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.
The effect was discovered by John C. Mallinson in 1973, and these "one-sided flux" structures were initially described by him as a "curiosity", although he recognised at the time the potential for significant improvements in magnetic tape technology.
In the 1980s, Lawrence Berkeley National Laboratory physicist Klaus Halbach, independently invented the Halbach array to focus accelerator particle beams.
Read more about Halbach Array: Halbach Cylinder, Halbach Spheres
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