Spin relaxation and resonant phonon trapping in [Gd2(fum)3(H2O)4]•3H2O

Results of ac-susceptibility, specific-heat, magnetization, and electron-spin-resonance studies of a [Gd-2(fum)(3)center dot(H2O)(4)]center dot 3H(2)O (fum=fumarate, C4H2O4) powder samples are reported. The results of these measurements enabled us to identify the studied compound as a three-dimensional S = 7/2 Heisenberg magnet with T-N = 0.19 K and dominant crystal-field anisotropy. The susceptibility studies conducted at audio frequencies and temperatures from 2 to 30 K revealed that the application of static magnetic fields induces a slow spin relaxation. The relaxation is not associated with an anisotropy energy barrier and is explicable assuming resonant phonon trapping. The magnetic field dependence of the relaxation time is consistent with the proposed scenario and suggests that a strong spin-lattice interaction may be the mechanism governing the relaxation properties in the studied system.