Quantum Phase Transitions in Antiferromagnets and Superfluids
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Antiferromagnetic phase transition and spin correlations in NiO
Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker
2009-01-01
We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested by...... process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...
Quantum Phase Transitions of Antiferromagnets and the Cuprate Superconductors
Sachdev, Subir
I begin with a proposed global phase diagram of the cuprate superconductors as a function of carrier concentration, magnetic field, and temperature, and highlight its connection to numerous recent experiments. The phase diagram is then used as a point of departure for a pedagogical review of various quantum phases and phase transitions of insulators, superconductors, and metals. The bond operator method is used to describe the transition of dimerized antiferromagnetic insulators between magnetically ordered states and spin-gap states. The Schwinger boson method is applied to frustrated square lattice antiferromagnets: phase diagrams containing collinear and spirally ordered magnetic states, Z_2 spin liquids, and valence bond solids are presented, and described by an effective gauge theory of spinons. Insights from these theories of insulators are then applied to a variety of symmetry breaking transitions in d-wave superconductors. The latter systems also contain fermionic quasiparticles with a massless Dirac spectrum, and their influence on the order parameter fluctuations and quantum criticality is carefully discussed. I conclude with an introduction to strong coupling problems associated with symmetry breaking transitions in two-dimensional metals, where the order parameter fluctuations couple to a gapless line of fermionic excitations along the Fermi surface.
Phase transitions in n=4 type II antiferromagnets
The Landau-Ginzburg-Wilson (LGW) Hamiltonian associated with n=4 type II fcc antiferromagnets is discussed. It is shown that the model is expected to exhibit a first order transition in d=3 dimensions. Recent experimental results on CeS, CeSe and CeTe are discussed. (author)
Design of Co/ Pd multilayer system with antiferromagnetic-to-ferromagnetic phase transition
Thiele, Jan-Ulrich; Hauet, Thomas; Hellwig, Olav
2008-01-01
International audience Among the known magnetic material systems, most are either purely antiferromagnetic or purely ferromagnetic at temperatures up to their critical temperature. There are only very few examples of materials that undergo a temperature dependent phase transition from an antiferromagnetic to a ferromagnetic phase or vice versa, and of these, only the chemically ordered alloy FeRh exhibits this transition near room temperature. Here we present a perpendicular anisotropy mul...
Pressure-induced antiferromagnetic transition and phase diagram in FeSe
We report measurements of resistance and ac magnetic susceptibility on FeSe single crystals under high pressure up to 27.2 kbar. The structural phase transition is quickly suppressed with pressure, and the associated anomaly is not seen above ∼18 kbar. The superconducting transition temperature evolves nonmonotonically with pressure, showing a minimum at ∼12 kbar. We find another anomaly at 21.2 K at 11.6 kbar. This anomaly most likely corresponds to the antiferromagnetic phase transition found in μSR measurements. The antiferromagnetic and superconducting transition temperatures both increase with pressure up to ∼25 kbar and then level off. The width of the superconducting transition anomalously broadens in the pressure range where the antiferromagnetism coexists. (author)
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu, E-mail: taniyama.t.aa@m.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
2015-08-24
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu
2015-08-01
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Imaging the antiferromagnetic to ferromagnetic first order phase transition of FeRh
Mariager, S. O.; Guyader, L. Le; Buzzi, M.; Ingold, G.; Quitmann, C.
2013-01-01
The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic circular dichroism using photoemission electron microscopy. The FM phase is magnetized in-plane due to shape anisotropy, but the magnetocrystalline anisotropy is negligible and there is no preferred in-plane magnetization direction. When heating through the AFM to FM phase transition the nucleation of the FM phase occurs at many independent nucleat...
Bond-Dilution-Induced Quantum Phase Transitions in Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Takayama, Hajime
2006-01-01
Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of the quantum Monte Carlo simulation. It is found that, when the ground state of the non-diluted system is a non-magnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid gap in the original spin gap, and under a further stronger bond dilution an antiferromagnetic long-...
Excitations and phase transitions in random anti-ferromagnets
Cowley, R.A.; Birgeneau, R.J.; Shirane, G.
1979-01-01
Neutron scattering techniques can be used to study the magnetic excitations and phase transitions in the randomly mixed transition metal fluorides. The results for the excitations of samples with two different types of magnetic ions show two bands of excitations; each associated with excitations propagating largely on one type of ion. In the diluted salts the spectra show a complex line shape and greater widths. These results are in good accord with computer simulations showing that linear spin wave theory can be used, but have not been described satisfactorily using the coherent potential approximation. The phase transitions in these materials are always smeared, but it is difficult to ascertain if this smearing is due to macroscopic fluctuations in the concentration or of an intrinsic origin. Studies of these systems close to the percolation point have shown that the thermal disorder is associated with the one-dimensional weak links of the large clusters. Currently theory and experiment are in accord for the two-dimensional Ising system but features are still not understood in Heisenberg systems in both two and three dimensions.
Excitations and phase transitions in random anti-ferromagnets
Neutron scattering techniques can be used to study the magnetic excitations and phase transitions in the randomly mixed transition metal fluorides. The results for the excitations of samples with two different types of magnetic ions show two bands of excitations; each associated with excitations propagating largely on one type of ion. In the diluted salts the spectra show a complex line shape and greater widths. These results are in good accord with computer simulations showing that linear spin wave theory can be used, but have not been described satisfactorily using the coherent potential approximation. The phase transitions in these materials are always smeared, but it is difficult to ascertain if this smearing is due to macroscopic fluctuations in the concentration or of an intrinsic origin. Studies of these systems close to the percolation point have shown that the thermal disorder is associated with the one-dimensional weak links of the large clusters. Currently theory and experiment are in accord for the two-dimensional Ising system but features are still not understood in Heisenberg systems in both two and three dimensions
Field-induced phase transitions in antiferromagnetic systems
Neutron scattering experiments and magnetization measurements are carried out on cobalt bromide hexahydrate, of which 48% of the water molecules are replaced by deuterium oxide molecules. Results were compared with data obtained from non-deuterated cobalt bromide hexahydrate. Neutron scattering experiments showed the importance of the deuterium fraction. Interplay exists between the crystallographic system and the magnetic system, which is influenced by changing the deuterium fraction. Neutron scattering and magnetization experiments on partially deuterated RbFeCl3.2H2O and CsFeCl3.2H2O were performed to study the magnetic phase transitions in these quasi one-dimensional Ising compounds. The observed behaviour in the various phases can be described by the nucleation theory of chain reversals. (Auth.)
Néel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions
Ayuela, Andrés; Klein, Douglas J.; March, Norman H.
2013-01-01
In a recent article,1 a wide variety of phase transitions, with transition (t) temperature Tt , were shown to be usefully characterized by the form kBTt Echar exp1/ λ where λ measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Néel temperature TN. It is first argued that the characteristic energy Echar can be usefully represented by kBθ, where θ is the Curie-Weiss ...
Low-temperature specific-heat measurements on YbRh2Si2 at the second order antiferromagnetic (AF) phase transition reveal a sharp peak at TN=72 mK. The corresponding critical exponent α turns out to be α=0.38, which differs significantly from that obtained within the framework of the fluctuation theory of second order phase transitions based on the scale invariance, where α≅0.1. We show that under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point leading to a violation of the critical universality of the fluctuation theory. This change of the phase transition is generated by the fermion condensation quantum phase transition. Near the tricritical point the Landau theory of second order phase transitions is applicable and gives α≅1/2. We demonstrate that this value of α is in good agreement with the specific-heat measurements.
Entropy-driven phase transition in low-temperature antiferromagnetic Potts models
Kotecký, R.; Sokal, A.D.; Swart, Jan M.
2014-01-01
Roč. 330, č. 3 (2014), s. 1339-1394. ISSN 0010-3616 R&D Projects: GA ČR GA201/09/1931; GA ČR GAP201/12/2613 Institutional support: RVO:67985556 Keywords : Antiferromagnetic Potts model * proper coloring * plane quadrangulation * phase transition * diced lattice Subject RIV: BA - General Mathematics Impact factor: 2.086, year: 2014 http://library.utia.cas.cz/separaty/2014/SI/swart-0429507.pdf
Bipartite entanglement, entanglement spectrum, and Schmidt gap in S=1 bond-alternative antiferromagnetic Heisenberg chain are investigated by the infinite time-evolving block decimation (iTEBD) method. The quantum phase transition (QPT) from the singlet-dimer phase to the Haldane phase can be detected by the singular behavior of bipartite entanglement, the sudden change of the entanglement spectrum, and the completely vanishing of the Schmidt gap. The critical point is determined to be around rc ≃ 0.587, and the second-order character of the QPT is verified. Doubly degenerate entanglement spectra of both even and odd bonds are observed in the Haldane phase, by which one can distinguish the Haldane phase from the singlet-dimer phase easily. Nearest-neighbor antiferromagnetic correlations and next-nearest-neighbor ferromagnetic correlations are found in the whole parameter region. At the critical massless point, although exponentially decaying antiferromagnetic correlation is observed, it approaches to a constant value finally. Therefore, long-range correlations exist and the correlation length becomes divergent at the critical point. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Ramm, Paul; Radu, Ilie; Weber, Alexander; Back, Christian [Institut fuer Angewandte und Experimentelle Physik, Universitaet Regensburg (Germany); Stamm, Christian; Kachel, Torsten; Pontius, Niko; Duerr, Hermann [BESSY GmbH, Berlin (Germany); Raabe, Joerg; Quitmann, Christoph; Joly, Luiic [Paul Scherrer Institut, Villigen PSI (Switzerland); Thiele, Jan-Ulrich [Hitachi Global Storage Technologies, San Jose Research Center (United States)
2007-07-01
The antiferromagnetic-to-ferromagnetic phase transition present on the FeRh thin film alloy is studied by employing static magneto-optic Kerr effect (MOKE), X-ray magnetic circular dichroism (XMCD) and X-ray photoemission electron microscopy (XPEEM) techniques, which give information on the average magnetization, the element-specific magnetic moments as well as the domain structure, respectively. The element-specific hysteresis provided by the XMCD measurements near the transition temperature reveal the growth of the Fe magnetic moment and development of the small but crucial induced Rh magnetic moment in the ferromagnetic phase. Using temperature dependent XPEEM in the vicinity of the phase transition we observe the formation and the partial reproducibility of the magnetic domain structure. The temperature hysteresis of the magnetic contrast deduced from the XPEEM data is in good agreement with the temperature dependent MOKE measurements.
A holographic model for antiferromagnetic quantum phase transition induced by magnetic field
Cai, Rong-Gen; Kusmartsev, F V
2015-01-01
We propose a gravity dual of antiferromagnetic quantum phase transition (QPT) induced by magnetic field and study the criticality in the vicinity of quantum critical point (QCP). Results show the boundary critical theory is a strong coupling theory with dynamic exponent $z=2$. The hyperscaling law is violated and logarithmic corrections appear near the QCP. We compare our theoretical results with experimental data on variety of materials including low-dimensional magnet, BiCoPO$_5$ and pyrochlores, Er$_{2-2x}$Y$_{2x}$Ti$_2$O$_7$. Our model describes well the existing experiments and predicts QCP and other high field magnetic properties of these compounds.
Critical space-time networks and geometric phase transitions from frustrated edge antiferromagnetism
Trugenberger, Carlo A.
2015-12-01
Recently I proposed a simple dynamical network model for discrete space-time that self-organizes as a graph with Hausdorff dimension dH=4 . The model has a geometric quantum phase transition with disorder parameter (dH-ds) , where ds is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean-field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.
Critical Space-Time Networks and Geometric Phase Transitions from Frustrated Edge Antiferromagnetism
Trugenberger, Carlo A
2015-01-01
Recently I proposed a simple dynamical network model for discrete space-time which self-organizes as a graph with Hausdorff dimension d_H=4. The model has a geometric quantum phase transition with disorder parameter (d_H-d_s) where d_s is the spectral dimension of the dynamical graph. Self-organization in this network model is based on a competition between a ferromagnetic Ising model for vertices and an antiferromagnetic Ising model for edges. In this paper I solve a toy version of this model defined on a bipartite graph in the mean field approximation. I show that the geometric phase transition corresponds exactly to the antiferromagnetic transition for edges, the dimensional disorder parameter of the former being mapped to the staggered magnetization order parameter of the latter. The model has a critical point with long-range correlations between edges, where a continuum random geometry can be defined, exactly as in Kazakov's famed 2D random lattice Ising model but now in any number of dimensions.
Quantum Phase Transitions in d-wave Superconductors and Antiferromagnetic Kagome Lattices
Huh, Yejin
Strongly correlated systems are of interest due to their exotic collective behavior. In this thesis we study low energy effective theory and quantum phase transitions of d-wave superconductors and spin liquids. First we examine the quantum theory of the spontaneous breaking of lattice rotation symmetry in d-wave superconductors on the square lattice. This is described by a field theory of an Ising nematic order parameter coupled to the gapless fermionic quasiparticles. We determine the structure of the renormalization group to all orders in a 1/Nf expansion, where Nf is the number of fermion spin components. Asymptotically exact results are obtained for the quantum critical theory in which, as in the large Nf theory, the nematic order has a large anomalous dimension, and the fermion spectral functions are highly anisotropic. Next we study quantum phase transitions in antiferromagnetic kagome lattices. Due to the high geometric frustration, this system poses as a good candidate for a spin liquid with exotic excitations. Here we look at physics of the spinon and vison sector. In the spinon sector, we investigate the zero-temperature phase diagram of the nearest-neighbor kagome antiferromagnet in the presence of Dzyaloshinksii-Moriya interaction. We develop a theory for the transition between Z 2 spin liquids with bosonic spinons and a phase with antiferromagnetic long-range order. Connections to recent numerical studies and experiments are discussed. Finally in the vison sector, we present a projective symmetry group (PSG) analysis of the spinless excitations of Z2 spin liquids on the kagome lattice. In the simplest case, vortices carrying Z2 magnetic flux ('visons') are shown to transform under the 48 element group GL(2, Z3 ). Alternative exchange couplings can also lead to a second case with visons transforming under 288 element group GL(2, Z3 ) x D3. We study the quantum phase transition in which visons condense into confining states with valence bond solid order
Dos Santos Lima, Leonardo
We study the two-dimensional Heisenberg antiferromagnetic model with ion single anisotropy in the square lattice in the presence of nonmagnetic impurities at T = 0 using the SU(3) Schwinger boson theory. In particular, we discuss the influence of site disorder on the quantum phase transition of this model at Dc that separates the Néel phase, D Dc . We find that the long-range order in D CNPq, FAPEMIG, CAPES.
Chandrashekhar P. Bhole
2012-07-01
Full Text Available This paper describes the synthesis of multiferroic BiFeO3 ceramics was prepared by solid state reaction and high energy ball milling method. The structural studies was carried out by using an X-ray diffraction pattern and demonstrated that the BiFeO3 ceramic crystallizes in a rhombhohedral perovskite phase. The ferroelectric hystersis loop measured at room temperature demonstrates a lossy loop with unsaturated behavior and symbolize a partial reversal of polarization. A dielectric constant with temperature measurement for BiFeO3 ceramic represents an anomaly around 350°C for all frequencies and intimately associated with antiferromagnetic to paramagnetic phase transition (TN of BiFeO3.
Phase transitions in the antiferromagnetic Ising model on a body-centered cubic lattice are studied on the basis of the replica algorithm by the Monte Carlo method and histogram analysis taking into account the interaction of next-to-nearest neighbors. The phase diagram of the dependence of the critical temperature on the intensity of interaction of the next-to-nearest neighbors is constructed. It is found that a second-order phase transition is realized in this model in the investigated interval of the intensities of interaction of next-to-nearest neighbors
Shore, Joel D.; Thurston, George M.
2015-12-01
We report a charge-patterning phase transition on two-dimensional square lattices of titratable sites, here regarded as protonation sites, placed in a low-dielectric medium just below the planar interface between this medium and a salt solution. We calculate the work-of-charging matrix of the lattice with use of a linear Debye-Hückel model, as input to a grand-canonical partition function for the distribution of occupancy patterns. For a large range of parameter values, this model exhibits an approximate inverse cubic power-law decrease of the voltage produced by an individual charge, as a function of its in-lattice separation from neighboring titratable sites. Thus, the charge coupling voltage biases the local probabilities of proton binding as a function of the occupancy of sites for many neighbors beyond the nearest ones. We find that even in the presence of these longer-range interactions, the site couplings give rise to a phase transition in which the site occupancies exhibit an alternating, checkerboard pattern that is an analog of antiferromagnetic ordering. The overall strength W of this canonical charge coupling voltage, per unit charge, is a function of the Debye length, the charge depth, the Bjerrum length, and the dielectric coefficients of the medium and the solvent. The alternating occupancy transition occurs above a curve of thermodynamic critical points in the (p H-p K ,W ) plane, the curve representing a charge-regulation analog of variation of the Néel temperature of an Ising antiferromagnet as a function of an applied, uniform magnetic field. The analog of a uniform magnetic field in the antiferromagnet problem is a combination of p H-p K and W , and 1 /W is the analog of the temperature in the antiferromagnet problem. We use Monte Carlo simulations to study the occupancy patterns of the titratable sites, including interactions out to the 37th nearest-neighbor category (a distance of √{74 } lattice constants), first validating simulations
Heidarian, A.; Bali, R.; Grenzer, J.; Wilhelm, R.A.; Heller, R.; Yildirim, O.; Lindner, J.; Potzger, K.
