can hold up to two electrons. But since the 4f-subshell contains 7 orbitals, and most rare earth elements contain less than 14 f-electrons, these elements tend to have multiple orbitals with only one electron. For example, neodymium atoms have four such loners, while dysprosium and samarium have five. Crucially, these unpaired electrons tend to point or spin in the same direction, Boyd said. “This is what creates the north and south poles that we traditionally understand as magnetic forces.”
Because these isolated f electrons fly around behind the valence electron shell, their synchronized spins are somewhat protected from demagnetizing forces such as heat and other magnetic fields, making them ideal for building permanent magnet. Permanent magnets, such as the picture on the refrigerator door, passively generate a magnetic field generated by their atomic structure, unlike electromagnets, which require an electric current and can be turned off.
But even with their shielding, rare earths have limitations. For example, pure neodymium corrodes and fractures easily, and its magnetism begins to lose strength above 80 degrees Celsius. So manufacturers mix some rare earths with other metals to create more resilient magnets, says theoretical physicist Durga Paudyal of Ames National Laboratory in Iowa. This works because some rare earths can coordinate the magnetic fields of other metals, he said. Just as a weighted dice would preferentially fall on one side, some rare earth elements such as neodymium and samarium exhibit stronger magnetism in certain directions because their 4f-subshells contain orbitals that are not uniformly filled. This directionality, called magnetic anisotropy, can be used to coordinate the magnetic fields of other metals, such as iron or cobalt, to form strong, extremely powerful magnets.
The most powerful rare earth alloy magnets are NdFeB magnets. For example, a three kilogram neodymium magnet can lift objects weighing more than 300 kilograms. More than 95% of the permanent magnets in the world are made of this rare earth alloy. Neodymium iron boron magnets generate vibrations in smartphones, sound in earbuds and headphones, read and write data in hard drives and generate magnetic fields for MRI machines. Adding a little dysprosium to these magnets increases the alloy’s heat resistance, making it ideal for the rotors that spin inside the hot interior of many electric vehicle engines.
The samarium cobalt magnet, developed in the 1960s, was the first rare earth magnet to become popular. Although slightly weaker than NdFeB magnets, SmCo magnets have excellent heat resistance and corrosion resistance, so they are used in high-speed motors, generators, speed sensors for automobiles and aircraft, and some thermal track missiles. Samarium cobalt magnets are also at the heart of most traveling wave tubes, which boost signals from radar systems and communication satellites. Some of these pipelines are transmitting data from the Voyager 1 spacecraft — the most distant human-made object to date — at a distance of more than 23 billion kilometers (SN: 7/31/21, p. 18).
Because they are strong and reliable, rare earth magnets are supporting green technology. They are found in electric motors, drivetrains, power steering systems and many other components of electric vehicles. Tesla’s use of neodymium alloy magnets in its longest-range Model 3 car sparks supply chain concerns; China supplies most of the world’s neodymium (Serial Number: 1/11/23).
Rare earth magnets are also used in many offshore wind turbines to replace gearboxes, increasing efficiency and reducing maintenance. In August, Chinese engineers unveiled Rainbow, the world’s first maglev train line based on rare-earth magnets, which allows the train to float without consuming electricity.
In the future, rare earths may even advance quantum computing. While conventional computers use binary bits (those 1s and 0s), quantum computers use qubits, which can occupy two states at once. It turns out that crystals containing rare earth elements make good qubits, Zhong said, because the shielded f electrons can store quantum information for a long time. One day, he said, computer scientists might even use the light-emitting properties of rare earths in qubits to share information between quantum computers and give birth to a quantum internet.
It may be too early to predict exactly how rare earth metals will continue to impact the scaling of these evolving technologies. But one thing’s for sure: we’re going to need more rare earths.