OBSERVATION OF MESOSCOPIC QUANTUM TUNNELING OF THE MAGNETIZATION IN SYSTEMS WITH STRONG RANDOM MAGNETIC-ANISOTROPY

Relaxation of the remanence of the random-magnetic-anisotropy (Gd1-xTbx)2Cu (X greater-than-or-equal-to 0.2) amorphous alloys has been measured between 1.7 and 60 K. The time dependence of remanent magnetization has been found to closely follow a lnt dependence for the whole series, and the magnetic viscosity S has been obtained as a function of the temperature and concentration x. The dependence of S with the temperature is linear and shows a nonzero intercept at 0 K for the compounds with concentrations higher than x = 0.2. This indicates the existence of relaxation at zero temperature for these samples and points to a mesoscopic-scale quantum tunneling in three-dimensional systems with strong random magnetic anisotropy. The average tunneling volumes have been determined and they have been found to be of the order of the short-range ferromagnetically correlated volumes existing in these systems.