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Try picking up coins, paperclips, cutlery and jewellery with a fridge magnet and you’ll find that very few metals stick. Only three elements are strongly magnetic at room temperature — iron, cobalt and nickel — with gadolinium joining them on a cool day. Everything else is either weakly attracted, weakly repelled, or unaffected in any way you’d notice.
Three kinds of magnetism
All matter responds to magnetic fields in some way. There are three main types of response.
Ferromagnetism — strongly attracted, can be permanently magnetized
- Iron, cobalt, nickel (and gadolinium below about 20 °C).
- This is what people usually mean by “magnetic”.
Paramagnetism — weakly attracted, only while in a field
- Aluminium, platinum, oxygen gas, and many transition metal compounds.
- Caused by unpaired electrons. Liquid oxygen, poured between the poles of a strong magnet, hangs there — a striking demonstration.
Diamagnetism — weakly repelled
- Copper, silver, gold, bismuth, water, carbon (graphite).
- All materials have some diamagnetism, but it’s usually swamped by other effects. It’s very weak, though strong magnets can levitate diamagnetic objects — even, famously, a living frog.
What makes a material ferromagnetic?
It starts with the electrons. Each electron behaves like a tiny magnet because of its spin. In most atoms, electrons pair up with opposite spins and their magnetism cancels. Atoms with unpaired electrons have a net magnetic moment — that’s why iron, with four unpaired 3d electrons in a free atom, can be magnetic.
But unpaired electrons alone only give paramagnetism. Ferromagnetism needs something extra: a quantum mechanical effect called exchange interaction that makes neighbouring atoms’ magnetic moments line up in the same direction. In iron, cobalt and nickel, the atoms are just the right distance apart for this to happen.
The aligned regions are called magnetic domains. In an unmagnetized piece of iron, the domains point in random directions and cancel out. Put it in a magnetic field and the domains aligned with the field grow — the iron becomes a magnet. In “hard” magnetic materials, the domains stay aligned when the field is removed, giving a permanent magnet.
The Curie temperature
Heat a ferromagnet enough and thermal vibrations scramble the aligned domains. Above its Curie temperature, it becomes merely paramagnetic.
| Element | Curie temperature |
|---|---|
| Cobalt | ~1,115 °C |
| Iron | ~770 °C |
| Nickel | ~358 °C |
| Gadolinium | ~20 °C |
The name honours Pierre Curie, who studied the effect in the 1890s. Gadolinium’s Curie point is so close to room temperature that it’s ferromagnetic in a cold room and not in a warm one — which makes it useful in research on magnetic refrigeration.
Several other rare earths — terbium, dysprosium, holmium and erbium — are ferromagnetic too, but only well below room temperature.
Why the strongest magnets use rare earths
The most powerful permanent magnets are alloys:
- Neodymium magnets (Nd₂Fe₁₄B): the strongest commercial permanent magnets, in electric car motors, wind turbines, headphones and hard drives.
- Samarium–cobalt magnets: slightly weaker, but keep their magnetism at higher temperatures.
- Alnico (aluminium–nickel–cobalt) and ferrites (iron oxides with barium or strontium): cheaper, used in fridge magnets and loudspeakers.
Rare earth atoms contribute large magnetic moments from their 4f electrons, and the alloy’s crystal structure holds the magnetization firmly in one direction. See rare earth elements.
Everyday puzzles explained
- Stainless steel sometimes isn’t magnetic. The most common kitchen stainless steels (austenitic grades like 304) have a crystal structure that isn’t ferromagnetic, even though they’re mostly iron. Other grades (ferritic, martensitic) are magnetic.
- Coins vary. Many coins are steel plated with copper or nickel and stick to magnets; others are copper alloys and don’t.
- Magnetite, Fe₃O₄, is a naturally magnetic mineral — lodestone — used in the earliest compasses. It’s actually ferrimagnetic, a close cousin of ferromagnetism.
Quick answers
Which elements are magnetic? Iron, cobalt and nickel at room temperature; gadolinium below about 20 °C.
Is gold magnetic? No — gold is weakly diamagnetic. A “gold” item that sticks to a magnet contains another metal.
Is aluminium magnetic? Only very weakly (paramagnetic). It won’t stick to a fridge magnet.
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