2015-09-01
Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20 keV Ne{sup +} ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift of the transition temperature towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetisation at 5 K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne{sup +} fluence of 3 × 10{sup 14} ions/cm{sup 2}. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.
Heidarian, A.; Bali, R.; Grenzer, J.; Wilhelm, R. A.; Heller, R.; Yildirim, O.; Lindner, J.; Potzger, K.
2015-09-01
Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20 keV Ne+ ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift of the transition temperature towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetisation at 5 K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne+ fluence of 3 × 1014 ions/cm2. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase
Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Li, Wei [Department of Physics, Beihang University, Beijing 100191 (China); You, Wen-Long [School of Physical Science and Technology, Soochow University, Suzhou, Jiangsu 215006 (China); Su, Gang [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, College of Physical Sciences, University of Chinese Academy of Sciences, P.O. Box 4588, Beijing 100049 (China); Tian, Guang-Shan [School of Physics, Peking University, Beijing 100871 (China)
2015-03-01
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase.
Huang, Yi-Zhen; Xi, Bin; Chen, Xi; Li, Wei; Wang, Zheng-Chuan; Su, Gang
2016-06-01
The quantum phase transition, scaling behaviors, and thermodynamics in the spin-1/2 quantum Heisenberg model with antiferromagnetic coupling J >0 in the armchair direction and ferromagnetic interaction J'ratio Q2 and spin stiffness ρ in two directions for various coupling ratios α =J'/J under different lattice sizes, we found that a quantum phase transition from the dimerized phase to the stripe phase occurs at the quantum critical point αc=-0.93 . Through the finite-size scaling analysis on Q2, ρx, and ρy, we determined the critical exponent related to the correlation length ν to be 0.7212(8), implying that this transition falls into a classical Heisenberg O(3) universality. A zero magnetization plateau is observed in the dimerized phase, whose width decreases with increasing α . A phase diagram in the coupling ratio α -magnetic field h plane is obtained, where four phases, including dimerized, stripe, canted stripe, and polarized, are identified. It is also unveiled that the temperature dependence of the specific heat C (T ) for different α 's intersects precisely at one point, similar to that of liquid 3He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q2, ρ , and C (T ) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.
Phase separation of holes in antiferromagnets
It is shown that dilute holes in an antiferromagnet are unstable against phase separation into a hole-rich phase and a no-hole phase. When the spin exchange interaction J exceeds a critical value Jc, one phase consists of all holes, the other all electrons. The argument is presented in detail for the t--J model but evidence of phase separation in other models is mentioned. 11 refs
Zverev, M V; Clark, J W
2001-01-01
On the basis of analysis of the Landau-Pitaevskii one has determined that antiferromagnetic transition follows fermion condensation and rearrangement of single-particle degrees of freedom. It results in the spectrum of single-particle excitations. The derived results are used to explain structure of slit in the spectrum at T = 0 in two-dimensional high-temperature superconductors with a square lattice. They may be, as well, used to describe superfluid states of strongly correlated systems with fermion condensation
Ordered Phase in the Fermionized Heisenberg Antiferromagnet
Azakov, S.; Dilaver, M.; Oztas, A. M.
1999-01-01
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using saddle point approximation in path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into acc...
Spin-Flop Transition and a Tilted Canted Spin Structure in a Coupled Antiferromagnet
Shimahara, Hiroshi; Ito, Kazuhiro
2016-04-01
We study a uniaxial coupled Heisenberg antiferromagnet that consists of two subsystems of classical spins with small and large lengths and spin-flop transitions in a magnetic field parallel to the magnetic easy axis. It is proved that the anisotropy of inter-subsystem coupling stabilizes an asymmetric canted antiferromagnetic phase with a tilted direction of antiferromagnetism that is not perpendicular to the magnetic field. In contrast to the conventional first-order spin-flop transition, the spin-flop transition from the Néel phase to such a tilted canted antiferromagnetic (TCAF) phase is of the second order in the absence of simple anisotropic energies in the subsystems. The transition from the TCAF phase to the high-field saturated spin phase is of the second order in the strong coupling limit of the exchange interactions J1 between the small spins, whereas when J1 is finite, it becomes first-order. Therefore, in the former case, the TCAF phase converts the Néel phase continuously into the saturated phase. The transitions to the TCAF phase are accompanied by additional spontaneous symmetry breaking, causing the uniform magnetization to have a nonzero component perpendicular to the magnetic field.
The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet
Cherepanov, V B; Podivilov, E V
2001-01-01
The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance
The magnetic phases of the randomly mixed two-dimensional antiferromagnet K2Cosub(x)Fesub(1-x)F4 have been explored, utilizing neutron diffraction, Moessbauer absorption spectroscopy, and nuclear magnetic resonance techniques. Ordered phases similar to those found in K2FeF4 and K2CoF4 have been detected for low and high x, respectively. By virtue of the competition between the orthogonal anisotropies of the Fe2+ and Co2+ ions a third ordered so-called oblique phase is found for 0.20 2+ and Co2+. Studies have been undertaken of the critical behavior, the sublattice magnetization and the magnetization of individual ions, and the magnetic excitations, for compositions x and temperatures T covering all relevant parts of the phase diagram. In addition, the magnetic structure of a system which enters the oblique phase is investigated in an external magnetic field. Strong nonequilibrium behavior, related to random-field effects, has been observed
Solé, Ricard V
2011-01-01
Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation o
Golovenchits, E I
2001-01-01
One studied spin dynamics and dynamics of lattice in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu) crystals within 20-250 GHz frequency range and within 50350 K temperature interval. One detected abrupt variation of absorption coefficient within wide range of frequencies above 120 GHz at 20, 80 and 150 K temperatures in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu), respectively. Absorption jumpings result from structural phase transitions. Wide ranges of spin-wave excitations were observed in all examined crystals in high-temperature phase. Close to temperatures of phase transitions within wide range of frequencies including frequencies corresponding to ranges of spin-wave excitations one observed lines of a absorption caused by lattice dynamics
Veinger, A. I.; Zabrodskii, A. G.; Tisnek, T. V.; Goloshchapov, S. I.; Semenikhin, P. V. [Ioffe Institute, 194021 St. Petersburg (Russian Federation); Makarova, T. L. [Ioffe Institute, 194021 St. Petersburg, Russia and Umea University, Universitetomradet 90187, Umea (Sweden)
2014-08-20
The low-temperature transformation from antiparallel to parallel spin orientation in a nonmagnetic compensated system Ge:As semiconductor near the metal-insulator phase transition has been experimentally observed. This effect is manifested in the temperature dependences of the impurity magnetic susceptibility obtained by integration of the spin resonance absorption line. These dependences show that the spin density falls in the medium temperature range (10-100 K) and grows at low temperatures. The effect is confirmed by the specific temperature features of the g-factor and inverse magnetic susceptibility. As the relative content of a compensating impurity (gallium) is made lower than 0.7, the transition temperature begins to decrease and, at a degree of compensation < 0.3, falls outside the temperature range under study (i.e., below 2 K)
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a open-quotes single lobeclose quotes spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ℎωBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. copyright 1998 The American Physical Society
Microscopic theory of antiferromagnetic and double superconducting transitions in UPt3
The antiferromagnetic and double superconducting transitions in UPt3 are studied by using a high-degeneracy model. Within the model, superconductivity is stimulated by long-range antiferromagnetic order. Two scenarios of the temperature behaviour are possible for the close-packed hexagonal structure. In the first scenario the double superconducting transition follows an antiferromagnetic transition (TN1 > Tc1 > Tc2). In the second scenario the superconducting transition follows two consecutive antiferromagnetic transitions (TN1>TN2>Tc. For both scenarios the superconducting gap is anisotropic and vanishes along lines on the Fermi surface. The specific heat has the T2 behaviour in the superconducting state. (author)
Quantum phase competition in antiferromagnetic spin-1 ladders
Motivated by recent chemical explorations into organic-radical-based higher-spin ladder systems, we study the ground-state properties of a wide class of antiferromagnetic spin-1 ladders. Numerical analysis featuring the level-spectroscopy technique reveals the rich phase diagram, correcting a preceding nonlinear-sigma-model prediction. A variational analysis well interprets the phase competition with particular emphasis on the re-entrant phase boundary on the way from single to coupled chains. (author)
Physical properties of FeRh alloys: The antiferromagnetic to ferromagnetic transition
Kudrnovský, J.; Drchal, V.; Turek, I.
2015-01-01
The electronic, magnetic, thermodynamical, and transport properties of FeRh alloys are studied from first principles. We present a unified approach to the phase stability, an estimate of exchange interactions in various magnetic phases, and transport properties including the effect of temperature which are all based on the same electronic-structure model. Emphasis is put on the transition between the ferromagnetic (FM) and antiferromagnetic (AFM) phases. Such a study is motivated by a recent suggestion of FeRh as a room-temperature antiferromagnetic memory resistor. The theory predicts the order-disorder transformation from the hypothetical disordered bcc phase into ordered B2 phase. Comparison of exchange interactions in the magnetically ordered FM and AFM phases with corresponding spin-disordered counterparts allows us to identify relevant interactions which are precursors of magnetically ordered phases. The most important result is the explanation of a dramatic decrease of the resistivity accompanying the AFM to FM phase transition which is due to the spin disorder present in the system. The study of the anisotropic magnetoresistance in the AFM phase found recently experimentally is extended also to finite temperatures.
Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films
Cossu, F.
2013-06-21
Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.
Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.
2016-08-01
The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.
Spin waves in the block checkerboard antiferromagnetic phase
Lu Feng; Dai Xi
2012-01-01
Motivated by the discovery of a new family of 122 iron-based superconductors,we present the theoretical results on the ground state phase diagram,spin wave,and dynamic structure factor obtained from the extended J1-J2 Heisenberg model.In the reasonable physical parameter region of K2Fe4Ses,we find that the block checkerboard antiferromagnetic order phase is stable.There are two acoustic spin wave branches and six optical spin wave branches in the block checkerboard antiferromagnetic phase,which have analytic expressions at the high-symmetry points.To further compare the experimental data on neutron scattering,we investigate the saddlepoint structure of the magnetic excitation spectrum and the inelastic neutron scattering pattern based on linear spin wave theory.
Antiferromagnetism and metal-insulator transition in high temperature superconductors
The ground state of the three band Hubbard Hamiltonian for the CuO2 planes of high temperature superconductors is investigated using local ansatz approach which includes local correlations between holes. For sufficiently large Coulomb interaction, U, or charge transfer energy, Δ, one finds a transition from a nonmagnetic metal to an antiferromagnetic (AF) insulator. If the parameters determined by the local density approximation are used, the ground state is a charge-transfer antiferromagnet, with the magnetic moments of m=0.47μΒ and 0.56μΒ, for La2CuO4 and YBa2Cu3O6, respectively. Correlations and the presence of interoxygen hopping reduce drastically the stability of the AF long-range order which disappears at the doping of either 0.06 hole or 0.08 electron, respectively. The effective mass is enhanced by a factor less than two due to correlations. (author). 27 refs.; 5 figs
Ground state and zero temperature phase diagrams of the XXZ antiferromagnetic spin- {1}/{2} chain
Zhou, P.
1990-05-01
An expression of the XXZ model is given from which the Ising, isotropic XY and Heisenberg models may be more properly obtained by varying only one anisotropy parameter. The ground state and spin configuration of the antiferromagnetic quasi-classical s = {1}/{2}XXZ chain in a magnetic field of arbitrary direction are studied. The phase diagrams with a longitudinal ( h⊥ = 0) and a transverse field ( h‖ = 0) are presented. Because we take into account an effect of anisotropy in the Zeeman interaction, the phase diagrams are quite different from those given by Kurmann, et al. [Physica A 112 (1982) 235]. A ferromagnetic-antiferromagnetic first order phase transition is indicated for the Ising case with h⊥=0.
Small-scale phase separation in doped anisotropic antiferromagnets
We analyse the possibility of nanoscale phase separation manifesting itself in the formation of ferromagnetic (FM) polarons (FM droplets) in the general situation of doped anisotropic three- and two-dimensional antiferromagnets. In these cases, we calculate the shape of the most energetically favourable droplets. We show that the binding energy and the volume of a FM droplet in the three-dimensional (3D) case depend upon only two universal parameters J-bar=(Jx+Jy+Jz)S2 and teff (txtytz)1/3, where J-bar and teff are effective antiferromagnetic (AFM) exchange and hopping integrals, respectively. In the two-dimensional (2D) case these parameters have the form J-bar=(Jx+Jy)S2 and teff (txty)1/2. The most favourable shape of a ferromagnetic droplet corresponds to an ellipse in the 2D case and to an ellipsoid in the 3D case
Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal
Coldea, A. I.; Seabra, L.; McCollam, A.; Carrington, A.; Malone, L.; Bangura, A. F.; Vignolles, D.; van Rhee, P.G.; McDonald, R. D.; Sorgel, T.; Jansen, M.; Shannon, N; Coldea, R.
2014-01-01
Frustrated magnets can exhibit many novel forms of order when exposed to high magnetic fields, however, much less is known about materials where frustration occurs in the presence of itinerant electrons. Here we report thermodynamic and transport measurements on micron-sized single crystals of the triangular-lattice metallic antiferromagnet 2H-AgNiO2, in magnetic fields of up to 90 T and temperatures down to 0.35 K. We observe a cascade of magnetic phase transitions at 13.5 20, 28 and 39T in ...
Paramagnetic to antiferromagnetic transition in epitaxial tetragonal CuMnAs (invited)
Hills, V.; Wadley, P., E-mail: petewadley@gmail.com; Campion, R. P.; Beardsley, R.; Edmonds, K. W.; Gallagher, B. L. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Novak, V. [Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6 (Czech Republic); Ouladdiaf, B. [Institut Laue-Langevin, 6 Rue Jules Horowitz, 38042 Grenoble (France); Jungwirth, T. [Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6 (Czech Republic); School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)
2015-05-07
In this paper, we use neutron scattering and electrical transport to investigate the paramagnetic to antiferromagnetic phase transition in tetragonal CuMnAs films on GaP(001). X-ray diffraction and cross-sectional transmission electron microscopy measurements show that the films are chemically ordered with high structural quality. The temperature dependence of the structurally forbidden (100) neutron scattering peak is used to determine the Néel temperature, T{sub N}. We then demonstrate the presence of a clear peak in the temperature derivative of the resistivity around T{sub N}. The effect of disorder-induced broadening on the shape of the peak is discussed.
SDW antiferromagnetic phase in the two-dimensional Hubbard model: Eliashberg approach
Szczes' niak, R. [Institute of Physics, Czestochowa University of Technology, Al. Armii Krajowej 19, 42-200 Czestochowa (Poland)], E-mail: szczesni@mim.pcz.czest.pl
2009-01-19
The two-dimensional Hubbard model was used for the description of the spin density wave (SDW) antiferromagnetic phase. The calculations were conducted in the framework of the Eliashberg formalism. The SDW phase that characterizes with the order parameter of the s-, extended s- or d-wave symmetry has been considered. The Eliashberg equations for the half-filled electron band have been constructed, with a use of which, it has been shown that only the SDW phase of the s-wave symmetry induces in the system. Next, the dependence of the s-wave SDW transition temperature on the value of the on-site Coulomb repulsion parameter was determined.
Magnetic and calorimetric studies of antiferromagnetic transitions in erbium sesquisulfide
Wang, C.R.; Chen, Y.Y.; Yao, Y.D.; Lin, Y.S.; Ou, M.N.; Taher, S.M.A.; Hamdeh, H.H.; Zhang, X.; Ho, J.C. E-mail: james.ho@wichita.edu; Gruber, J.B.John B
2004-03-01
Magnetic measurements reveal an antiferromagnetic transition in erbium sesquisulfide ErS{sub 1.5} (Er{sub 2}S{sub 3}). The Neel temperature T{sub N} decreases from approximately 3 K at low fields to below 1.8 K at 9000 G. A Curie-Weiss fit to the low-field data between 100 and 300 K yields an effective magnetic moment of 9.65 {mu}{sub B} per Er{sup 3+}. Zero-field calorimetric measurements between 0.7 and 8 K also show a corresponding specific heat peak at T{sub N}. Not expected, however, is the presence of a lower-temperature specific heat shoulder near 2 K. An entropy analysis indicates that both anomalies provide a total of R ln 2 as expected for the Er{sup 3+} ordering, suggesting that the two non-equivalent Er{sup 3+} sites in the monoclinic lattice have different transition temperatures near 3 and 2 K, respectively.
On Julia sets concerning phase transitions
QIAO; Jianyong(乔建永)
2003-01-01
The sets of the points corresponding to the phase transitions of the Potts model on the diamondhierarchical lattice for antiferromagnetic coupling are studied. These sets are the Julia sets of a family ofrational mappings. It is shown that they may be disconnected sets. Furthermore, the topological structures ofthese sets are described completely.
The phase-separated states in antiferromagnetic semiconductors with polarizable lattice
Nagaev, E. L.
2000-01-01
The possibility of the slab or stripe phase separation (alternating ferromagnetic highly- conductive and insulating antiferromagnetic layers) is proved for isotropic degenerate antiferromagnetic semiconductors. This type of phase separation competes with the droplet phase separation (ferromagnetic droplets in the antiferromagnetic host or vice versa). The interaction of electrons with optical phonons alone cannot cause phase-separated state with alternating highly-conductive and insulating re...
