Glassy Behavior Research Articles

Study of the synergistic role of multivalence states of 3d cations on the crystal lattice distortion and magnetic behavior of Sr2FeCoO6-δ: A spectroscopic study

In perovskite oxides, the multiple charge states of cations influence their local structure and correlated physical properties. In this report, we studied the role of multivalence cations on the local structure and magnetic behavior of the oxygen-deficient system Sr2FeCoO6-δ (SFCO), prepared by the solid-state synthesis technique. A detailed structural and geometrical analysis confirmed the coexistence of orthorhombic (Brownmillerite) and cubic crystal symmetries and a gesture of the Jahn-Teller (JT) distortion. The intense Raman modes are allowed to be indexed for BO-polyhedra and JT-distortion. Experimental and theoretical analysis of the X-ray photoelectron spectroscopy (XPS) spectra supported the mixed oxidation state of Fe (Fe3+/Fe4+) and Co (Co2+/Co3+), further confirmed by theoretically simulated X-ray absorption spectroscopy (XAS) spectra. The presence of the multivalence states leads to AFM/FM exchange interaction in the sample which further leads to glassy magnetic behavior.

Photodegradation of polylactic acid: Characterisation of glassy and melt behaviour as a function of molecular weight

During the COVID-19 pandemic, UV-C germicidal lamps became widely available, even for household applications. However, their long-term degradation effects on the mechanical and rheological properties of polylactic acid (PLA) are still not well established. The relationship between degradation and its effects on the molecular structure and macroscale properties are hardly known. In this study, we investigated the effects of long-term exposure to UV-C irradiation on the properties of PLA and interpreted the results at the molecular scale. We performed gel permeation chromatography, Fourier-transform infrared spectroscopy and UV–Vis spectroscopy to analyse changes in chemical structure induced by the UV-irradiation. Then, we carried out thermal, rheological and tensile tests to investigate mechanical and melting properties, and we investigated the applicability of these test results to estimate molecular weight loss. We have created a 3D irradiation map that can facilitate the design of disinfection devices. Based on our results, we propose a maximum number of sterilisation cycles (13 cycles) for the tested PLA films that do not result in significant changes in tensile strength and modulus.

Z-shaped dejamming phase diagram of colloidal gels

For physically gelled colloidal suspensions, there are two routes to transform the gel from solid to liquid. One is to raise the temperature, and the other is to increase the shear deformation. In this investigation, we found that the phase boundary of this solid-to-liquid transformation exhibits a surprising Z-shaped curve in the strain-temperature plane. This nonmonotonic feature in phase transition appears to be present in various nanoparticle-filled colloidal gels with significant differences in chemical composition, filler type, structure, particle shape, average diameter, and particle size distribution. By applying the Kraus model to the breakage and restoration of filler networks and comparing our findings to nonequilibrium glassy behavior, we found that this nonmonotonic phenomenon can be theoretically predicted by combining the glassy melting kinetics of filler networks at high temperatures with the viscosity-retarded dissociation between particles at low temperatures.

Fingerprints of super spin-glass state in two-dimensional nanoscopic system

Novel two-dimensional magnetic assembly was designed, manufactured, and its static and dynamic magnetic response was investigated. The assembly contains Fe3O4 nanoparticles of nominal size 7 nm which were deposited on plasma-treated polypropylene substrate using a grafting technique. The nanoparticles create agglomerates with size distribution ranging nominally from 10 nm to 110 nm. The temperature dependence of zero-field and field-cooled susceptibility is consistent with glassy behavior. The relative shift of maximum in alternating susceptibility Γ ≈ 0.075 and zυ = 10 obtained from critical slowing down analysis also support the formation of the collective states akin to super spin-glass. However, the absence of collapse in dynamic scaling of alternating susceptibility data using predictions for three-dimensional spin-glass with Gaussian distribution of magnetic coupling and two-dimensional bimodal spin-glass suggests that the studied system is not representative of the used limiting models. The investigation of memory effects revealed the coexistence of relaxation phenomena of collective degrees of freedom and individual nanoparticles. The obtained results suggest that the studied assembly is appropriate for the investigation of super spin-glass state in two-dimensional magnetic system with dominant dipolar interaction.

