Magnetic properties of two-dimensional SNS-type Josephson junction arrays

The field dependence of the magnetic moment of square ($100\times100$) SNS-type Josephson junction arrays was studied by a SQUID magnetometer. A considerable difference in the behavior of this dependence was revealed for the cases of the entry of magnetic flux into the array and its exit from it. The branches of the curve obtained with increasing field strength had the form of regular periodic dependences with peaks corresponding to integer and half-integer numbers of flux quanta per cell. The curves obtained with decreasing field strength had no noticeable features and, in particular, no periodic structure. Magnetic flux avalanches were not observed in the SNS-type arrays, although the critical parameter of the system was sufficiently great ($LI_{C}/\Phi_{0} \gg 1$) to satisfy the necessary condition of the self-organized criticality. The quasi-hydrodynamic flux motion in the array was explained by the considerable viscosity characterizing the vortex motion through the Josephson junctions.