Revealing novel quantum phases in quantum antiferromagnets on random lattices
R. Yu
2009-01-01
Full Text Available Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by applying a magnetic field or pressure on the sample. When doping the system with non-magnetic impurities, novel inhomogeneous phases emerge from the interplay between geometric randomness and quantum fluctuations. In this paper we review our recent work on quantum phase transitions and novel quantum phases realized in disordered quantum magnets. The system inhomogeneity is found to strongly affect phase transitions by changing their universality class, giving the transition a novel, quantum percolative nature. Such transitions connect conventionally ordered phases to unconventional, quantum disordered ones - quantum Griffiths phases, magnetic Bose glass phases - exhibiting gapless spectra associated with low-energy localized excitations.
Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer
GUO Guang-Hua; ZHANG Guang-Fu; SUN Li-Yuan; Peter A. J. de Groot
2008-01-01
Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner-Wohifarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easyaxis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k,1 and k,2 plane, where k,1 and k,2 are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.
Geometric phase of a central spin coupled to an antiferromagnetic environment
Yuan, Xiao-Zhong; Zhu, Ka-Di
2010-01-01
Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated.
Hubbard one-particle Green function in the antiferromagnetic phase
An analytic approach is presented of electronic one-particle spectra of the one-band Hubbard model at half filling in the antiferromagnetic phase. Starting from the strong-coupling regime U>t, a projection technique is used to set up self-consistent coupled equations for the electron Green function, which are valid down to values U∼t. The self-consistent equation for the hole propagator is a direct generalization of the one found from the t-J model. This gives further support to the open-quotes stringclose quotes picture, where propagation of holes creates strings of overturned spins with which the holes interact. Hopping of holes (or electrons) with up spin on the down sublattice is also taken into acount, as well as transitions between the lower and upper Hubbard bands. These are shown to change significantly the incoherent part of the t-J model spectra, by smearing out the shake-off peaks, reminiscent of higher bound string states due to multispin scattering. Coherent (quasiparticle) peaks exist at the band edges, on both sides of the insulating gap. With decreasing U the quasiparticle concept loses its meaning for wave vectors at the center of the magnetic Brillouin zone (MBZ). For large values of U the dispersion of the quasiparticle is found to scale with its band width, which is of order J. Extrema are always found at k=(π/2,π/2). The weight of the quasiparticle at this k value decreases logarithmically with increasing U. In the strong-coupling limit the spectrum tends to be symmetric, i.e., to become an even function of the frequency around the chemical potential, for any wave vector. For small values of U the dispersion at the edge of the MBZ flattens away. The spectral function in this regime, for wave vectors away from the edge of the MBZ, is concentrated mainly on one side of the chemical potential. copyright 1996 The American Physical Society
A model with simultaneous first and second order phase transitions
Messager, Alain; Nachtergaele, Bruno
2005-01-01
We introduce a two dimensional nonlinear XY model with a second order phase transition driven by spin waves, together with a first order phase transition in the bond variables between two bond ordered phases, one with local ferromagnetic order and another with local antiferromagnetic order. We also prove that at the transition temperature the bond-ordered phases coexist with a disordered phase as predicted by Domany, Schick and Swendsen. This last result generalizes the result of Shlosman and...
With a mean field approach, the heavy Fermi liquid in the two-dimensional Kondo lattice model is carefully considered in the presence of short-range antiferromagnetic correlations. As the ratio of the local Heisenberg superexchange coupling to the Kondo coupling increases, the Fermi surface structure changes dramatically. From the analysis of the ground state energy density, multiple Lifshitz type phase transitions occur at zero temperature.
Disorder-induced phases in the S=1 antiferromagnetic Heisenberg chain
Lajkó, Péter; Carlon, Enrico; Rieger, Heiko; Iglói, Ferenc
2005-09-01
We use extensive density matrix renormalization group (DMRG) calculations to explore the phase diagram of the random S=1 antiferromagnetic Heisenberg chain with a power-law distribution of the exchange couplings. We use open chains and monitor the lowest gaps, the end-to-end correlation function and the string order parameter. For this distribution at weak disorder, the system is in the gapless Haldane phase with a disorder dependent dynamical exponent, z , and z=1 signals the border between the nonsingular and singular regions of the local susceptibility. For strong enough disorder, which approximately corresponds to a uniform distribution, a transition into the random singlet phase is detected, at which the string order parameter as well as the average end-to-end correlation function are vanishing and at the same time the dynamical exponent is divergent. Singularities of physical quantities are found to be somewhat different in the random singlet phase and in the critical point.
Cosmological phase transitions
Kolb, E.W. [Fermi National Accelerator Lab., Batavia, IL (United States)]|[Chicago Univ., IL (United States)
1993-10-01
If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions.
Cosmological phase transitions
If modern ideas about the role of spontaneous symmetry breaking in fundamental physics are correct, then the Universe should have undergone a series of phase transitions early in its history. The study of cosmological phase transitions has become an important aspect of early-Universe cosmology. In this lecture I review some very recent work on three aspects of phase transitions: the electroweak transition, texture, and axions
High Resolution Far Infrared Study of Antiferromagnetic Resonance Transitions in α-Fe2O3 (hematite)
Chou, Shin Grace; Plusquellic, David F.; Stutzman, Paul E.; Wang, Shuangzhen; Garboczi, Edward J.; Egelhoff, William F.
2012-02-01
In this study, we report high resolution optical measurements of the temperature dependence of the antiferromagnetic (AFM) transition in α-Fe2O3 (hematite) between (0.5 and 10) cm-1. The absorption peak position, over a large temperature range, is found to be in agreement with a modified spin-wave model at both the high and low temperature phases, where the temperature is above and below the Morin transition temperature, respectively. The high spectral resolution optical measurements as demonstrated in this study allow unprecedented zero-field spectral analysis of the zone center AFM magnon in a previously challenging spectral region, giving insights into the role of temperature and strain on the exchange and anisotropy interactions in the system. The results also suggest that the frequency-resolved measurement platform could be extended for room-temperature non-destructive examination and imaging applications for antiferromagnetic materials and devices.
Sato, Toshihiro; Tsunetsugu, Hirokazu
2016-08-01
We numerically study optical conductivity σ (ω ) near the "antiferromagnetic" phase transition in the square-lattice Hubbard model at half filling. We use a cluster dynamical mean field theory and calculate conductivity including vertex corrections and, to this end, we have reformulated the vertex corrections in the antiferromagnetic phase. We find that the vertex corrections change various important details in temperature and ω dependencies of conductivity in the square lattice, and this contrasts sharply the case of the Mott transition in the frustrated triangular lattice. Generally, the vertex corrections enhance variations in the ω dependence, and sharpen the Drude peak and a high-ω incoherent peak in the paramagnetic phase. They also enhance the dip in σ (ω ) at ω =0 in the antiferromagnetic phase. Therefore, the dc conductivity is enhanced in the paramagnetic phase and suppressed in the antiferromagnetic phase, but this change occurs slightly below the transition temperature. We also find a temperature region above the transition temperature in which the dc conductivity shows an insulating behavior but σ (ω ) retains the Drude peak, and this region is stabilized by the vertex corrections. We also investigate which fluctuations are important in the vertex corrections and analyze momentum dependence of the vertex function in detail.
El Bahraoui, T.; Sekkati, M.; Taibi, M.; Abd-Lefdil, M.; El-Naggar, A. M.; AlZayed, N. S.; Albassam, A. A.; Kityk, I. V.; Maciag, A.
2016-01-01
The monitoring of the Eu3+ doped BiFeO3 nanopowders was performed near the antiferromagnetic transformation by photoinduced optical second harmonic generation. As photoinduced laser beams we have used bicolor coherent excitations of the Er:glass laser emitting at 1540 nm with frequency repetition about 15 ns. The studies of the photoinduced SHG were performed versus temperature including the temperature range of ferromagnetic-ferroelectric transition (350 °C…390 °C). The optimal light polarization and intensity ratio were chosen; the sensitivity of the photoinduced SHG to the multiferroic phase transitions was explored.
Finazzi, M.; Brambilla, A.; Biagioni, P.; Graf, J.; Gweon, G.-H.; Scholl, A.; Lanzara, A.; Duo, L.
2006-09-07
We report experimental evidence for a transition in theinterface coupling between an antiferromagnetic film and a ferromagneticsubstrate. The transition is observed in a thin epitaxial NiO film grownon top of Fe(001) as the film thickness is increased. Photoemissionelectron microscopy excited with linearly polarized x rays shows that theNiO film is antiferromagnetic at room temperature with in-plane uniaxialmagnetic anisotropy. The anisotropy axis is perpendicular to the Fesubstrate magnetization when the NiO thickness is less than about 15A,but rapidly becomes parallel to the Fe magnetization for a NiO coveragehigher than 25 A.
In recent years, quantum phase transitions have attracted the interest of both theorists and experimentalists in condensed matter physics. These transitions, which are accessed at zero temperature by variation of a non-thermal control parameter, can influence the behaviour of electronic systems over a wide range of the phase diagram. Quantum phase transitions occur as a result of competing ground state phases. The cuprate superconductors which can be tuned from a Mott insulating to a d-wave superconducting phase by carrier doping are a paradigmatic example. This review introduces important concepts of phase transitions and discusses the interplay of quantum and classical fluctuations near criticality. The main part of the article is devoted to bulk quantum phase transitions in condensed matter systems. Several classes of transitions will be briefly reviewed, pointing out, e.g., conceptual differences between ordering transitions in metallic and insulating systems. An interesting separate class of transitions is boundary phase transitions where only degrees of freedom of a subsystem become critical; this will be illustrated in a few examples. The article is aimed at bridging the gap between high-level theoretical presentations and research papers specialized in certain classes of materials. It will give an overview on a variety of different quantum transitions, critically discuss open theoretical questions, and frequently make contact with recent experiments in condensed matter physics
Symmetry origin of the phase transitions and phase separation in manganites at low doping
Wang, ZD; Zhong, F
1999-01-01
We analyze the symmetry changes of paramagnetic to A-type antiferromagnetic and to ferromagnetic phase transitions in undoped and moderately doped LaMnO 3, respectively. We show that in orthorhombic-distorted perovskite manganites the phase separation at low doping is associated with the noncollinear nature of the magnetic orders permitted by symmetry. A simple model for the competition between the two phase transitions is put forward within the framework of the Landau theory of phase transit...
Neutron Scattering Studies of the Anti-ferromagnetic Phase of Cd1-xMnxTe
Giebultowicz, T.; Minor, W.; Buras, B.; Lebech, Bente; Galazka, R. R.
1982-01-01
Studies of the magnetic properties of crystals of the mixed semiconductors Cd1-xMnxTe indicate that: (i) for x ≤ 0.17 the crystals are paramagnetic at all temperatures, (ii) for 0.17
Magnetic phase diagram of the low-anisotropy antiferromagnet Cs2FeCl5·H2O
From magnetization and ac susceptibility measurements we obtain the complete magnetic phase diagram of single crystals of Cs2FeCl5·H2O for magnetic field up to 15 T. The magnetic field was applied along the directions parallel and perpendicular to the easy axis and the magnetization measured to temperatures down to 0.5 K. At zero magnetic field the antiferromagnetic ordering occurs at TN=6.63 K. For the field applied parallel to the easy axis the antiferromagnetic (AF) to the spin-flop (SF) transition occurs for fields from 1.4 T to 1.1 T depending on the temperature. The low temperature transition from the (SF) to the paramagnetic (P) phase occurs at 13.15 T. In the perpendicular configuration this transition occurs at fields around 13.5 T. From the extrapolation of the transition fields to zero temperature, we obtain a ratio of the anisotropy field HA to exchange field HE, α=HA/HE=(1.4±0.2)×10−2. A comparison with the phase diagram measured for MnF2 is included. - Highlights: • Complete phase diagram of Cs2FeCl5·H2O for magnetic fields up to 15 T. • Direct determination of the anisotropy ratio=HA/HE. • Partial phase diagram of the diluted sample. • Estimative of the high field transition value for MnF2
Computing quantum phase transitions
Vojta, Thomas
2007-01-01
This article first gives a concise introduction to quantum phase transitions, emphasizing similarities with and differences to classical thermal transitions. After pointing out the computational challenges posed by quantum phase transitions, a number of successful computational approaches is discussed. The focus is on classical and quantum Monte Carlo methods, with the former being based on the quantum-to classical mapping while the latter directly attack the quantum problem. These methods ar...
Petry, W.; Neuhaus, J. [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)
1996-11-01
Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.
Cosmological phase transitions
If the universe stated from conditions of high temperature and density, there should have been a series of phase transitions associated with spontaneous symmetry breaking. The cosmological phase transitions could have observable consequences in the present Universe. Some of the consequences including the formation of topological defects and cosmological inflation are reviewed here. One of the most important tools in building particle physics models is the use of spontaneous symmetry breaking (SSB). The proposal that there are underlying symmetries of nature that are not manifest in the vacuum is a crucial link in the unification of forces. Of particular interest for cosmology is the expectation that are the high temperatures of the big bang symmetries broken today will be restored, and that there are phase transitions to the broken state. The possibility that topological defects will be produced in the transition is the subject of this section. The possibility that the Universe will undergo inflation in a phase transition will be the subject of the next section. Before discussing the creation of topological defects in the phase transition, some general aspects of high-temperature restoration of symmetry and the development of the phase transition will be reviewed. 29 references, 1 figure, 1 table
Phase transitions modern applications
Gitterman, Moshe
2014-01-01
This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.
许可; 李未
1999-01-01
Phase transition is an important feature of SAT problem. For random k-SAT model, it is proved that as r（ratio of clauses to variables） increases, the structure of solutions will undergo a sudden change like satisfiability phase transition when r reaches a threshold point (r=rcr). This phenomenon shows that the satisfying truth assignments suddenly shift from being relatively different from each other to being very similar to each other.##属性不符
Successive phase transitions in the orthovanadate TmVO3
Sarkar, Tapati; Ivanov, Sergey A.; Bazuev, G. V.; Nordblad, Per; Mathieu, Roland
2015-09-01
Synthesis and crystal structure, magnetization and heat capacity measurements of phase pure polycrystalline TmVO3 are reported. TmVO3 was stabilized in the orthorhombic structure by thermal treatment of the precursor TmVO4 in a reducing atmosphere. Magnetization and heat capacity measurements reveal the presence of several successive structural and magnetic phase transitions in this compound. At T = 108 K, the sample undergoes a transition from a paramagnetic state to an antiferromagnetic state, followed by a second transition at 78 K which is related to spin and orbital reorientation. The heat capacity measurements reveal the presence of a third transition in the paramagnetic state (at T = 175 K), which corresponds to a structural phase transition and orbital ordering. At low temperatures (~15 K) and weak fields, there is an anomaly in the magnetization, which may be associated with antiferromagnetic short range ordering of the Tm3+ ions.
Successive phase transitions in the orthovanadate TmVO3
Synthesis and crystal structure, magnetization and heat capacity measurements of phase pure polycrystalline TmVO3 are reported. TmVO3 was stabilized in the orthorhombic structure by thermal treatment of the precursor TmVO4 in a reducing atmosphere. Magnetization and heat capacity measurements reveal the presence of several successive structural and magnetic phase transitions in this compound. At T = 108 K, the sample undergoes a transition from a paramagnetic state to an antiferromagnetic state, followed by a second transition at 78 K which is related to spin and orbital reorientation. The heat capacity measurements reveal the presence of a third transition in the paramagnetic state (at T = 175 K), which corresponds to a structural phase transition and orbital ordering. At low temperatures (∼15 K) and weak fields, there is an anomaly in the magnetization, which may be associated with antiferromagnetic short range ordering of the Tm3+ ions. (paper)
Su, W. P.
2005-01-01
To understand the interplay of d-wave superconductivity and antiferromagnetism in the cuprates, we consider a two-dimensional extended Hubbard model with nearest neighbor attractive interaction. Free energy of the homogeneous (coexisting superconducting and antiferromagnetic) state calculated a s a function of the band filling shows a region of of phase separation. The phase separation caused by the intersite attractive force leads to novel insights into salient features of the pseudogap phas...
Lifshitz transitions in magnetic phases of the periodic Anderson model
We investigate the reconstruction of a Fermi surface, which is called a Lifshitz transition, in magnetically ordered phases of the periodic Anderson model on a square lattice with a finite Coulomb interaction between f electrons. We apply the variational Monte Carlo method to the model by using the Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, ferromagnetic, and charge-density-wave states. We find that an antiferromagnetic phase is realized around half-filling and a ferromagnetic phase is realized when the system is far away from half-filling. In both magnetic phases, Lifshitz transitions take place. By analyzing the electronic states, we conclude that the Lifshitz transitions to large ordered-moment states can be regarded as itinerant-localized transitions of the f electrons. (author)
Supersymmetry "protected" topological phases of isostatic lattices and kagome antiferromagnets
Lawler, Michael J
2015-01-01
I generalize the theory of phonon topological band structures of isostatic lattices to frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs and its connection to local constraints satisfied by ground states. The Witten index of the SUSY model demands the Maxwell-Calladine index of mechanical structures. "Spontaneous supersymmetry breaking" is identified as the need to gap all modes in the bulk to create the...
Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)
1997-09-01
The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.
L. Wang
2013-08-01
Full Text Available Magnetic thermal hysteresis (MTH associated with a paramagnetic (PM-antiferromagnetic (AFM phase transition was found in an Fe-24.4Mn-5.9Si-5.1Cr shape-memory alloy. Aside from the magnetic field (H, the driving rate (v can also tune the critical temperature of the magnetic transition and cause an increase in MTH. The magnetic phase diagram obtained is discussed. The equation for MTH was deduced based on the Landau model for a PM-AFM transition that includes H and v dependence, which gives a reasonable account of the experimental results.
