Magnetic Relaxation in the Heisenberg Spin Glass

On the basis of a dynamical theory for Heisenberg spin glasses the isothermal magnetic relaxation R(t) = M(t)/H after switching off a magnetic field H at t = 0 is calculated. The extreme short time relaxation shows an exponential decay with a temperature dependent relaxation time τ( T ) and is essentially influenced by many‐body quantum effects in the spin glass state. An estimation of the long time relaxation yields in the qualitative agreement to experimental investigation a non‐exponential behaviour R(t) ∼ t −1/γ , where γ = 2 in an intermediate time region is found for T ≦ T f . This anomalous relaxation is caused by a broad distribution of relaxation times owing to a distribution of local fields.