First-order Transition Research Articles

Proof of Avoidability of the Quantum First-Order Transition in Transverse Magnetization in Quantum Annealing of Finite-Dimensional Spin Glasses

It is rigorously shown that an appropriate quantum annealing for any finite-dimensional spin system has no quantum first-order transition in transverse magnetization. This result can be applied to finite-dimensional spin-glass systems, where the ground state search problem is known to be hard to solve. Consequently, it is strongly suggested that the quantum first-order transition in transverse magnetization is not fatal to the difficulty of combinatorial optimization problems in quantum annealing.

Magnetic properties and large cryogenic magnetocaloric effects in the RE2SiO5 (RE = Gd, Dy, Ho, and Er) silicates

We herein investigated four rare earth (RE)-based oxides, the RE2SiO5 (RE = Gd, Dy, Ho, and Er) silicates, regarding their structural and cryogenic magnetic properties. All the RE2SiO5 silicates are found to crystallized in a monoclinic structure. X-ray photoemission spectroscopy spectra illustrate that RE, Si and O elements in RE2SiO5 silicates are present as RE3+, Si4+, and O2−, respectively. The Dy2SiO5 reveals a first-order magnetic transition around 4.5 K. The magnetic phase transition temperatures are probably below 2 K for the RE2SiO5 (RE = Gd, Ho, and Er) silicates. Large cryogenic magnetocaloric effects (MCE) and good magnetocaloric performances were observed in the RE2SiO5 silicates. The MCE parameters in terms of the maximum magnetic entropy changes, the temperature-averaged entropy change (5 K-lift) and refrigerant capacity under a magnetic field change of 0–5 T are determined to be 35.5, 30.4 J/kgK, and 215.7 J/kg for Gd2SiO5, to be 13.3, 12.9 J/kgK, and 190.5 J/kg for Dy2SiO5, to be 15.3, 15.1 J/kgK, and 274.1 J/kg for Ho2SiO5 and to be 17.9, 16.5 J/kgK, and 181.14 J/kg for Er2SiO5, respectively. These derived values of MCE parameters of the RE2SiO5 silicates, especially for Gd2SiO5, are at similarly high level with or better than those of the updated candidate materials, making them also of potential for practical magnetic refrigeration applications.

Ising model for the freezing transition.

We introduce a three-state Ising model with entropy-volume coupling suitably incorporating a packing mechanism into a lattice gas with no attractive interactions. On working in a great grand canonical ensemble in which the energy, volume, and number of particles are all allowed to fluctuate simultaneously, the model's mean-field solutions illuminate a strictly first-order transition akin to hard-sphere freezing while describing the thermodynamics of solid and fluid phases. Further implementation of attractive interactions in a natural way allows every aspect of the phase diagram of a simple substance to be reproduced, thereby accomplishing the van der Waals picture of the states of matter from first principles of statistical mechanics. This fairly accurate qualitative description plausibly renders mean-field theory a reasonable approach for freezing in three dimensions. At the same time, our mean-field treatment itself suggests freezing to persist in infinitely many dimensions, as advanced from recent simulations [Charbonneau et al., Eur. Phys. J. E 44, 101 (2021)10.1140/epje/s10189-021-00104-y].

Phase transitions of smectic-isotropic phase in liquid crystals

Smectic phases formed by rod-like molecules with long axes that are parallel and also arranged in planes. The smectic-isotropic phase transition is a phase change from the liquid crystal to the liquid phase. In this work, we use a mobile 6-state Potts model to study the nature of the smectic-isotropic phase transition. Microscopic interactions between neighbouring molecules in this model are supplemented with the Lennard-Jones potential. This study applies Monte Carlo simulation with the Wang-Landau algorithm to determine the characteristics of smectic-isotropic phase transitions. It is shown clearly that the smectic phase goes to the isotropic phase and undergoes a first-order transition. The results also point out that when the temperature increases, molecules on the surface are orientationally disordered, then the molecules gradually lose their positional order. These results are in agreement with experiments that revealed the coexistence of the smectic and isotropic phasesduring the phase transition process in accordance with experimental studies.

