Magnets can be created by running currents through wires, finding a suitable material
that naturally has all the magnetic fields of its atoms aligned, or forcing the magnetic
fields of atoms to align.
But there's one more kind of magnetism that all materials exhibit, even those whose constituent
atoms aren't magnetic - though it's so weak that the other kinds of magnetism often overwhelm
it.
Basically, an external magnetic field causes the electrons around atoms in a material to
change course, and their new motion generates an opposing magnetic field.
This field is pretty weak, but it does cause the material to be repulsed from the magnet
a little bit - for example, if you hang a wooden toothpick in a magnetic field, the
ends will repel the field and it will end up aligning across the magnetic field.
This is a convenient way to remember the name of this kind of magnetism - diamagnetism - since
"dia" means across, like the "diameter" measured across a circle.
Diamagnetic materials will repel a magnet, and a diamagnetic "compass" will point across
the magnetic field - that is, it will orient east/west.
As weak as it is, diamagnetism is pretty darn awesome because it's a repulsive effect: any
diamagnetic material will levitate in a strong enough magnetic field!
Like this chunk of graphene, or, since water is diamagnetic, this frog.
In principle, humans could also be levitated this way, though the magnetic fields required
would be enormous.
There are also a lot of subtleties we've skated over, like the fact that nitrogen is diamagnetic
even though as an atom it has unpaired electrons - one might think that it *should* be at the
very least paramagnetic.
But nitrogen atoms bond to form N2 molecules which have full outer electron shells and
are thus only diamagnetic.
On the other hand, molecular O2, as we've seen, still has unpaired electrons, and it's
paramagnetic.
You've probably also seen how superconductors can levitate in a magnetic field, which is
a kind of perfect diamagnetism - not only do the currents in a superconductor create
opposing magnetic fields, they expel magnetic fields from the material entirely.
But the root cause is very very different, and that's a journey for another day.