What is magnetism?

 

Magnets. Cool playthings. They attract other magnetic substances. Two magnets repel when their like poles face each other, attract when their unlike poles are brought together. We all know the basics. We also know that they are used in innumerable ways in our daily lives. In televisions, phones, microphones, refrigerators, giant cranes that lift junk cars at a scrap yard are just a few examples to begin with. But, what are these magnets and how do they get such a cool property? 

Let’s just dive right into it. Magnetism is a physical phenomenon produced by the motion of electric charges, which results in attractive and repulsive forces between objects. Yes, that’s right. It is caused by a moving electric charge. Now, we know that matter is made up of atoms and atoms have subatomic particles such as protons, electrons, etc. These charged particles create a field around them when they are in motion.

This field interacts with the field, similar to it, created by other moving charged particles present in other objects. This field or the area surrounding the object where the magnetic force is experienced is known as the magnetic field. So, simply put, magnets are objects that exhibit magnetism. 

Since all objects are made up of subatomic particles that are in motion, shouldn’t they all exhibit magnetism? To understand this, we must take into consideration a couple of things. Firstly, the magnetic field of every object/atom is not the same. For example, the magnetic field of a proton is much weaker than that of an electron. Some materials could exhibit magnetism, but due to their weak magnetic field, we may not see them moving other magnetic objects towards or away from them.

Secondly, the net magnetic field of an object/atom could be zero. Try and imagine this – every electron in motion produces a magnetic field around it. Therefore, they act as tiny magnets themselves. Now, each of these electrons has a spin, i.e. an intrinsic angular momentum.

The electrons with opposite spins (spin up and spin down) pair together while filling the electron orbitals of an atom.  In an atom with a completely filled outer electron orbital, the net magnetic field is zero as the electrons with opposite spins produce magnetic fields in the opposite direction which tend to cancel out each other. But, if an atom has a half-filled outer electron orbital, then the electrons have the same spin (either spin up or spin down) and they all produce a magnetic field in the same direction. Hence, the net magnetic field of the atom is not zero. This can be seen in atoms with one or more unpaired electrons too. 

The more popular magnetic substances are iron, nickel, and cobalt as magnets apply an attractive force on these metals. These metals exhibit a property called “ferromagnetism”. There is a history behind the name that we will explore some other time. What we need to know is that if a large number of unpaired electrons with the same spin align, they produce magnetic fields in the same direction, strong enough to be experienced at a macroscopic level. But, it is not enough that an atom or all atoms of a substance produce net magnetic fields. It is necessary that these net magnetic fields of each atom in that said substance are in the same direction for them to not cancel out each other. Chromium is an example of a metal that has a magnetic field at the atomic level, but not at a macroscopic level. What this means is, the atoms of chromium have net magnetic fields, but when a piece of chromium metal is taken, a net magnetic field is not observed. How is that even possible, right? Well, it exhibits something called “antiferromagnetism”. What is antiferromagnetism? Are there other types of magnetism than these two? There are. But, that is a topic for another day.

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– Beena P V