Phase behavior of triblock copolymer and homopolymer blends: Effect of copolymer topology

Two distinct linear triblock copolymers with different block sequences, ABA or BAB, are obtained when two identical AB diblock copolymers are jointed at their B or A ends, respectively, resulting in three homologous, AB diblock, ABA, and BAB triblock copolymers with the same chemical composition but different topologies. We demonstrate that the topological effect on the phase behaviors of these copolymers is amplified when A homopolymers are added to the system. Specifically, the phase behaviors of binary blends composed of ABA or BAB linear triblock copolymers and A homopolymers are studied by using the random-phase approximation (RPA) and self-consistent field theory (SCFT). The RPA analysis predicts that the Lifshitz point for the ABA/A blends behaves like a second-order transition but that for the BAB/A blends behaves like a first-order transition. The Lifshitz point of the BAB/A mixtures is found to occur at a much lower homopolymer concentration than that of the ABA/A mixtures, indicating a poorer miscibility of the A homopolymers into the BAB than ABA triblocks, which is also confirmed by SCFT. For sphere-forming triblock copolymers mixed with homopolymers, the poorer miscibility and the more diffused distribution of the A homopolymers in the BAB/A blends result in a phase behavior drastically different from that of the ABA/A and AB/A blends. The ABA/A blends stabilize the Frank-Kasper (FK) phases similar to the AB/A blends, but the stability window of FK phases becomes negligibly small in the corresponding BAB/A blends. Our results demonstrate that the topological effect of block copolymers on the equilibrium phase behaviors can be more prominent in multicomponent systems and thus more attention should be paid to copolymer topologies in the design of polymeric blends. Published by the American Physical Society 2024

Emergent topological ordered phase for the Ising-XY model revealed by cluster-updating Monte Carlo method

The two-component cold atom systems with anisotropic hopping amplitudes can be phenomenologically described by a two-dimensional Ising-XY coupled model with spatial anisotropy. At low temperatures, theoretical predictions [Phys. Rev. A 72 053604 (2005)] and [arXiv: 0706.1609] indicate the existence of a topological ordered phase characterized by Ising and XY disorder but with 2XY ordering. However, due to ergodic difficulties faced by Monte Carlo methods at low temperatures, this topological phase has not been numerically explored. We propose a linear cluster updating Monte Carlo method, which flips spins without rejection in the anisotropy limit but does not change the energy. Using this scheme and conventional Monte Carlo methods, we succeed in revealing the nature of topological phases with half-vortices and domain walls. In the constructed global phase diagram, Ising and XY-type transitions are very close to each other and differ significantly from the schematic phase diagram reported earlier. We also propose and explore a wide range of quantities, including magnetism, superfluidity, specific heat, susceptibility, and even percolation susceptibility, and obtain consistent and reliable results. Furthermore, we observed first-order transitions characterized by common intersection points in magnetizations for different system sizes, as opposed to the conventional phase transition where Binder cumulants of various sizes share common intersections. The critical exponents of different types of phase transitions are reasonably fitted. The results are useful to help cold atom experiments explore the half-vortex topological phase.

Non-equilibrium dynamics and phase transitions in Potts model and interacting Ehrenfest urn model

We show that the recently proposed interacting Ehrenfest M-urn model at equilibrium (Cheng et al., 2020) can be exactly mapped to a mean-field M-state Potts model. By exploiting this correspondence, we show that the M-state Potts model with M≥3, with transition rates motivated by the non-equilibrium urn model, can exhibit rich non-equilibrium spin dynamics such as non-equilibrium steady states and non-equilibrium periodic states. Monte Carlo simulations of the 3-state Potts model are performed to demonstrate explicitly the first-order transitions for the equilibrium and non-equilibrium steady states, as well as the far-from-equilibrium periodic states.

Tuning the low-temperature phase behavior of aqueous ionic liquids.