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, left-angle φ right-angle T is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of left-angle φ right-angle T. In very minimal extensions of the standard model it is quite easy to increase left-angle φ right-angle T so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value left-angle φ right-angle = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state left-angle φ right-angle = 246 GeV unstable. The requirement that the state left-angle φ right-angle = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field
Chen, Zhi; Yu, Clare C.
2006-03-01
Noise is present in many physical systems and is often viewed as a nuisance. Yet it can also be a probe of microscopic fluctuations. There have been indications recently that the noise in the resistivity increases in the vicinity of the metal-insulator transition. But what are the characteristics of the noise associated with well-understood first and second order phase transitions? It is well known that critical fluctuations are associated with second order phase transitions, but do these fluctuations lead to enhanced noise? We have addressed these questions using Monte Carlo simulations to study the noise in the 2D Ising model which undergoes a second order phase transition, and in the 5-state Potts model which undergoes a first order phase transition. We monitor these systems as the temperature drops below the critical temperature. At each temperature, after equilibration is established, we obtain the time series of quantities characterizing the properties of the system, i.e., the energy and magnetization per site. We apply different methods, such as the noise power spectrum, the Detrended Fluctuation Analysis (DFA) and the second spectrum of the noise, to analyze the fluctuations in these quantities.
Kopaev, YuV
1992-01-01
Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle ele
Critical phase for the antiferromagnetic Z(5) model on a square lattice
The existence of a critical phase for the antiferromagnetic Z(5) model on a square lattice is suggested based on results of Monte Carlo (MC) simulations and of Migdal Kadanoff Renormalization Group calculations (MKRG). The MKRG simulates a line of fixed points which it is interpreted as the locus of attraction of a critical phase. The MC simulations are compatible with this interpretation. (Author)
Phase Transitions in Neutron Stars
Heiselberg, Henning; Hnorth-Jensen, Morten
1998-01-01
Phase transitions in neutron stars due to formation of quark matter, kaon condensates, etc. are discussed with particular attention to the order of these transitions. Observational consequences of phase transitions in pulsar angular velocities are examined.
Finite-size effect of antiferromagnetic transition and electronic structure in LiFePO4
Shu, G. J.; Wu, M. W.; Chou, F. C.
2012-01-01
The finite-size effect on the antiferromagnetic (AF) transition and electronic configuration of iron has been observed in LiFePO4. Determination of the scaling behavior of the AF transition temperature (TN) versus the particle-size dimension (L) in the critical regime 1-TN(L)/TN(XTL)\\simL^-1 reveals that the activation nature of the AF ordering strongly depends on the surface energy. In addition, the effective magnetic moment that reflects the electronic configuration of iron in LiFePO4 is fo...
Photoinduced phase transitions
Nasu, K
2004-01-01
A new class of insulating solids was recently discovered. Whenirradiated by a few visible photons, these solids give rise to amacroscopic excited domain that has new structural and electronicorders quite different from the starting ground state. This occurrenceis called "photoinduced phase transition", and this multi-authoredbook reviews recent theoretical and experimental studies of this newphenomenon.
Elastically controlled magnetic phase transition in Ga-FeRh/BaTiO3(001) heterostructure
Suzuki, Ippei; Itoh, Mitsuru; Taniyama, Tomoyasu
2014-01-01
We demonstrate elastically induced ferromagnetic to antiferromagnetic phase transition of Ga-substituted FeRh thin films on BaTiO3(001). It is found that two abrupt changes of magnetization occur at the successive phase transitions from the tetragonal to orthorhombic and the orthorhombic to rhombohedral phases of BaTiO3. Magnetization and magnetoresistance together clearly reveal that a ferromagnetic to antiferromagnetic phase transition is induced due to the compressive lattice strain accompanied by the orthorhombic to rhombohedral structural phase transition, while the tetragonal to orthorhombic phase transition causes a change in the symmetry of the magnetic anisotropy in the ferromagnetic phase of FeRh.
Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number
Zhang, Wen; Zhou, Zhaofeng, E-mail: zfzhou@xtu.edu.cn; Zhong, Yuan; Zhang, Ting; Huang, Yongli [Key Laboratory of Low-Dimensional Materials and Application Technologies(Ministry of Education)Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Changqing [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)
2015-11-15
Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (T{sub N}) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the T{sub N} by adjusting the atomic cohesive energy. The T{sub N} is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the T{sub N} of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe
Emergence and Phase Transitions
Sikkema, Arnold
2006-05-01
Phase transitions are well defined in physics through concepts such as spontaneous symmetry breaking, order parameter, entropy, and critical exponents. But emergence --- also exhibiting whole-part relations (such as top-down influence), unpredictability, and insensitivity to microscopic detail --- is a loosely-defined concept being used in many disciplines, particularly in psychology, biology, philosophy, as well as in physics[1,2]. I will review the concepts of emergence as used in the various fields and consider the extent to which the methods of phase transitions can clarify the usefulness of the concept of emergence both within the discipline of physics and beyond.1. Robert B. Laughlin, A Different Universe: Reinventing Physics from the Bottom Down (New York: Basic Books, 2005). 2. George F.R. Ellis, ``Physics and the Real World'', Physics Today, vol. 58, no. 7 (July 2005) pp. 49-54.
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
Gottwald, Tobias
2010-08-27
In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe
Understanding quantum phase transitions
Carr, Lincoln
2010-01-01
Quantum phase transitions (QPTs) offer wonderful examples of the radical macroscopic effects inherent in quantum physics: phase changes between different forms of matter driven by quantum rather than thermal fluctuations, typically at very low temperatures. QPTs provide new insight into outstanding problems such as high-temperature superconductivity and display fundamental aspects of quantum theory, such as strong correlations and entanglement. Over the last two decades, our understanding of QPTs has increased tremendously due to a plethora of experimental examples, powerful new numerical meth
Entanglement and quantum phase transitions
Gu, Shi-Jian; Tian, Guang-Shan; Lin, Hai-Qing
2005-01-01
We examine several well known quantum spin models and categorize behavior of pairwise entanglement at quantum phase transitions. A unified picture on the connection between the entanglement and quantum phase transition is given.
Phase diagram of the BCC S=1/2 Heisenberg antiferromagnet with first and second neighbour exchange
Full text: The occurrence of competing exchange interactions in magnetic materials can give rise to a rich variety of magnetic ordered states, and of phase transitions between them. Studies of such phenomena, within the classical 'molecular-field' approximation go back half a century or more. It is perhaps surprising that open questions remain, but, at least for quantum models, this is the case. In this work we use linked-cluster series expansions, both at T=0 and at high temperature, to analyse the phase structure of the spin-1/2 Heisenberg antiferromagnet on the body-centred-cubic lattice with first and second-neighbor exchange H= J1 Σ/ Si . Sj + J 2 Σ/[ij] Sk . Sl. At zero temperature we find a first-order quantum phase transition at J2 /J1 = 0.705 ± 0.005 between AF1 (Neel) and AF2 ordered phases. The high temperature series yield quite precise estimates of the critical line separating the AF1 and paramagnetic phases, and an apparent critical line for the AF2 phase, with a bicritical point at J2/J1 = 0.71, kBT / J1 = 0.34. The possibility that this latter transition is first-order cannot be excluded
Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice
Zhang, Hao; Lamas, Carlos A.; Arlego, Marcelo; Brenig, Wolfram
2016-06-01
We study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb lattice including interlayer frustration. Using a set of complementary approaches, namely, Schwinger bosons, dimer series expansion, bond operators, and exact diagonalization, we map out the quantum phase diagram. Analyzing ground-state energies and elementary excitation spectra, we find four distinct phases, corresponding to three collinear magnetic long-range ordered states, and one quantum disordered interlayer dimer phase. We detail that the latter phase is adiabatically connected to an exact singlet product ground state of the bilayer, which exists along a line of maximum interlayer frustration. The order within the remaining three phases will be clarified.
Dimension changing phase transitions in instanton crystals
We investigate lattices of instantons and the dimension-changing transitions between them. Our ultimate goal is the 3D→4D transition, which is holographically dual to the phase transition between the baryonic and the quarkyonic phases of cold nuclear matter. However, in this paper (just as in http://dx.doi.org/10.1007/JHEP11(2012)047) we focus on lower dimensions — the 1D lattice of instantons in a harmonic potential V∝M22x22+M32x22+M42x42, and the zigzag-shaped lattice as a first stage of the 1D→2D transition. We prove that in the low- and moderate-density regimes, interactions between the instantons are dominated by two-body forces. This drastically simplifies finding the ground state of the instantons’ orientations, so we made a numeric scan of the whole orientation space instead of assuming any particular ansatz. We find that depending on the M2/M3/M4 ratios, the ground state of instanton orientations can follow a wide variety of patterns. For the straight 1D lattices, we found orientations periodically running over elements of a ℤ2, Klein, prismatic, or dihedral subgroup of the SU(2)/ℤ2, as well as irrational but link-periodic patterns. For the zigzag-shaped lattices, we detected 4 distinct orientation phases — the anti-ferromagnet, another abelian phase, and two non-abelian phases. Allowing the zigzag amplitude to vary as a function of increasing compression force, we obtained the phase diagrams for the straight and zigzag-shaped lattices in the (force,M3/M4), (chemical potential,M3/M4), and (density,M3/M4) planes. Some of the transitions between these phases are second-order while others are first-order. Our techniques can be applied to other types of non-abelian crystals
Valence Bond Glass Phase in the Diluted Kagome Antiferromagnets
Singh, R. R. P.
2010-01-01
We present a theory for site dilution in the Valence Bond Crystal Phase of the Kagome Lattice Heisenberg Model. The presence of an empty site leads to strong singlet bond across the impurity. It also creates a free spin, which delocalizes inside the unit cell. Finite concentration of quenched impurities leads to a Valence Bond Glass phase. This phase has short-range Valence Bond order, no spin-gap, large spin susceptibilities, linear specific heat due to two-level systems, as well as singlet ...
Huang, Chien-Lung; Loehneysen, Hilbert von [Karlsruher Institut fuer Technologie, Physikalisches Institut, 76031 Karlsruhe (Germany); Karlsruher Institut fuer Technologie, Institut fuer Festkoerperphysik, 76021 Karlsruhe (Germany); Fritsch, Veronika; Kittler, Wolfram [Karlsruher Institut fuer Technologie, Physikalisches Institut, 76031 Karlsruhe (Germany)
2012-07-01
The resistivity and specific heat of a CeAu{sub 2}Ge{sub 2} single crystal grown from Au-Ge flux were measured between 1.8 and 200 K. Two transitions were observed in the specific heat at 11.5 and 14.5 K, confirming our recent susceptibility results. We observe three field-induced transitions in the magnetoresistance measured at 1.6 K in accordance with the B-T phase diagram constructed from magnetization. In addition, we have measured the magnetization under pressure. The antiferromagnetic transition temperature T{sub N} is linearly enhanced by pressure with a small rate of 0.067 K/kbar, which suggests that, if attributed to a pure volume effect, this compound is close to the maximum transition temperature of the Doniach phase diagram. The transition fields B{sub M} between the field-induced phases increase linearly upon applying pressure. The comparable Grueneisen parameters of T{sub N} and B{sub M} indicate that the energy scale depending on the sample's volume is determined by the antiferromagnetic correlations.
Hiroshi Akiba
2012-07-01
Full Text Available Quasi-two-dimensional organic conductor λ-BETS2FeCl4 (BETS = bis(ethylenedithiotetraselenafulvalene transforms from a paramagnetic metal (PM to an antiferromagnetic insulator (AFI at a transition temperature, TMI, of 8.3 K under zero magnetic field. To understand the mechanism of this PM-AFI phase transition, we studied the thermodynamic properties of λ-BETS2FeCl4. We observed, below TMI, a six-level Schottky hump in its specific heat and a broad shoulder in its magnetic susceptibility. Just below the transition temperature TMI, about 80% of 3d spin degree of freedom is sustained. These temperature dependences clarify that π and 3d spins do not cooperatively form the AF order at TMI. In λ-BETS2FexGa1−xCl4 system, the increasing Fe 3d spin density enhances the internal magnetic field caused by π spin antiferromagnetic (AF ordering, although the 3d spin itself maintains large entropy against the AF ordering. It was confirmed that the Fe 3d spin provided favorable conditions for this mysterious PM-AFI phase transition in the π electron system. We propose that this phase transition originates from the magnetic anisotropy introduced by the π-d interaction, which suppressed the low dimensional fluctuation in the π spin system.
Sadeghi, Azam; Alaei, Mojtaba; Shahbazi, Farhad; Gingras, Michel J. P.
2015-04-01
FeF3, with its half-filled Fe3 +3 d orbital, hence zero orbital angular momentum and S =5 /2 , is often put forward as a prototypical highly frustrated classical Heisenberg pyrochlore antiferromagnet. By employing ab initio density functional theory, we obtain an effective spin Hamiltonian for this material. This Hamiltonian contains nearest-neighbor antiferromagnetic Heisenberg, biquadratic, and Dzyaloshinskii-Moriya interactions as dominant terms and we use Monte Carlo simulations to investigate the nonzero temperature properties of this minimal model. We find that upon decreasing temperature, the system passes through a Coulomb phase, composed of short-range correlated coplanar states, before transforming into an "all-in/all-out" (AIAO) state via a very weakly first-order transition at a critical temperature Tc≈22 K, in good agreement with the experimental value for a reasonable set of Coulomb interaction U and Hund's coupling JH describing the material. Despite the transition being first order, the AIAO order parameter evolves below Tc with a power-law behavior characterized by a pseudo "critical exponent" β ≈0.18 in accord with experiment. We comment on the origin of this unusual β value.
Cubic to hexagonal iron phase transition promoted by interstitial hydrogen
Castedo, A.; Sanchez, J.; Fullea, J.; de Andrade, M. C.; de Andres, P. L.
2011-01-01
Using ab-initio density functional theory we study the role of interstitial hydrogen on the energetics of the phase transformation of iron from bcc to hcp along Bain's pathway. The impurity creates an internal stress field that can be released through a tetragonal distortion of the lattice, promoting the bcc (ferromagnetic) $\\rightarrow$ fcc (frustrated antiferromagnetic) $\\rightarrow$ hcp (ferromagnetic) transition. The transformation between crystal systems is accompanied by a drastic magne...
Investigation Of Mean-Field Equations Of ANNNI Model For The Phase Transition In UNi2Si2
The phase transition from the uncompensated antiferromagnetic state to a simple antiferromagnet, experimentally observed in UNi2Si2 is a subject of intensive discussion in recent few years. We present a study of initial mean-field equations of Axial-Next-Next-Neighbour Ising (ANNNI) model applied to the transition. The temperature evolution of a magnetic phase diagram within ANNNI model is presented. Results are discussed in comparison with other previous investigations of this topic. (Authors)
Dynamic Phase Transitions in Superconductivity
Ma, Tian; Wang, Shouhong
2007-01-01
In this Letter, the dynamic phase transitions of the time-dependent Ginzburg-Landau equations are analyzed using a newly developed dynamic transition theory and a new classification scheme of dynamics phase transitions. First, we demonstrate that there are two type of dynamic transitions, jump and continuous, dictated by the sign of a nondimensional parameter R. This parameter is computable, and depends on the material property, the applied field, and the geometry of domain that the sample oc...
Room temperature write-read operations in antiferromagnetic memory
Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo
2015-01-01
B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the N\\'eel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-ord...
Yu, Rong; Roscilde, Tommaso; Haas, Stephan
2006-01-01
Site dilution of spin-gapped antiferromagnets leads to localized free moments, which can order antiferromagnetically in two and higher dimensions. Here we show how a weak magnetic field drives this order-by-disorder state into a novel disordered-free-moment phase, characterized by the formation of local singlets between neighboring moments and by localized moments aligned antiparallel to the field. This disordered phase is characterized by the absence of a gap, as it is the case in a Bose gla...
Pressure-induced phase transitions in UN: A density functional theory study
Mei, Zhi-Gang, E-mail: zmei@anl.gov; Stan, Marius
2014-03-05
Highlights: • Isostructural and magnetic phase transitions were predicted by DFT in UN. • Thermodynamic properties of UN were well predicted by DFT. • Pressure–temperature phase diagram of UN was calculated from Gibbs energy. -- Abstract: We studied the structural behavior and phase stability of UN under high pressures up to 200 GPa and temperatures up to 1500 K using density functional theory calculations in the generalized gradient approximation. The results show that a pressure-induced structural transition from the cubic to the rhombohedral phase occurs at 23.5 GPa. The calculated structural and magnetic properties of the rhombohedral phase suggest that an isostructural transition occurs at 22.5 GPa. The low-pressure rhombohedral phase has a fcc-like structure. We predict that under further compression, an antiferromagnetic to nonmagnetic transition occurs. This phase transition has been not observed by experiment yet. To evaluate conditions under which other new phase transitions might occur, we studied the phase stability of UN at finite temperature by taking into account the lattice vibrational and thermal electronic contributions to Gibbs energy. Based on the Gibbs energy models, the pressure–temperature phase diagram of UN was studied and the phase boundaries of the antiferromagnetic rhombohedral phase were also determined. We predict that, although metastable, the antiferromagnetic rhombohedral phase might be stabilized at low-temperature by quenching from the high-pressure phase.
