To overcome this, the horseshoe magnet was invented by Daniel Bernoulli in 1743. Ī straight iron magnet tends to demagnetize itself by its own magnetic field. By the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. This led to the development of the navigational compass, as described in Dream Pool Essays in 1088. In the 11th century in China, it was discovered that quenching red hot iron in the Earth's magnetic field would leave the iron permanently magnetized. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia. The earliest known surviving descriptions of magnets and their properties are from Anatolia, India, and China around 2500 years ago. Lodestones, suspended so they could turn, were the first magnetic compasses.

The word magnet was adopted in Middle English from Latin magnetum ' lodestone', ultimately from Greek μαγνῆτις ( magnētis ) meaning ' from Magnesia', a place in Anatolia where lodestones were found (today Manisa in modern-day Turkey). Often, the coil is wrapped around a core of 'soft' ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.Īncient people learned about magnetism from lodestones (or magnetite) which are naturally magnetized pieces of iron ore. The local strength of magnetism in a material is measured by its magnetization.Īn electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops.

The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. 'Hard' materials have high coercivity, whereas 'soft' materials have low coercivity.

To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. Permanent magnets are made from 'hard' ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.įerromagnetic materials can be divided into magnetically 'soft' materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically 'hard' materials, which do. These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. and attracts or repels other magnets.Ī permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. A magnet is a material or object that produces a magnetic field.

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