Reexamination of critical dynamic scaling in spin glasses

Abstract

The frequently used scaling form for χ″(ω), the imaginary part of the ac susceptibility, is χ″(ω)T=ωβ/zνf(ω/tzν), where t≡(T−Tc)/Tc. 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/ω1/zν, one can use a linear scaling plot of χ″T/ωβ/zν vs t/ω1/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 Tc separately and independently of each other. Application is made to Cd0.6Mn0.4Te and other spin glasses. A method as also presented for determining Tc and distinguishing between activated versus conventional dynamics by considering (χeq−χ′)/χ″ vs T. Reexamination of previous work reveals a general tendency to underestimate zν and overestimate Tc.