Observation of Griffiths phase, spin glass behaviour and magnetocaloric effect in frustrated Ga2Mn2-xCrxO7 (x = 0, 0.1, 0.3, 0.5) pyrochlore compounds

New series of pyrochlore compounds Ga2Mn2-xCrxO7 (x = 0–0.5) has been synthesized by conventional solid-state reaction method. The X-ray diffraction analysis confirms a single-phase cubic structure of the prepared compounds. All compounds undergo a paramagnetic-antiferromagnetic transition at the Néel transition temperature, close to 42 K. Below ∼12 K temperature, magnetization measurements reveal a glassy behaviour. The value of frustration parameter indicates the presence of a spin frustration. All the compounds exhibit the Griffiths phase. The Arrott's plots confirmed a second-order magnetic phase transition. Moreover, under 5 T applied magnetic field, the maximum value of magnetic entropy change −ΔS was 1.36 J/kg.K for Ga2Mn2O7 compound, which slightly increased to 1.47 J/kg.K for the compound with x = 0.5. At 21 K, the relative cooling power value enhanced from 42.96 J/kg to 47.73 J/kg with Cr4+-ion content changing from x = 0 to x = 0.5.

Hydration solids.

Hygroscopic biological matter in plants, fungi and bacteria make up a large fraction of Earth's biomass1. Although metabolically inert, these water-responsive materials exchange water with the environment and actuate movement2-5 and have inspired technological uses6,7. Despite the variety in chemical composition, hygroscopic biological materials across multiple kingdoms of life exhibit similar mechanical behaviours includingchanges in size and stiffness with relative humidity8-13. Here we report atomic force microscopy measurements on the hygroscopic spores14,15 of a common soil bacterium and develop a theory that captures the observed equilibrium, non-equilibrium and water-responsive mechanical behaviours, finding that these are controlled by the hydration force16-18. Our theory based on the hydration force explains an extreme slowdown of water transport and successfully predicts a strong nonlinear elasticity and a transition in mechanical properties that differs from glassy and poroelastic behaviours. These results indicate that water not only endows biological matter with fluidity but also can-through the hydration force-control macroscopic properties and give rise to a 'hydration solid' with unusual properties. A large fraction of biological matter could belong to this distinct class of solid matter.

Electronic and magnetic properties of Lu and LuH2

Clarifying the electronic and magnetic properties of lutetium, lutetium dihydride, and lutetium oxide is very helpful to understand the emergent phenomena in lutetium-based compounds (such as superconductivity-like transitions near room temperature). However, this kind of study is still scarce at present. Here, we report on the electronic and magnetic properties of lutetium metals, lutetium dihydride powders, and lutetium oxide powders. Crystal structures and chemical compositions of these samples were characterized by x-ray diffraction and x-ray photoemission spectroscopy, respectively. Electrical transport measurements show that the resistance of lutetium has a linear behavior depending on temperature, whereas the resistance of lutetium dihydride powders changes little with decreasing the temperature. More interestingly, paramagnetism-ferromagnetism-spin glass transitions were observed at near 240 and 200 K, respectively, in lutetium metals. To understand their origins, the measurement of inductively coupled plasma optical emission spectroscopy was performed, revealing that the concentrations of dilute magnetic impurities in lutetium and lutetium dihydride are around 0.01%, which can lead to the presence of spin glassy behavior. Our work uncovers the complex magnetic properties of lutetium and lutetium dihydride and suggests their close connections to the electronic and magnetic transitions of Lutetium-based compounds (such as Lu–H–N).

