Magnetic field induces transition in the distorted Fe2+-Fe2+ pairs (quantum dots) from the initial bonding singlet state to the high spin antibonding state providing decay of the pairs for two separated Fe2+ ions. Dislocations moving under internal stresses easily overcome separated Fe2+ ions in comparison with Fe2+-Fe2+ pairs lying close to the glide plane. Non-monotonous field dependence of dislocation displacements under internal stresses governed by short (100 mu s) impulse of high magnetic fields up to 31 T was revealed in NaCl:Fe crystals. This non-typical dependence is the fingerprint of the Landau-Zener non-adiabatic spin transition between singlet and high spin states in quantum dots distorted by mechanical stresses of moving dislocations.