Water's anomalous behavior is often explained using a two-liquid model, where two types of water, high-density liquid (HDL) and low-density liquid (LDL), can be separated via a liquid-liquid phase transition (LLPT) at low temperature. Mixtures of water and the ionic liquid hydrazinium trifluoroacetate were suggested to also show an LLPT but with the advantage that there is no rapid ice crystallization hampering its observation. It remains controversial whether these solutions exhibit an LLPT or are instead associated with complex phase separation phenomena. We here show detailed low-temperature calorimetry and diffraction experiments on aqueous solutions containing hydrazinium trifluoroacetate and other similar ionic liquids, all at a solute mole fraction of x = 0.175. Hydrazinium trifluoroacetate, ammonium trifluoroacetate, ethylammonium trifluoroacetate and hydrazinium pentafluoropropionate all boast exothermic transitions unrelated to crystallization as well as remarkable structural changes upon cooling into the glassy state. We propose a model inspired by micelle formation and decomposition in surfactant solutions, which is complemented by MD simulations and allows rationalizing the rich phase behavior of our mixtures during cooling. The fundamental aspect of the model is the hydrophobic nature of fluorinated anions that enables aggregation, which is reversed upon cooling and culminates in the remarkable exothermic first-order transition observed at low temperature. That is, we assign the first-order transition not to an LLPT but to phase-separations similar to the ones when falling below the Krafft temperature. All other solutions merely show simple vitrification behavior. Still, they exhibit distinct differences in liquid fragility, which is decreased continuously with decreasing hydrophobicity of the anions. This might enable the systematic tuning of ionic liquids with the goal of designing aqueous solutions of specific fragility.

Activity-induced phase transition and coarsening dynamics in dry apolar active nematics.

Using the Lebwohl-Lasher interaction for reciprocal local alignment, we present a comprehensive phase diagram for a dry, apolar, active nematic system using its stochastic off-lattice dynamics. The nematic-isotropic transition in this system is first-order and occurs alongside a fluctuation-dominated phase separation. Our phase diagram identifies three distinct regions based on activity and orientational noise relative to alignment strength: a homogeneous isotropic phase, a nematic phase with giant density fluctuations, and a coexistence region. Using mean-field analysis and hydrodynamic theory, we demonstrate that reciprocal interactions lead to a density fluctuation-induced first-order transition and derive a phase boundary consistent with numerical results. Quenching from the isotropic to nematic phase reveals coarsening dynamics where nematic ordering precedes particle clustering. Both the nematic and density fields exhibit similar scaling behaviors, exhibiting dynamic exponents zS ≈ 2.5 and zρ ≈ 2.34, consistently falling within the range of 2 and 3.

Enhanced magnetocaloric effect accompanying successive magnetic transitions in TbMn2Si2-xGex compounds

The lack of magnetic refrigeration (MR) materials with high magnetocaloric effect (MCE) and large relative cooling power (RCP) in the temperature range required for hydrogen liquefaction (20 K–77 K) is a bottleneck for practical applications of MR cooling systems. The present investigation of TbMn2Si2-xGex compounds (x = 0.1, 0.2) by variable temperature neutron and synchrotron X-ray diffraction, magnetization and heat capacity measurements, establish that substitution of Si with Ge in TbMn2Si2 leads to a significant enlargement of the unit cell and modification of the magnetic properties. Two consecutive ferromagnetic first-order transitions occur below 77 K with the third transition from paramagnetism to a collinear antiferromagnetic state being determined around 500 K. The resultant plateau-like MCE with large RCP below 77 K in these designed compounds offers scope for application for hydrogen liquefaction. Detailed neutron investigation confirm that four magnetic states exist within the temperature range 5 K to 500 K, with two successive first-order magnetic transitions below 77 K responsible for the large MCE. Our specific heat studies provide evidence of strong contributions from the nuclear specific heat and the corresponding nuclear specific heat coefficients of A = 430 ± 50 mJ mol−1 K and A = 418 ± 60 mJ mol−1 K have been determined for TbMn2Si2-xGex with x = 0.1 and x = 0.2, respectively. The overlapping entropy curves near these successive transitions lead to a plateau-like magnetothermal effect as well as a large reversible MCE for both samples (e.g. ΔSMmax = 14.0 J/kg K and ΔTmax = 7.6 K; RCP = 379 J/kg for TbMn2Si1.9Ge0.1 for an applied field of 5 T) indicating that the material can operate over a wide temperature range – particularly for hydrogen liquefaction.

