Lattice effects on the spin dynamics in antiferromagnetic molecular rings

[摘要] We investigate spin dynamics in antiferromagnetic molecular rings at finite temperature in the presence of spin-phonon (s-p) interaction. We derive a general expression for the spin susceptibility in the weak s-p coupling limit and then focus on the low-frequency behavior in order to discuss a possible microscopic mechanism for nuclear relaxation in this class of magnetic materials. To lowest order in a perturbative expansion, we find that the susceptibility takes a Lorentzian profile and all spin operators (S-x,S-y,S-z) contribute to spin dynamics at wave vectors q not equal 0. Spin anisotropies and local s-p coupling play a key role in the proposed mechanism. Our results prove that small changes in the spatial symmetry of the ring induce qualitative changes in the spin dynamics at the nuclear frequency, providing a mechanism for nuclear relaxation. Possible experiments are proposed.

[发布日期] 2005-12-01