Re-entrant Glass Research Articles

Observation of the multiple magnetic phases in double perovskite Pr1.8La0.2CoFeO6

The structural and magnetic properties of the double perovskite Pr1.8La0.2CoFeO6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism withTN ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (TG ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; HSEB∼ 1.8 kOe and giant conventional exchange bias, HCEB∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below TN, clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly.

From flocking to glassiness in dense disordered polar active matter

AbstractLiving materials such as biological tissues or bacterial colonies are collections of heterogeneous entities of different sizes, capable of autonomous motion, and often capable of cooperating. Such a degree of complexity brings to collective motion on large scales. However, how the competition between geometrical frustration, autonomous motion, and the tendency to move cooperatively impact large-scale behavior remains an open question. We implement those three ingredients in a model of active matter and show that the system, in forming migratory patterns, can arrange in bands or develop long-range order, depending on the density of the system. We also show that the active material undergoes a reentrant glass transition triggered by the alignment interaction that typically causes only collective migratory motion. Finally, we observe that polar order destroys active phase separation, producing homogeneous, disordered moving configurations.

High-Temperature Ferroic Glassy States in SrTiO_{3}-Based Thin Films.

Disordered ferroics hold great promise for next-generation magnetoelectric devices because their lack of symmetry constraints implies negligible hysteresis with low energy costs. However, the transition temperature and the magnitude of polarization and magnetization are still too low to meet application requirements. Here, taking the prototype perovskite of SrTiO_{3} as an instance, we realize a coexisting spin and dipole reentrant glass states in SrTiO_{3} homoepitaxial films via manipulation of local symmetry. Room-temperature saturation magnetization and spontaneous polarization reach ∼ 10 emu/cm^{3} and ∼ 25 μC/cm^{2}, respectively, with high transition temperatures (101K and 236K for spin and dipole glass temperatures and 556K and 1100K for Curie temperatures, respectively). Our atomic-scale investigation points out an underlying mechanism, where the Ti/O-defective unit cells break the local translational and orbital symmetry to drive the formation of unusual slush states. This study advances our understanding of the nature of the intricate couplings of ferroic glasses. Our approach could be applied to numerous perovskite oxides for the simultaneous control of the local magnetic and polar orderings and for the exploration of the underlying physics.

Ultrahigh thermal stability of dielectric permittivity in 0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Ti0.875Nb0.125)O3

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior.

The kinetics of reentrant glass transition in metallic liquids

Reentrant glass transition is a new glass-transition phenomenon in which a devitrified liquid reenters a second glassy state and is well-known in some colloidal systems. Reentrant glass transition has been recently discovered in metallic-liquid systems but its ongoing mechanisms remain mostly unknown. Here, the reentrant glass transition of a series of Pd-Ni-P metallic liquids are investigated using fast-calorimetric analyses and ab-initio molecular dynamics simulation. While the amount of heat release of reentrant glass transition in different Pd-Ni-P liquids are similar, the change of liquid kinetics itself results in different reentrant-glass-transition behaviors: the transition kinetics is governed by the fast hopping of P atoms rather than the cooperative liquid motions related with vitrification. The reentrant glass transition is found to be related to medium-range structural ordering process through vertex-sharing of the P-centered polyhedral clusters. The kinetics map of liquid freezing for Pd-Ni-P glass-forming liquids over broad ranges of heating-rate and composition is presented.

Double glassy states and large spontaneous and conventional exchange bias in La1.5Ca0.5CoFeO6 ferrimagnetic double perovskite

The structural and magnetic properties of hole doped double perovskite La1.5Ca0.5CoFeO6 have been investigated by measuring x-ray photoemission spectroscopy, neutron powder diffraction and magnetization. A ferrimagnetic transition is observed at T C∼ 167 K. The presence of anti-site disorder (ASD) in La1.5Ca0.5CoFeO6 has also been demonstrated. Double re-entrant cluster glass transitions (T 1∼ 11 K and TS ∼ 35 K) were observed which has been attributed to the ASD effect. The presence of both large spontaneous exchange bias H SEB ∼ 2.106 kOe and giant conventional exchange bias H CEB ∼ 1.56 T at 5 K has also been observed which can be attributed to the coexistence of long range magnetic ordering and glassy state. The experimental observations were explained with the results obtained by the density functional theory calculation. The presence of double glassy states, large exchange-bias effect and different magnetic phases make this system a potential candidate for spintronic applications.

