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 projects. 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 generation and microphones.
• Electrical to mechanical - such as motors, loudspeakers, charged particle deflection.
• Mechanical to heat - such as eddy current and hysteresis torque devices.
• Special effects - such as magneto resistance, Hall effect devices, and magnetic resonance.

There are four classes of modern commercialized magnets, each based on its material composition. Within each class is a family of grades with their own magnetic properties. These general classes are:

• Neodymium iron boron
• Samarium cobalt
• Ferrite
• Alnico

Neodymium iron boron and samarium cobalt 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 as 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. 2:17 types, with high Hci values, offer greater inherent stability that the 1:5 types.

Ferrite magnets, also known as ferrite magnets (general composition BaFe₁₂O₁₉or SrFe₁₂19₃) have been commercialized since the 1950’s and continue to be extensively used today due to their low cost. A special form of ferrite magnet is “Flexible” material, made by bonding ferrite powder in a flexible binder. Alnico magnets (general composition Al-Ni-Co) were commercialized in the 1930’s and are still used extensively today.

These materials span a range of properties that accommodate a wide variety of application requirements. The following pages are intended to give a broad but practical overview of the factors that must be considered in selecting the proper material, grade, shape, and size of magnet for a specific applications. The chart below shows typical values of the key characteristics for selected grades of various materials for comparison.

Basic problems of permanent magnet design revolve around estimating the distribution of magnetic flux in a magnetic circuit, which may include permanent magnets, air gaps, high permeability conduction elements, and electrical currents. Exact solutions of magnetic fields require complex analysis of many factors, although approximate solutions are possible based on certain simplifying assumptions. Obtaining an optimum magnet design often involves experience and tradeoffs.