Muons in spin ice

Monopoles, magnetricity and the stray field from spin ice.
Stephen J. Blundell 
Phys. Rev. Lett. 108, 147601 (2012)
ArXiv 1111.3657 (2011)

Distribution of B_mu in the vicinity of (a-c) two spins at positions (+-a; 0; 0), showing the field in the y = 0 (left) and x = 0 (right) planes, and (d-e) fourspins on the corners of a tetrahedron (inscribed in a cube of side length d, centered at the origin), satisfying the ice rules.