Rare earths’ hidden electrons make much of modern tech possible

Nov 17, 2023

The Shanghai Transrapid is a high-speed magnetic levitation (maglev) train that travels at speeds up to 430 kilometers (270 miles) per hour. The magnets needed for such systems rely on rare-earth metals. Six railways currently offer high-speed, low-energy maglev service.

Christian Petersen-Clausen/Moment Open/Getty Images Plus

By Nikk Ogasa

May 4, 2023 at 6:30 am

The first volume of Frank Herbert's Dune series debuted back in 1965. Mining a precious natural substance called spice melange was a driving theme in that epic space saga. This spice granted people the ability to navigate vast expanses of the cosmos. It also became the basis of an intergalactic civilization. That was, of course, fiction.

Back here on Earth, in real life, a group of metallic elements has made possible our own technology-driven society. Called rare earths, these 17 elements are crucial to nearly all modern electronics. And demand for these metals has been skyrocketing.

Fifteen rare earths make up a whole row on most periodic tables. Known as lanthanides, they run from lanthanum to lutetium — atomic numbers 57 through 71. Also included in the rare earths are scandium (atomic number 21) and yttrium (atomic number 39). Those last two elements tend to occur in the same ore deposits as lanthanides. They also have similar chemical properties.

The rare earth cerium can serve as a catalyst to process crude oil into a host of useful products. Nuclear reactors rely on another: gadolinium. It captures neutrons to control the production of energy by a reactor's fuel.

But the most outstanding capabilities of rare earths are their luminescence and magnetism. For instance, we rely on rare earths to color our smartphone screens. They fluoresce to signal that euro banknotes are the real deal. They relay signals through fiber-optic cables along the seafloor. They also help build some of the world's strongest, most reliable magnets. These metals generate sound waves in your headphones and boost digital data through space.

More recently, rare earths have been driving the growth of green technologies, such as wind power and electric vehicles. They may even give rise to new parts used in quantum computers.

"They’re everywhere," says Stephen Boyd of these metals. He's a synthetic chemist and independent consultant based in Dixon, Calif. When it comes to the uses of rare earths, he says, "The list just goes on and on."

Rare earths tend to be malleable (easy to deform). These metals also have high melting and boiling points. But their secret power lies in their electrons.

All atoms have a nucleus surrounded by electrons. Those tiny electrons inhabit zones called orbitals. Electrons in the orbitals farthest from the nucleus are known as valence electrons. They take part in chemical reactions and form bonds that link atoms together.

Most lanthanides possess another important set of electrons. These "f-electrons" dwell in a Goldilocks zone. It's located near the valence electrons but slightly closer to the nucleus. "It's these f-electrons that are responsible for both the magnetic and luminescent properties of the rare-earth elements," says Ana de Bettencourt-Dias. She's an inorganic chemist at the University of Nevada, Reno.

When stimulated, rare-earth metals radiate light. The trick is to tickle their f-electrons, says de Bettencourt-Dias. An energy source such as a laser beam can jolt one f-electron in a rare earth element. The energy boosts the electron into an excited state. Later, it will drop back to its starting — or ground — state. As they do, these f-electrons emit light.

The group of 17 elements (highlighted in blue on this periodic table) are known as rare earths. A subset of them, known as the lanthanides — lutetium, Lu, plus the row starting with lanthanum, La — appear in a single row. Rare-earth elements have a subshell of electrons (called f-electrons) that give these metals magnetic and luminescent properties.

After being excited, each rare earth reliably emits precise wavelengths (colors) of light, de Bettencourt-Dias notes. This allows engineers to carefully tune the electromagnetic radiation (light) in many electronics. Terbium, for instance, emits light at a wavelength of about 545 nanometers. That makes it good for creating green-glowing phosphors in the screens used in TVs, computers and smartphones. Europium, which has two common forms, is used to make red and blue phosphors. Such phosphors can paint screens with most shades of the rainbow.

Rare earths also radiate useful invisible light. Yttrium is a key ingredient in yttrium-aluminum-garnet, or YAG, crystals. They form the core of many high-powered lasers. Engineers tune the wavelengths of these lasers by lacing YAG crystals with another rare earth. The most popular: a neodymium-laced YAG laser. These are used for a broad range of things — from slicing steel and removing tattoos to laser range-finding. And erbium-YAG laser beams are a good option for certain surgeries. They won't slice too deeply because their light is readily absorbed by the water in our tissues.

Beyond lasers, lanthanum is crucial for making the infrared-absorbing glass in night-vision goggles. "And erbium drives our internet," says Tian Zhong. He's a molecular engineer at the University of Chicago in Illinois. Much of our digital data travels through optical fibers as light. It typically has a wavelength of about 1,550 nanometers — the same as erbium emits. The signals in fiber-optic cables dim as they travel far from their source. Because those cables can stretch for thousands of kilometers across the seafloor, erbium is added to fibers to boost their signals.

