The Fine Structure of the Relaxation Rates of the Spin Glass Aging Curves

Contrary to the traditional interpretation that there is only one extremum in the relaxation rates of spin-glass aging curves, we find that there are three local extrema: two minima and one maximum for the relaxation rates of the thermoremanent magnetization. We studied the properties of the extrema under variation of magnetic field at 0.9 T_g of a CuMn sample. The global minimum of the relaxation rates gradually switches from the minimum at longer time scale to the minimum at shorter time scale as the magnetic field strength increases. The time scale corresponding to the local maximum increases with the field, and the variation of the second minimum is related to the nonlinear Zeeman energy term. The underlying physical process will be presented.