Pressure-induced phase transitions in UN: A density functional theory study
Highlights: • Isostructural and magnetic phase transitions were predicted by DFT in UN. • Thermodynamic properties of UN were well predicted by DFT. • Pressure–temperature phase diagram of UN was calculated from Gibbs energy. -- Abstract: We studied the structural behavior and phase stability of UN under high pressures up to 200 GPa and temperatures up to 1500 K using density functional theory calculations in the generalized gradient approximation. The results show that a pressure-induced structural transition from the cubic to the rhombohedral phase occurs at 23.5 GPa. The calculated structural and magnetic properties of the rhombohedral phase suggest that an isostructural transition occurs at 22.5 GPa. The low-pressure rhombohedral phase has a fcc-like structure. We predict that under further compression, an antiferromagnetic to nonmagnetic transition occurs. This phase transition has been not observed by experiment yet. To evaluate conditions under which other new phase transitions might occur, we studied the phase stability of UN at finite temperature by taking into account the lattice vibrational and thermal electronic contributions to Gibbs energy. Based on the Gibbs energy models, the pressure–temperature phase diagram of UN was studied and the phase boundaries of the antiferromagnetic rhombohedral phase were also determined. We predict that, although metastable, the antiferromagnetic rhombohedral phase might be stabilized at low-temperature by quenching from the high-pressure phase
Parente, Walter E. F.; Pacobahyba, J. T. M.; Araújo, Ijanílio G.; Neto, Minos A.; Ricardo de Sousa, J.
2015-11-01
We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii-Moriya interaction (D) and a uniform longitudinal (H) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagram in the H - D plane on a simple cubic lattice (z=6). We analyzed the cases: anisotropic Heisenberg - case I: (Δ = 1), anisotropic Heisenberg - case II: (Δ = 0.5) and anisotropic Heisenberg - case III: (Δ = 0), where only second order phase transitions are observed.
Spin-current probe for phase transition in an insulator.
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z Q; Saitoh, Eiji
2016-01-01
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices. PMID:27573443
Magnetic resonance of phase transitions
Owens, Frank J; Farach, Horacio A
1979-01-01
Magnetic Resonance of Phase Transitions shows how the effects of phase transitions are manifested in the magnetic resonance data. The book discusses the basic concepts of structural phase and magnetic resonance; various types of magnetic resonances and their underlying principles; and the radiofrequency methods of nuclear magnetic resonance. The text also describes quadrupole methods; the microwave technique of electron spin resonance; and the Mössbauer effect. Phase transitions in various systems such as fluids, liquid crystals, and crystals, including paramagnets and ferroelectrics, are also
Sequential write-read operations in FeRh antiferromagnetic memory
Moriyama, Takahiro; Matsuzaki, Noriko; Kim, Kab-Jin; Suzuki, Ippei; Taniyama, Tomoyasu; Ono, Teruo
2015-09-01
B2-ordered FeRh has been known to exhibit antiferromagnetic-ferromagnetic (AF-F) phase transitions in the vicinity of room temperature. Manipulation of the Néel order via AF-F phase transition and recent experimental observation of the anisotropic magnetoresistance in antiferromagnetic FeRh has proven that FeRh is a promising candidate for antiferromagnetic memory material. In this work, we demonstrate sequential write and read operations in antiferromagnetic memory resistors made of B2-orderd FeRh thin films by a magnetic field and electric current only, which open a realistic pathway towards operational antiferromagnetic memory devices.
Antiferromagnetic transitions in `tetragonal-like' BiFeO3
MacDougall, Gregory J [ORNL; Christen, Hans M [ORNL; Siemons, Wolter [ORNL; Biegalski, Michael D [ORNL; Zarestky, Jerel L [ORNL; Liang, Shuhua [ORNL; Dagotto, Elbio R [ORNL; Nagler, Stephen E [ORNL
2012-01-01
Recent studies have reported the existence of an epitaxially-stabilized tetragonal-like (`T-like') monoclinic phase in BiFeO3 thin-films with high levels of compressive strain. Though there is abundant evidence that structural and ferroelectric properties are di erent than in rhombohedral-like (`R-like') films with lower levels of strain, little information exists on magnetic properties. Here,we report a detailed neutron scattering study of a nearly phase-pure film of T-like BiFeO3. By tracking the temperature dependence and relative intensity of several superstructure peaks in the reciprocal lattice cell, we confirm antiferromagnetism with largely G-type character and T_N = 324 K. A minority magnetic phase with C-type character is also reported with T_N= 260 K. The co-existence of the two phases in T-like BiFeO3 and the difference in ordering temperatures between R-like and T-like systems is explained through simple Fe-O-Fe bond distance considerations.
Antiferromagnetic transitions in 'tetragonal-like' BiFeO3
Recent studies have reported the existence of an epitaxially-stabilized tetragonal-like ('T-like') monoclinic phase in BiFeO3 thin-films with high levels of compressive strain. Though there is abundant evidence that structural and ferroelectric properties are different than in rhombohedral-like ('R-like') films with lower levels of strain, little information exists on magnetic properties. Here,we report a detailed neutron scattering study of a nearly phase-pure film of T-like BiFeO3. By tracking the temperature dependence and relative intensity of several superstructure peaks in the reciprocal lattice cell, we confirm antiferromagnetism with largely G-type character and TN = 324 K. A minority magnetic phase with C-type character is also reported with TN = 260 K. The co-existence of the two phases in T-like BiFeO3 and the difference in ordering temperatures between R-like and T-like systems is explained through simple Fe-O-Fe bond distance considerations.
Non-equilibrium phase transitions
Henkel, Malte; Lübeck, Sven
2009-01-01
This book describes two main classes of non-equilibrium phase-transitions: (a) static and dynamics of transitions into an absorbing state, and (b) dynamical scaling in far-from-equilibrium relaxation behaviour and ageing. The first volume begins with an introductory chapter which recalls the main concepts of phase-transitions, set for the convenience of the reader in an equilibrium context. The extension to non-equilibrium systems is made by using directed percolation as the main paradigm of absorbing phase transitions and in view of the richness of the known results an entire chapter is devoted to it, including a discussion of recent experimental results. Scaling theories and a large set of both numerical and analytical methods for the study of non-equilibrium phase transitions are thoroughly discussed. The techniques used for directed percolation are then extended to other universality classes and many important results on model parameters are provided for easy reference.
Multiobjective Optimization and Phase Transitions
Seoane, Luís F
2015-01-01
Many complex systems obey to optimality conditions that are usually not simple. Conflicting traits often interact making a Multi Objective Optimization (MOO) approach necessary. Recent MOO research on complex systems report about the Pareto front (optimal designs implementing the best trade-off) in a qualitative manner. Meanwhile, research on traditional Simple Objective Optimization (SOO) often finds phase transitions and critical points. We summarize a robust framework that accounts for phase transitions located through SOO techniques and indicates what MOO features resolutely lead to phase transitions. These appear determined by the shape of the Pareto front, which at the same time is deeply related to the thermodynamic Gibbs surface. Indeed, thermodynamics can be written as an MOO from where its phase transitions can be parsimoniously derived; suggesting that the similarities between transitions in MOO-SOO and Statistical Mechanics go beyond mere coincidence.
First-order superfluid-to-Mott-insulator phase transitions in spinor condensates
Jiang, J.; Zhao, L.; Wang, S.-T.; Chen, Z.; Tang, T.; Duan, L.-M.; Liu, Y.
2016-06-01
We observe evidence of first-order superfluid-to-Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include the hysteresis effect, significant heatings across the phase transitions, and changes in spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory and suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid-to-Mott-insulator phase transitions.
The low-temperature phase of the Heisenberg antiferromagnet in a fermionic representation
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of a single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using a saddle point approximation in the path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into account the single occupancy condition is discussed at all steps. (author)
In this paper, we study the critical behavior of the three-dimensional antiferromagnetic Ising model in both uniform longitudinal (H) and transverse (Ω) magnetic fields. Using the effective field theory (EFT) with finite cluster N = 1 spin (EFT) we calculate the phase diagrams in the H–T, Ω–T and Ω–H planes for a simple cubic lattice. We have only found second-order phase transitions for all values of fields and reentrant behavior was observed at low temperature. (paper)
In-situ microscopy of the first-order magnetic phase transition in FeRh thin films
Baldasseroni, Chloe
2013-01-01
Simple ferromagnetic (FM) and antiferromagnetic (AF) materials such as Fe and Cr become paramagnetic when heated above some critical temperature, in what is known as a second-order phase transition. Less usual magnetic transitions are found in the magnetic world, for example a first-order magnetic phase transition from AF to FM with increasing temperature. Equiatomic FeRh has been known to exhibit such a transition for over 50 years, with a transition temperature slightly above room tempera...
H. Satz(University of Bielefeld)
2000-01-01
At high temperatures or densities, hadronic matter shows different forms of critical behaviour: colour deconfinement, chiral symmetry restoration, and diquark condensation. I first discuss the conceptual basis of these phenomena and then consider the description of colour deconfinement in terms of symmetry breaking, through colour screening and as percolation transition.
Phase transition in finite systems
Chomaz, Ph.; Duflot, V. [Grand Accelerateur National d' Ions Lourds (GANIL), 14 - Caen (France); Duflot, V.; Gulminelli, F. [Laboratoire de Physique Corpusculaire, LPC-ISMRa, CNRS-IN2P3, 14 - Caen (France)
2000-07-01
The general problem of the definition of a phase transition without employing the thermodynamical limit is addressed. Different necessary conditions are considered and illustrated with examples from different nuclear and general physics phenomenologies. (authors)
Phase transition in finite systems
The general problem of the definition of a phase transition without employing the thermodynamical limit is addressed. Different necessary conditions are considered and illustrated with examples from different nuclear and general physics phenomenologies. (authors)
Phenomenology of cosmic phase transitions
The evolution of the cosmic matter from Planck temperature to the atomic combination temperature is considered from a phenomenological point of view. Particular emphasis is devoted to the sequence of cosmic phase transitions. The inflationary era at the temperature of the order of the grand unification energy scale and the quantum chromodynamic confinement transition are dealt with in detail. (author) 131 refs.; 26 figs
First-order transition to a noncollinear antiferromagnetic structure in U2Rh3Si5
We have determined the antiferromagnetic structure of monoclinic U2Rh3Si5 and the temperature dependence of the magnetically ordered moment μ via single-crystal neutron diffraction. The value of μ exhibits a sharp discontinuity at the ordering temperature TN=25.5 K, jumping from 1.6μB to zero within a narrow temperature interval [ΔTN=0.2 K, μ(9 K)=2.35μB]. This demonstrates the first-order nature of the transition. The magnetically ordered structure is a noncollinear arrangement of the eight uranium magnetic moments within the crystallographic unit cell. The moments are oriented parallel to nearest-neighbor U-Rh bonds, creating uniaxial (Ising-type) magnetic behavior, with canted local easy axes. The temperature dependence of the lattice parameters, as determined via high-resolution x-ray diffraction, exhibit pronounced discontinuities at TN. These data demonstrate a strong magnetoelastic coupling. copyright 1997 The American Physical Society
Quantum Heisenberg antiferromagnets: a survey of the activity in Firenze
Over the years the research group in Firenze has produced a number of theoretical results concerning the statistical mechanics of quantum antiferromagnetic models, which range from the theory of two-magnon Raman scattering to the characterization of the phase transitions in quantum low-dimensional antiferromagnetic models. Our research activity was steadily aimed to the understanding of experimental observations
Optical investigation of magneto-structural phase transition in FeRh
Saidl, V.; Brajer, M.; Horak, L.; Reichlova, H.; Vyborny, K.; Veis, M.; Janda, T.; Trojanek, F.; Fina, I.; Marti, X.; Jungwirth, T.; Nemec, P.
2015-01-01
Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near infrared spectral ranges. This phenomenon was used to measure the phase transition temperature in FeRh films with thicknesses from 6 to 100 nm and it was observed that the hysteretic transition re...
Quantum Phase Transition, Dissipation, and Measurement
Chakravarty, Sudip
2009-01-01
A selected set of topics in quantum phase transition is discussed. It includes dissipative quantum phase transitions, the role of disorder, and the relevance of quantum phase transition to measurement theory in quantum mechanics.
Structural and magnetic phase transitions in NdCoAsO under high pressures
We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.
Physical properties of antiferromagnetic Mn doped ZnO samples: Role of impurity phase
Structural, morphological, optical, and magnetic properties of nanocrystalline Zn1−xMnxO samples (x=0.01, 0.02, 0.04, 0.06, 0.08 and 0.10) prepared by the sol–gel route are studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–visible absorption spectroscopy, Superconducting quantum interference device (SQUID) magnetometry and positron annihilation lifetime spectroscopy (PALS). XRD confirms formation of wurzite structure in all the Mn-substituted samples. A systematic increase in lattice constants and decrease in grain size have been observed with increase in manganese doping concentration up to 6 at% in the ZnO structure. An impurity phase (ZnMnO3) has been detected when percentage of Mn concentration is 6 at% or higher. The optical band gap of the Mn-substituted ZnO samples decrease with increase in doping concentration of manganese whereas the width of the localized states increases. The antiferromagnetic exchange interaction is strong in the samples for 2 and 4 at% of Mn doping but it reduces when the doping level increases from 6 at% and further. Positron life time components τ1 and τ2 are found to decrease when concentration of the dopant exceeds 6 at%. The changes in magnetic properties as well as positron annihilation parameters at higher manganese concentration have been assigned as due to the formation of impurity phase. - highlights: • Single phase structure has been observed up to 6 at% of Mn doping. • Impurity phase has been developed above 6 at% of Mn doping. • Antiferromagnetic and paramagnetic interactions are present in the samples. • Defect parameters show sharp fall as Mn concentration above 6 at%. • The magnetic and defect properties are modified by the formation of impurity phase
Phase transition in Liouville theory
We suggest that the vortices arising in a Kosterlitz-Thouless phase transition in Liouville theory correspond to transitions between different genera, producing the ''plumber's nightmare'' and other phases that have been predicted in fluid membrane theory from energetic considerations. This transition has previously been invoked by Cates to explain the degeneration of numerical simulations of Gaussian random surfaces into branched polymers. The difficulty in quantizing Liouville theory for d>1 is conjectured to be due to our insistence on working at a fixed genus
Berry Phases and Quantum Phase Transitions
Hamma, A
2006-01-01
We study the connection between Berry phases and quantum phase transitions of generic quantum many-body systems. Consider sequences of Berry phases associated to sequences of loops in the parameter space whose limit is a point. If the sequence of Berry phases does not converge to zero, then the limit point is a quantum critical point. Quantum critical points are associated to failures of adiabaticity. We discuss the remarkable example of the anisotropic XY spin chain in a transverse magnetic field and detect the XX region of criticality.
Phase transitions in field theory
By means of an example for which the effective potential is explicitly calculable (up to the one loop approximation), it is discussed how a phase transition takes place as the temperature is increased and pass from spontaneously broken symmetry to a phase in which the symmetry is restored. (Author)
Field-induced phase transitions in neutron-irradiated haematite
Moessbauer spectra of three neutron-irradiated polycrystalline haematite (α-Fe2O3) samples have been recorded at 4.2 K in applied fields of up to 10 T. Field-induced phase transitions were observed, and were found to differ markedly from those that occur in non-irradiated haematite. In two lightly irradiated samples, transitions were detected from a state with Fe3+ spins near the [111] axis ('antiferromagnetic phase') to one where the spins are almost perpendicular to both the applied field and to the [111] axis ('weak ferromagnetic phase'). In the case of a heavily irradiated sample, in which the spins were initially in the weak ferromagnetic phase, the spins were observed to lie almost perpendicular to applied fields of greater than ∼ 4.5 T. The difference in behaviour in irradiated and non-irradiated haematite is attributed to a smaller difference in anisotropy energy, in the irradiated samples, between the antiferromagnetic and weak ferromagnetic phases at 4.2 K. (Author)
Magnetic phase diagram of the low-anisotropy antiferromagnet Cs{sub 2}FeCl{sub 5}·H{sub 2}O
Freitas, R.S., E-mail: freitas@if.usp.br; Paduan-Filho, A.; Becerra, C.C.
2015-01-15
From magnetization and ac susceptibility measurements we obtain the complete magnetic phase diagram of single crystals of Cs{sub 2}FeCl{sub 5}·H{sub 2}O for magnetic field up to 15 T. The magnetic field was applied along the directions parallel and perpendicular to the easy axis and the magnetization measured to temperatures down to 0.5 K. At zero magnetic field the antiferromagnetic ordering occurs at T{sub N}=6.63 K. For the field applied parallel to the easy axis the antiferromagnetic (AF) to the spin-flop (SF) transition occurs for fields from 1.4 T to 1.1 T depending on the temperature. The low temperature transition from the (SF) to the paramagnetic (P) phase occurs at 13.15 T. In the perpendicular configuration this transition occurs at fields around 13.5 T. From the extrapolation of the transition fields to zero temperature, we obtain a ratio of the anisotropy field H{sub A} to exchange field H{sub E}, α=H{sub A}/H{sub E}=(1.4±0.2)×10{sup −2}. A comparison with the phase diagram measured for MnF{sub 2} is included. - Highlights: • Complete phase diagram of Cs{sub 2}FeCl{sub 5}·H{sub 2}O for magnetic fields up to 15 T. • Direct determination of the anisotropy ratio=HA/HE. • Partial phase diagram of the diluted sample. • Estimative of the high field transition value for MnF{sub 2}.
