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Refrigerator magnet

Small magnet used to post items on a refrigerator door

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Manufacture

The first refrigerator magnets were inflexible magnets in a cylindrical or rectangular prism shape. Ferrite magnets are commonly used, with decorative elements attached to the magnets with adhesive. They were created in the 1920s.

Flexible flat refrigerator magnet

Later, a flexible magnet was developed, composed of a high-coercivity ferrimagnetic or ferromagnetic compound (usually barium ferrite) mixed with a plastic binder, extruded as a sheet.

Halbach array polarization

Unlike most conventional magnets that have distinct north and south poles, most flexible refrigerator magnets are magnetized during manufacture in a sophisticated magnetization pattern called a Halbach array. This construction almost doubles the magnetic field on the refrigerator side and almost zero magnetic field on the other.

This pattern can be impressed on the sheet by rolling a line of powerful cylindrical permanent magnets arranged with alternating magnetic poles. This pattern can be felt by taking two similar (or identical) refrigerator magnets and sliding them against each other with the refrigerator sides facing each other: the magnets will alternately repel and attract as they are moved a few millimeters. The pole-pole distance is on the order of 5 mm, but varies with manufacturer.

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