Magnetism is the force of nature responsible not only for our ability to live on a rock floating through space, but also for major technological achievements that have advanced the human race like never before. Computers rely on them, our livelihood on Earth depends on their principles and our greatest science experiments use the most powerful magnets ever created by man. Were it not for magnetism we simply would not exist, and indeed without discovering the power of this fundamental force of nature, our life on Earth would bear no resemblance to what it is today.
Scientists over the years have employed magnetism in new and innovative ways, delving into realms of particle physics otherwise unexplored, but let’s take a look at how basic magnets are made. It’s fairly common knowledge that objects can be magnetized, making them stick to other magnetic objects, and we know that things such as a fridge or horseshoe magnet always have magnetism. To make permanent magnets like these, substances such as magnetite or neodymium are melted into an alloy and grounded into a powder. This powder can be moulded into any shape by compressing it with hundreds of pounds of pressure. A huge surge of electricity is then passed through it for a brief period of time to permanently magnetize it. Typically, a permanent magnet will lose about one per cent of its magnetism every ten years unless it is subjected to a strong magnetic or electric force, or heated to a high temperature.
Now let’s take a look at the magnets themselves, and what’s in and around them. Surrounding every magnet is a magnetized area known as a magnetic field that will exert a force, be it positive or negative, on an object placed within its influence. Every magnet also has two poles, a north and south. Two of the same poles will repel while opposite poles attract. Inside and outside a magnet there are closed loops known as magnetic field lines, which travel through and around the magnet from the north to south pole. The closer together the field lines of this magnetic field are, the stronger it will be. This is why unlike poles attract – the magnetic forces are moving in the same direction, so the field lines leaving the south of one magnet have an easy route into the north of another, creating one larger magnet. Conversely, like poles repel as the forces are moving in opposite directions, hitting one another and pushing away. It’s the same effect as other forces. If you push a revolving door while someone pushes from the other side, the door stays still and your forces repel. If you push in the same direction, however, the door swings round and you end up back at your starting point.
The defining feature of magnetic poles is that they always occur in pairs. Cut a bar magnet in half and a new north and south pole will instantly be created on each of the two new magnets. This is because each atom has its own north and south pole, which we will talk about later. However, the obvious question is why the poles are there in the first place. Why do magnets have to have these field lines moving from north to south? The answer involves magnetic domains. It is best to picture a magnet as smaller magnet chunks put together. Each chunk (or domain) has its own north and south pole and again, as explained before, magnetic field lines travel from north to south. This means that all the domains stick together, with their forces concentrated in the same direction. They combine to make a larger magnet, exactly the same effect as when two magnets are stuck together. Each domain has about 1,000,000,000,000,000 (1 quadrillion) atoms, while 6,000 domains are approximately equivalent to the size of a pinhead. Domains within a magnet are always aligned, but elements such as iron, which can become magnetic, initially have their domains pointing in random directions when the iron is unmagnetized. They cancel each other out until a magnetic field or current is introduced, making them point in the same direction and magnetizing the iron, which creates its own new magnetic field.
To really understand magnets, though, we need to get into exactly what is happening inside these domains. For that, we need to get right down into the atom. Let’s take an iron atom, for example. Electrons circle the nucleus of an atom in cloud-like orbitals, commonly described as rigid shells (although in actuality, their motion is much more random). Each atom has a particular number of shells depending on how many protons and neutrons it has, while within each shell electrons orbit in pairs. Electrons are just like tiny magnets, each one having its own north and south pole. In their pairs, the electrons cancel out one another so there is no overall magnetic force. In an atom such as that of iron, however, this is not the case. There are four electrons that are unpaired, which exert a magnetic force on the atom. When all the atoms are combined together and aligned, as we explained when talking about domains, the iron itself becomes magnetized and attracts other magnetic objects.
So we’ve snapped our magnet, broken it into chunks and subsequently examined the atoms of those tiny chunks. But can we go deeper? The answer to that is yes and no, as we delve into the unknown areas of quantum physics. The underlying principle of magnetism is that in the universe there are four fundamental forces of nature, being gravity, electromagnetism, the weak force and the strong force. Even smaller than atoms and electrons are fundamental particles known as quarks and leptons, which are responsible for these forces. Any force – such as gravity, magnetism, nuclear decay or friction – results from these fundamental forces. A force such as magnetism at this level is ‘thrown’ between particles on what are known as force carrier particles, pushing or pulling the other particles around accordingly.
Unfortunately, however, at this level magnetism enters a completely different realm – that of theoretical physics, entering areas of quantum physics that have not yet been explored in as great detail as particle physics. For now, however, this standard model of physics explains magnetism to a level that can only actually be furthered when science can advance our understanding of quantum physics in the future.
So what’s the difference between the atoms of magnetic and non-magnetic elements? Well, the main difference is the appearance of unpaired electrons. Atoms that have all their electrons in pairs can’t be magnetized, as the magnetic fields cancel each other out. However, atoms that can be magnetised have several unpaired electrons. All electrons are essentially tiny magnets, so when they are unpaired they can exert their own force – known as a magnetic moment – on the atom. When they combine with electrons in the other atoms, the element as a whole gains a north and south pole and becomes magnetized.
Types of magnetism
The strongest magnet in this list, a ferromagne will retain its magnetism unless heated to a temperature known as the Curie point. Cooling it again will return its ferromagnetic properties. Every atom in a ferromagnetic material aligns when a magnetic field is applied. Horseshoe magnets are ferromagnets.
Ferrimagnets have a constant amount of magnetisation regardless of any applied magnetic field. Natural magnets like lodestones (magnetite) are ferrimagnets, containing iron and oxygen ions. Ferrimagnetism is caused by some of the atoms in a mineral aligning in parallel. It is different from ferromagnetism in that not every atom aligns.
At low temps, the atoms in an antiferromagnet align in antiparallel. Applying a magnetic field to an antiferromagnet such as chromium will not magnetise it, as the atoms remain opposed. Heating to Neel temp (when paramagnetism can occur) will allow weak magnetism, but further heating will reverse this.
Paramagnets, such as magnesium and lithium, have a weak attraction to a magnetic field but don’t retain any magnetism after. It’s caused by at least one unpaired electron in the atoms of a material.
Gold, silver and many other elements in the periodic table are diamagnets. Their magnetic loops around the atoms oppose applied fields, so they repel magnets. All materials have some magnetism, but only those with a form of positive magnetism can cancel the negative effects caused by diamagnetism.
What is electromagnet?
One of the four fundamental forces in the universe, electromagnetism results from the interaction of electrically charged particles. Physicist Michael Faraday deduced that a changing magnetic field produces an electric field, while James Maxwell discovered that the reverse is also true: a changing electric field produces a magnetic field. This is the basis of how an electromagnet works.