Magnetic particle–particle interaction in frozen magnetic fluids - Morais, P. C.; Lara, M. C. F. L.; Tronconi, A. L.; Tourinho, F. A.; Pereira, A. R.; Pelegrini, F. (American Institute of Physics (AIP), 1996)
http://dx.doi.org/10.1063/1.362407
Keywords: U