Let’s Stick Together: A history of permanent magnets

Dan Reardon is an Australian astrophysicist: he researches supermassive black holes in distant galaxies using data from the MeerKAT radio telescope in South Africa. With his colleagues, he is creating new knowledge about the universe’s fundamental structure.

Dan has also achieved a degree of fame by getting magnets stuck up his nose. At the start of the Covid-19 lockdown in March 2020, he was designing a magnet-based device to alert its user if they touched their face. But initial experiments went wrong and bored Dan, with ‘the same logic as clipping pegs to your ears’, ended up with three magnets in his left and one in his right nostril, stuck together through the connecting fleshy bit (or ‘septum’) so he couldn’t remove them. Removing them required a hospital trip, after which Dan could resume researching supermassive black holes from home.

Dan’s magnets were small – tiny enough to fit three in one nostril. Yet, even pulling hard with a pair of pliers, he couldn’t shift them – they even magnetised the pliers. Powerful magnets like this are everywhere. They are often referred to as permanent magnets because they can maintain their magnetism for a long time. We can use Dan’s minor misfortune to kick off a brief history of magnets.

First, some definitions. A magnet is an object which produces a magnetic field. The planet Earth is itself a giant magnet, with a core mostly of iron, and magnetic North and South poles. There are many different types of magnet, the main two being permanent magnets, and electro-magnets. The former exert a continual magnetic field due to inherent properties of the materials used, such as iron and nickel, and have been made increasingly powerful. The latter rely on an electric current to generate a magnetic field: without the current, it ceases to be magnetic. In homage to Dan’s nose and his magnet ordeal, this story will concentrate on permanent magnets.

The word ‘magnet’ derives from ‘Magnesia’, a district in the Greek province of Thessalia, rich in the magnetic iron ore magnetite. Greek philosopher Thales wrote of this ‘Magnesian rock’ and its properties in 600 BCE. Today, a magnet is recognised as having particular properties: it has a north pole and a south pole, with a magnetic field stretching from the north to the south. The field comprises defined lines, which work on magnetic materials, and which attract or repel other magnets – opposites attract, likes repel.

Pieces of magnetite became called ‘Lodestones’ – ‘Lode’ is Old English for ‘path’ or ‘course’, which indicates how they were used – in compasses for navigation. They were highly prized, and some survive complete with decorative metal mountings and containers. Lodestones were the subject of philosophical study. In China around 1000 CE, lodestones or magnetised iron bars placed in bowls of water were found to always line up with the magnetic poles aligned north-south. Petrus Peregrinus de Maricourt wrote describing their properties in around 1269, and William Gilbert wrote his De Magnete in 1600, describing the first systematic experiments into magnetism.

Seafarers and other navigators around the world developed a body of practical knowledge about how permanent magnets could be used in navigation compasses, with the steel needles magnetised to align with the earth’s magnetic field. Lodestones and compasses were kept in pairs, the compass needles occasionally ‘touched’ to the lodestone to re-magnetise them, so they kept pointing a true course.

Permanent magnets were found in many different places. They were deep underground, in miners’ compasses used to plot the routes of underground mineral seams. They figured prominently in the demonstrations of popular lecturers; even King George III had magnets in his experimental collection.

The twentieth century saw huge research interest in the composition of permanent magnets. The magnetic force exerted by a magnet of constant size doubled about every twelve years – compared to a lodestone, a modern neodymium magnet can possess the same magnetic force but have only one thousandth of the mass. The consequences of this trend are now being felt around the world. Let’s find out how.

Since the 1950s, magnet development has been driven by the inclusion of ‘rare earth elements’, metallic elements like samarium or platinum, to enhance their magnetic properties and make them more powerful. 

However, supplies of these elements were - and remain - very difficult to establish, making them expensive and limiting supplies.

In Japan, Masato Sagawa pioneered the development and manufacture of a permanent magnet using more abundant neodymium, boron, and iron. Masato patented his innovation in 1982, before devoting himself to working out how to mass-produce his new magnets.

Forty years later, Masato was awarded the Queen Elizabeth Prize for Engineering in recognition of his pioneering work on the world’s most powerful permanent magnets. They’ve transformed many technologies we take for granted in everyday life. For instance, early computer hard disk drives could weigh 30kg, but now they can be carried easily between finger and thumb.

Any device or machine using permanent magnets can be shrunk. When you think that in 2005, electric motors using permanent magnets accounted for over half of Japan’s power demand, their potential to drive down energy use can be appreciated. Masato aims for his magnets to be ‘used in electric vehicles which has the world's highest performance’. But, they will have an impact way beyond just cars, from wind turbines to domestic appliances, mobile phones and MRI scanners.

So, the most powerful permanent magnet can play a crucial role reducing energy use and helping the world reach Net Zero in our fight against climate change. Dan Reardon did not get magnets stuck up his nose in vain.