Structural modulation and spin glassiness upon oxidation in oxygen storage material LnFeMnO4+x for Ln = Y, Lu, and Yb

The mixed valence multiferroic LnFe2+Fe3+O4 (where Ln = Y, Lu, and Yb) can reversibly uptake oxygen into its lattice, which is evidenced by a crystallographic phase transition along with the appearance of structural modulations. In this study, we show that the Mn-substituted version of this multiferroic can also be readily oxidized to LnFe3+Mn3+O4.5 revealing similar oxygen storage behavior. Through neutron, electron, and synchrotron x-ray diffraction studies, we observe a structural modulation that we attribute to a displacement wave in the fully oxidized compound. This wave exhibits commensurability with a wavevector q = (−2/7, 1/7, 0). Bond valence summation analysis of plausible interstitial oxygen positions suggests that oxygen insertion likely occurs at the middle of the Fe/Mn–O bipyramid layers. The structural modulation of LnFeMnO4.5 is two-dimensional, propagates along the ab-plane, and is highly symmetric as 12 identical modulation vectors are observed in the diffraction patterns. The nature of the lanthanide, Ln3+, does not seem to influence such modulations since we observe identical satellite reflections for all three samples of Ln = Y, Lu, and Yb. Both LnFeMnO4 and LnFeMnO4.5 display spin glassy behavior with 2D short-range magnetic ordering being observed in LnFeMnO4. Analysis of the neutron diffraction data reveals a correlation length of ∼10 nm. Upon oxidation to LnFeMnO4.5, the short-range magnetic order is significantly suppressed.

Tailoring amide N-substitution to direct liquid crystallinity in benzanilide-based dimers

The design of liquid crystalline dimers containing tertiary benzanilide groups has proved challenging due to their strong preference for the E amide conformation. In this work we have investigated the effect of different N-substituents on the amide conformation of model benzanilide monomers and found this had effectively no effect on conformation. Based on this observation, we investigated the effect of introducing large, flexible decyl chains at the amide nitrogen and compare their properties to the corresponding benzanilide-based dimers with lateral methyl substituents. The introduction of the decyl chain decreases the melting temperatures, and the tendency to crystallise, promoting glassy behaviour. This allows for nematic behaviour to be seen to much lower temperatures.

Emergent Glassy Behavior in a Kagome Rydberg Atom Array.

We present large-scale quantum MonteCarlo simulation results on a realistic Hamiltonian of kagome-lattice Rydberg atom arrays. Although the system has no intrinsic disorder, intriguingly, our analyses of static and dynamic properties on large system sizes reveal emergent glassy behavior in a region of parameter space located between two valence bond solid phases. The extent of this glassy region is demarcated using the Edwards-Anderson order parameter, and its phase transitions to the two proximate valence bond solids-as well as the crossover towards a trivial paramagnetic phase-are identified. We demonstrate the intrinsically slow (imaginary) time dynamics deep inside the glassy phase and discuss experimental considerations for detecting such a quantum disordered phase with numerous nearly degenerate local minima. Our proposal paves a new route to the study of real-time glassy phenomena and highlights the potential for quantum simulation of a distinct phase of quantum matter beyond solids and liquids in current-generation Rydberg platforms.

Coexistence of superparamagnetism and superspin glass in non-stoichiometric Zn0.5Ca0.5Fe2O4 nanoferrite

In this manuscript, we report the coexistence of superparamagnetic-super spin glass phase in aggregated non-stoichiometric Zn0.5Ca0.5Fe2O4 ferrite nanoparticles (ZCF NPs). A polycrystalline sample of ZCF NPs was synthesized by the self-ignition sol–gel route and characterized using a variety of techniques. Extensive temperature, field and wait-time dependent dc-magnetization & ac-susceptibility measurements were performed for elucidating the magnetism of ZCF NPs. M−H & Mössbauer data at 300 K and M−T curves in ZFC & FC protocols revealed that ZCF NPs exhibit dominant superparamagnetic (SPM) character at 300 K with Ms = 16 emu/g & TB ∼ 120 K. Magnetically disordered surface over a single domain core of ZCF NPs has been established by the shift in coercivity at 5 K in ZFC and FC protocols. ZFC magnetization for a single stop and wait protocol exhibited an ageing dip at the stop temperature (72 K) with waiting time. It is shown that the in-phase peak of ac-susceptibility vs. temperature curves shifts towards higher temperature with driving frequencies and obeys dynamic scaling & Vogel-Fulcher law. These findings affirmed presence of glassy states in ZCF NPs due to interacting magnetic nanoparticles. On cooling the random ensemble of ZCF NPs, interparticle dipolar interactions lead to genesis of glassy behaviour, which is identified as superspin glass (SSG). Observation of memory and rejuvenation in a quasi-equilibrium magnetic state due to the collective nature of low-temperature spin dynamics differ ZCF NPs from canonical spin-glass. Extensive magnetic studies on ZCF NPs revealed a crossover of SPM to SSG phase just below TB at 115 K due to the random distribution of magnetic momenta, anisotropy and interparticle interactions.

