Take a moment to picture a magnet in your mind. If you can, try drawing a quick sketch of a magnet on a piece of scrap paper. Whether you imagined the magnet or had the opportunity to draw a magnet, chances are you pictured a traditional horseshoe magnet. This iconic U-shape remains the most popular depiction of a magnet, but what is the story behind this design?
The story of horseshoe magnets begins in England in 1825. Apprenticed as a shoemaker before joining the army, physicist and inventor William Sturgeon began experimenting with magnets. He created the first horseshoe magnet when he wrapped wire around a horseshoe-shaped piece of iron, then ran an electric current through the wires. In addition to being the first horseshoe magnet, this was also the first electromagnet, and the first magnet capable of lifting a greater amount of mass than the magnet itself.
The horseshoe magnet swiftly replaced the bar magnet, as the design of a horseshoe magnet inherently has more strength than a bar magnet. The reason for this is that the U-shape places the poles of the magnet closer to each other and within the same plane. This allows the magnetic field to be concentrated, as the magnetic lines of flux are able to flow along a more direct path between the two poles.
Why Do Magnets Have a Horseshoe Shape?
When a magnet is in a horseshoe shape, its coercivity is increased as well. With higher coercivity, the magnet becomes far less vulnerable to demagnetization over time. This is very important in the context of low-coercivity magnetic materials such as iron and alnico. The earliest magnets, made of iron, had a short life span because their coercivity was so low that the magnet would demagnetize itself with its own field.
Magnets with higher coercivity, such as neodymium magnets, are not sold in a horseshoe shape because they do not need to augment their strength or resistance to demagnetization. Additionally, the brittleness of neodymium magnets makes them ill-suited to a U-shaped design. However, alnico magnets are still widely manufactured in horseshoe shapes.
There are many reasons to choose a horseshoe shaped alnico magnet. Alnico magnets boast excellent resistance to heat and provide excellent strength at a low price point. When designed in a horseshoe shape, alnico magnets gain increased strength and increased resistance to demagnetization.