Glass-like State Research Articles

Formation of magnetic glass in calcium-doped YBaCo2O5.5cobaltites

The d.c. magnetization and magnetic relaxation studies of the calcium doped samples, Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5, show the existence of a magnetic glass like behaviour in the family of cobaltites for the first time. Our investigations reveal glass-like arrest of kinetics at low temperature which prevents the system from reaching its magnetic ground state. We show that the low temperature state of these calcium doped phases, which consists of coexisting antiferromagnetic and ferro (or ferri) magnetic phase fractions, can be tuned in a number of ways. Our observations establish that the low temperature state of this oxide is not in thermal equilibrium. The glassy state is formed with the assistance of an external magnetic field, which makes it distinctly different from the more well known metastable state, the spin glass state. The cooling field can tune the fractions of the coexisting phases, and the glass-like state formed at low temperature can also be devitrified by warming the sample. The role of Ca doping in the appearance of these phenomena is discussed in terms of phase separation, involving Co3+ disproportionation into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters.

Magnetic ordering and slow dynamics in a Ho-based bulk metallic glass with moderate random magnetic anisotropy

Results of magnetic measurements are presented for a Ho-based bulk metallic glass, which shows similarities and differences with conventional spin glasses (SGs), and significant differences with weak random magnetic anisotropy (RMA) systems. Both ac and dc magnetic measurements indicate a single transition from paramagnetic to speromagnetic or spin glasslike state around 5.6 K. The moderate RMA prevents the formation of long- (or quasilong)-range magnetic order and slows down the spin dynamics in the critical region. Further its isothermal remnant magnetization exhibits a small maximum, instead of a gradual increase with field in SGs. The roles of RMA in the magnetic structure and dynamics of disordered and frustrated systems are discussed by comparisons between the weak RMA system, the moderate or strong RMA system, and conventional SG.

Relaxor ferroelectricity and the freezing of short-range polar order in magnetite

A thorough investigation of single crystalline magnetite using broadband dielectric spectroscopy and other methods provides evidence for relaxor-like polar order in Fe3O4. We find long-range ferroelectric order to be im-peded by the continuous freezing of polar degrees of freedom and the formation of a tunneling-dominated glasslike state at low temperatures. This also explains the lack of clear evidence for a non-centrosymmetric crystal structure below the Verwey transition. Within the framework of recent models assuming an intimate relation of charge and polar order, the charge order, too, can be speculated to be of short-range type only and to be dominated by tunneling at low temperatures.

Phase field theory of proper displacive phase transformations: Structural anisotropy and directional flexibility, a vector model, and the transformation kinetics

A phase field theory of proper displacive transformations is developed to address the microstructure evolution and its response to applied fields in decomposing and martensitic systems. The theory is based on the explicit equation for the non-equilibrium free energy function of the transformation strain obtained by a consistent separation of the total strain into transformation and elastic strains. The transformation strain is considered to be a relaxing long-range order parameter evolving in accordance with the system energetics rather than as a fixed material constant used in the conventional Eshelby theory of coherent inclusions. The elastic strain is defined as a coherency strain recovering the crystal lattice compatibility. The obtained free energy function of the transformation strain leads to the concepts of structural anisotropy and directional flexibility of low symmetry phases. The formulated vector model of displacive transformation makes apparent a similarity between proper displacive transformation and ferromagnetic/ferroelectric transformation and, in particular, a similarity between the structural anisotropy and magnetic/polar anisotropy of ferromagnetic/ferroelectric materials. It even predicts the feasibility of a glass-like structural state with unlimited directional flexibility of the transformation strain that is conceptually similar to a ferromagnetic glass. The thermodynamics of the equilibrium between low symmetry phases and the thermodynamic conditions leading to the formation of adaptive states are formulated.