Chloroplasts in plant cells show active glassy behavior under low-light conditions

Plants have developed intricate mechanisms to adapt to changing light conditions. Besides phototropism and heliotropism (differential growth toward light and diurnal motion with respect to sunlight, respectively), chloroplast motion acts as a fast mechanism to change the intracellular structure of leaf cells. While chloroplasts move toward the sides of the plant cell to avoid strong light, they accumulate and spread out into a layer on the bottom of the cell at low light to increase the light absorption efficiency. Although the motion of chloroplasts has been studied for over a century, the collective organelle motion leading to light-adapting self-organized structures remains elusive. Here, we study the active motion of chloroplasts under dim-light conditions, leading to an accumulation in a densely packed quasi-2D layer. We observe burst-like rearrangements and show that these dynamics resemble systems close to the glass transition by tracking individual chloroplasts. Furthermore, we provide a minimal mathematical model to uncover relevant system parameters controlling the stability of the dense configuration of chloroplasts. Our study suggests that the meta-stable caging close to the glass transition in the chloroplast monolayer serves a physiological relevance: Chloroplasts remain in a spread-out configuration to increase the light uptake but can easily fluidize when the activity is increased to efficiently rearrange the structure toward an avoidance state. Our research opens questions about the role that dynamical phase transitions could play in self-organized intracellular responses of plant cells toward environmental cues.

Glass Formation in Mechanically Interlocked Ring Polymers: The Role of Induced Chain Stiffness

Polymer-related materials exhibit rich glassy behaviors at different length scales due to their various molecular structures and topological constraints. Recent studies have identified transient interpenetration of the long-chain rings contributing to dynamic arrest on the center-of-mass level. Interpenetration of rings is proposed as an approach to facilitate glass formation in polymer melts. In this work, inspired by recent advances in the synthesis of mechanically interlocked polymers, we investigate glass transition on the nanometer-scale segments influenced by permanent interpenetration of rings using molecular dynamics simulations. We find that decreasing chain length in the mechanically interlocked system is equivalent to inducing an effective chain stiffness on the subrings. The induced stiffness provides a unified explanation for these unique structural features and transient dynamic arrest in the system of interlocked rings with rather short chains. Further, a crossover is observed in the scaling relation between localization and glassy depth upon cooling. Our work reveals a dynamic transition from weak to strong caging at the crossover temperature. According to the localization model, we demonstrate that the chain stiffness increases the critical temperature and oscillation distance, which therefore leads to more fragile dynamics and a deeper glassy state. These findings are consistent with the predictions of molecular simulations and theories for polymers with real local stiffness. Our work deepens the understanding of the role of induced stiffness on glass transition, and it opens up a new direction to design rich glass materials by manipulating stiffness through mechanical bonds.

Logarithmic Relaxation of the Nonequilibrium State of the Charge Density Wave in TbTe3 and HoTe3 Compounds

The measurements of electronic transport including the dynamic properties of the charge density wave (CDW) in the quasi-two-dimensional compound HoTe3 have been performed. The effects of the slow relaxation of the nonequilibrium state of the CDW during isothermal exposure in the zero current mode, previously observed in TbTe3, have been discovered and studied. A significant increase in the exposure time made it possible to clearly demonstrate that the relaxation is logarithmic. Relaxation features were studied in different temperature and time ranges. The data obtained indicate the glassy behavior of the CDW pinning centers in rare-earth tritellurides.

CaFeFeNbO6 - an iron-based double double perovskite.

