Characteries of Halbach Array Magnets 

A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the
array while cancelling the field to near zero on the other side.This is achieved by having a spatially rotating pattern of
magnetisation.

The rotating pattern of permanent magnets (on the front face; on the left, up, right, down) can be continued indefinitely
and have the same effect. The effect of this arrangement is roughly similar to many horseshoe magnets placed adjacent
to each other, with similar poles touching.
 
Application: 

The advantages of one sided flux distributions are twofold:

1. The field is twice as large on the side on which the flux is confined (in the idealized case).
2. There is no stray field produced (in the ideal case) on the opposite side. This helps with field confinement, usually a
     problem in the design of magnetic structures.

Although one-sided flux distributions may seem somewhat abstract, they have a surprising number of applications ranging
from the refrigerator magnet through industrial applications such as the brushless DC motor, voice coils, magnetic drug
targeting to high-tech applications such as wiggler magnets which are used in particle accelerators and free-electron lasers.