Giant Nonhysteretic Responses of Two-Phase Nanostructured Alloys

A new class of functional materials with giant nonhysteretic strain responses to applied fields is considered. They are decomposed two-phase systems consisting of single-domain nanoprecipitates of a low-symmetry phase. Their strain response is caused by the field-induced change of structural orientation of the domain states of these precipitates. The superresponse follows from the novel concept of structural anisotropy that is analogous to the magnetic anisotropy. Its vanishing produces a new glasslike structural state. The developed phase field theory and modeling allow us to formulate criteria for searching superresponsive two-phase nanostructured alloys.

Influence of silicon coating on the corrosion resistance of Zn-Al-Mg-RE-Si alloy

The electric arc spraying method was used to prepare the Zn-Al-Mg-RE-Si alloy coating with different content of silicon. The corrosion resisting property was measured by copper accelerated salt spray (CASS) and corrosion weightless test. The influence of silicon content on the corrosion resisting property was investigated by XRD, SEM, polarization curve and electrochemical impedance spectroscopy (EIS) and the electrochemical property of coating in the corrosion process was analyzed. The results showed that the density of coating was improved significantly since the major nonequilibrium glass-like state phase was composed of silicon and other metals existed in the Zn-Al-Mg-RE-Si alloy coating, which prevented the corrosive medium and retarded the corrosion velocity because of compact corrosion products in the corrosion embryo. The Zn-Al-Mg-RE-Si coating had better corrosion resistance than the Zn-Al-Mg-RE because of more positive potential, half corrosion current density and double electrochemical reaction resistance.

Vitrification of human and mouse embryos using the Rapid-i™

OBJECTIVE: Vitrification normally uses direct contact with liquid nitrogen to facilitate the glass-like state. Concerns have been raised with regards to the safety and sterility of this procedure. The Rapid-i™ is a unique device that uses super-cooled air to vitrify the sample. Following development and optimization using mouse oocytes/embryos the Rapid-i™ has been used to vitrify day 3 human embryos. DESIGN: Experimental design and clinical evaluation. MATERIALS AND METHODS: Mouse oocytes, pronuclear oocytes, 8 cell embryos and blastocysts (n = >50 for each group) were vitrified using the Rapid-i™. Oocytes/embryos were warmed immediately and subsequent survival, embryo development and blastocyst cell number were recorded and compared to sibling non-vitrified controls. Embryo transfers were performed to determine viability following vitrification. For clinical evaluation day 3 human embryos from 34 patients were vitrified/warmed as described above and subsequently transferred. Statistical analysis: Fisher's exact test. RESULTS: Survival rates for mouse oocytes/embryos was >95%. Subsequent blastocyst development (Day 5) was >80%, which did not differ significantly from non-vitrified control embryos. The mean cell number in the resulting blastocysts of vitrified embryos was also not significantly different from the control. Embryo transfer of mouse blastocysts generated from vitrified pronuclear oocytes resulted in fetuses with developmental parameters comparable to control embryos. Of the 99 warmed human embryos 87% survived. A mean of 2.1 embryos were transferred resulting in a clinical pregnancy rate of 41%. CONCLUSION: The Rapid-i™, which has no direct liquid nitrogen contact during vitrification or storage, is successful at vitrifying mouse oocytes/embryos. The Rapid-i™ is capable of vitrifying day 3 human embryos with survival and pregnancy rates comparable to the open system (cryoloop) normally used.

Polymorphism of the glass former ethanol confined in mesoporous silicon

X-ray diffraction patterns of ethanol confined in parallel-aligned channels of ≈10 nm diameter and 50 µm length in mesoporous silicon have been recorded as a function of filling fraction, temperature and for varying cooling and heating rates. A sorption isotherm, recorded in the liquid state, indicates a three monolayer thick, strongly adsorbed wall layer and a capillary condensed fraction of molecules in the pore centre. Though the strongly adsorbed film remains in an amorphous state for the entire temperature range investigated, the capillary condensed molecules reproduce the polymorphism of bulk solid ethanol, that is the formation of either crystalline or glass-like states as a function of cooling rate. The critical rate necessary to achieve a vitrification in the mesopores is, however, at least two orders of magnitude smaller than that in the bulk state. This finding can be traced to both pure geometrical constraints and quenched disorder effects, the characteristic of confinement in mesoporous silicon.

