Second-order Phase Research Articles

Investigation of Magnetic Entropy Change in Intermetallic Compounds SmNi3−xFex Based on Maxwell Relation and Phenomenological Model

In this study, we investigate the crystal structure, magnetic, and magnetocaloric effect properties in the intermetallic compounds SmNi3−xFex using a phenomenological model based on Landau mean-field theory and Maxwell relation (conventional method). SmNi3−xFex compounds were prepared under high pure argon by arc melting. To minimize the amount of other possible impurity phases, the ingots were heat-treated at 1073 K for seven days. X-ray diffraction (XRD) under and without an applied magnetic field was used for the structural study. Rietveld analysis with FullProf computer code was used to analyze X-ray diffraction data. The magnetization against temperature was measured under several applied magnetic fields. After the partial substitutions of nickel atom with iron one, we notice an increase of cell parameters. In addition, Curie temperature value increases significantly with the increase of iron content. According to the Landau model, SmNi3−xFex compounds exhibit a second-order magnetic phase transition. The magnetic entropy change was determined with theoretical and experimental methods. Finally, a comparison between theoretical magnetic entropy change and the experimental show an agreement between the two methods.

MAGNETIC PHASE TRANSITION AND MAGNETOCALORIC EFFECT OF RE0.7Sr0.3MnO3 POLYCRYSTALLINE MATERIALS

In this report, we present some results of the magnetic phase transition nature and magnetocaloric effect of four polycrystalline ceramics of RE0.7Sr0.3MnO3 with RE = La, Pr, Nd and Sm, which were prepared by solid phase reaction method. X-ray diffraction data shows that all samples are single phase of RE0.7Sr0.3MnO3. The sample with RE = La belongs to the rhombohedral structure (space group: R3-c), whereas the other remaining samples belong to the orthorhombic one (space group: Pbnm). We pointed out that the difference in ionic radius at the RE site plays an important role in modifying the nature and Curie temperature (TC) of the ferromagnetic-paramagnetic phase transition of RE0.7Sr0.3MnO3 compounds. Namely, the RE = Nd sample has the characteristics of the first-order magnetic phase transition with TC = 242 K. Meanwhile, for RE = La, Pr, and Sm, the materials exhibit the characteristics of the second-order magnetic phase transition with TC = 360, 262, and 98 K, respectively. Among these, the magnetic phase transitions of two compounds with RE = Pr and Nd occur near room temperature with very large magnetocaloric effects. The values of the maximum magnetic entropy changes are higher than 3 J/kgK under magnetic field change of 10 kOe, suggesting their potential application in the field of civil magnetic refrigeration. The nature of the magnetic phase transition and the characteristic quantities related to the magnetocaloric effects of the RE0.7Sr0.3MnO3 compounds were studied and discussed in detail through the temperature and magnetic field dependences of the magnetization data.

Entropic topography associated with field-induced quantum criticality in a magnetic insulator DyVO4

Exploration of low temperature phase transitions associated with quantum critical point is one of the most mystifying fields of research which is under intensive focus in recent times. In this work, through comprehensive experimental evidences, we report the possibility of achieving quantum criticality in the neighborhood of a magnetic field-tuned tricritical point separating paramagnetic, antiferromagnetic and metamagnetic phases in a magnetic insulator, DyVO4. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at TN ~ 3.2 K. Field variation of Magnetic susceptibility and heat capacity, along with differential magnetic susceptibility and DC field dependent AC susceptibility gives evidence of the modification of the antiferromagnetic structure below the tricritical point; implying the presence of a field-induced first order metamagnetic transition which persists down to 1.8 K. Further, the magnetic field dependence of the thermodynamic quantity − dM/dT, which is related to magnetic Gruneisen parameter, approaches a minimum, followed by a crossover near 5 kOe to a maximum; along with a hyperbolic divergence in temperature response of dM/dT in the critical field regime. Temperature response of heat capacity at 5 kOe also shows a deviation from the conventional behavior. Entropic topography phase diagram allows tracking of the variation of the entropy, which indicates towards the emergence of the peak at quantum critical point into a V-shaped region at high temperatures. Our studies yield an inimitable phase diagram describing a tricritical point at which the second-order antiferromagnetic phase line terminates followed by a first order line of metamagnetic transition, as the temperature is lowered, leading to metamagnetic quantum critical end point.

