Time decay of the remanent magnetization in a CuMn spin glass

The glassy behaviour of poorly crystalline Fe2O3 nanorods obtained by thermal decomposition of ferrous oxalate

Nanorod ferrous oxalate dihydrate (FeC2O4 × 2H2O) which had been synthesized by the microemulsion method, was used as a precursor in the thermal decomposition process performed in air atmosphere. The formation of nanocrystalline hematite as the final product was preceded by the appearence of an intermediate product. Comprehensive study comprising several complementary techniques (x-ray diffraction, transmission electron microscopy, selected area electron diffraction, thermogravimetric/differential thermal analyses and SQUID magnetometry) confirmed that the intermediate product corresponds to the poorly crystalline Fe2O3. Due to the specific nanorod shape and poorly crystalline structure, the investigated Fe2O3 showed high coercive field value of ~0.5 T at 5 K. Special attention in this study was devoted to the peculiar magnetic properties of poorly crystalline Fe2O3, which were thoroughly investigated by employing sophisticated experimental procedures such as relaxation of thermoremanent magnetization for different cooling fields, zero field and field cooled memory effects as well as aging experiments for different waiting times. At low temperatures and weak applied magnetic fields, the investigated system behaves similarly to spin glasses, manifesting slow, collective relaxation dynamics of magnetic moments through memory, rejuvenation and aging effects.

Mesoscopic model of temporal and spatial heterogeneity in aging colloids

We develop a simple and effective description of the dynamics of dense hard sphere colloids in the aging regime deep in the glassy phase. Our description complements the many efforts to understand the onset of jamming in low density colloids, whose dynamics is still time-homogeneous. Based on a small set of principles, our model provides emergent dynamic heterogeneity, reproduces the known results for dense hard sphere colloids and makes detailed, experimentally-testable predictions for canonical observables in glassy dynamics. In particular, we reproduce the shape of the intermediate scattering function and particle mean-square displacements for jammed colloidal systems, and we predict a growth for the peak of the χ(4) mobility correlation function that is logarithmic in waiting-time. At the same time, our model suggests a novel unified description for the irreversible aging dynamics of structural and quenched glasses based on the dynamical properties of growing clusters of highly correlated degrees of freedom.

Ageing in dense colloids as diffusion in the logarithm of time

The far-from-equilibrium dynamics of glassy systems share important phenomenological traits. A transition is generally observed from a time-homogeneous dynamical regime to an ageing regime where physical changes occur intermittently and, on average, at a decreasing rate. It has been suggested that a global change of the independent time variable to its logarithm may render the ageing dynamics homogeneous: for colloids, this entails diffusion but on a logarithmic timescale. Our novel analysis of experimental colloid data confirms that the mean square displacement grows linearly in time at low densities and shows that it grows linearly in the logarithm of time at high densities. Correspondingly, pairs of particles initially in close contact survive as pairs with a probability which decays exponentially in either time or its logarithm. The form of the probability density function of the displacements shows that long-ranged spatial correlations are very long-lived in dense colloids. A phenomenological stochastic model is then introduced which relies on the growth and collapse of strongly correlated clusters ('dynamic heterogeneity'), and which reproduces the full spectrum of observed colloidal behaviors depending on the form assumed for the probability that a cluster collapses during a Monte Carlo update. In the limit where large clusters dominate, the collapse rate is [Formula: see text], implying a homogeneous, log-Poissonian process that qualitatively reproduces the experimental results for dense colloids. Finally, an analytical toy-model is discussed to elucidate the strong dependence of the simulation results on the integrability (or lack thereof) of the cluster collapse probability function.

Glassy dynamics in thermally activated list sorting

Sorting the integers 1 through N into an ordered list is a simple task that can be done rapidly. However, using an algorithm based on the thermally activated pairwise exchanges of neighboring list elements, we find sorting can display many features of a glass, even for lists as small as N=5. This includes memory and rejuvenation effects during aging-two hallmarks of glassy dynamics that have been difficult to reproduce in standard glass simulations.

Logarithmic decay in single-particle relaxation of hydrated lysozyme powder

We present the self-dynamics of protein amino acids of hydrated lysozyme powder around the physiological temperature by means of molecular dynamics simulations. The self-intermediate scattering functions of the amino acid residue center of mass display a logarithmic decay over 3 decades of time, from 2 ps to 2 ns, followed by an exponential alpha relaxation. This kind of slow dynamics resembles the relaxation scenario within the beta-relaxation time range predicted by mode coupling theory in the vicinity of higher-order singularities. These results suggest a strong analogy between the single-particle dynamics of the protein and the dynamics of colloidal, polymeric, and molecular glass-forming liquids.

New dissipation relaxation phenomenon in oscillating solid (4)He

We describe the first observations on the time-dependent dissipation when the drive level of a torsional oscillator containing solid (4)He is abruptly changed. The relaxation of dissipation in solid (4)He shows rich dynamical behavior including exponential and logarithmic time-dependent decays, hysteresis, and memory effects.

Nonequilibrium Dynamics in Amorphous Si3B3N7

We present extensive numerical investigations of the structural relaxation dynamics of a realistic model of the amorphous high-temperature ceramic a-Si3B3N7, probing the mean-square displacement of the atoms, the bond survival probability, the average energy, the specific heat, and the two-point energy average. Combining the information from these different sources, we identify a transition temperature Tc approximately 2000 K below which the system is no longer ergodic and physical quantities observed over a time t(obs) show a systematic parametric dependence on the waiting time t(w), or age, elapsed after the quench. The aging dynamics "stiffens" as the system becomes older, which is similar to the behavior of highly idealized models such as Ising spin glasses and Lennard-Jones glasses.

Anomalous rotational relaxation: a fractional Fokker-Planck equation approach

In this study we have analytically obtained the relaxation function in terms of rotational correlation functions based on Brownian motion for complex disordered systems in a stochastic framework. We found out that the rotational relaxation function has a fractional form for complex disordered systems, which indicates that relaxation has nonexponential character and obeys the Kohlrausch-William-Watts law, following the Mittag-Leffler decay.

Glasslike dynamical behavior in hierarchical models submitted to continuous cooling and heating processes

The dynamical behavior of a kind of models with hierarchically constrained dynamics is investigated. The models exhibit many properties resembling real structural glasses. In particular, we focus on the study of time-dependent temperature processes. In cooling processes, a phenomenon analogous to the laboratory glass transition appears. The residual properties are analytically evaluated, and the concept of fictive temperature is discussed on a physical basis. The evolution of the system in heating processes is governed by the existence of a normal solution of the evolution equations, which is approached by all the other solutions. This trend of the system is directly related to the glassy hysteresis effects shown by these systems. The existence of the normal solution is not restricted to the linear regime around equilibrium, but it is defined for any arbitrary, far-from-equilibrium, situation.

Slow logarithmic relaxation in models with hierarchically constrained dynamics

A general kind of model with hierarchically constrained dynamics is shown to exhibit logarithmic anomalous relaxation similar to a variety of complex strongly interacting materials. The logarithmic behavior describes most of the decay of the response function.