Tuning martensitic transformation and magnetocaloric effect with Bi substitution in MnCo1-xBixGe alloys

In this work, the substitution of Bi for Co atoms in MnCo1-xBixGe (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1) alloys was prepared. The crystal structure, magnetic properties, and magnetocaloric effect have been analyzed. By tuning the Bi-content in MnCoGe alloys, the reduction of martensitic transformation (MT) temperature and the presence of a first-order magnetostructural transition (MST) were observed. Magnetic field-induced MT indicates that the magnetic field is much harder to drive MT compared to the temperature. With the Bi-content for 0.01 ≤ x ≤ 0.06, orthorhombic-type phase and hexagonal-type phase coexist. Furthermore, we observed an increase in the fraction of the hexagonal-type phase and a corresponding decrease in the fraction of the orthorhombic-type phase. It is beneficial to the refrigeration capacity for the isothermal magnetization curves M(H) on magnetization and demagnetization procedures with small magnetic hysteresis loss. With a magnetic field of 5 T, magnetocaloric effect (MCE) can be observed involving magnetic entropy change (-ΔSM) of 26.42 J kg−1 K−1 for x = 0.06 and refrigeration capacity (RC) of 259.78 J kg−1 for x = 0.01. Thus, this material is considered a fabulous candidate for magnetic refrigeration cooling applications at room temperature.

Na(Co,Ti)O2 Cathodes for Na-Ion Batteries: A Proper Choice

Increased attention to sodium-containing materials during the last several years is caused by the rapid development of sodium-ion batteries (NIBs), considered as a potential successor for lithium-ion batteries (LIBs) [1]. Especially layered sodium oxides have gained large interest due to their potential applicability as electrode materials (both, as cathodes and anodes). Similar to LiCoO2 in LIBs, NaCoO2 shows an immense potential as a cathode in NIBs. A partial replacement of Co by Ti in a Na(Co,Ti)O2 cathode can stabilize the crystal structure during (de)sodiation and reduce the number of phase transformations. Although the phase diagram of the Na-Co-Ti-O system has not been studied yet, existence of single-phase and multi-phase regions in dependence on the Na-content and temperature is reported in the literature [2]. Typically, layered Na,Co,Ti-oxides adopt three very close structure types P2, O3 and P3, which differ in the oxygen surrounding for Na-cations (octahedral or prismatic) and in the number of the formula units in the crystal unit cell (2 or 3). For application in Na-batteries, however, a trial-and-error approach is mostly needed to evaluate a composition with outstanding electrochemical performance.The redox activity of Co and Ti cations is usually characterized by two well-separated cell potentials. The Co-oxidation (Co2+ → Co3+ and Co3+→ Co4+) occurs mostly at potentials between 3 and 4 V vs. Na+/Na, qualifying the material as cathode while Ti4+/Ti3+ redox process takes place below 1.5 V, as common for anode materials. Based on our experimental studies of layered Na,Co,Ti-oxides with different compositions as NaCo0.5Ti0.5O2 (O3) [3], Na0.65Co0.5Ti0.5O2 (P3) [3], Na0.67Co0.33Ti0.67O2 (P2- and O3-structures) [4] and Na0.8Co0.8Ti0.2O2 (P2) [5] as well as on literature report [6], we can conclude that the most stable cycling behavior can be realized, if the composition in the initial (discharged) state contains mainly Co3+ and not Co2+. The reason for this is a first-order spin-state transition of high-spin HS-Co2+ to low-spin LS-Co3+ and back upon (de)sodiation, which is accompanied by a phase transformation, leading to a huge potential hysteresis of about 2 V. This hysteresis only slightly depends on the temperature between 0 °C and 40 °C. Among the compositions mentioned above, Na0.8Co0.8Ti0.2O2 with the P2-structure is the best candidate for application as a cathode in Na-batteries. However, a deep discharge of the material below 1.6 V to reach the Na1.0Co0.8Ti0.2O2 composition is detrimental as well, since some amount of Co2+ appears, negatively influencing the cycling behavior.

Enhanced Heat Capacity in Carbon Nanotube-Dispersed Polymer Nanofluid Driven by First-Order Isotropic-Nematic Transition: A Theoretical Modeling

Enhanced Heat Capacity in Carbon Nanotube-Dispersed Polymer Nanofluid Driven by First-Order Isotropic-Nematic Transition: A Theoretical Modeling

Defect induced ferromagnetism in Mn3Ga

Ni-substituted Mn3Ga displays a weak ferromagnetism embedded in an antiferromagnetic (AF) phase. Upon field cooling, the alloy exhibits exchange bias and an open hysteresis loop, signifying kinetic arrest at room temperature. For the first time, a kinetic arrest is seen in a compound due to the first order transition of an embedded defect phase. A systematic study of crystal structure, local structure, and magnetic properties of Mn 3−x Ni x Ga (x = 0, 0.25) alloys reveal the origin of ferromagnetism in Mn2.75Ni0.25Ga is due to the segregation of a Heusler-type environment around Ni in the cubic Mn3Ga matrix. Upon temper annealing at 400 ∘C, these local structural defects around the Ni phase separate into a modulated ferromagnetic (FM) Ni-Mn-Ga Heusler phase. A strong interaction between the AF host and the FM defect phase gives rise to exchange bias. The first-order transition of the defect phase seems to be responsible for the observed kinetic arrest in Mn2.75Ni0.25Ga.