Information Propagation Influenced by Population Heterogeneity Behavioral Adoption on Weighted Network

In the realistic world, various individuals have distinct personalities, preferences, and attitudes toward new information and behavior acceptance, called population heterogeneity. It is seldom taken into account and theoretically analyzed in information propagation on a weighted network. Therefore, we divide individuals into fashionable and conservative individuals according to their passion degree and willingness for novel behaviors acceptance. Then, we build two behavior adoption threshold models corresponding to fashionable and conservative individuals on the weighted network to explore the effect of population heterogeneity on information propagation. Next, a partition theory based on edge weight and population heterogeneity is proposed to qualitatively analyze the information propagation mechanism. The theoretical analyses and simulation results show that fashionable individuals promote information propagation and behavior adoption. More importantly, the crossover phenomena of phase transition appear. When the fraction of fashionable individuals is relatively large, the increasing pattern of the final adoption size shows a second‐order continuous phase transition. In comparison, the increasing pattern alters to first‐order discontinuous phase transition with the decrease of the fraction of fashionable individuals. Moreover, reducing weight distribution heterogeneity promotes information propagation and slightly accelerates the change of the phase transition pattern from the first‐order discontinuous to the second‐order continuous. Besides, increasing the degree distribution heterogeneity accelerates the change of the phase transition pattern. Finally, our theoretical analyses coincide well with the simulation results.

Detecting scale anomaly in chiral phase transition of QCD: new critical endpoint pinned down

Violation of scale symmetry, scale anomaly, being a radical concept in quantum field theory, is of importance to comprehend the vacuum structure of QCD, and should potentially contribute to the chiral phase transition in thermal QCD, as well as the chiral and U(1) axial symmetry. Though it should be essential, direct evidence of scale anomalies has never been observed in the chiral phase transition. We propose a methodology to detect a scale anomaly in the chiral phase transition, which is an electromagnetically induced scale anomaly: apply a weak magnetic field background onto two-flavor massless QCD with an extremely heavy strange quark, first observe the chiral crossover; second, adjusting the strange quark mass to be smaller and smaller, observe the second-order chiral phase transition, and then the first-order one in the massless-three flavor limit. Thus, the second-order chiral phase transition, observed as the evidence of the quantum scale anomaly, is a new critical endpoint. It turns out that this electromagnetic scale anomaly gets most operative in the weak magnetic field regime, rather than a strong field region. We also briefly address accessibility of lattice QCD, a prospected application to dense matter system, and implications to astrophysical observations, such as gravitational wave productions provided from thermomagnetic QCD-like theories.

The behaviors of the solutions of the quark gap equation in the NJL model with the self-consistent mean field approximation

In this paper, we use the self-consistent mean field approximation to study the Quantum Chromodynamics (QCD) phase transition. In the self-consistent mean field approximation of the Nambu–Jona-Lasinio (NJL) model, a parameter [Formula: see text] is introduced, which reflects the weight of “direct” channel and the “exchange” channel and needs to be determined by experiments (as mentioned in a recent work [T. Zhao, W. Zheng, F. Wang, C.-M. Li, Y. Yan, Y.-F. Huang and H.-S. Zong, Phys. Rev. D 100, 043018 (2019)], the results with [Formula: see text] are in good agreement with astronomical observation data on the latest binary neutron star merging. This indicates that the contribution of “exchange” channel should be considered, and [Formula: see text] is a possible choice). By comparing the results with different parameter [Formula: see text]’s ([Formula: see text], [Formula: see text] and [Formula: see text]), we study the influence of “exchange” channel on the behavior of the solutions of the quark gap equation and the critical point of chiral phase transition. Our results show that the second-order chiral phase turns to the crossover from the chiral limit to the non-chiral limit around [Formula: see text] in the case of [Formula: see text]. The difference of the quark mass with different [Formula: see text]’s mainly occurs in the intermediate temperatures for the different fixed chemical potentials. At zero temperature and the chemical potential [Formula: see text] there will be two solutions (including a meta-stable solution) of gap equation with [Formula: see text], and as [Formula: see text] increases it will be only one solution left (the meta-stable solution will disappear until [Formula: see text]). Besides, the discrepancy of the critical temperature (above which the pseudo-Wigner solution and negative Nambu solution will disappear) in the three cases of [Formula: see text] will become large when the chemical potential increases.

Forward terahertz wave generation from liquid gallium in the non-relativistic regime

We characterize a terahertz (THz) source based on plasma in liquid gallium. The dependence of the emitted THz pulse energy on second-order phase, pump pulse energy, and polarization of the short laser pulse is demonstrated. Our study suggests that the THz emission mechanism is due to the ponderomotive force and is aided by a direct-field driven term. The proposed source and accompanying generation mechanism are studied under a non-relativistic regime ( 1 0 15 < I < 1 0 18 W / c m 2 ) for forward directed THz under a single pump excitation scheme.

