Theoretical $T_1$ Calculation for Isotropic High Spin Molecules

Abstract

We calculate the molecular-spin ($S$), temperature ($T$), and field ($H$) dependence of $1/T_1$ for a local magnetic probe coupled to an isotropic high spin molecule, based on spin-phonon interaction. We compare the calculation to recent NMR and $\mu$SR experiments in CrCu${}_6$ ($S=9/2$), CrNi${}_6$ ($S=15/2$) and CrMn${}_6$ ($S=27/2$). Although we can account for the high and intermediate temperature regimes, the calculation is fundamentally different from the data at $T⟶0$. Since $1/T_1$ must be due to coupling of the molecular spin to an external heat bath, and since phonon contribution is ruled out at low $T$, we conclude that at these temperatures hyperfine interactions must play an important role in the molecular spin dynamic.

12 pages, 5 figures