Paramagnetic tunneling state concept of the magnetic anomalies of   amorphous insulators
  A generalized tunneling model of insulating glasses is formulated, considering tunneling states to be paramagnetic centers of spin 1/2. The expression for magnetic field dependent contribution into the free energy is obtained. The derivation is made of the expression for the nonmonotonic magnetic field dependence of dielectric constant, recently observed in several glasses in the millikelvin temperature range. 
Alexander Borisenko and Alexander Bakai