Incommensurate phase transitions
Currat, R. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)
1996-11-01
We review the characteristic aspects of modulated crystals from the point of view of inelastic neutron scattering. We discuss the phenomenological Landau theory of the normal-to-incommensurate displacive instability and its predictions concerning the fluctuation spectrum of the modulated phase. General results on the form of the normal-mode eigenvectors and on the inelastic scattering channels through which they couple to the probe are established using the superspace approach. We illustrate these results on a simple discrete model symmetry and we review available inelastic neutron scattering data on several displacively modulated compounds. (author) 21 figs., 73 refs.
Phase transition in black holes
Roychowdhury, Dibakar
2014-01-01
The present thesis is devoted towards the study of various aspects of the phase transition phenomena occurring in black holes defined in an Anti-de-Sitter (AdS) space. Based on the fundamental principles of thermodynamics and considering a grand canonical framework we examine various aspects of the phase transition phenomena occurring in AdS black holes. We analytically check that this phase transition between the smaller and larger mass black holes obey Ehrenfest relations defined at the critical point and hence confirm a second order phase transition. This include both the rotating and charged black holes in Einstein gravity. Apart from studying these issues, based on a canonical framework, we also investigate the critical behavior in charged AdS black holes. The scaling laws for these black holes are found to be compatible with the static scaling hypothesis. Finally, based on the usual framework of AdS/CFT duality, we investigate the phase transition phenomena occurring in charged hairy black holes defined...
How generic scale invariance influences quantum and classical phase transitions
This review discusses a paradigm that has become of increasing importance in the theory of quantum phase transitions, namely, the coupling of the order-parameter fluctuations to other soft modes and the resulting impossibility of constructing a simple Landau-Ginzburg-Wilson theory in terms of the order parameter only. The soft modes in question are manifestations of generic scale invariance, i.e., the appearance of long-range order in whole regions in the phase diagram. The concept of generic scale invariance and its influence on critical behavior is explained using various examples, both classical and quantum mechanical. The peculiarities of quantum phase transitions are discussed, with emphasis on the fact that they are more susceptible to the effects of generic scale invariance than their classical counterparts. Explicit examples include the quantum ferromagnetic transition in metals, with or without quenched disorder; the metal-superconductor transition at zero temperature; and the quantum antiferromagnetic transition. Analogies with classical phase transitions in liquid crystals and classical fluids are pointed out, and a unifying conceptual framework is developed for all transitions that are influenced by generic scale invariance
Phase transition in evolutionary games
Cao, Z J; Cao, Zhen; Hwa, Rudolph C
1995-01-01
The evolution of cooperative behaviour is studied in the deterministic version of the Prisoners' Dilemma on a two-dimensional lattice. The payoff parameter is set at the critical region 1.8 < b < 2.0 , where clusters of cooperators are formed in all spatial sizes. Using the factorial moments developed in particle and nuclear physics for the study of phase transition, the distribution of cooperators is studied as a function of the bin size covering varying numbers of lattice cells. From the scaling behaviour of the moments a scaling exponent is determined and is found to lie in the range where phase transitions are known to take place in physical systems. It is therefore inferred that when the payoff parameter is increased through the critical region the biological system of cooperators undergoes a phase transition to defectors. The universality of the critical behaviour is thus extended to include also this particular model of evolution dynamics.
Field-Dependent Magnetic Phase Transitions in Mixed-Valent TmSe
Bjerrum Møller, Hans; Shapiro, S. M.; Birgenau, R. J.
1977-01-01
A neutron diffraction study of the field-dependent magnetic ordering in TmSe is reported. The magnetic strucutre in zero field is antiferromagnetic fcc type I with TN=3.2 K. The magnetic phase diagram may be understood as a successive domain reorientation and metamagnetic transitions for T...
Phase transitions precipitated by solitosynthesis
Kusenko, A
1997-01-01
Solitosynthesis of Q-balls in the false vacuum can result in a phase transition of a new kind. Formation and subsequent growth of Q-balls via the charge accretion proceeds until the solitons reach a critical charge, at which point it becomes energetically favorable for the Q-ball interior to expand filling space with the true vacuum phase. Solitosynthesis can destabilize a false vacuum even when the tunneling rate is negligible. In models with low-energy supersymmetry, where the Q-balls associated with baryon and lepton number conservation are generically present, solitosynthesis can precipitate transitions between the vacua with different VEV's of squarks and sleptons.
Superunification, phase transitions and cosmology
We survey the main features behind the idea of grand unification, both without and with (local) supersymmetry. We then study the high-temperature phase transitions in the theories so realized, and their relevance to the cosmology of the early universe. In particular, we review the basic ingredients of (super) grand unified models and we give the basic tools needed for the study of their phase transitions. After a short introduction to cosmology, we focus on the interplay between unified particle physics models and cosmology, with particular emphasis on the inflationary universe scenario. In the same perspective, new research directions, in the context of higher-dimensional theories, are also discussed. (author)
Quantum phase transition in dimerised spin-1/2 chains
Das, Aparajita; Bhadra, Sreeparna; Saha, Sonali
2015-11-01
Quantum phase transition in dimerised antiferromagnetic Heisenberg spin chain has been studied. A staircase structure in the variation of concurrence within strongly coupled pairs with that of external magnetic field has been observed indicating multiple critical (or critical like) points. Emergence of entanglement due to external magnetic field or magnetic entanglement is observed for weakly coupled spin pairs too in the same dimer chain. Though closed dimerised isotropic XXX Heisenberg chains with different dimer strengths were mainly explored, analogous studies on open chains as well as closed anisotropic (XX interaction) chains with tilted external magnetic field have also been studied.
Artificiality of multifractal phase transitions
Wolf, Martin; Schmiegel, Jürgen; Greiner, Martin
1999-01-01
A multifractal phase transition is associated to a nonanalyticity in the generalised dimensions. We show that its occurrence is an artifact of the asymptotic scaling behaviour of integral moments and that it is not observed in an analysis based on differential n-point correlation densities.
Phase transitions in finite systems
In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)
Symmetry structure and phase transitions
Ashok Goyal; Meenu Dahiya; Deepak Chandra
2003-05-01
We study chiral symmetry structure at ﬁnite density and temperature in the presence of external magnetic ﬁeld and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.
Phase transitions in finite systems
Chomaz, Ph. [Grand Accelerateur National d' Ions Lourds (GANIL), DSM-CEA / IN2P3-CNRS, 14 - Caen (France); Gulminelli, F. [Caen Univ., 14 (France). Lab. de Physique Corpusculaire
2002-07-01
In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)
Phase transitions in quantum chromodynamics
Meyer-Ortmanns, H
1996-01-01
The current understanding of finite temperature phase transitions in QCD is reviewed. A critical discussion of refined phase transition criteria in numerical lattice simulations and of analytical tools going beyond the mean-field level in effective continuum models for QCD is presented. Theoretical predictions about the order of the transitions are compared with possible experimental manifestations in heavy-ion collisions. Various places in phenomenological descriptions are pointed out, where more reliable data for QCD's equation of state would help in selecting the most realistic scenario among those proposed. Unanswered questions are raised about the relevance of calculations which assume thermodynamic equilibrium. Promising new approaches to implement nonequilibrium aspects in the thermodynamics of heavy-ion collisions are described.
Magnetic structure and phase transition on NiO
Neutron diffraction has been important technique to understand the magnetism. Louis Néel anticipated antiferromagnetic states theoretically and C. G. Shull et al. carried out neutron powder diffraction and found antiferromagnetic structure on transition metal monoxide TMO(TM=Mn, Fe, Co, and Ni). Since their pioneer works stimulated the research on various magnetic phenomena in condensed matter physics, many textbook explained TMOs as the introduction of antiferromagnetism with neutron powder diffraction. Many researchers who read the textbook thought their magnetic structure was already solved completely, but actually their magnetic moment directions have been unclear for so long time and one of most delicate problem in condensed matter physics. Crystal and magnetic transition occurred simultaneously by exchangestriction and magnetostriction that causes ferroelastic domain even though it was grown as single crystal. These twin domains induce the complicated condition on experiments and analysis of magnetic moment direction. R-3m crystal structure and magnetic propagating vector km=(0 0 1.5)h are well accepted for both MnO and NiO in the research community. Their magnetic moment direction is believed inside the hexagonal plane. However, MnO is 1st order phase transition while NiO is 2nd order phase transition experimentally. To explain the difference of magnetic structure and phase transition between MnO and NiO, we carried out time-of-flight neutron powder diffraction on NiO using SuperHRPD beamline in J-PARC, Japan. Even though we couldn’t observe monoclinic peak splitting which is too smaller than about Δd/d=0.02%, we constructed C2/m monoclinic structure with km=(0 1 0.5)m and assigned Γ2(Bg) magnetic structure on NiO by symmetry analysis. We argue that MnO magnetic moment direction is along 2-fold axis while NiO is inside mirror plane in C2/m. This different magnetic moment direction and symmetry will be responsible to 1st and 2nd order phase transition on
Phase transitions and critical phenomena
Domb, Cyril
2000-01-01
The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. It has moved into a central place in condensed matter studies.Statistical physics, and more specifically, the theory of transitions between states of matter, more or less defines what we know about 'everyday' matter and its transformations.The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable in
Magnetic phase transition in iron-rhodium thin films probed by ferromagnetic resonance
Mancini, E.; Pressacco, F.; Haertinger, M.; Fullerton, E. E.; Suzuki, T.; Woltersdorf, G.; Back, C. H.
2013-06-01
We report the results of ferromagnetic (FMR) resonance measurements on epitaxial FeRh/MgO(0 0 1) samples across the phase transition from the antiferromagnetic (AF) state of FeRh to its ferromagnetic (F) state. From temperature-dependent measurements of position, width and amplitude of the FMR line the phase transition is studied in detail. Our measurements indicate that the AF to F phase transition of FeRh is first order in nature. In addition, the angular and frequency-dependent FMR measurements are used to determine the anisotropy constants and the Gilbert damping parameter of the epitaxial FeRh films.
Phase diagram of uniaxial antiferromagnetic particles: Field perpendicular to the easy axis
We consider a spherical uniaxial antiferromagnetic particle in the presence of an external magnetic field perpendicular to its easy axis. The model is described by a classical Heisenberg Hamiltonian including a single-ion uniaxial anisotropy, where the magnetic moments of the particle are represented by continuous spin vectors. We employ mean-field calculations and Monte Carlo simulations to determine the phase diagram of the system. The phase diagram in the plane field versus temperature is obtained for particles with radii ranging from three up to twelve spacing lattice units. We have seen that a particle with more than nine shells behaves as a true thermodynamic system. We find the explicit dependence of the zero temperature critical field and the Neel temperature on the diameter of the particle. At low temperatures, we have also shown that, for particles with three or more shells, the critical field follows a T2 law, which is in agreement with the predictions of the spin-wave theory, when the field is perpendicular to the easy axis
Phase Transitions in the Universe
Gleiser, Marcello
1998-01-01
During the past two decades, cosmologists turned to particle physics in order to explore the physics of the very early Universe. The main link between the physics of the smallest and largest structures in the Universe is the idea of spontaneous symmetry breaking, familiar from condensed matter physics. Implementing this mechanism into cosmology leads to the interesting possibility that phase transitions related to the breaking of symmetries in high energy particle physics took place during the early history of the Universe. These cosmological phase transitions may help us understand many of the challenges faced by the standard hot Big Bang model of cosmology, while offering a unique window into the very early Universe and the physics of high energy particle interactions.
'Magnetic' phase transition in silver
Experimental and theoretical investigations of the magnetic susceptibility near the phase transition into the Condon domain state in silver are presented. We report about the precursor of the Condon instability of an electron gas by using data of the measurement of the magnetic field-dependence of the susceptibility. Experimental results are explained theoretically within the framework of the Lifshitz-Kosevich-Shoenberg theory. A good agreement between the theory and the experiment is obtained when de Haas-van Alphen oscillations are only originated from 'belly' oscillations, and as a result of this, the spherical modelling of the Fermi surface in silver is justified. It is shown that the phase transition into the Condon domain state is the critical point of the liquid-gas type at which the isothermal susceptibility does not diverge but possesses a finite value due to the nonzero demagnetization factor
Electroweak phase transition recent results
Csikor, Ferenc
2000-01-01
Recent results of four-dimensional (4d) lattice simulations on the finite temperature electroweak phase transition (EWPT) are discussed. The phase transition is of first order in the SU(2)-Higgs model below the end point Higgs mass 66.5$\\pm$1.4 GeV. For larger masses a rapid cross-over appears. This result completely agrees with the results of the dimensional reduction approach. Including the full Standard Model (SM) perturbatively the end point is at 72.1$\\pm$1.4 GeV. Combined with recent LEP Higgs mass lower bounds, this excludes any EWPT in the SM. A one-loop calculation of the static potential makes possible a precise comparison of the lattice and perturbative results. Recent 4d lattice studies of the Minimal Supersymmetric SM (MSSM) are also mentioned.
Mechanical stresses upon phase transitions
Pedersen, Tom Peder Leervad
2003-01-01
Mechanical stress studies were carried out on three different groups of functional coatings using a purpose-built system. Functional coatings have become increasingly important in recent years due to their interesting technological applications. In this work three different groups of coatings were studied. Transition metal oxides are used as optical coatings, hard coatings, etc., phase change films find application in optical data storage technology, while optically switchable coatings have b...
Paramagnetic to antiferromagnetic transition in epitaxial tetragonal CuMnAs
Hills, V.; Wadley, P.; Campion, R. P.; Novák, Vít; Beardsley, R.; Edmonds, K. W.; Gallagher, B. L.; Ouladdiaf, B.; Jungwirth, Tomáš
2015-01-01
Roč. 117, č. 17 (2015), , "172608-1"-"172608-2". ISSN 0021-8979 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.183, year: 2014
Magnetic Phase Transitions of CeSb. II: Effects of Applied Magnetic Fields
Meier, G.; Fischer, P.; Hälg, W.; Lebech, Bente; Rainford, B.D.; Vogt, O.
1978-01-01
For pt.I see ibid., vol.11, p.345 (1978). The metamagnetic phase transition and the associated phase diagram of the anomalous antiferromagnet CeSb were determined in a neutron diffraction study of the magnetic ordering of CeSb single crystals in applied magnetic fields parallel to the (001) and...... (011) directions (H<5 T). Because of the anisotropic exchange interactions that favours a (001) easy direction of magnetisation, the magnetic properties are similar to those of the Ising spin systems i.e. antiferromagnetism, ferrimagnetism and ferromagnetism occur at low temperatures and at increasing...... magnetic fields. The observed magnetic structures do not correspond to the stable configurations expected from the molecular field theory of the face-centred cubic lattice. The change from a first-order transition at the Neel temperature in zero field to second-order transition at high fields points to the...
Structural dynamics in FeRh during a laser-induced metamagnetic phase transition
Quirin, Florian; Vattilana, Michael; Shymanovich, Uladzimir; El-Kamhawy, Abd-Elmoniem; Tarasevitch, Alexander; Hohlfeld, Julius; von der Linde, Dietrich; Sokolowski-Tinten, Klaus
2012-01-01
Time-resolved x-ray diffraction with ultrashort x-ray pulses from a laser-produced plasma is used to study the lattice response of FeRh during a femtosecond laser-induced antiferromagnetic (AFM) to ferromagnetic (FM) phase transition. Pump-probe measurements at initial sample temperatures below as well as above the AFM-to-FM transition temperature and for different laser pump fluences allowed to disentangle the various contributions driving lattice expansion. In particular, the data reveal that the structural changes associated with the magnetic phase transition occur on a time scale of a hundred picoseconds.
Jungwirth, T.; Marti, X.; Wadley, P.; Wunderlich, J.
2016-03-01
Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics.
Phase transitions and critical phenomena
Domb, Cyril
2000-01-01
The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. No longer an area of specialist interest, it has acquired a central focus in condensed matter studies. The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable information on important recent developments.The two review articles in this volume complement each other in a remarkable way. Both deal with what m
Light scattering near phase transitions
Cummins, HZ
1983-01-01
Since the development of the laser in the early 1960's, light scattering has played an increasingly crucial role in the investigation of many types of phase transitions and the published work in this field is now widely dispersed in a large number of books and journals.A comprehensive overview of contemporary theoretical and experimental research in this field is presented here. The reviews are written by authors who have actively contributed to the developments that have taken place in both Eastern and Western countries.
Dynamical constraints on phase transitions
The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of central heavy ion reactions are parameterized in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows to discuss dynamical trajectories in phase space. The nonequilibrium state is characterized by non-isobaric, non-isochoric etc conditions, called iso-nothing conditions. Therefore a combination of thermodynamical observables is constructed which allows to locate instabilities and points of possible phase transition in a dynamical sense. We find two different mechanisms of instability, a short time surface - dominated instability and later a spinodal - dominated volume instability. The latter one occurs only if the incident energies are not exceeding much the Fermi energy and might be attributed to spinodal decomposition. Oppositely the fast surface explosion occurs far outside the spinodal and pertains also in the cases where the system develops too fast for suffering the spinodal decomposition and where the system approaches equilibrium outside the spinodal. (author)
Heidarian, Alireza
2016-01-01
The equiatomic FeRh alloy undergoes a first-order phase transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state at about 370 K with a small thermal hysteresis of about 10 K around the phase transition. The transition is accompanied by a unit cell volume expansion about 1% in the c lattice parameter. During the transition the new phase nucleates in the matrix of the original phase by reaching the critical temperature followed by a growth in size upon increasing temperature fur...
