Experimental Estimates of Dephasing Time in Molecular Magnets

Muon spin relaxation measurements in isotropic molecular magnets (MM) with a spin value S ranging from 7/2 to 27/2 are used to determine the magnitude and origin of dephasing time ${\tau }_{\varphi }$ of molecular magnets. It is found that ${\tau }_{\varphi }$ ~ 10 nsec with no S or ligand dependence. This indicates a nuclear origin for the stochastic field. Since ${\tau }_{\varphi }$ is a property of the environment, we argue that it is a number common to similar types of MM. Therefore, ${\tau }_{\varphi }$ is shorter than the Zener and tunneling times of anisotropic MM such as Fe8 or Mn4 for standard laboratory sweep rates. Our findings call for a stochastic Landau-Zener theory in this particular case.