Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: thedoc on 04/08/2012 06:30:01

Title: What are magnets made of?
Post by: thedoc on 04/08/2012 06:30:01

mike stone asked the Naked Scientists:
   
How is a magnet made and what materials are used to make a magnet? Does it originate from magnetite?

What do you think?

Title: Re: What are magnets made of?
Post by: CliffordK on 04/08/2012 06:47:53

Magnetite (http://en.wikipedia.org/wiki/Magnetite) is a naturally occurring magnetic mineral containing iron.

Most magnets are made with a type of alloy or ceramic containing iron.  Neodymium magnets (NdFeB) (http://en.wikipedia.org/wiki/Neodymium_magnet) are popular fairly strong rare earth magnets.  They can be demagnetized in a strong magnetic field, or with heat.

They would be non magnetic when produced, and the magnetic field is induced with a strong electromagnet.  And, thus the field can be oriented through any faces of the magnet.

Title: Re: What are magnets made of?
Post by: evan_au on 07/08/2012 22:28:59

All electrons act as a tiny bar magnet - but the majority of them pair up with another electron having the opposite spin, which cancels the magnetic field within the atom.

Many elements have one or more unpaired electrons in the outer shell, but as soon as these form a chemical bond (ionic or covalent), the electron is again paired with another of opposite spin, cancelling the magnetic field at the level of a pair of atoms.

Some elements have unpaired electrons on inner shells, where they are protected from external bonding. In most cases, adjacent atoms will have opposite magnetic fields, cancelling the external magnetic field.

In some elements, these magnetic fields can align with adjacent atoms, to form "magnetic domains" with a strong overall magnetic field.  In most cases, the domains are small, and adjacent domains have opposite magnetic fields, cancelling the effect at the microscopic level of crystal grains.

Some hard magnetic materials are resistant to moving the magnetic domain boundaries, so if the magnet is subjected to a very strong magnetic field during manufacture, it will preserve this magnetic field in the delivered magnet. http://en.wikipedia.org/wiki/Magnet#Types_of_permanent_magnets

Each magnetic material has a Curie Temperature, above which the thermal motion of the atoms will disorder any magnetic field. http://en.wikipedia.org/wiki/Curie_temperature

Title: Re: What are magnets made of?
Post by: Lab Rat on 13/12/2012 21:06:58

Just for general knowledge, magnetite is also known as lodestone.