In 1945, scientists constructed the world's first programmable, general-purpose digital computer. Its formal name was ENIAC. But scientists quickly nicknamed it the "Giant Brain." And that was apt. It weighed more than four elephants and covered an area roughly two-thirds the size of a tennis court.

Less than 80 years later, our smartphones boast far more computing power than ENIAC ever had. Society owes this shrinking of electronic technology in large part to the exceptional magnetic power of rare earths. And those f-electrons are the reason why.

Rare earths have many orbitals of electrons, but the f-electrons inhabit a specific group — or subshell — of seven orbitals. Each orbital can house up to two electrons. But most rare earths contain multiple orbitals in this subshell with just one electron.

Neodymium atoms, for instance, possess four of these loners. Dysprosium and samarium are two rare earths with five loner electrons. Crucially, those unpaired electrons tend to point — or spin — in the same direction, Boyd says. "That's what creates the north and the south poles that we classically understand as magnetism."

These lone f-electrons flitter behind a shell of valence electrons. That somewhat shields their synchronized spins from heat and other demagnetizing forces. And that makes these metals great for building permanent magnets, Zhong says.

The magnetic fields in permanent magnets, like the ones that hold up pictures on a fridge door, arise from the magnets’ atomic structure. (Electromagnets, in contrast, need an electric current. Turn it off and the magnetism turns off, too.)

But even with their shielding, rare-earth magnets have limits. Pure neodymium, for example, readily corrodes and fractures. Its magnetic pull also starts to lose strength above 80° Celsius (176° Fahrenheit). So manufacturers often make alloys of rare earths with some other metals. This makes those magnets more resilient than if they had been made from rare earths alone, says Durga Paudyal. He's a theoretical physicist at Ames National Laboratory in Iowa.

This alloy approach works well, he adds, because some rare earths can orchestrate the magnetic fields of other metals. Just as weighted dice will preferentially land on one side, some rare earths — such as neodymium and samarium — exhibit stronger magnetism in certain directions. It's because the orbitals in their 4f-subshells are unevenly filled. This directionality can be used to coordinate the fields in other metals, such as iron or cobalt. The result: robust, extremely powerful magnets.

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The most powerful alloy magnets are NIBs — a mix of neodymium, iron and boron. A 3-kilogram (6.6-pound) NIB magnet can lift objects more than 100 times its weight. More than 95 percent of the world's permanent magnets are made from this rare-earth alloy. These are the magnets that generate vibrations in smartphones and produce sounds in earbuds and headphones. They enable the reading and writing of data on hard-disk drives. They also create the magnetic fields used in MRI machines.

Adding a bit of dysprosium to these magnets can boost their heat resistance. Now they become a good choice for the rotors that spin in the hot interiors of the motors driving many electric vehicles.

Developed in the 1960s, a samarium-cobalt alloy went into the first popular rare-earth magnets. Though slightly weaker than NIB magnets, samarium-cobalt ones have superior resistance to heat and corrosion. That makes them great for use in high-speed motors, generators, speed sensors in cars and airplanes — and in the moving parts of some heat-seeking missiles. Samarium-cobalt magnets also form the heart of the devices used to boost signals emitted by most radar systems and communications satellites. Some of these rare-earth-based signal boosters are transmitting data from the Voyager 1 spacecraft. Launched in September 1977, that craft is the most distant human-made object — already more than 23 billion kilometers (14 billion miles) away.

Strong and reliable, rare-earth magnets are at the heart of many green technologies, too. They’re in the motors, drivetrains, power steering and many other parts used in electric cars. Tesla's use of neodymium-alloy magnets in its farthest-ranging Model 3 cars has sparked worries that magnet-makers may soon find it hard to get enough neodymium (which is mined largely in China).

Rare-earth magnets also replace gearboxes in many offshore wind turbines. They help boost the turbines’ efficiency and cut their need for servicing. And in August, Chinese engineers introduced "Rainbow." It's the world's first magnetically levitated train line to rely on rare earths. Its magnets enable the trains to float above their tracks without consuming electricity.

Rare earths may even soon advance quantum computing. Conventional computers store and record data as binary bits — 0s and 1s. Quantum computers instead use quantum bits. Also called qubits, they can occupy two data states at once. Crystals containing rare earths make good qubits, Zhong says, because their shielded f-electrons can store quantum data for long periods of time. One day, scientists might even manipulate the light-emitting properties of rare-earth qubits to share information between quantum computers. It could give birth to a quantum internet, Zhong says.

