How do magnets magnetise other objects?


The other day I had a metal spelk in my finger, and couldn’t grab it with my tweezers so had to attach a magnet to it them to pull the spelk out.

The atoms in magnets are angled in the same direction which is what gives it the magnet the magnetic effect, but how does this make other metals magnetic without changing the atomic structure of the metals and why does it only work on some metals and not all?

In: Physics

Some metals have the ability to re-orient at the level of the atom (or magnetic domain) without screwing up or being restricted by the lattice/crystal structure of the material. The physics just says that getting “magnetized” is possible. The atoms can stay bonded to each other even when the magnetic field forces the atoms into a higher energy state.

Making something into a magnet is about alignment of the areas, as you already described.

Transition metals have incomplete d orbitals and each orbital can fit 2 electrons of opposite spin (think of it as an arrow pointing up or down). As a result, the alignment of the electrons determines whether a metal is:

– ferromagnetic (always magnetic, always aligned)

– diamagnetic (all paired, only opposing magnets) or

– paramagnetic (has unpaired electrons which align under a magnet but not otherwise).

Some other variations exist, antiferromagnetism for example. Again, under the influence of a magnetic field, the electrons will align (spin direction).

Magnetism is quite weird and complicated. Magnetic force itself is directly connected to relativity which is where complicated and unintuitive physics starts appearing. Also to explain magnets you need quantum mechanics which is another branch with it’s own level of weirdness.

The basic rule for magnetism is that magnetic field is created by moving charged particles and this magnetic field will affect the movement of other charged particles.

For magnet to exist there has to some charged particle moving in it. In atoms electrons do a sort of “quantum motion” called spin. Spin can either be up or down. And spin up produces magnetic field that is the opposite of spin down so they cancel each other. In atom majority of electrons form pairs of spin up and spin down electron so there is no magnetic field. However some materials have electrons without pair that create some net magnetic field.

However even if you have this small magnetic field created by one atom, objects are made out of billions of billions of atoms. Since those unpaired electrons dont have a preference for spin up and spin down what will happen is that half of atoms will have spin up and another half spin up and so you are without magnet again.

When those atoms get close to a magnetic field there are few options that can happen. They can either allign and spin against the magnetic field. This is called diamagnetism and diamagnetic materials are reppeled by magnets and also weaken magnetic fields going through them. A good example of those materials is copper.

Alternatively those electrons can allign with the magnetic field and strenghten it. This is called paramagnetism and paramagnetic materials are attracted to magnets (weakly) and also strenghten magnetic field going through it.

However for most materials after they leave the magnetic field the electrons will unalign and they will no longer create magnetic field. But there exist few materials that are called ferromagnetic that have the right electron structure that when once electrons in them are alligned those electrons inside the atom and atoms around it are strong enough to remain alligned and thus they create a permanent magnet.