Reexamination of critical dynamic scaling in spin glasses

The frequently used scaling form for χ](ω), the imaginary part of the ac susceptibility, is χ](ω)T=ω ^β/zνf(ω/t^zν), where t≡(T-T _c)/T_c. Comparison of data to this form has generally been done using a 3-parameter visual fit on a log-log plot, which often conceals good departures from scaling. By recasting the argument of the scaling function to t/ω^1/zν, one can use a linear scaling plot of χ]T/ω^β/zν vs t/ω^1/zν, which more nearly resembles χ](ω) vs T for a more revealing display of departures from good scaling. This procedure suggests a new method to determine β/zν,zν, and T_c separately and independently of each other. Application is made to Cd_0.6Mn_0.4Te and other spin glasses. A method as also presented for determining T_c and distinguishing between activated versus conventional dynamics by considering (χ_eq-χ')/χ] vs T. Reexamination of previous work reveals a general tendency to underestimate zν and overestimate T_c.