Spatiotemporal Patterns of Oscillatory Electrochemical Reactions in the Presence of a Low-Pass Filter

In many electrochemical measurements, the measured signals are often filtered to remove experimental noise, for example, with a low-pass filter (LPF). At the same time, various electrical coupling (potential drop in the electrolyte) and feedback (galvanostatic constraints) effects can generate spatiotemporal patterns. In this contribution, we study the synchronization patterns of electrochemical oscillators induced by feedback in the presence of a low-pass filter. Close to a Hopf bifurcation, without the filter, as expected[1], the synchronization transition took place above a critical coupling strength following a second-order phase (Kuramoto) transition. With LPF, the transition occurred through explosive synchronization, which corresponds to a first-order phase transition and multistability between synchronized and desynchronized states. These experimental results confirm recent theoretical development on the impact of LPF on the synchronization of Stuart-Landau oscillators[2]. Further away from Hopf bifurcation, the LPF can generate patterns with one- and two-cluster states from a desynchronized state. The cluster formation and stability can be understood using a theory that estimates the LPF induced amplitude attenuation and phase shift of the coupling functions in the phase model of the oscillatory process. Our study points to the importance of using filtering in engineering synchronization states of oscillatory electrochemical reactions. Kiss, I.Z., Y. Zhai, and J.L. Hudson, Emerging Coherence in a Population of Chemical Oscillators. Science, 2002. 296(5573): p. 1676.Zou, W., M. Zhan, and J. Kurths, Phase transition to synchronization in generalized Kuramoto model with low-pass filter. Physical Review E, 2019. 100(1): p. 012209.

Structural, magnetic and theoretical investigation of the magnetocaloric effect of La0.6Sr0.4MnO3/x(Sb2O3) compound

ABSTRACT We report the structural and magnetocaloric properties of the perovskite manganite composites (La0.6Sr0.4MnO3)/x(Sb2O3) (LSMO/Sb2O3) (x = 0.07 and 0.18) synthesized by the solid-state reaction method. X-ray diffraction (XRD) study was employed to confirm the formation of both the phases in composites. The results of magnetic measurements indicate that Sb2O3 mainly segregates at the grain boundaries of LSMO. Arrott analysis and master curve behavior reveal a second-order magnetic phase transition in the composite samples. Magnetic entropy change increases with increasing Sb2O3 content and a maximum of 3 J/kg. K at 2 T has been observed in the LSMO/(0.18) Sb2O3 sample. The enhanced ΔSM of these composites makes them attractive for potential applications.

SERVICE DISTRIBUTION AND SATISFACTION TOWARD CUSTOMER LOYALTY

Automated Teller Machines (ATMs) are a medium for financial transactions. This study investigates the impact of service distribution and service satisfaction on customer loyalty on ATM usage of the BRI Syariah Sub-Branch Office (KCP) Pamekasan. Data obtained from primary data in ATM user respondents' Form, the data analyzed by SEM with PLS approach. The calculation is carried out in two phases, the first-order phase, and the second-order phase. A validity and reliability test revealed that all three variables were valid and reliable in the first-order phase. At the same time, the second-order phase was used, CFA, and Construct Reliability. Subsequently, an Inner Model test uncovered that the Service Distribution has no significant effect on Customer Loyalty. Contrastively, Service Satisfaction has a significant positive impact on customer loyalty. The goodness of Fit based on R-Square reveals that Service Distribution and Service Satisfaction can explain Service Loyalty at BRI Syariah KCP Pamekasan ATM very well.

Theoretical Description of the Magnetocaloric Effect With Second-Order Magnetic Phase Transitions in La0.65Ce0.05Sr0.3Mn1−xCuxO3 (x = 0 and x = 0.15) Manganite Using the Bean–Rodbell Model of Magneto–volume Coupling

Theoretical Description of the Magnetocaloric Effect With Second-Order Magnetic Phase Transitions in La0.65Ce0.05Sr0.3Mn1−xCuxO3 (x = 0 and x = 0.15) Manganite Using the Bean–Rodbell Model of Magneto–volume Coupling

Modeling of Magnetic and Magnetocaloric Properties by the Molecular Mean Field Theory in La0.6Sr0.4Mn0.9V0.1O3 Oxide