Dynamic Phase Transitions in PVT Systems
Ma, Tian
2007-01-01
The main objective of this article are two-fold. First, we introduce some general principles on phase transition dynamics, including a new dynamic transition classification scheme, and a Ginzburg-Landau theory for modeling equilibrium phase transitions. Second, apply the general principles and the recently developed dynamic transition theory to study dynamic phase transitions of PVT systems. In particular, we establish a new time-dependent Ginzburg-Landau model, whose dynamic transition analysis is carried out. It is worth pointing out that the new dynamic transition theory, along with the dynamic classification scheme and new time-dependent Ginzburg Landau models for equilibrium phase transitions can be used in other phase transition problems, including e.g. the ferromagnetism and superfluidity, which will be reported elsewhere. In addition, the analysis for the PVT system in this article leads to a few physical predications, which are otherwise unclear from the physical point of view.
Effects of strain and surfaces on the antiferromagnetic and ferromagnetic phases of thin film FeRh
Hellman, Frances; Bordel, Catherine; Baldasseroni, Chloe; Antonakos, Cory; Schneider, Oliver; Pal, Gunar; Valencia, Sergio; Unal, Akin; Kronast, Florian; Nemsak, Slavo; Fadley, Chuck; Borchers, Julie; Maranville, Brian
2014-03-01
FeRh undergoes an unusual antiferromagnetic (AFM) to ferromagnetic (FM) first order transition just above room temperature. This transition can be tuned by pressure, magnetic field, composition, and strain. The underlying source of the transition is still under much discussion, but it is clear from a variety of measurements that electronic structure, lattice, and magnetic excitations all play roles in contributing the underlying entropy difference and hence the competition between AFM and FM states. The surface and bottom interface of thin films are often found to be FM even while the bulk of the film is AFM. The source of this effect, along with the dependence of strain on both anisotropy and transition temperature will be presented and discussed. Thanks to DOE BES LBNL magnetism program for support.
Symmetry and Phase Transitions in Nuclei
Phase transitions in nuclei have received considerable attention in recent years, especially after the discovery that, contrary to expectations, systems at the critical point of a phase transition display a simple structure. In this talk, quantum phase transitions (QPT), i.e. phase transitions that occur as a function of a coupling constant that appears in the quantum Hamiltonian, H, describing the system, will be reviewed and experimental evidence for their occurrence in nuclei will be presented. The phase transitions discussed in the talk will be shape phase transitions. Different shapes have different symmetries, classified by the dynamic symmetries of the Interacting Boson Model, U(5), SU(3) and SO(6). Very recently, the concept of Quantum Phase Transitions has been extended to Excited State Quantum Phase Transitions (ESQPT). This extension will be discussed and some evidence for incipient ESQPT in nuclei will be presented. Systems at the critical point of a phase transition are called 'critical systems'. Approximate analytic formulas for energy spectra and other properties of 'critical nuclei', in particular for nuclei at the critical point of the second order U(5)-SO(6) transition, called E(5), and along the line of first order U(5)-SU(3) transitions, called X(5), will be presented. Experimental evidence for 'critical nuclei' will be also shown. Finally, the microscopic derivation of shape phase transitions in nuclei within the framework of density functional methods will be briefly discussed.(author)
Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh
Mariager, S. O.; Pressacco, F.; Ingold, G.; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Mancini, E.; Moyerman, S.; Fullerton, E. E.; Feidenhans'L, R.; Back, C. H.; Quitmann, C.
2012-02-01
We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ1˜30ps). This is significantly faster than the magnetic response (τ2˜60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.
Structural and magnetic dynamics of a laser induced phase transition in FeRh
Mariager, S. O.; Pressacco, F.; Ingold, G.; Mancini, E; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Moyerman, S.; Fullerton, E.; Feidenhans'l, R.; Back, C.H.; Quitmann, C.
2011-01-01
We use time-resolved x-ray diffraction and magnetic optical Kerr effect to study the laser induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (\\tau_1 ~ 30ps). This is significantly faster than the magnetic response (\\tau_2 ~ 60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases co-exist on short time-scales and that the phase transition is limited b...
Quantum phase transitions (QPTs) in one-dimensional S=1 XXZ model with uniaxial single-ion anisotropy are investigated. Bipartite entanglement, entanglement spectrum, and Schmidt gap are found to be capable of describing all the QPTs, even the infinite-order Berezinskii–Kosterlitz–Thouless (BKT) transition. According to the singular behavior of the second-order derivative of ground-state energy, the QPT between XY2 and antiferromagnetic phases is a second-order but not a BKT transition. Energy level crossing, accompanied with discontinuous entanglement entropy and entanglement spectrum, is observed at the transition point between the large-D and antiferromagnetic phases, therefore it should be a first-order QPT. In addition, doubly degenerate entanglement spectrum in the Haldane phase is observed.
Quark Deconfinement Phase Transition in Neutron Stars
Alaverdyan, G B
2009-01-01
The hadron-quark phase transition in the interior of compact stars is investigated, when the transition proceeds through a mixed phase. The hadronic phase is described in the framework of relativistic mean-field theory, when also the scalar-isovector delta-meson mean-field is taken into account. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. The results of calculation of structure of the mixed phase (Glendenning construction) are compared with the results of usual first-order phase transition (Maxwell construction).
QCD Phase Transitions, Volume 15
Schaefer, T.; Shuryak, E.
1999-03-20
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
Phase Transition Induced Fission in Lipid Vesicles
Leirer, C.; Wunderlich, B.; Myles, V.M.; Schneider, M F
2009-01-01
Abstract In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>Tm) through the phase transition into the gel state (T
Cloud regimes as phase transitions
Stechmann, Samuel N.; Hottovy, Scott
2016-06-01
Clouds are repeatedly identified as a leading source of uncertainty in future climate predictions. Of particular importance are stratocumulus clouds, which can appear as either (i) closed cells that reflect solar radiation back to space or (ii) open cells that allow solar radiation to reach the Earth's surface. Here we show that these clouds regimes -- open versus closed cells -- fit the paradigm of a phase transition. In addition, this paradigm characterizes pockets of open cells as the interface between the open- and closed-cell regimes, and it identifies shallow cumulus clouds as a regime of higher variability. This behavior can be understood using an idealized model for the dynamics of atmospheric water as a stochastic diffusion process. With this new conceptual viewpoint, ideas from statistical mechanics could potentially be used for understanding uncertainties related to clouds in the climate system and climate predictions.
Phases and phase transitions in disordered quantum systems
Vojta, Thomas
2013-01-01
These lecture notes give a pedagogical introduction to phase transitions in disordered quantum systems and to the exotic Griffiths phases induced in their vicinity. We first review some fundamental concepts in the physics of phase transitions. We then derive criteria governing under what conditions spatial disorder or randomness can change the properties of a phase transition. After introducing the strong-disorder renormalization group method, we discuss in detail some of the exotic phenomena...
Kim, MinJae; Kim, Beom Hyun; Choi, Hong Chul; B. I. Min
2009-01-01
KO2 exhibits concomitant antiferromagnetic (AFM) and structural transitions, both of which originate from the open-shell 2p electrons of O$_{2}^{-}$ molecules. The structural transition is accompanied by the coherent tilting of O$_{2}^{-}$ molecular axes. The interplay among the spin-orbital-lattice degrees of freedom in KO2 is investigated by employing the first-principles electronic structure theory and the kinetic-exchange interaction scheme. We have shown that the insulating nature of the...
Quantum phase transitions out of the heavy Fermi liquid
Senthil, T. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Sachdev, Subir [Department of Physics, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States)]. E-mail: subir.sachdev@yale.edu; Vojta, Matthias [Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, 76128 Karlsruhe (Germany)
2005-04-30
We review recent work on the instability of the heavy Fermi liquid state (FL) of the Kondo lattice towards a magnetic metal in which the local moments are not part of the Fermi sea. Using insights drawn from the theory of deconfined quantum criticality of insulating antiferromagnets, we discuss the possibility of a direct second-order transition between the heavy Fermi liquid and such a magnetic metal. We suggest the presence of at least two distinct diverging time scales-the shorter one describes fluctuations associated with the reconstruction of the Fermi surface, while a longer one describes fluctuations of the magnetic order parameter. The intermediate time scale physics on the magnetic side is suggested to be that of a novel fractionalized Fermi liquid (FL*) state with deconfined neutral S=12 excitations. This could ultimately devolve into the magnetic phase with conventional order at one of the larger time scales. Experimental implications for this scenario are noted.
Quantum phase transitions out of the heavy Fermi liquid
We review recent work on the instability of the heavy Fermi liquid state (FL) of the Kondo lattice towards a magnetic metal in which the local moments are not part of the Fermi sea. Using insights drawn from the theory of deconfined quantum criticality of insulating antiferromagnets, we discuss the possibility of a direct second-order transition between the heavy Fermi liquid and such a magnetic metal. We suggest the presence of at least two distinct diverging time scales-the shorter one describes fluctuations associated with the reconstruction of the Fermi surface, while a longer one describes fluctuations of the magnetic order parameter. The intermediate time scale physics on the magnetic side is suggested to be that of a novel fractionalized Fermi liquid (FL*) state with deconfined neutral S=12 excitations. This could ultimately devolve into the magnetic phase with conventional order at one of the larger time scales. Experimental implications for this scenario are noted
Li, W. C.; Song, X.; Feng, J. J.; Zeng, M.; Gao, X. S.; Qin, M. H., E-mail: qinmh@scnu.edu.cn [Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China); Jia, X. T. [School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000 (China)
2015-07-07
In this work, the effects of the random exchange interaction on the phase transitions and phase diagrams of classical frustrated Heisenberg model are investigated by Monte Carlo simulation in order to simulate the chemical doping effect in real materials. It is observed that the antiferromagnetic transitions shift toward low temperature with the increasing magnitude of the random exchange interaction, which can be qualitatively understood from the competitions among local spin states. This study is related to the magnetic properties in the doped iron-based superconductors.
In this work, the effects of the random exchange interaction on the phase transitions and phase diagrams of classical frustrated Heisenberg model are investigated by Monte Carlo simulation in order to simulate the chemical doping effect in real materials. It is observed that the antiferromagnetic transitions shift toward low temperature with the increasing magnitude of the random exchange interaction, which can be qualitatively understood from the competitions among local spin states. This study is related to the magnetic properties in the doped iron-based superconductors
Magnetic Phase Transition in FeRh
Gu, R. Y.; Antropov, V.P.
2005-01-01
Density functional calculations are performed to investigate the phase transition in FeRh alloy. The effective exchange coupling, the critical temperature of magnetic phase transition and the adiabatic spin wave spectrum have been obtained. Different contributions to the free energy of different phases are estimated. It has been found that the antiferro-ferromagnetic transition in FeRh occurs mostly due to the spin wave excitations.
Thermal behavior in the magnetic phase diagram of the easy axis antiferromagnet Cs2FeCl5·H2O
Freitas, R. S.; Paduan-Filho, A.; Becerra, C. C.
2016-03-01
The specific heat at a constant applied field C H(T) and at fixed temperatures C T(H) of single crystals of the low anisotropy antiferromagnet Cs2FeCl5·H2O was measured across the different boundaries of its magnetic phase diagram, in magnetic fields up to 9 T applied parallel and perpendicular to the easy axis direction and to temperatures down to 0.3 K. The specific heat data indicate that the critical behavior along the antiferromagnetic to paramagnetic phase boundary and the spin-flop to paramagnetic phase boundary, are basically the same. We also measured the specific heat when the first order antiferromagnetic to spin-flop phase boundary is crossed at a fixed temperature. The entropy of the different magnetic phases is discussed.
Phase transitions in semidefinite relaxations.
Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico
2016-04-19
Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856
Phase-matched sum frequency generation of antiferromagnetic film in THz frequency field
We report on a way to obtain a new source in THz frequency field based on sum frequency (SF) generation of an antiferromagnetic film (AFF). The continuous SF output windows versus the infrared signal wave frequencies are shown. We found that the highest SF outputs can be induced when the frequencies of the two signal waves are both situated at the vicinity of the same resonant frequency of AFF. In addition, the incident angles are in the smaller angle regions. An optimum interact length is defined which should be necessary for the choice of AFF thickness in the experiments. Finally, the frequencies of highest SF outputs can be modulated by controlling the external magnetic field strength. - Highlights: • SF generation of antiferromagnetic film. • New source available with the SF generation method in THz field. • SF conversion efficiency affected by incident frequencies, angles and thickness film
Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs
Wadley, P.; Novák, Vít; Campion, R. P.; Rinaldi, C.; Martí, Xavier; Reichlová, Helena; Železný, Jakub; Gazquez, J.; Roldan, M.A.; Varela, M.; Khalyavin, D.; Langridge, S.; Kriegner, D.; Máca, František; Mašek, Jan; Bertacco, R.; Holý, V.; Rushforth, A.W.; Edmonds, K. W.; Gallagher, B. L.; Foxon, C. T.; Wunderlich, Joerg; Jungwirth, Tomáš
2013-01-01
Roč. 4, Aug (2013), s. 2322. ISSN 2041-1723 R&D Projects: GA MŠk(CZ) LG13058; GA MŠk(CZ) LM2011026 EU Projects: European Commission(XE) 268066 - 0MSPIN Grant ostatní: AVČR(CZ) Premium Academiae Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 10.742, year: 2013
Magnetic Phase Transitions of CeSb. I
Fischer, Pernille Hertz; Lebech, Bente; Meier, G.; Rainford, B. D.; Vogt, O.
1978-01-01
The magnetic ordering of the anomalous antiferromagnet CeSb, which has a NaCl crystal structure, was determined in zero applied magnetic field by means of neutron diffraction investigations of single crystals and powder. Below the Neel temperature TN of (16.1+or-0.1)K, there exist six partially...... disordered magnetic phases of antiphase domain type ((100) superstructures) with (100) orientation of the magnetic moments. At 4.4K, the ordered magnetic moment equals (2.10+or-0.04) mu B, which corresponds to the free-ion value of 2.14 mu mB for Ce3+. The temperature dependence of the ordered moment shows a...... first-order phase transition at TN. At approximately TN/2 there is a first-order phase transition to a FCC type IA low-temperature configuration. The unusual magnetic properties of CeSb, which result from anisotropic exchange and crystalline electric field effects, resemble those of certain actinide Na...
Magnetization dynamics across the first order phase transition in FeRh thin films
Pressacco, Federico
2014-01-01
The metallic alloy FeRh undergoes a phase transition from an antiferromagnetic phase (AFP) to a ferromagnetic phase (FP) when heated above 400 K. The change in the magnetic order results in a change in the net magnetization of the system from zero up to 1.2 kA/m after increasing the system temperature. This is an uncommon character for a magnetic material since usually one observes a decrease of the magnetization upon heating. This discloses the possibility to apply FeRh to Heat-Assisted Magn...
Magnetization dynamics across the first order phase transition in FeRh thin films
Pressacco, Federico
2014-08-01
The metallic alloy FeRh undergoes a phase transition from an antiferromagnetic phase (AFP) to a ferromagnetic phase (FP) when heated above 400 K. The change in magnetic order results in a change in the net magnetization of the system from zero up to 1.2 kA/m after increasing the system temperature. This is an uncommon characteristic for a magnetic material since usually one observes a decrease of the magnetization upon heating. This discloses the possibility to apply FeRh to Heat-Assisted Magnetic Recording (HAMR) devices.
Switchable thermal antenna by phase transition
Ben-Abdallah, Philippe; Besbes, Mondher
2013-01-01
We introduce a thermal antenna which can be actively switched by phase transition. The source makes use of periodically patterned vanadium dioxide, a metal-insulator phase transition material which supports a surface phonon-polariton (SPP) in the infrared range in its crystalline phase. Using electrodes properly registred with respect to the pattern, the phase transition of VO2 can be localy triggered within few microseconds and the SPP can be diffracted making the thermal emission highly directionnal. This switchable antenna could find broad applications in the domain of active thermal coatings or in those of infrared spectroscopy and sensing.
Phase-transitions and nuclear clusterization
After reviewing some basic features of the temperature-governed phase-transitions in macroscopic systems and in atomic nuclei we consider non-thermal phase-transitions of nuclear structure in the example of cluster states. Phenomenological and semimicroscopical algebraic cluster models with identical interactions are applied to binary cluster systems of closed and non-closed shell clusters. Phase-transitions are observed in each case between the rotational (rigid molecule-like) and vibrational (shell-like) cluster states. The phase of this finite quantum system shows a quasi-dynamical symmetry. (author)
Gruner, M. E.; Hoffmann, E.; Entel, P.
2002-01-01
Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature induced metamagnetic phase transition, which experimentally is observed for stoichiometric alpha-FeRh. A first-principle spin-based model allows to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange...
Inhomogeneous nucleation in quark hadron phase transition
Shukla, P K; Sen-Gupta, S K; Gleiser, Marcello; Gleiser, Marcelo
2000-01-01
The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles created due to thermal fluctuations introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For sufficiently strong transitions, as is expected to be the case for the quark-hadron transition, we show that the amount of phase mixing at the critical temperature remains much below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP) within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogenity of the medium is incorporated consistently by modelling the subcritical bubbles as Gaussian fluctuations, resulting in a large reduction of the nucleation barrier for the critical bubbles. Using the corrected nucle...
Intersubband-transition-induced phase matching
Almogy, Gilad; Segev, Mordechai; Yariv, Amnon
1994-01-01
We suggest the use of the refractive-index changes associated with the intersubband transitions in quantum wells for phase matching in nonlinear materials. An improvement in the conversion efficiency of mid-IR second-harmonic generation by almost 2 orders of magnitude over non-phase-matched bulk GaAs is predicted. We also show that the linear phase contributions of intersubband transitions used for resonant enhancement of second-harmonic generation must be considered, as they could limit the ...
