Spin-glass dynamics from magnetic noise, relaxation, and susceptibility measurements (invited)

Abstract

We present a quantitative comparison between dynamic measurements on spin glasses. The case of CdIn0.3Cr1.7S4 is discussed in detail and references are made to CsNiFeF6 and Ag:Mn (2.6%). The measured quantities are the relaxation of the thermoremanent magnetization MTRM(t) in the range of observation times 1–105 s, the out-of-phase susceptibility χ″(ω) in the range 10−3–5×104 Hz, and the magnetic noise power spectrum M2(ω) between 10−2 and 103 Hz. The aging of the thermoremanent magnetization relaxation is analyzed on the basis of a phenomenological theory of time scaling which allows to derive the form of the equilibrium relaxation. It is shown that the measured values of χ″ and ∼(M2(ω)) are related according to the fluctuation dissipation theorem (FDT). The consequences of the applicability of the FDT in the frequency domain are discussed, with reference to the expected violation of the theorem in the spin-glass phase at ω=0. An important modification of the frequency dependence of χ″(ω) is observed at Tg, supporting a previous dynamic scaling approach. There is good agreement between the low-temperature stationary behaviors of MTRM(t) and χ″(ω), but they show an unexplained discrepancy close to Tg.