Based on the mean-field theory, the magnetic and magnetocaloric behavior of La0.6Sr0.4Mn0.9V0.1O3 manganese oxide has been analyzed. The Bean-Rodbell equation of state presents a second-order magnetic phase transition with a η factor of η = 0.71. Using the experimental data of magnetization M (H, T), the molecular mean-field parameter is found to be λ1 = 2.19 T g emu−1. The Brillouin function makes it possible to determine the total angular moment J, the saturation magnetization MS, and the Lande factor g for La0.6Sr0.4Mn0.9V0.1O3 sample. We simulated the magnetization as a function of the magnetic field and the temperature by applying the mean-field theory, as well as the variation of the magnetic entropy change ΔSM(T). As observed, the simulated results close with experimental data. The magnetic entropy changes for the samples were also estimated by using the mean-field scaling theory, and the results show a difference between the theoretical and experimental values.

Control of non-minimum phase systems with dead time: a fractional system viewpoint

In this paper, a unified theory is proposed for the fractional control of the non-minimum phase plus dead time systems via the introduction of the fractional filter-PID control and stability inequality. More precisely, three Theorems from a fractional system-theoretic viewpoint are developed. The first Theorem deals with the controller design through the notion of generalised internal model control. That embeds the fractional filter-PID controller coupled with the unified form of the Smith predictor and the inverse compensator. The second Theorem designs a bound on the fractional filter parameter that leads to a stable feedback system. The third Theorem deals with the stability of a fractional quasi-characteristic polynomial of the commensurate order arising from the control of non-minimum phase systems with dead time. Two illustrative second-order plus dead time non-minimum phase systems are presented to test the efficacy of the resulting fractional filter-PID controller that obeys the stability bound. Controller and sensitivity performance indices for the nominal as well as mismatch cases reveal the effectiveness and robustness of the proposed method for enhanced closed-loop performance. Thus, the generalised inverse compensator, the fractional filter-PID controller and the stability inequality in corroboration with numerical simulations demonstrate the better control of non-minimum phase systems with dead time.

Mobility edges and critical exponents in the disordered double chains with long-range correlation

Abstract In this paper, we investigate the localization-delocalization transitions of two types of disordered double chain models with long-range correlation. Based on the empirical methods, we find the exact positions of the two pairs of mobility edges between the localized states and the extended states, which are perfectly in agreement with the numerical results obtained by the transfer matrix method. In the case with interchain correlation in on-site energy (a linear relationship between the corresponding site energies of the two chains), a second-order quantum phase transition has been identified, which is manifested as the jump of critical exponent of the localization length. While for the case without interchain correlation in on-site energy, i.e., the disordered on-site energies of the two chains are independently, the critical exponent is determined by one of the two chains, of which the degree of long-range correlation is smaller.

Magnetic Phase Transitions to an Incommensurate Structure in LiMn2O4 Compound

Possible second-order magnetic phase transitions to the incommensurate magnetic structure in the orthorhombic phase of LiMn2O4 compound have been investigated. It is shown that “weak Lifshitz condition” holds for this compound (i.e., Lifshits invariants are immaterial in all transitions being considered), and only the incommensurate phase, in which the wavevector near the transition point varies continuously with temperature and pressure, can be formed. A transition is considered both in the exchange approximation occurring in three irreducible representations forming an exchange multiplet as well as in one and two irreducible representations. Expressions have been derived for the mean density of the magnetic moment emerging because of such transitions. It is found that structures of the types of a longitudinal spin wave, a transverse spin wave with polarization along the crystallographic axes perpendicular to the wavevector of the structure, as well as certain superpositions of these waves can be formed in the system.

A Simplified Dispersion Compensation Algorithm for the Interpretation of Guided Wave Signals

Due to the multimodal and dispersive characteristics of guided waves, guided wave testing signals are always overlapped and difficult to separate for correct interpretations. To this end, a simplified dispersion compensation algorithm is put forward in this paper. The dispersion elimination is accomplished by compensating the second-order nonlinear phase shift of guided wave signals, which is the cause of the dispersion when narrow band exciting signals are used. This algorithm is easy to implement and has no need of prior knowledge of the guided wave dispersion relationship. Considering that the center frequency, which is a key parameter for this algorithm, is nearly impossible to determine accurately in practical applications, the effect of the center frequency deviation on the algorithm is further studied. Both theoretical analysis and numerical simulation indicate the insensitivity of the algorithm to the deviation of the center frequency, and hence, there is no need to determine the center frequency accurately, facilitating the practical use of the algorithm. Based on this simplified dispersion compensation algorithm and in cooperation with the matching pursuit method, the mode separation is further performed for interpreting of overlapped guided wave signals. Dispersion compensation is first applied to the testing signal with respect to a certain mode which will compress the waveform of the mode while the others still spread. Then, this compressed waveform is separated with the Gabor based matching pursuit method. Both simulation and experiment are designed to demonstrate the effectiveness of the proposed methods.

