Permanent Magnet Materials Explained
There are a number of categories of commercially available permanent magnetic materials and we thought, what better way to get a full understanding of what each one does than by giving an in-depth breakdown of each category of magnet and what its characteristics and applications are.
In our previous blog on this subject we focused on just four groups, but now we add Bonded Magnets and also explain a little further about Rare Earth Magnets and why they are classed as such.
This was the first modern magnetic material developed in the 1930’s. Before the introduction of rare-earth magnets, these were the strongest type of permanent magnet available. The name is an acronym that refers to the alloys; Aluminium (Al), Nickel (Ni) and Cobalt (Co). This material can be used at 550 Deg C and has the ability to throw its field further than other materials.
Ferrite was developed in the 1950’s and is a similar strength to AlNiCo. Despite this, it was seen as an incremental development because it is more stable in shorter lengths. This meant that thin disc magnets could be produced, as well as being corrosion resistant and very cheap to produce.
Samarium-Cobalt (SmCo) (Rare Earth Magnet*)
This was the first Rare Earth permanent magnetic material, and was developed in the 1970’s. It is seven times the strength of Ferrite, which means that magnetic assemblies can be miniaturised accordingly. As long as its brittle nature is taken into account, it can be used at high temperature (300 Deg C) and will not rust.
Neodymium Iron Boron (NdFeB) (Rare Earth Magnet*)
This is the strongest commercially available magnet material, with energy products of up to 52 MGOe or, in layman’s terms, a 1cm disc can lift up 3.5 kilos in weight.
Continued development since the early 1980’s has seen grades produced with improved working temperatures (200 Deg C ) and increased corrosion resistance to compete with the much more expensive SmCo material.
Bonded magnet materials can be made from Ceramic, NdFeB, or SmCo powders which are combined with a variety of plastic binders (Matrix). They can be either Injection Moulded or Compression Bonded into complex magnet shapes with a range of finished dimensions.
Bonded magnet materials have a moderate resistance to corrosion and a low tolerance to heat (because of the binder material) and are commonly used in automotive parts as they lend themselves to large production quantities and because complex shapes can be produced at a low cost.
To find out more about our categories of permanent magnets, please watch our video where our Magnet Technical Developer Dave Woods takes us through each one in more detail.
* Samarium Cobalt Magnets (SmCo) and Neodymium Iron Boron Magnets (NdFeB) are called Rare Earth Magnets because Neodymium and Samarium are found in the rare earth elements on the periodic table.