Reentrant strain glass transition in Ti-Ni-Cu shape memory alloy

Reentrant glass transition, referring to a reversible transition from a high-temperature ordered phase to a low-temperature glassy phase, is unusual and difficult to be understood, because at low temperature the glassy phase is usually less thermodynamically stable than the ordered phase. In this work, we report a systematic study of a reentrant strain glass (RSTG) transition between a strain-ordered martensitic phase and a strain glass in a Ti50Ni34Cu16 shape memory alloy. This transition is characterized by a temperature invariance of average B19 martensitic structure, a deviation in heat flow and resistivity curves, a frequency-dependent behavior of storage modulus and internal friction curves, and a peak in a zero-field cooling curve. In-situ microstructural observations show that the B19 martensitic domain pattern keeps unchanged upon cooling while nanodomains with local 4H symmetry gradually emerge and grow in large martensitic domains. Moreover, the RSTG transition exhibits low modulus (∼24 GPa) and high damping (tan δ > 0.075) over a large temperature range. Based on experimental results, we established a new Ti50Ni50-xCux phase diagram with the RSTG state included. This phase diagram helps understand the abnormal formation of RSTG: since Cu dopants stabilize the B19 phase instead of B19’ phase, with sufficient Cu dopants (x = 16) the B19-B19’ transition is thermodynamically suppressed and the RSTG transition appears, which resembles the conventional strain glass formation in a Ti50-xNi50+x phase diagram. The microstructural evolution of RSTG with nanodomains embedded in large domains explains novel properties and puzzles in Ti-Ni-Cu alloys. We further predict more unusual properties could be found in RSTG materials.

Structural and short-time vibrational properties of colloidal glasses and supercooled liquids in the vicinity of the re-entrant glass transition.

We investigate the short-time vibrational properties and structure of two-dimensional, bidisperse, colloidal glasses and supercooled liquids in the vicinity of the re-entrant glass transition, as a function of interparticle depletion attraction strength. The long-time spatiotemporal dynamics of the samples are measured to be non-monotonic, confirming that the suspensions evolve from repulsive glass to supercooled liquid to attractive glass with increasing depletion attraction. Here, we search for vibrational signatures of the re-entrant behavior in the short-time spatiotemporal dynamics, i.e., dynamics associated with particle motion inside its nearest-neighbor cage. Interestingly, we observe that the anharmonicity of these in-cage vibrations varies non-monotonically with increasing attraction strength, consistent with the non-monotonic long-time structural relaxation dynamics of the re-entrant glass. We also extract effective spring constants between neighboring particles; we find that spring stiffness involving small particles also varies non-monotonically with increasing attraction strength, while stiffness between large particles increases monotonically. Last, from study of depletion-dependent local structure and vibration participation fractions, we gain microscopic insight into the particle-size-dependent contributions to short-time vibrational modes in the glass and supercooled liquid states.

Emergence of metamagnetic transition, re-entrant cluster glass and spin phonon coupling in Tb2CoMnO6

The double perovskite compound Tb2CoMnO6 has been investigated using x-ray absorption spectroscopy (XAS), Raman spectroscopy, magnetic measurements and ab initio band structure calculations. It is observed that both anti-ferromagnetic (AFM) and ferromagnetic (FM) phase coexist in this material. The presence of anti-site disorder (ASD) has been established from the analysis of neutron diffraction data. Moreover, a prominent metamagnetic transition is observed in the M(H) behavior that has been explained with the drastic reorientation of the pinned domain which are aligned antiparallel by the antiphase boundaries (APBs) at zero field. The ASD further gives rise to spin frustration at low temperature which leads to the re-entrant cluster glass ∼33 K. The coupling between phononic degree of freedom and spin in the system has also been demonstrated. It is observed that the theoretical calculation is consistent with that of the experimentally observed behavior.

The Spontaneous Exchange Bias Effect on La1.5Ba0.5CoMnO6

La1.5Ba0.5CoMnO6 is a re-entrant cluster glass material exhibiting a robust negative exchange bias (EB) effect even after being cooled from an unmagnetized state down to low temperature in zero magnetic field. Here we thoroughly investigate this phenomena by performing magnetization as a function of applied field [M(H)] measurements at several different temperatures and maximum applied magnetic fields (Hm). The spontaneous EB (SEB) effect is observed below 20 K, and shows a maximum value for Hm = 75 kOe. The effect is greatly enhanced when the M(H) curves are measured after the system is cooled in the presence of a magnetic field. The asymmetry of the M(H) curves here investigated can be well described by a recently proposed model based on the unconventional relaxation of the SG-like moments during the hysteresis cycle.