It's too early to predict exactly how rare-earth metals will boost the expansion of all these emerging technologies. But it's probably safe to say: Rare earths better not be too rare, because we’re going to need a lot of them.

alloy: A blend of a metal and one or more elements (metallic or non-metallic) in which the individual elements are thoroughly mixed at a microscopic level.

atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

atomic number: The number of protons in an atomic nucleus, which determines the type of atom and how it behaves.

banknote: A term for the foldable paper currency (some nations may now use plastic). Banknotes — sometimes called bills, as in a "20-dollar bill" — come in different denominations, and may vary by color or size. U.S. banknotes are often called "greenbacks" due to their predominantly green color.

binary: Something having two integral parts. (in mathematics and computer science) A number system where values are represented using two symbols 1 (on) or 0 (off).

bit: (in computer science) The term is short for binary digit. It has a value of either 0 or 1.

bond: (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It's formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

boron: The chemical element having the atomic number 5. Its scientific symbol is B.

catalyst: (v. catalyze) A substance that helps a chemical reaction to proceed faster. Examples include enzymes and elements such as platinum and iridium.

chemical reaction: A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).

consultant: Someone who performs work as an outside expert, usually for a company or industry. "Independent" consultants often work alone, as individuals who sign a contract to share their expert advice or analytical skills for a short time with a company or other organization.

core: Something — usually round-shaped — in the center of an object.

corrode: (n. corrosion) A chemical process that weakens or destroys normally robust materials, such as metals or rock.

cosmos: (adj. cosmic) A term that refers to the universe and everything within it.

crude oil: Petroleum in the form as it comes out of the ground.

digital: (in computer science and engineering) An adjective indicating that something has been developed numerically on a computer or on some other electronic device, based on a binary system (where all numbers are displayed using a series of only zeros and ones).

electric current: A flow of electric charge — electricity — usually from the movement of negatively charged particles, called electrons.

electricity: A flow of charge, usually from the movement of negatively charged particles, called electrons.

electromagnetic radiation: Energy that travels as a wave, including forms of light. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light.

electron: A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.

electronics: Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

element: A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

engineer: A person who uses science and math to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

europium: A rare chemical element that appears as a silver metal when it is pure. It is found in some minerals, and can be used to trace the source of mineral grains carried long distances by water or wind.

f-electrons: These are the electrons (up to 14) that may live in the shell of larger atoms. There are seven orbitals in this "f" shell. Each of those orbitals is able to host up to two electrons.

fiber: Something whose shape resembles a thread or filament.

fiction: (adj. fictional) An idea or a story that is made-up, not a depiction of real events.

field: (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field), mass (by a Higgs field) or electricity (by an electrical field).

fluoresce: (adj. fluorescent) The process of absorbing light of one wavelength (color) and reemitting as a different wavelength. That reemitted light is known as fluorescence.

force: Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

fracture: (noun) A break. (verb) To break something and induce cracks or a splitting apart of something.

generator: A device used to convert mechanical energy into electrical energy.

Goldilocks zone: A term that scientists may use to describe some narrow range within a continuum that is "just right" for something to happen.

green: (in chemistry and environmental science) An adjective to describe products and processes that will pose little or no harm to living things or the environment.

host: (v.) The act of providing a home or environment for something. A website, for instance, could host photos, news or other types of information.

intergalactic: An adjective that describes some position between galaxies.

internet: An electronic communications network. It allows computers anywhere in the world to link into other networks to find information, download files and share data (including pictures).

iron: A metallic element that is common within minerals in Earth's crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

lanthanides: A series of 15 metals, all of them radioactive —and therefore toxic. They tend to be shown below the top seven rows on a conventional periodic table of the elements. They have atomic numbers running from 57 (lanthanum) to 71 (lutetium). Actinides were first isolated from gadolinite, a mineral found in Ytterby, Sweden, in 1787. That city's name gave rise to the name ytterbium (atomic number 70), for one of the elements eventually isolated from gadolinite. Like actinides, the lanthanide elements are known as rare-earth metals.

laser: A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.

luminescence: The glow produced by a chemical process at relatively low temperatures. Some animals are able to luminesce, based on chemical reactions inside their bodies.

magnet: A material that usually contains iron and whose atoms are arranged so they attract certain metals.

magnetic field: An area of influence created by certain materials, called magnets, or by the movement of electric charges.

magnetism: The attractive influence, or force, created by certain materials, called magnets, or by the movement of electric charges.

malleable: Something whose shape can be altered, usually by hammering or otherwise deforming with pressure. (in social science) Attitudes or behaviors that can be changed with social pressure or logic.

metal: Something that conducts electricity well, tends to be shiny (reflective) and is malleable (meaning it can be reshaped with heat and not too much force or pressure).

model: A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

motor: A device that converts electricity into mechanical motion. (in biology) A term referring to movement.

