A Magnet Carries a Field
Every magnet is surrounded by an invisible region of force called a magnetic field. You cannot see it, but you can feel it any time you try to push two magnets together the wrong way around. That field stretches out for a short distance around the magnet, and anything sensitive to it will respond when it enters that zone.
What Makes a Metal Magnetic
Only certain metals respond. The most familiar ones are iron, nickel, and cobalt. What sets them apart is a property called ferromagnetism. Inside these metals, very small regions called domains behave like tiny magnets of their own, each with its own north and south. They form naturally because of how the atoms inside the metal are arranged.
Normally, the Domains Cancel Out
In a piece of plain iron sitting on a table, those tiny domains point in lots of different directions. Some lean north, some lean south, some sideways. The result is that their magnetic effects cancel each other out, and the iron, as a whole, does not act like a magnet. You can hold a piece of iron in your hand and feel no pull at all from it. The magnetism is there in the material, but it is jumbled up.
What Changes Near a Real Magnet
When you bring a strong magnet close, its field reaches into the metal and pulls those scrambled little domains into alignment. Suddenly most of them are pointing the same way. The piece of iron becomes, briefly, a magnet itself, with its own north and south end. That induced magnetism is what gets attracted to the magnet you are holding — and that is why a fridge magnet "sticks" so confidently to a steel pan.
Why Some Metals Are Indifferent
Most metals are not ferromagnetic. Gold, silver, copper, and aluminium do not have those tiny aligned domains inside them, so a magnetic field cannot produce the same response. A magnet will not stick to them, no matter how strong it is at the kind of strength you find around the house. This is also a quiet, useful test: if a metal does not respond to a magnet at all, it is almost certainly not made of iron or steel. The pull, or the lack of one, is a window into what is hiding inside the material itself.
Source
This article was written using information from Wikipedia.