Effect of strain on the phase separation and devitrification of the magnetic glass state in thin filmsof La5/8 − yPryCa3/8MnO3 (y = 0.45)

We present our study of the effect of substrate induced strain onLa5/8 − yPryCa3/8MnO3 (y = 0.45) thin filmsgrown on LaAlO3, NdGaO3 and SrTiO3 substrates that show large scale phase separation. It is observed that unstrained films grown onNdGaO3 behave quite similarly to bulk material but the strained films grown onSrTiO3 show melting of the insulating phase to the metallic phase at low temperatures. However,the large scale phase separation and metastable glass-like state is observed in all the filmsdespite differences in substrate induced strain. The measurements of resistivity as afunction of temperature under a cooling and heating in unequal field (CHUF) protocolelucidate the presence of a glass-like metastable phase generated due to kinetic arrest of thefirst order transformation in all the films. Like structural glasses, these magneticglass-like phases show evidence of devitrification of the arrested charge orderantiferromagnetic insulator (CO-AFI) phase to the equilibrium ferromagneticmetallic (FMM) phase with isothermal increase of magnetic field and/or iso-fieldwarming. These measurements also clearly show the equilibrium ground state ofthis system to be FMM and the metastable glass-like phase to be AFI phase.

Structural and physical properties evolution of BaIr 1−xMn xO 3 solid solutions synthesized by high-pressure sintering

The BaIr 1− x Mn x O 3 (0.0≤ x≤1.0) solid solutions were synthesized by using the solid-state chemical method and high pressure sintering in the pressure range 0–5 GPa. According to the pressure–composition “phase diagram” at 1000 °C, the 9M BaIr 1− x Mn x O 3 transforms to the 6M form at 5 GPa and x≤1/6. In the x range 0.5–1.0, it transforms to the 9R form in a large pressure range. For the 9M BaIrO 3, the Mn ions substitution for Ir ions enhances the semiconducting property, and reduces the weak ferromagnetism. When x is larger than 1/3, the 9M/9R BaIr 1− x Mn x O 3 behave spin–glass-like state at low temperature, with the glass transition temperature T g about 60 K. For the 6M BaIrO 3, the Mn ions doping results in that it transforms to insulator and spin–glass-like magnetism from the initial paramagnetic metal.

Deep supercooling, vitrification and limited survival to –100°C in the Alaskan beetleCucujus clavipes puniceus(Coleoptera: Cucujidae) larvae

Larvae of the freeze-avoiding beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) in Alaska have mean supercooling points in winter of -35 to -42 degrees C, with the lowest supercooling point recorded for an individual of -58 degrees C. We previously noted that some larvae did not freeze when cooled to -80 degrees C, and we speculated that these larvae vitrified. Here we present evidence through differential scanning calorimetry that C. c. puniceus larvae transition into a glass-like state at temperatures<-58 degrees C and can avoid freezing to at least -150 degrees C. This novel finding adds vitrification to the list of insect overwintering strategies. While overwintering beneath the bark of fallen trees, C. c. puniceus larvae may experience low ambient temperatures of around -40 degrees C (and lower) when microhabitat is un-insulated because of low snow cover. Decreasing temperatures in winter are correlated with loss of body water from summer high levels near 2.0 to winter lows near 0.4 mg mg(-1) dry mass and concomitant increases in glycerol concentrations (4-6 mol l(-1)) and thermal hysteresis. Finally, we provide direct evidence that Cucujus from Wiseman, Alaska, survive temperatures to -100 degrees C.

