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 τ_φ of molecular magnets. It is found that τ_φ~10 nsec with no S or ligand dependence. This indicates a nuclear origin for the stochastic field. Since τ_φ is a property of the environment, we argue that it is a number common to similar types of MM. Therefore, τ_φ 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.