Ordering of cations is important for controlling properties of ABO3 perovskites, and CaFeFeNbO6 is the first example of an Fe-based AA'BB'O6 double double perovskite, with Ca2+/Fe2+ ordered on A-site columns, and Fe3+/Nb5+ at the octahedral B-sites. Substantial (37%) antisite disorder of the latter cations leads to spin glassy magnetism below a freezing transition at 12 K. The CaMnFeNbO6 analogue also shows substantial cation disorder and spin glassy behaviour. Comparison of synthesis pressures for ordered materials based on different A-site transition metals, suggests that pressures of at least 14-18 GPa will be required to discover the expected plethora of double double perovskites based on A' cations smaller than Mn2+.

Field-driven Modulation of Spin Hall Magnetoresistance in Nanoscale-layered Pt/IrMn₃/NiFe Heterostructures

Spin Hall magnetoresistance (SMR) emerges from both spin Hall effect (SHE) and inverse spin Hall effect (ISHE), which is usually investigated in a nonmagnetic heavy metal (NM) in contact with a ferromagnet (FM). Depending on the orientation of FM magnetization and spin polarization of NM layer, the transmission or reflection of the spin current at the FM\NM interface could occur. SMR was investigated in 1.5 nm NiFe\3.0 nm IrMn₃\3.0 nm Pt magnetic heterostructures. IrMn₃ thin film grown on ferromagnetic NiFe layer exhibits the glassy magnetic behavior and displays spin reorientation transition in the magnetic field-temperature space. Below the Néel temperature of IrMn₃, the angle dependence of MR measurement in the xy and xz plane showed a normal positive SMR. However, a sign change in SMR was observed in the magnetic field applied in the yz plane. The switching from negative to positive SMR occurs at the field above a critical value of 6 kG. Our results provide a potential advantage for the source of spin flow in the signal in multilayer heterostructures and highlight the importance of magnetic structure (Néel vector) in AF, which opens the possible way to manipulate the spin current transportation and AF memory devices.

Nickel substitution induced reentrant spin glass behavior in EuGa4

Typically, atomic scale disorder is essential to show glassy behavior and amorphous materials can be the optimum candidates in this regard. Generating local disorder in an ordered material by substitution of another metal is a challenging task. In this paper, we successfully substituted Ni in ${\mathrm{EuGa}}_{4}$ (${\mathrm{EuNi}}_{0.37}{\mathrm{Ga}}_{3.63}$) to induce spin glass (SG) behavior. The compound was characterized by single-crystal x-ray diffraction, dc magnetization, frequency-dependent ac susceptibility, isothermal magnetization at various temperatures, spin relaxation, specific heat, and electric resistivity. Two distinct anomalies were observed in dc susceptibility $\ensuremath{\sim}16.5$ and 5.2 K corresponding to long-range antiferromagnetic (AFM) ordering and SG transition, respectively. Their characteristic peaks in specific heat capacity further support the AFM and SG behavior. The irreversibility temperature is fitted with the Almeida-Thouless equation, confirming the Ising SG. The SG behavior is further confirmed by shift of maxima to a high temperature in ac susceptibility with increasing frequency. Nonzero spin relaxation after 7200 s, fitted with stretched exponential model, provides the value of $\ensuremath{\beta}=0.41$. This material can be identified as a possible reentrant SG as AFM and SG behavior coexist in the low-temperature range. Additionally, a spin-flip transition is observed in the AFM region ($5.2\phantom{\rule{0.28em}{0ex}}\mathrm{K}<T<16.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$). Our first-principles calculations show Ni substitution induces the distortion in electronic band structure as compared with parent ${\mathrm{EuGa}}_{4}$. A minimal difference between the different magnetic configurations for Ni-substituted ${\mathrm{EuGa}}_{4}$ suggests the frustration in the lattice, pointing toward SG behavior.

