Most everyday materials fall into one of three magnetic categories: ferromagnetic materials that strongly attract magnets, paramagnetic materials that respond only weakly, and diamagnetic materials that are slightly repelled. The materials you probably think of as “magnetic” are ferromagnetic, and only three pure elements at room temperature qualify: iron, nickel, and cobalt. But the full picture is more interesting than that.
Ferromagnetic Materials: The Strong Ones
Ferromagnetic materials are what most people mean when they say something is “magnetic.” These are materials that can be permanently magnetized and will stick to a magnet on your fridge. Iron, nickel, and cobalt are the three common ferromagnetic elements, and they share a key trait: their atoms contain unpaired electrons whose tiny magnetic fields spontaneously line up in the same direction within regions called domains. When enough domains point the same way, the material produces a strong magnetic field of its own, even without an external magnet nearby.
The internal forces that keep these atomic magnets aligned are extraordinarily powerful, equivalent to a field roughly a million times stronger than Earth’s magnetic field. That’s why a chunk of iron can hold its magnetism for years.
Most “magnetic” objects you encounter aren’t pure elements, though. They’re alloys. Steel (iron plus carbon) is ferromagnetic. So are Alnico magnets (aluminum, nickel, and cobalt) and the ceramic magnets found in refrigerator magnets. These engineered mixtures let manufacturers tune magnetic strength, durability, and heat resistance for specific jobs.
Rare Earth Magnets: The Strongest Available
The most powerful permanent magnets in common use are rare earth magnets, which come in two main types. Neodymium magnets are an alloy of neodymium, iron, and boron. Samarium-cobalt magnets combine samarium with cobalt and sometimes copper or zirconium. Both produce magnetic fields exceeding 1.2 tesla, more than double the strength of standard ceramic magnets, which top out around 0.5 to 1 tesla.
Neodymium magnets are the stronger and cheaper of the two, which is why they show up in headphones, hard drives, electric vehicle motors, and wind turbines. Samarium-cobalt magnets tolerate much higher temperatures (operating above 700°C compared to around 310–400°C for neodymium), making them the better choice for aerospace and military applications where heat is a factor.
Paramagnetic Materials: Weakly Attracted
Paramagnetic materials are drawn toward a magnet, but so weakly that you’d never notice in daily life. Their atoms have built-in magnetic moments from unpaired electrons, but unlike ferromagnetic materials, those moments point in random directions and don’t spontaneously align. Place a paramagnetic material in a magnetic field and the atomic magnets partially rotate toward the field, creating a faint attraction. Remove the field and the alignment vanishes instantly.
Common paramagnetic materials include aluminum, platinum, and most transition metals. Oxygen gas is paramagnetic too, which is why liquid oxygen can be visibly attracted to a strong magnet in lab demonstrations. The alkali metals (lithium, sodium, potassium) and alkaline earth metals (magnesium, calcium) are also paramagnetic.
Diamagnetic Materials: Slightly Repelled
Every material is at least a little diamagnetic. When you place any substance in a magnetic field, its electrons adjust their orbits slightly, creating a tiny opposing field. In most materials this effect is completely overpowered by stronger magnetic behaviors. But in materials with no unpaired electrons at all, diamagnetism is the only game in town, and the result is a very slight repulsion from magnets.
The list of diamagnetic materials is long: water, table salt, diamond, graphite, copper, silver, gold, lead, zinc, and nitrogen gas. Copper and silver are often assumed to be magnetic because they’re metals, but they have no unpaired electrons available to create a net magnetic moment. Copper’s diamagnetic response is so faint it takes an enormously powerful magnet to detect it at all.
Diamagnetism does have one dramatic party trick. With a strong enough magnet, you can levitate diamagnetic objects. Researchers have famously levitated water droplets, strawberries, and even a live frog using powerful electromagnets, all because water is diamagnetic.
Ferrimagnetic and Antiferromagnetic Materials
These two categories sit between ferromagnetic and non-magnetic, and they matter most in geology and electronics. In an antiferromagnetic material, neighboring atoms have magnetic moments that point in exactly opposite directions, canceling each other out. Hematite, the reddish iron oxide mineral found all over Earth (and on Mars), is the classic example. Its iron atoms alternate in nearly opposite magnetic orientations, but a tiny angular offset of about 0.065 degrees from perfect cancellation gives it a weak residual magnetism.
Ferrimagnetic materials are similar, but the opposing magnetic moments are unequal in strength, leaving a meaningful net magnetism. Magnetite, the most naturally magnetic mineral on Earth, is ferrimagnetic. So are the ceramic ferrite magnets used in speakers, electric motors, and the magnetic strips on credit cards. Ferrimagnetic materials behave a lot like ferromagnetic ones in practice, which is why the distinction rarely comes up outside of physics courses.
When Magnetic Materials Stop Being Magnetic
Every ferromagnetic material has a temperature threshold, called the Curie temperature, above which it loses its permanent magnetism. Heat disrupts the aligned domains, and the material becomes merely paramagnetic. For iron, this happens at about 770°C (1,043 K). Cobalt holds out the longest at roughly 1,121°C (1,394 K). Nickel gives up earliest at around 358°C (631 K).
This is why magnets can be damaged by heat. A neodymium magnet left on a hot engine or exposed to temperatures above 310°C will permanently lose its strength. Samarium-cobalt magnets survive to about 720–800°C, which is one reason they cost more.
Magnetic Liquids and Gases
Liquids and gases aren’t usually thought of as magnetic, but both can be. Liquid oxygen is paramagnetic and visibly responds to strong magnets. Ferrofluids, the spiky black liquids you may have seen in science videos, are engineered to be strongly magnetic. They’re colloidal suspensions of iron oxide nanoparticles, typically around 10 nanometers in diameter, suspended in a carrier liquid like water or kerosene oil. A surfactant coating on each particle prevents them from clumping together.
The nanoparticles are so small (20 nanometers or less) that they’re superparamagnetic: they respond strongly to an external magnetic field but don’t retain magnetism once the field is removed. When you bring a magnet close, the particles orient into chain-like structures, and the fluid surface erupts into the distinctive pattern of peaks and valleys known as the Rosensweig instability. Ferrofluids are used in speaker cooling systems, hard drive seals, and increasingly in biomedical applications where water-based versions can be safely introduced into the body.
Soft Versus Hard Magnetic Materials
Engineers split ferromagnetic materials into two practical categories based on how easily they can be magnetized and demagnetized. Soft magnetic materials, like silicon steel and pure iron, magnetize easily but also lose their magnetism quickly when the external field disappears. Their coercivity (the resistance to demagnetization) is extremely low, on the order of Earth’s magnetic field or less. This makes them ideal for transformer cores and electric motor components, where the magnetic field needs to switch direction many times per second.
Hard magnetic materials resist demagnetization. Alnico alloys, ceramic ferrites, and rare earth magnets are all hard magnetic materials. Once magnetized, they stay that way, which is exactly what you want in a permanent magnet for a refrigerator door, a magnetic latch, or a generator. The tradeoff is that hard magnets require more energy to magnetize in the first place.