2D ISING MODEL WITH COMPETING INTERACTIONS AND ITS APPLICATION TO CLUSTERS AND ARRAYS OF π-RINGS, GRAPHENE AND ADIABATIC QUANTUM COMPUTING

We study the two-dimensional Ising model with competing nearest-neighbour and diagonal interactions and investigate the phase diagram of this model. We show that the ground state at low temperatures is ordered either as stripes or as the Néel antiferromagnet. However, we also demonstrate that the energy of defects and dislocations in the lattice is close to the ground state of the system. Therefore, many locally stable (or metastable) states associated with local energy minima separated by energy barriers may appear forming a glass-like state. We discuss the results in connection with two physically different systems. First, we deal with planar clusters of loops including a Josephson π-junction (a π-rings). Each π-ring carries a persistent current and behaves as a classical orbital moment. The type of particular state associated with the orientation of orbital moments in the cluster depends on the interaction between these orbital moments and can be easily controlled, i.e. by a bias current or by other means. Second, we apply the model to the analysis of the structure of the newly discovered two-dimensional form of carbon, graphene. Carbon atoms in graphene form a planar honeycomb lattice. Actually, the graphene plane is not ideal but corrugated. The displacement of carbon atoms up and down from the plane can be also described in terms of Ising spins, the interaction of which determines the complicated shape of the corrugated graphene plane. The obtained results may be verified in experiments and are also applicable to adiabatic quantum computing where the states are switched adiabatically with the slow change of coupling constant.

Collection and Cryopreservation of Hamster Oocytes and Mouse Embryos

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al.1 and Wilmut 2 separately described that mouse embryos could be frozen and stored at -196 °C and, a few years later, Parkening et al. 3 reported the birth of live offspring resulting from in vitro fertilization (IVF) of cryopreserved oocytes. Since then, the use of cryopreservation techniques has rapidly spread to become an essential component in the practice of human and animal assisted reproduction and in the conservation of animal genetic resources. Currently, there are two main methods used to cryopreserve oocytes and embryos: slow freezing and vitrification. A wide variety of approaches have been used to try to improve both techniques and millions of animals and thousands of children have been born from cryopreserved embryos. However, important shortcomings associated to cryopreservation still have to be overcome, since ice-crystal formation, solution effects and osmotic shock seem to cause several cryoinjuries in post-thawed oocytes and embryos. Slow freezing with programmable freezers has the advantage of using low concentrations of cryoprotectants, which are usually associated with chemical toxicity and osmotic shock, but their ability to avoid ice-crystal formation at low concentrations is limited. Slow freezing also induces supercooling effects that must be avoided using manual or automatic seeding 4. In the vitrification process, high concentrations of cryoprotectants inhibit the formation of ice-crystals and lead to the formation of a glasslike vitrified state in which water is solidified, but not expanded. However, due to the toxicity of cyroprotectants at the concentrations used, oocytes/embryos can only be exposed to the cryoprotectant solution for a very short period of time and in a minimum volume solution, before submerging the samples directly in liquid nitrogen 5. In the last decade, vitrification has become more popular because it is a very quick method in which no expensive equipment (programmable freezer) is required. However, slow freezing continues to be the most widely used method for oocyte/embryo cryopreservation. In this video-article we show, step-by-step, how to collect and slowly freeze hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

Influence of A-site size and disorder on metamagnetic transformation in A-site substituted Pr0.5Ca0.5MnO3

The influence of A-site size and disorder on metamagnetic transformation in polycrystalline Pr0.5−xLaxCa0.5MnO3 and Pr0.5Ca0.5−xBaxMnO3 at low temperature has been systematically investigated. The introduction of larger A-site cations such as La3+ or Ba2+ will locally suppress the lattice distortion. This “counterdistortion” effect becomes more pronounced with the increase in the A-site average ionic radius ⟨rA⟩, which is favorable to ferromagnetism. Thus the critical field HC1 corresponding to the first sharp metamagnetic step will decrease, and the field-induced magnetization M5 T will increase. However, the A-site ionic radii variance σ2 will dramatically increase when more barium is introduced and a spin glasslike state is induced, which is unfavorable to the stability of ferromagnetism state. Therefore, HC1 will increase and M5 T will decrease. Moreover, the evolution of resistivity at low temperature with σ2 exhibits strong correlation with that of magnetic properties.