High-Pressure Synthesis and Magnetic and Electrical Properties of Fe-Doped Bi3Re3O11 and Bi3Os3O11

Under high-pressure and high-temperature conditions, doped Bi3Re3O11 and Bi3Os3O11 with Fe up to 29 atomic % were synthesized. The crystal structures and chemical compositions of Bi3Os2.45Fe0.55O11 and Bi3Re2.13Fe0.87O11 were determined by synchrotron powder X-ray diffraction and electron probe microanalysis. Both crystal structures were explained by a KSbO3-type model with the space group Pn3̅. Magnetic and electronic transport property measurements showed that Bi3Os2.45Fe0.55O11 exhibited a ferrimagnetic transition at the highest magnetic ordering temperature of 490 K in the KSbO3-type, while Bi3Re2.13Fe0.87O11 exhibited a spin glassy behavior below 22 K. The magnetoresistance at 5 K and 90 kOe was almost zero for Bi3Os2.45Fe0.55O11, but -10% for Bi3Re2.13Fe0.87O11. These results suggest that KSbO3- type 5d oxides, which exhibit only weak temperature-dependent paramagnetism to date, are a group of compounds that can be converted into spintronic materials by doping with 3d elements, leading to the development of new KSbO3-type materials with both theoretical and practical significance.

Active glassy dynamics is unaffected by the microscopic details of self-propulsion.

Recent years have seen a rapid increase of interest in dense active materials, which, in the disordered state, share striking similarities with the conventional passive glass-forming matter. For such passive glassy materials, it is well established (at least in three dimensions) that the details of the microscopic dynamics, e.g., Newtonian or Brownian, do not influence the long-time glassy behavior. Here, we investigate whether this still holds true in the non-equilibrium active case by considering two simple and widely used active particle models, i.e., active Ornstein-Uhlenbeck particles (AOUPs) and active Brownian particles (ABPs). In particular, we seek to gain more insight into the role of the self-propulsion mechanism on the glassy dynamics by deriving a mode-coupling theory (MCT) for thermal AOUPs, which can be directly compared to a recently developed MCT for ABPs. Both theories explicitly take into account the active degrees of freedom. We solve the AOUP- and ABP-MCT equations in two dimensions and demonstrate that both models give almost identical results for the intermediate scattering function over a large variety of control parameters (packing fractions, active speeds, and persistence times). We also confirm this theoretical equivalence between the different self-propulsion mechanisms numerically via simulations of a polydisperse mixture of active quasi-hard spheres, thereby establishing that, at least for these model systems, the microscopic details of self-propulsion do not alter the active glassy behavior.

A viscoelastic-viscoplastic constitutive model for nanoparticle-reinforced epoxy composites: Particle, temperature, and strain rate effects

The mechanical behavior of nanoparticle-reinforced epoxy (NP/epoxy) exhibits highly nonlinear characteristics accompanied by particle, temperature, and strain rate effects, which are of great significance in the study of composites. This study presents a viscoelastic-viscoplastic (VE-VP) constitutive model applied to rigid silica and soft rubber nanoparticle reinforced epoxies (SNP/epoxy and RNP/epoxy), which are subjected to a wide strain rates and temperatures. The proposed constitutive model is based on the decomposition of the Helmholtz free energy into equilibrium and non-equilibrium parts. The equilibrium part employs the hyperelastic strain energy density function to capture the rubbery state property. The non-equilibrium part is decomposed into viscoelastic strain energy density functions and viscoplastic dissipation potential to capture the glassy state behavior. Temperature- and particle- dependent models were introduced into the proposed VE-VP model. To validate the effectiveness of the VE-VP model, the uniaxial compressive responses of the SNP/epoxy and RNP/epoxy were systematically tested. The results demonstrate that the VE-VP constitutive model can capture the nonlinear compressive behaviors of SNP/epoxy and RNP/epoxy over a strain-rate range of 10 − 2 s − 1 to 10 3 s − 1 and a temperature range of − 80 ℃ to 80 ℃ . Finally, the analysis of the model parameters indicates that the strain softening and hardening are strongly affected by the temperature and strain rate. • Two typical nanoparticles (rigid silica and soft rubber) are utilized to reinforced epoxy. • A viscoelastic-viscoplastic constitutive model for nanoparticles reinforced epoxy incorporating the particle, temperature and strain rate effects is proposed. • The compressive behaviors over wide range of temperature and strain rate are experimentally investigated and well predicted by proposed model. • The activation energy and hyperelastic coefficient in proposed model are strongly affected by temperature and strain rate.