Roles of Re-entrant cluster glass state and spin–lattice coupling in magneto–dielectric behavior of giant dielectric double perovskite La1.8Pr0.2CoFeO6

La based Co–Fe combined double perovskite (La1.8Pr0.2CoFeO6) was synthesized and the dielectric (zero-field and in-field), magnetic, x-ray absorption and Raman spectroscopy measurements have been investigated for La1.8Pr0.2CoFeO6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto–dielectric (MD) is found in two temperature regions (25–80 K and 125–275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin–lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view.

Reentrant glass transition leading to ultrastable metallic glass

Abstract Polyamorphs are often observed in amorphous matters, and a representative example is the reentrant glass transition in colloid systems. For metallic amorphous alloys, however, the cases reported so far are limited to metallic glasses (MGs) that undergo electronic transitions under gigapascal applied pressure, or the presence of two liquids at the same composition. Here we report the first observation of a reentrant glass transition in MGs. This unusual reentrant glass transition transforms an MG from its as-quenched state (Glass I) to an ultrastable state (Glass II), mediated by the supercooled liquid of Glass I. Specifically, upon heating to above its glass transition temperature under ambient pressure, Glass I first transitions into its supercooled liquid, which then transforms into a new Glass II, accompanied by an exothermic peak in calorimetric scan, together with a precipitous drop in volume, electrical resistance and specific heat, as well as clear evidence of local structural ordering on the short-to-medium-range scale revealed via in-situ synchrotron X-ray scattering. Atomistic simulations indicate enhanced ordering of locally favored motifs to establish correlations in the medium range that resemble those in equilibrium crystalline compounds. The resulting lower-energy Glass II has its own glass transition temperature higher than that of Glass I by as much as 50 degrees. This route thus delivers a thermodynamically and kinetically ultrastable MG that can be easily retained to ambient conditions.

B-site disorder driven multiple-magnetic phases: Griffiths phase, re-entrant cluster glass, and exchange bias in Pr2CoFeO6

The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques. The study revealed that Pr2CoFeO6 adopted a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating antiferromagnetic ground state. Magnetization measurements revealed that the system possesses a spectrum of competing magnetic phases, viz., long range canted antiferromagnetic (AFM) spin ordering (TN ∼ 269 K), Griffiths-like phase, re-entrant cluster glass (TG ∼ 34 K), and exchange bias effects. The neutron diffraction study divulged the exhibition of a long range G-type of canted AFM spin ordering. The random nonmagnetic dilution of magnetic Fe3+ (high spin) ions by Co3+ (low spin) ions due to B-site disorder essentially played a crucial role in manifesting such magnetic properties of the system.

B-Site Disorder and Spin States Driven Multiple-Magnetic Phases: Griffiths Phase, Re-Entrant Cluster Glass and Exchange Bias in Pr <sub>2</sub>CoFeO <sub>6</sub>

The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization, neutron powder diffraction (NPD) and X-ray magnetic circular dichroism (XMCD) techniques. Structural study revealed that Pr2CoFeO6 adopts a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating anti-ferromagnetic ground state. Magnetization measurements revealed the system to possess a spectrum of competing magnetic phases viz., long range antiferromagnetic (canted) spin ordering (TN ~269 K), Griffiths phase, re-entrant cluster glass (RCG) (TG ~34 K) and exchange bias effects. The Neutron diffraction divulged the exhibition of a long range canted G-type spin ordering by Fe spins. Moreover, the electronic structure probed by the X-ray absorption spectroscopy (XAS) study suggested a nominal valance state of +3 for both the B-site ions (Co/Fe). The random non-magnetic dilution of magnetic Fe3+ (HS) ions by Co3+ (LS) ions due to B-site disorder essentially played a crucial role in manifesting the magnetic properties of the system.

Reentrant superspin glass state and magnetization steps in the oxyborate Co2AlBO5

An oxyborate Co2AlBO5 belonging to the ludwigite family is investigated using structural, thermodynamic, dielectric and magnetic measurements. Magnetic measurements indicate that this system is seen to exhibit long range magnetic ordering at T{_N} = 42 K, signatures of which are also seen in the specific heat, dielectric susceptibility, and the lattice parameters. The absence of a structural phase transition down to the lowest measured temperatures, distinguishes it from the more extensively investigated Fe-based ludwigites. At low temperatures, the system is seen to stabilize in a reentrant superspin glass phase at T{_G} = 10.6 K from within the magnetically ordered state. This ground state is also characterized by magnetic field induced metamagnetic transitions, which at the lowest measured temperatures exhibit a number of sharp magnetization steps, reminiscent of that observed in the mixed valent manganites.