Two-dimensional Ising model with competing interactions: Phase diagram and low-temperature remanent disorder

The two-dimensional Ising model with competing nearest-neighbor and diagonal interactions on the square lattice is studied by the transfer-matrix technique and by the Monte Carlo simulations. The phase diagram of this model is constructed with a special emphasis to the analysis of a glassy state arising as an order to disorder transition at low temperatures. Evidence of the glassy state (based, in particular, on the calculation of the average length of domain walls and on the Edwards-Anderson order parameter) and its characteristics are presented. It was shown that, in the frustrated Ising model, the domain-wall length correlates to the onset of the glassy state, that is, it may play the role of the order parameter for the Ising glass or for glasslike states in other frustrated magnetic systems.

Domain boundary pinning and elastic softening inKMnF3 and KMn1−xCaxF3

Anelastic softening related to the movement of twin boundaries is observed in improper ferroelasticKMnF3 andKMn1−xCaxF3. Wallmovement in KMnF3 shows a frequency dependence which is described in terms of an extended Debye relaxationwith an extension exponent of 0.54. This exponent indicates a fairly narrow distribution ofactivation energies near 0.43 eV. Wall movements in Ca-doped samples are best described interms of Vogel–Fulcher (VF) relaxations with a VF energy of 0.23 eV. The activationenergies are related to interaction between F vacancies or interstitials and the movingdomain walls; Ca doping appears to increase the tendency to form glass-like states. Nodomain freezing occurs at temperatures above the subsequent phase transitionI4/mcm–Pnma;the Pnma phase does not show any domain movement and anelastic behaviour. Elastic precursorsoftening is observed above the transition temperature between the cubic and thetetragonal phase. The softening can be described empirically using a power law:[(T−To)/To]−K with values ofthe exponent K around 0.5.

Glasslike state in PbFe1/2Nb1/2O3 single crystal

Magnetic properties of PbFe1/2Nb1/2O3 single crystal showed onset of glasslike behavior at 120 K, saturation of onset at 28 K, and freezing of glasslike state at 27.6 K. Zero field cooled (ZFC) and field cooled magnetization curves displayed sharp cusp in ZFC. Almeida and Toulouse line illustrated stability over 1000 Oe with unstable onset for low field. Magnetic hysteresis was observed below glasslike freezing temperature having steplike behavior and low coercive field ∼296 Oe, which may be due to chemical inhomogeneity, strong anisotropy, and weak dipole interaction.

Spin glass-like behaviour in Ce-based Kondo systems arising from d-type nonmagnetic atoms disorder

The effect of Rh or Sb doping in Kondo insulator CeNiSn, and Rh doping in the Kondo lattice system CePdAl is investigated. The studies indicated the spin glass-like states in these materials caused by a statistical distribution of the nonmagnetic transition elements.

A possible glass-like state in θ-(BEDT-TTF)2CsZn(SCN)4 at low temperature

We present the results of measurements of conductivity anddielectric permittivity of the quasi-two-dimensional organic saltθ-(BEDT-TTF)2CsZn(SCN)4 along the in-plane direction in a wide temperature range from room temperaturedown to liquid helium temperature. At temperatures below about 20 K the acconductivity corresponds to correlated electron motion in disordered systems.Temperature and frequency dependences of the dielectric permittivity exhibit themain features of the slowing down behavior characteristic of various disorderedsystems. We explain our results by assuming that this low temperature staterepresents one form of a glass state—a frozen conglomerate of domains of the twoq1 and q2 short-range charge orders.

Magnetic properties of a high energy ball-milled amorphous Gd 5Si 1.8Ge 1.8Sn 0.4 alloy

Amorphous Gd 5Si 1.8Ge 1.8Sn 0.4 has been obtained with the help of a high-energy ball milling technique. XRD and DSC measurements confirm the amorphous nature of the milled alloy. The separation of FC and ZFC curves below the ferromagnetic transition temperature indicates a spin glass-like state in the amorphous alloy. Thermal hysteresis has been significantly reduced in the high energy ball-milled alloy compared with that of a crystalline one. For the amorphous Gd 5Si 1.8Ge 1.8Sn 0.4, magnetic phase transition takes place in a wide temperature span and the RC value reaches around 495 J kg −1.