Magnets are an important part of our daily lives, serving as essential components in everything from electric motors, loudspeakers, computers, compact disc players, microwave ovens and the family car, to instrumentation, production equipment, and research. Their contribution is often overlooked because they are built into devices and are usually out of sight.
Magnets function as transducers, transforming energy from one form to another, without any permanent loss of their own energy. General categories of permanent magnet functions are:
- Mechanical to mechanical – such as attraction and repulsion
- Mechanical to electrical – such as generators and microphones.
- Electrical to mechanical – such as motors, loudspeakers, charged particle deflection
- Mechanical to heat – such as eddy current and torque devices
- Special effects – such as magneto resistance, Hall effect sensors, and magnetic resonance
The following sections will provide a brief insight into the design and application of permanent magnets. There are four classes of modern commercialised magnets, each based on their material composition. Within each class is a family of grades with their own magnetic properties. These general classes are:
Neodymium Iron Boron
NdFeB and SmCo are collectively known as Rare Earth magnets because they are both composed of materials from the Rare Earth group of elements. Neodymium Iron Boron (general composition Nd2Fe14B, often abbreviated to NdFeB) is the most recent commercial addition to the family of modern magnet materials.
At room temperatures, NdFeB magnets exhibit the highest properties of all magnet materials.
Samarium Cobalt is manufactured in two compositions: Sm1Co5 and Sm2Co17 – often referred to as the SmCo 1:5 or SmCo 2:17 types. Samarium 2:17 has higher Hci values, offer greater inherent stability than the 1:5 types.
Ceramic, also known as Ferrite, magnets (general composition BaFe2O3 or SrFe2O3) have been commercialized since the 1950s and continue to be extensively used today due to their low cost. A special form of flexible ceramic magnetic material can be made by bonding ceramic powder in a flexible binder.
Alnico magnets (general composition Al-Ni-Co) were commercialized in the 1930s and are still extensively used today.