Near-Room-Temperature Magnetocaloric Properties of Fe75–xMnxAl25 Alloys

Magnetic cooling systems near room temperature have attracted attention as an attractive, “green,” thermal management technology, offering high energy efficiency and environmental friendliness. There is an urgent need for low-cost, easy-to-manufacture magnetocaloric materials for such applications. We report the magnetocaloric properties of low-cost, high-relative-cooling-power (RCP) Fe75–xMnxAl25 ( $12.5 \le x \le 25$ ) alloys with tunable Curie temperatures. A second-order magnetic phase transition, with negligible magnetic and thermal hysteresis, was observed. Fe60Mn15Al25 and Fe57.5Mn17.5Al25 buttons exhibited high values of RCP, i.e., 395 and $430\,\,\text {J}\cdot \text {kg}^{-1}$ , respectively, and Curie temperatures near room temperature. Universal scaling behavior and local exponent analyses of the thermodynamic data were performed. The low cost, easy availability, and established manufacturing technology are additional advantages of these alloys.

Hirschfeld surface analysis and short-range ferromagnetic ordering in La0.5Ca0.4Ag0.1MnO3 based on critical behavior study

We investigated the Hirschfeld surface analysis and critical behaviour in La0.5Ca0.4Ag0.1MnO3 near the second-order ferromagnetic phase transition at Curie temperature TC. We determined the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The study of Hirshfeld surface reflects that both the electrostatic and intermolecular interactions are short range. The values for critical exponents obtained from magnetic measurements are very close to those predicted by the mean field tri-critical model. The critical-exponent values deduced here were in a good conform to those obtained using the modified Arrott plot and Widom scaling relation.

New Deep Superfluid Phases of Spin-1 Bosons in Optical Lattice

We analyse theoretically a spin-1 Bose gas loaded into a three-dimensional optical lattice in order to emerge different superfluid phases with external magnetic field. To achieve this, we generalize the mean-field perturbation theory up to the sixth hopping order for the underlying spin-1 Bose–Hubbard model. Our results indicate that the condensate density can be valid deep in the superfluid phase in comparison with that of the fourth hopping order. At zero temperature, new deep superfluid phases for an anti-ferromagnetic interaction are determined in the presence of the external magnetic field. Moreover, we find the second-order quantum phase transition between Mott insulator and superfluid phase for both ferromagnetic and anti-ferromagnetic interactions. Within the anti-ferromagnetic interaction, the transitions between respective superfluid phases can be of the first order.

Effect of Small Fe Content on the Structure, Magnetic and Magnetocaloric Properties of SmNi3−x Fe x (x = 0; 0.3 and 0.8) Intermetallic Compounds

The SmNi3−x Fe x (x = 0; 0.3 and 0.8) were synthesized by arc melting and annealed at 1073 K for 1 week. The Rietveld refinement showed that these compounds crystallize in the PuNi3-type structure ( $R\bar 3m$ -Space group) and the substitution of nickel by iron leads to an increase of the unit cell volume. The Curie temperature (T C ) of the SmNi3−x Fe x (x = 0; 0.3 and 0.8) samples increases from 60 K for SmNi3 to 230 K for SmNi2.2Fe0.8, the enhancement of T C is ruled by electronic and magnetovolumic effects. All the samples exhibit a second-order magnetic phase transition at Curie temperature T C . The magnetic entropy change ΔS M was estimated from isothermal magnetization curves and it decreases with the increase of Fe content from 2.3 J/kg.K (x = 0) to 0.6 J/kg.K (x = 0.8) at 50 kOe. The critical properties of SmNi2.7Fe0.3 (as an example) intermetallic compound at the ferromagnetic-paramagnetic (FM-PM) transition have been analyzed. The estimated critical exponents derived from the magnetic data using various methods such as modified Arrott plot, Kouvel-Fisher method and critical magnetization isotherms M(T C , H). The critical exponent values for the material are in a close agreement with those predicted for the mean-field theory. The reason for this behavior may be long-range interactions between spins in this system.