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.

Energy flow, partial equilibration, and effective temperatures in systems with slow dynamics

“…From what we know from the time-scales of real spin-glasses [20,22], if the time after the quench is of the order of 10 minutes, and the period of the L-C circuit is of the order of the second, we are probing (at least partially) the aging regime: the temperature (defined as the average energy of the capacitor) should be different from the bath temperature. We believe that it would be interesting to return to the magnetization noise experiments [21] with the purpose of measuring the effective temperature: this would give us, for instance, useful insights into the nature of the spin-glass transition. Throughout this paper we have used as a test model a spherical disordered model with p-spin interactions.…”

“…This definition of the frequency-and waiting-time-dependent correlation C O (ω o , t w ) and out-ofphase susceptibility χ ′′ O (ω o , t w ) closely follows the actual experimental procedure for their measure: one considers a time window around t w consisting of a few cycles (so that phase and amplitude can be defined) and small enough respect to t w so that the measure is "as local as possible in time". In fact, these two quantities are standard in the experimental investigation of aging phenomena in spin-glasses [20][21][22].…”

Experimental investigation of the fluctuation dissipation relation in a spin glass

“…This clustering complicates the analysis of the experimental results as will be shown below, but it is the reason of the large susceptibility and fluctuations amplitude, allowing good noise measurements which would be impossible in a canonical metallic spin glass in the present state of the experimental possibilities. Extensive investigations of the aging properties of the magnetic response were performed in this compound: aging of TRM relaxation 21 and of the out-of-phase susceptibility 22 , effect of the temperature variations. 23 With it, the first (and probably the only) systematic measurement of the aging of the magnetic noise power spectrum in a spin glass was performed by collecting an ensemble average of noise power at 10 −2 Hz.…”

Aging dynamics in a reentrant ferromagnet:Cu0.2Co0.8Cl2−FeCl3Suzuki1, Suzuki2 2005Phys. Rev. B3240View full textAdd to dashboardCite

“…Theoretically 18,19 and experimentally 20,21,22,23,24,25,26,27,28,29,30 it has been accepted that the time variation of χ ZF C (t) may be described by a product of a power-law form and a stretched exponential function…”