Correlated rearrangements of disordered colloidal suspensions in the vicinity of the reentrant glass transition

We experimentally investigate correlated rearrangements (dynamic heterogeneity) in disordered colloidal suspensions as a function of increasing inter-particle attraction strength across the reentrant glass transition. Attractive interactions between constituent spheres are induced by polymer depletion forces at fixed particle volume fraction. We vary sample inter-particle attraction strength and concurrently measure particle trajectories by confocal microscopy at each attraction strength. The reentrant transition from repulsive glass to ergodic fluid and from ergodic fluid to attractive glass is readily observed. As the inter-particle attraction increases, we find that inter-particle bonding causes an increasing number of particles to undergo cooperative or correlated displacements; the length scale associated with these correlated rearrangements exhibits reentrant behavior. Other dynamical quantities such as the mean square displacement, the long-time diffusion constant, and the non-Gaussian parameter also exhibit changes as a function of attraction strength. Notably, the arrested (glass) states show small particle displacements at long lag times, whereas the fluid states exhibit fast dynamics over large length scales.

Dynamical facilitation governs glassy dynamics in suspensions of colloidal ellipsoids.

One of the greatest challenges in contemporary condensed matter physics is to ascertain whether the formation of glasses from liquids is fundamentally thermodynamic or dynamic in origin. Although the thermodynamic paradigm has dominated theoretical research for decades, the purely kinetic perspective of the dynamical facilitation (DF) theory has attained prominence in recent times. In particular, recent experiments and simulations have highlighted the importance of facilitation using simple model systems composed of spherical particles. However, an overwhelming majority of liquids possess anisotropy in particle shape and interactions, and it is therefore imperative to examine facilitation in complex glass formers. Here, we apply the DF theory to systems with orientational degrees of freedom as well as anisotropic attractive interactions. By analyzing data from experiments on colloidal ellipsoids, we show that facilitation plays a pivotal role in translational as well as orientational relaxation. Furthermore, we demonstrate that the introduction of attractive interactions leads to spatial decoupling of translational and rotational facilitation, which subsequently results in the decoupling of dynamical heterogeneities. Most strikingly, the DF theory can predict the existence of reentrant glass transitions based on the statistics of localized dynamical events, called excitations, whose duration is substantially smaller than the structural relaxation time. Our findings pave the way for systematically testing the DF approach in complex glass formers and also establish the significance of facilitation in governing structural relaxation in supercooled liquids.

Multiple reentrant glass transitions in confined hard-sphere glasses.

Glass-forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro- and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition.

Reentrance in an active glass mixture.

Active matter, whose motion is driven, and glasses, whose dynamics are arrested, seem to lie at opposite ends of the spectrum in nonequilibrium systems. In spite of this, both classes of systems exhibit a multitude of stable states that are dynamically isolated from one another. While this defining characteristic is held in common, its origin is different in each case: for active systems, the irreversible driving forces can produce dynamically frozen states, while glassy systems vitrify when they get kinetically trapped on a rugged free energy landscape. In a mixture of active and glassy particles, the interplay between these two tendencies leads to novel phenomenology. We demonstrate this with a spin glass model that we generalize to include an active component. In the absence of a ferromagnetic bias, we find that the spin glass transition temperature depresses with the active fraction, consistent with what has been observed for fully active glassy systems. When a bias does exist, however, a new type of transition becomes possible: the system can be cooled out of the glassy phase. This unusual phenomenon, known as reentrance, has been observed before in a limited number of colloidal and micellar systems, but it has not yet been observed in active glass mixtures. Using low order perturbation theory, we study the origin of this reentrance and, based on the physical picture that results, suggest how our predictions might be measured experimentally.

Normal-stress coefficients and rod climbing in colloidal dispersions

We calculate tractable microscopic expressions for the low-shear normal-stress coefficients of colloidal dispersions. Although restricted to the low rate regime, the presented formulas are valid for all volume fractions below the glass transition and for any interaction potential. Numerical results are presented for a system of colloids interacting via a hard-core attractive Yukawa potential, for which we explore the interplay between attraction strength and volume fraction. We show that the normal-stress coefficients exhibit nontrivial features close to the critical point and at high volume fractions in the vicinity of the reentrant glass transition. Finally, we exploit our formulas to make predictions about rod-climbing effects in attractive colloidal dispersions.