Emergent self-duality in a long-range critical spin chain: From deconfined criticality to first-order transition

Emergent self-duality in a long-range critical spin chain: From deconfined criticality to first-order transition

Strong enhancement of magnetic ordering temperature and structural/valence transitions in EuPd3S4 under high pressure.

We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd3S4, by electrical transport, X-ray diffraction, time-domain 151Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, TN, increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with TN is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the TN plateau. Mössbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu2+:Eu3+ to fully Eu3+ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances TN, most likely via enhanced hybridization between the Eu 4f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state.

Burst-like features observed from different techniques at the first-order magnetic transition of La(Fe,Co,Si)13

La(Fe,Si)13 alloys are prone to display burst-like phenomena at their first-order ferromagnetic transition, such as a latent heat decomposed into a succession of heat flux avalanches. For some extreme cases, these phenomena are so pronounced that they can yield recalescence/antirecalescence events. It turns out that these features are also highly sensitive to the technical specificities of the employed measurement systems. Here, we compare the thermal events at the first-order magnetic transition of LaFe11.4Si1.31Co0.29 using magnetization, two differential scanning calorimeters and a thermometry probe specially designed for the present study. These techniques are complementary to each other, and allow to make a distinction between the properties influenced by thermal coupling and those more intrinsic to the compound or to the sample. A simple thermal model is built to account for the thermal lags in the different devices, and to provide insights into the dependence of the duration of the transition on the thermal sweep rate. Looking in closer detail at the development of the transition, we found evidence of a rate independent initial regime, followed by a second one along which the same shape of temporal profile is spread over a more or less long duration depending on the sweep rate. Possible underlying mechanisms corresponding to these regimes are discussed.

Higher orders for cosmological phase transitions: a global study in a Yukawa model

We perform a state-of-the-art global study of the cosmological thermal histories of a simple Yukawa model, and find higher perturbative orders to be important for determining both the presence and strength of strong first-order phase transitions. Using high-temperature effective field theory, we calculate the free energy density of the model up to O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(y5T4), where y is the Yukawa coupling and T is the temperature. The locations of phase transitions are found using the results of lattice Monte-Carlo simulations, and the strength of first-order transitions are evaluated within perturbation theory, to 3-loop order. This is the first global study of any model at this order. Compared to a vanilla 1-loop analysis, accurate to O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(y2T4), reaching such accuracy enables on average a five-fold reduction in the relative uncertainty in the predicted critical temperature Tc, and an additional ∼ 50% strong first-order transitions with latent heat L/Tc4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ L/{T}_c^4 $$\\end{document}> 0.1 to be identified in our scan.

Giant magnetocaloric effect for (Mn, Fe, V)2(P, Si) alloys with low hysteresis

The Fe2P type Mn–Fe–P–Si alloys exhibit a giant magneto-elastic first-order transition, but the large hysteresis limits their performance. Crystal structure evolution and magnetocaloric performance were investigated by varying the Mn and Fe contents at a constant V substitution of 0.02 in Fe2P-type (Mn1.17-xFe0.73-yV0.02) (P0.5Si0.5) (where x + y = 0.02). The V substitution of Fe content shows a larger reduction of hysteresis compared with the same substitution amount of Mn content. During magnetoelastic phase transition, V-substitution reduces the volume change and the volumetric stresses, providing a superior mechanical stability. Compound with the V substitution of Fe (y = 0.02) shows the best magnetocaloric effect with a low thermal hysteresis of 0.6 K. Our developed Mn1.17-xFe0.73-yV0.02P0.5Si0.5 alloys are excellent materials for room-temperature magnetic heat-pumping applications by using a permanent magnet.

First-order transition in LK-99 containing Cu2S

First-order transition in LK-99 containing Cu2S