MRI: Short for magnetic resonance imaging. It's an imaging technique to visualize soft, internal organs, like the brain, muscles, heart and cancerous tumors. MRI uses strong magnetic fields to record the activity of individual atoms.

nanometer: A billionth of a meter. It's such a small unit that researchers use it as a yardstick for measuring wavelengths of light or distances within molecules. For perspective, an average human hair is about 60,000 nanometers wide.

navigate: To find one's way through a landscape using visual cues, sensory information (like scents), magnetic information (like an internal compass) or other techniques.

neodymium: A chemical element which appears as a soft, silvery metal when it is pure. It is found in some minerals and can be used to trace the source of mineral grains carried long distances by water or wind. Its scientific symbol is Nd.

neutron: A subatomic particle carrying no electric charge that is one of the basic pieces of matter. Neutrons belong to the family of particles known as hadrons.

nucleus: Plural is nuclei. (in biology) A dense structure present in many cells. Typically a single rounded structure encased within a membrane, the nucleus contains genetic information. (in astronomy) The rocky body of a comet, sometimes carrying a jacket of ice or frozen gases. (in physics) The central core of an atom, containing most of its mass.

optical fiber: A long strand of glass or some other fiber used to transmit light signals (such as those used to send telephone, television and other communications signals).

orbital: Adjective for something relating to orbits. (in chemistry and subatomic physics) The pattern(s) of electrons (and their density) that form(s) within an atom or molecule.

ore: A naturally formed rock or mineral that contains a metal that can be extracted for some new use.

phosphor: A synthetic chemical that glows when excited by electrons. It typically is used (often in combination with others) to coat LEDs, fluorescent lamps or cathode-ray tubes to produce a desired color of light.

physicist: A scientist who studies the nature and properties of matter and energy.

poles: (in physics and electrical engineering) The ends of a magnet.

programmable: A device or system that contains a computer, which allows the functions to change in a prescribed way, usually as determined by the user or manufacturer.

quantum: (pl. quanta) A term that refers to the smallest amount of anything, especially of energy or subatomic mass.

radar: A system for calculating the position, distance or other important characteristic of a distant object. It works by sending out periodic radio waves that bounce off of the object and then measuring how long it takes that bounced signal to return. Radar can detect moving objects, like airplanes. It also can be used to map the shape of land — even land covered by ice.

radiate: (in physics) To emit energy in the form of waves. (n. radiation)

range: The full extent or distribution of something. For instance, a plant or animal's range is the area over which it naturally exists.

rare earths: (in Earth science) These are a group of metal elements that tend to be soft, bendable and chemically reactive.

resilient: (n. resilience) To be able to recover fairly quickly from obstacles or difficult conditions. (in materials) The ability of something to spring back or recover to its original shape after bending or otherwise contorting the material.

resistance: (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

satellite: A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.

sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

shell: (in physics) The orbital paths that electrons take around the nucleus of an atom.

smartphone: A cell (or mobile) phone that can perform a host of functions, including search for information on the internet.

society: An integrated group of people or animals that generally cooperate and support one another for the greater good of them all.

sound wave: A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

synthetic: An adjective that describes something that did not arise naturally, but was instead created by people. Many synthetic materials have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have a chemical makeup and structure identical to the original.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body's circulatory system. Similarly, trains, platforms, tracks, roadway signals and overpasses are among the potential components of a nation's railway system. System can even be applied to the processes or ideas that are part of some method or ordered set of procedures for getting a task done.

technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

theoretical: An adjective for an analysis or assessment of something that based on pre-existing knowledge of how things behave. It is not based on experimental trials. Theoretical research tends to use math — usually performed by computers — to predict how or what will occur for some specified series of conditions. Experimental testing or observations of natural systems will then be needed to confirm what had been predicted.

tissue: Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

valence: (in chemistry and physics) The electrons of an atom that are involved in chemical bonding. Valence electrons usually are the outermost electrons (those orbiting farthest from the nucleus).

visible light: A type of electromagnetic radiation with wavelengths that range between 380 nanometers (violet) and 740 nanometers (red). Visible light has wavelengths that are shorter than infrared light, microwaves, and radio waves but longer than ultraviolet light, X-rays and gamma rays.

wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It's also one of the "yardsticks" used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

wind turbine: A wind-powered device — similar to the type used to mill grain (windmills) long ago — used to generate electricity.

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Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News. He has a master's degree in geology from McGill University, and a master's degree in science communication from the University of California, Santa Cruz.

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