Field dependent critical fluctuations aboveT g in the ESR line width of the spin glassAgMn

The ESR of the spin glassAgMn (2.7 and 9.6 at %) has been investigated below and aboveT_g(0.1T_g<T<5T_g) at various microwave frequencies. The analysis yields:1) No explicit frequency dependence but strong magnetic field effects, inherent with ESR-experiments.2) Part of the excess line width is identified as critical spin fluctuations, following a power law. However, because of the presence of the applied field, the reduced temperaturet is not a good scaling variable. We choose the non-linear susceptibility X_s divided byH², which scales as the order parameter susceptibility. The experiment yieldsW_ex(X_s/H²)^p,p=0.42. From this we deduce z3.