#181 Why are some metals not magnetic?

I learned this today. Some metals are nonmagnetic because the magnetic poles of the atoms within them point in different directions and are weakly repelled by both poles of the magnet.

There are different kinds of magnets. Some are permanent magnets, some are magnetized metals, and some are electromagnets. Magnetized metals are magnetic only if exposed to a magnet and then they return to normal. Electromagnets are only magnetic when they are exposed to an electric current. When the current is turned off, they return to normal. Permanent magnets are permanently magnetic. Hence the name.

Magnetism is caused by an electric charge in the metal. Electrons circle the nucleus of an atom and they generate an electric current, which makes a very small and very weak magnetic field. Some of the atoms group together to make billions of tiny magnets inside the metal. Each pairing has a north pole and a south pole. However, they are not all pointing in the same direction. When a permanent magnet is made, it is melted and then a magnetic field is applied while it cools. This aligns all of the atoms and the magnetic fields in the same directions. They always stay this way and cannot go out of alignment. This is what makes a permanent magnet permanent.

Not any metal can be made into a permanent magnet. It only works on ferromagnetic metals. These are iron, cobalt, nickel, gadolinium, neodymium, and ferromagnetic ceramics.

A magnet attracts other magnetic metals because opposites attract. The electrons in the permanent magnet are all aligned with north and south poles. The north pole has a negative charge and the south pole has a positive charge. Opposites attract so a negative charge attracts a positive and a positive charge attracts a negative charge. A metal like iron has electrons that create magnetic fields, but these electrons point in lots of different directions. When a magnet is brought close to a metal like iron, all of the poles align with the magnet. The north poles point to the south pole of the magnet and the south poles point towards the north pole of the magnet. The magnetic poles of the magnet don’t just align the poles in the iron, they also attract the electrons towards them, making the iron stick to the magnet.

Not everything is magnetic. Wood will not stick to a magnet. Wood is diamagnetic. This means that the atoms in wood are not attracted to the magnetic poles of the magnet. When the magnetic field is applied to a magnetic metal, all of the poles align with the field. When a magnetic field is applied to a nonmagnetic substance, the poles of the atoms point in different directions and end up cancelling each other out. Some point towards the magnetic and are attracted, but an equal number point away and are repelled. The net result is that wood is not attracted to a magnet.

Many metals are not magnetic and the same thing happens to them. Gold is a nonmagnetic metal and the poles flip in it to keep it neutral. A magnet can be used to test for real gold or silver. If it sticks to a magnet, it is not real, or at least not pure.

Adding a ferrous metal to a nonmagnetic metal can make them magnetic. Interestingly, stainless steel is magnetic because it contains iron. Most stainless steel has between 12.5 to 17% iron in it, which is enough to make it magnetic. However, you can prevent this by adding austenite to the stainless steel. With the ferrous metal, all of the electrons can align with the magnetic field, but austenite has a micro-crystalline structure that keeps the atoms in a random arrangement, which means there are always some aligned and some opposed to the magnetic field. It gives the same effect as wood.

So, a magnet realigns the north south pairings of atoms in a metal. It can then attract it. Some metals are not magnetic because when a magnet is brought close to them, their atom pairings point in random directions. Some are attracted to the magnet and an equal number are repelled by it, leaving the metal neutral and not magnetic. And this is what I learned today.

Photo By Eurico Zimbres FGEL/UERJ – the author is owner, CC BY-SA 2.0 br, https://commons.wikimedia.org/w/index.php?curid=333496

Sources: