Giant field dependence of the low temperature relaxation of the magnetization in a dysprosium(III)-DOTA complex

The square antiprismatic Na[Dy(DOTA)(H2O)]center dot 4H(2)O complex was characterised by single crystal X-ray diffraction and ac magnetic susceptometry. Two competing mechanisms for magnetic relaxation as well as the remarkable increase of six orders of magnitude in the relaxation time upon application of a static magnetic field were detected.