Permanent Magnet Dipoles

A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the dimensions of the source are reduced to zero while keeping the magnetic moment constant.Dipoles consist of a pair of magnets across a gap.  They come in many shapes/sizes and the magnets are usually mounted on a steel frame (also called a yoke) for magnetic efficiency, magnetic shielding and mechanical strength.  Dipoles are used when an application requires a specific magnetic field strength and uniformity over a specific volume.  Pole pieces are sometimes used to enhance uniformity within the gap.

China Magnets Source Material Ltd has built hundreds of different types of dipoles, each optimized for a particular application.  Field strengths have ranged as high as 3.0 Tesla (30,000 Gauss).  Generally, higher fields are associated with small air gaps.  Higher uniformity is generally associated with large air gaps.

Permanent magnet dipoles are used to:

Calibrate/initialize magnetic sensors
Erase computer hard disk drives
Orient thin layers of magnetic material as they are deposited as thin films
Divert or focus beams of energized particles

Materials:
Neodymium Iron Boron and Samarium Cobalt are often used when large magnetic fields are required.  Hard ferrite is used if cost is more important than large magnetic fields. Alnico is generally used if dipole is to be used in high temperature environment (>300°C).