Spin Ice Monopoles

Physicists have made analogies of magnetic monopoles in spin ice.
Image courtesy of Claudio Castelnovo (Royal Holloway University of London), Artistic representation by A.Canossa (2011)

Spin ice is like magnetic ice.  Ice is made of water molecules bound together in a crystal structure and when the crystal structure is formed there are four magnetic dipoles, atoms with a north and south pole, which are located at the corners of a tetrahedron in the crystal structure.  Two of the north poles face one way and two face the other, creating a favorable energetic state.  When one dipole is facing the opposite direction, it creates a magnetic monopole.