Where magnetism comes from
We tend to think of magnets as special objects — the thing on the fridge, the strip on a credit card. But magnetism actually begins much deeper, inside every single atom. The key idea is simple: a moving electric charge makes a magnetic field. An electron is a tiny bundle of electric charge, and inside an atom it is never sitting still. So each atom ends up acting like an unimaginably small bar magnet, with a north end and a south end.
We call that little atomic bar magnet the magnetic moment. The word moment here has nothing to do with time — it is an old physics word for "turning strength," the same way a long wrench gives you more turning strength on a bolt. A magnetic moment is a measure of how strongly something twists to line up with a magnetic field, and which way it points. You can picture it as a tiny arrow attached to the atom, like the needle of a compass.
Two things inside the atom build this moment. First, electrons orbit the nucleus, and a charge going around in a loop is exactly a little current — and a current loop is a magnet. Second, and more importantly, each electron has its own built-in property called spin, which behaves as if the electron were a spinning charged ball making its own field. You don't have to picture the spin literally; just treat it as a permanent, tiny magnet that every electron carries.
Diamagnetism: the gentle push-away
Now bring an external magnet near a material. Even an atom with no net moment of its own reacts a little. When you switch on a field, the orbiting electrons subtly adjust their motion to oppose the change — they conjure up a faint field of their own pointing the *other* way. The result is diamagnetism: the material is feebly repelled by a magnet. It is the universe's default; every material does it, though usually the effect is buried under stronger ones.
It is a tiny effect, but real. Water, wood, plastic, copper, and your own body are all diamagnetic. With a strong enough magnet you really can levitate a drop of water or a small frog — the gentle push-away, multiplied by a powerful field, becomes enough to fight gravity. Think of diamagnetism as nature's reflex: poke matter with a field, and it flinches back.
Paramagnetism: a crowd of compasses with no leader
Materials whose atoms *do* keep some unpaired electrons carry a real magnetic moment on every atom. With no field around, these tiny compasses point every which way, randomized by heat — the endless jiggling we call thermal motion. Their arrows cancel on average, so the lump shows no magnetism overall. But switch on an external field, and each little compass tries to swing into line with it.
This is paramagnetism: the material is weakly attracted to a magnet, the opposite sign from diamagnetism. But it is a tug-of-war. The field pulls the compasses into line; heat knocks them back out of line. So the alignment is always partial and frail, and the moment you remove the field the compasses scatter again. There is no memory here — paramagnets do not stay magnetized.
There is even a quieter cousin worth a passing nod. In metals, the sea of freely roaming electrons gives a faint, temperature-steady attraction called Pauli paramagnetism. You don't need its details now — just know that metals add their own small flavour of magnetism from their mobile electrons, on top of whatever their atoms do.
Susceptibility: a number for "how magnetic?"
Physicists like a single number that answers "if I apply a field, how strongly does this stuff respond?" That number is the magnetic susceptibility. It compares how much magnetism you get out to how much field you put in. The sign of the number tells you the whole story at a glance.
- A negative susceptibility means the material pushes back against the field — that is diamagnetism. The number is tiny.
- A small positive susceptibility means the material is gently pulled into the field — that is paramagnetism.
- A huge positive susceptibility hints that something far stronger is going on — the cooperative magnetism we meet in the next guide.
Measuring how susceptibility changes with temperature is one of the first things a scientist does with a new material. As we saw, heat fights alignment, so for a simple paramagnet the susceptibility falls steadily as you warm it up. That clean trend is so dependable it has a name and a tidy rule, which sets up our next story beautifully.
Why this matters
Most of the world is only feebly magnetic. The strong magnets we actually use are rare and special, and to understand *them* we first had to understand the gentle background everything else lives in. Diamagnetism and paramagnetism are that background: a quiet conversation between fields, spinning electrons, and heat. Everything dramatic in the guides ahead is built on these same three players.
Here is the thread to carry forward. In a paramagnet the atomic compasses ignore one another — each only answers to the outside field. The dramatic magnets of the next guides arise when the compasses stop ignoring each other and start *talking*: when one atom's moment can feel and influence its neighbour's. The moment that conversation begins, gentle magnetism turns into something that can stick to a fridge.