The Cosmological QCD Phase Transition Revisited
Schettler, Simon; Boeckel, Tillmann; Schaffner-Bielich, Jurgen
2010-01-01
The QCD phase diagram might exhibit a first order phase transition for large baryochemical potentials. We explore the cosmological implications of such a QCD phase transition in the early universe. We propose that the large baryon-asymmetry is diluted by a little inflation where the universe is trapped in a false vacuum state of QCD. The little inflation is stopped by bubble nucleation which leads to primordial production of the seeds of extragalactic magnetic fields, primordial black holes a...
Ising metamagnet driven by propagating magnetic field wave: Nonequilibrium phases and transitions
The nonequilibrium responses of Ising metamagnet (layered antiferromagnet) to the propagating magnetic wave are studied by Monte Carlo simulation. Here, the spatio-temporal variations of magnetic field keep the system away from equilibrium. The sublattice magnetisations show dynamical symmetry breaking in the low temperature ordered phase. The nonequilibrium phase transitions are studied from the temperature dependences of dynamic staggered order parameter, its derivative and the dynamic specific heat. The transitions are marked by the peak position of dynamic specific heat and the position of dip of the derivative of dynamic staggered order parameter. It is observed that, for lower values of the amplitudes of the propagating magnetic field, if the system is cooled from a high temperature, it undergoes a phase transition showing sharp peak of dynamic specific heat and sharp dip of the derivative of the dynamic staggered order parameter. However, for higher values of the amplitude of the propagating magnetic field, system exhibits multiple phase transitions. A comprehensive phase diagram is also plotted. The transition, for vanishingly small value of the amplitude of the propagating wave, is very close to that for equilibrium ferro–para phase transition of cubic Ising ferromagnet. - Highlights: • Ising metamagnet. • Driven by propagating magnetic field wave. • Studied by Monte Carlo Simulation. • Nonequlibrium phase transition is studied. • The phase diagram is drawn
Interplay between chiral and deconfinement phase transitions
Mukherjee T.K.
2011-04-01
Full Text Available By using the dressed Polyakov loop or dual chiral condensate as an equivalent order parameter of the deconfinement phase transition, we investigate the relation between the chiral and deconfinement phase transitions at finite temperature and density in the framework of three-flavor Nambu-Jona-Lasinio (NJL model. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole (T,µ plane. In the case of explicit chiral symmetry breaking, it is found that the phase transitions are flavor dependent. For each flavor, the transition temperature for chiral restoration $T^{mathcal{X}}_c$ is smaller than that of the dressed Polyakov loop $T^{mathcal{D}}_c$ in the low baryon density region where the transition is a crossover, and, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. Therefore, there are two critical end points, i.e, $T^{u,d}_{CEP}$ and $T^{s}_{CEP}$ at finite density. We also explain the feature of $T^{mathcal{X}}_c$ = $T^{mathcal{D}}_c$ in the case of 1st and 2nd order phase transitions, and $T^{mathcal{X}}_c$ < $T^{mathcal{D}}_c$ in the case of crossover, and expect this feature is general and can be extended to full QCD theory.
The 1-K phase transition in UCu5, showing up in specific-heat data within the antiferromagnetic state below TN≅15 K, was investigated. Neither the average internal fields seen by the μ+ nor the magnetic and nuclear Bragg reflections in the neutron-diffraction data reflect the phase transition while the muon relaxation rates increase drastically below 1.2 K. These results are interpreted in terms of some additional small-moment magnetic order or spin-density-wave phenomenon, implying the coexistence of two rather independent electronic subsystems, one involving ''heavy'' electrons, associated with the weak magnetism, and the other associated with the ''conventional'' antiferromagnetic order
Phase transitions in QCD and string theory
We develop a unified effective field theory approach to the high-temperature phase transitions in QCD and string theory, incorporating winding modes (time-like Polyakov loops, vortices) as well as low-mass states (pseudoscalar mesons and glueballs, matter and dilaton supermultiplets). Anomalous scale invariance and the Z3 structure of the centre of SU(3) decree a first-order phase transition with simultaneous deconfinement and Polyakov loop condensation in QCD, whereas string vortex condensation is a second-order phase transition breaking a Z2 symmetry. We argue that vortex condensation is accompanied by a dilaton phase transition to a strong coupling regime, and comment on the possible role of soliton degrees of freedom in the high-temperature string phase. (orig.)
Dynamics of weak first order phase transitions
Gleiser, Marcello
1994-01-01
The dynamics of weak vs. strong first order phase transitions is investigated numerically for 2+1 dimensional scalar field models. It is argued that the change from a weak to a strong transition is itself a (second order) phase transition, with the order parameter being the equilibrium fractional population difference between the two phases at the critical temperature, and the control parameter being the coefficient of the cubic coupling in the free-energy density. The critical point is identified, and a power law controlling the relaxation dynamics at this point is obtained. Possible applications are briefly discussed.
Phase transitions in copper(II) orthovanadate
Data on the polymorphs of copper(II) orthovanadate are reported. The Cu3V2O8 phase synthesized in this laboratory exhibits phase transitions between 460deg and 560degC. These phase transitions are identified through detailed DTA and high temperature XRD techniques; it is observed that these structural transitions are rapid and reversible. The crystal structure of Cu3V2O8 is similar to that of Mg3V2O8, Zn3V2O8, Co3V2O8 and Ni3V2O8. (author). 12 refs., 3 figs., 1 tab
Chiral Magnetic Effect and Chiral Phase Transition
FU Wei-Jie; LIU Yu-Xin; WU Yue-Liang
2011-01-01
We study the influence of the chiral phase transition on the chiral magnetic effect.The azimuthal chargeparticle correlations as functions of the temperature are calculated.It is found that there is a pronounced cusp in the correlations as the temperature reaches its critical value for the QCD phase transition.It is predicted that there will be a drastic suppression of the charge-particle correlations as the collision energy in RHIC decreases to below a critical value.We show then the azimuthal charge-particle correlations can be the signal to identify the occurrence of the QCD phase transitions in RHIC energy scan experiments.
Phase transitions in dissipative Josephson chains
The authors of this paper study the zero temperature phase transitions of a chain of Josephson junctions, taking into account the quantum fluctuations due to the charging energy and the effects of an Ohmic dissipation. The authors map the problem onto a generalized coulomb gas model, which then is transformed into a sine-Gordon field theory. Apart from the expected dipole unbinding transition, which describes a transition between globally superconducting and resistive behavior, the authors find a quadrupole unbinding transition at a critical strength of the dissipation. This transition separates two superconducting states characterized by different local properties
Calvo, Rafael; Sartoris, Rosana P.; Calvo, Hernán L.; Chagas, Edson F.; Rapp, Raul E.
2016-05-01
We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2•H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0=(-2.12±0.08) cm-1 (defined as ℋex(i,i+1) = -2J0SiṡSi+1), between neighbor coppers at 4.49 Å along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0=(-2.27±0.02) cm-1 and g = 2.091±0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 Å cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1≤|2J1|≤0.4 cm-1, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain
Phase transition phenomenon: A compound measure analysis
Kang, Bo Soo; Park, Chanhi; Ryu, Doojin; Song, Wonho
2015-06-01
This study investigates the well-documented phenomenon of phase transition in financial markets using combined information from both return and volume changes within short time intervals. We suggest a new measure for the phase transition behaviour of markets, calculated as a return distribution conditional on local variance in volume imbalance, and show that this measure successfully captures phase transition behaviour under various conditions. We analyse the intraday trade and quote dataset from the KOSPI 200 index futures, which includes detailed information on the original order size and the type of each initiating investor. We find that among these two competing factors, the submitted order size yields more explanatory power on the phenomenon of market phase transition than the investor type.
Quantum Phase Transitions in Quantum Dots
Rau, I. G.; Amasha, S.; Oreg, Y.; Goldhaber-Gordon, D.
2013-01-01
This review article describes theoretical and experimental advances in using quantum dots as a system for studying impurity quantum phase transitions and the non-Fermi liquid behavior at the quantum critical point.
The fishnet as anti-ferromagnetic phase of world sheet Ising spins
We identify the strong coupling fishnet diagram with a certain Ising spin configuration in the light cone world sheet description of planar TrPHI3 field theory. Then, using a mean field formalism, we take the remaining planar diagrams into account in an average way. Since the fishnet spin configuration is regular but non-uniform, we introduce two mean fields phi,phi' where the fishnet diagram is the case phi=1, phi'=0. For general values of these fields, the system is then approximated as a light-cone quantized string with a field dependent effective string tension Teff(phi,phi'). We also calculate the world sheet energy density E(phi,phi'), and find the field values that minimize it in the presence of a transverse space infra-red cutoff ε>0. The criterion for string formation is that the tension in this minimum energy state remains non-zero as ε→0. In the most simple-minded implementation of the mean field method, which neglects all short range correlations of the Ising spins, we find, in this limit, that the tension vanishes for weak and moderate coupling, but for very large coupling does indeed stay non-zero. However, a more elaborate treatment, taking temporal correlations into account (but still neglecting spatial correlations), removes this 'phase transition' and the string tension of the minimum energy state vanishes for all values of the coupling when ε→0. Our mean field analysis thus suggests that the 'fishnet phase' of TrPHI3 theory is unstable, and there is no string formation for any value of the coupling. This is probably a reasonable outcome given the instability of the underlying theory. It is encouraging for our method, that an approach designed for a string description can predict, where appropriate, the absence of string formation within an intuitive and simple approximation
The AFM-FM phase transition in FeRh investigated using XMCD
Stamm, Christian; Duerr, Hermann A.; Eberhardt, Wolfgang [BESSY, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Back, Christian [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstr. 31, 93040 Regensburg (Germany); Radu, Ilie [BESSY, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, Universitaetsstr. 31, 93040 Regensburg (Germany); Thiele, Jan-Ulrich [Hitachi Global Storage Technologies, 3403 Yerba Buena Road, San Jose, CA 95135 (United States)
2008-07-01
The phase transition from antiferromagnetic to ferromagnetic ordering in FeRh is investigated in an element specific way by means of X-ray absorption spectroscopy. Dichroism sum rules allow us to determine spin and orbital moments of the two elements. Increasing the temperature from 300 to 450 Kelvin, the magnetic moments in Fe and Rh both evolve from zero to their final value, while the ratio of Rh to Fe moments stays constant. We attribute this to a coexistence of the AFM and FM phases.
The Structural Phase Transition in Octaflournaphtalene
Mackenzie, Gordon A.; Arthur, J. W.; Pawley, G. S.
1977-01-01
The phase transition in octafluoronaphthalene has been investigated by Raman scattering and neutron powder diffraction. The weight of the experimental evidence points to a unit cell doubling in the a direction, but with no change in space group symmetry. Lattice dynamics calculations support this...... evidence and indicate that the mechanism of the phase transition may well be the instability of a zone boundary acoustic mode of librational character. The structure of the low-temperature phase has been refined and the Raman spectra of the upper and lower phases are reported....
Giant atomic displacement at a magnetic phase transition in metastable Mn3O4
Hirai, Shigeto [Stanford University; Moreira Dos Santos, Antonio F [ORNL; Shapiro, Max C [Stanford University; Molaison, Jamie J [ORNL; Pradhan, Neelam [ORNL; Guthrie, Malcolm [Carnegie Institution of Washington; Tulk, Christopher A [ORNL; Fisher, Ian R [Stanford University; Mao, Wendy [Stanford University
2013-01-01
We present x-ray, neutron scattering, and heat capacity data that reveal a coupled first-order magnetic and structural phase transition of the metastable mixed-valence postspinel compound Mn3O4 at 210 K. Powder neutron diffraction measurements reveal a magnetic structure in which Mn3+ spins align antiferromagnetically along the edge-sharing a axis, with a magnetic propagation vector k = [1/2,0,0]. In contrast, the Mn2+ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn2+ spins do not directly participate in the magnetic phase transition at 210 K, structural refinements reveal a large atomic shift at this phase transition, corresponding to a physical motion of approximately 0.25 angstrom, even though the crystal symmetry remains unchanged. This "giant" response is due to the coupled effect of built-in strain in the metastable postspinel structure with the orbital realignment of the Mn3+ ion.
Elastic anomalies at the magnetic phase transitions of TbTe3
Saint-Paul, M.; Guttin, C.; Lejay, P.; Leynaud, O.; Monceau, P.
2016-08-01
We report sound velocity and ultrasonic attenuation measurements in the vicinity of the successive magnetic phase transitions Tmag1~6.5 K, Tmag2~5.8 K and Tmag3~5.3 K in the charge density wave TbTe3 compound. A detailed investigation of the critical contributions to the temperature dependences of the sound velocity and ultrasonic attenuation is presented. Anisotropic stress dependences ∂Tmag1 / ∂σ found at the antiferromagnetic phase transition Tmag1 is associated with the layered structure of this compound. An abrupt step-like increase in the velocity and a sharp peak in the attenuation are observed with the longitudinal and shear modes at the lock-in magnetic phase transition Tmag3=5.3 K. The critical velocity and attenuation behaviors in the high temperature paramagnetic above Tmag1 are described in terms of a phenomenological dynamic scaling expression.
Electrochemical control of the phase transition of ultrathin FeRh films
Jiang, M.; Chen, X. Z.; Zhou, X. J.; Cui, B.; Yan, Y. N.; Wu, H. Q.; Pan, F.; Song, C.
2016-05-01
We investigate the electrical manipulation of the phase transition in ultrathin FeRh films through a combination of ionic liquid and oxide gating. The 5 nm-thick FeRh films show an antiferromagnetic-ferromagnetic transition at around 275 K with in-plane magnetic field of 70 kOe. A negative gate voltage seriously suppresses the transition temperature to ˜248 K, while a positive gate voltage does the opposite but with a smaller tuning amplitude. The formation of electric double layer associated with a large electric field induces the migration of oxygen ions between the oxide gate and the FeRh layer, producing the variation of Fe moments in antiferromagnetic FeRh accompanied by the modulation of the transition temperature. Such a modulation only occurs within several nanometers thick scale in the vicinity of FeRh surface. The reversible control of FeRh phase transition by electric field might pave the way for non-volatile memories with low power consumption.
Phase Transitions, Diffraction Studies and Marginal Dimensionality
Als-Nielsen, Jens Aage
1985-01-01
Continuous phase transitions and the associated critical phenomena have been one of the most active areas of research in condensed matter physics for several decades. This short review is only one cut through this huge subject and the author has chosen to emphasize diffraction studies as a basic...... experimental method and illustrate how diffraction experiments have revealed the role of dimensionality in the general classification of phase transitions...
Modelling of phase transitions: do it yourself
We present the basics of a powerful contemporary statistical mechanical technique that can be used by students to explore first-order phase transitions by themselves and for models of their own construction. The technique is a generalization of the well-known Peierls argument and is applicable to various models on a lattice. We illustrate the technique with the help of two simple models that were recently used to simulate phase transitions on surfaces. (paper)
Modelling of phase transitions: do it yourself
Medved', I.; Huckaby, D. A.; Trník, A.; Valovičová, L'
2013-01-01
We present the basics of a powerful contemporary statistical mechanical technique that can be used by students to explore first-order phase transitions by themselves and for models of their own construction. The technique is a generalization of the well-known Peierls argument and is applicable to various models on a lattice. We illustrate the technique with the help of two simple models that were recently used to simulate phase transitions on surfaces.
Thin film dynamics with surfactant phase transition
Köpf, M. H.; Gurevich, S. V.; Friedrich, R.
2009-01-01
A thin liquid film covered with an insoluble surfactant in the vicinity of a first-order phase transition is discussed. Within the lubrication approximation we derive two coupled equations to describe the height profile of the film and the surfactant density. Thermodynamics of the surfactant is incorporated via a Cahn-Hilliard type free-energy functional which can be chosen to describe a transition between two stable phases of different surfactant density. Within this model, a linear stabilit...
Interplay between chiral and deconfinement phase transitions
Xu, Fukun; Chen, Huan; Huang, Mei
2011-01-01
By using the dressed Polyakov loop or dual chiral condensate as an equivalent order parameter of the deconfinement phase transition, we investigate the relation between the chiral and deconfinement phase transitions at finite temperature and density in the framework of three-flavor Nambu--Jona-Lasinio (NJL) model. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole $(T,\\mu)$ plane. In the case of explicit chiral symmetry breaking, it is found that the phase transitions are flavor dependent. For each flavor, the transition temperature for chiral restoration $T_c^{\\chi}$ is smaller than that of the dressed Polyakov loop $T_c^{{\\cal D}}$ in the low baryon density region where the transition is a crossover, and, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. Therefore, there are two critical end points, i.e, $T_{CEP}^{u,d}$ and $T_{CEP}^{s}$ a...
Phase transitions in two dimensions
Although a two-dimensional solid with long-range translational order cannot existin the thermodynamic limit (N → ∞, V →∞, N/V finite) macroscopic samples of two-dimensional solids can exist. In this work, stability of the phase was determined by the usuar method of equating the pressure and chemical potential of the phases. (A.C.A.S.)
Molecular markers of phase transition in locusts
ARNOLD DE LOOF; ILSE CLAEYS; GERT SIMONET; PETER VERLEYEN; TIM VANDERSMISSEN; FILIP SAS; JURGEN HUYBRECHTS
2006-01-01
The changes accompanying the transition from the gregarious to the solitary phase state in locusts are so drastic that for a long time these phases were considered as distinct species. It was Boris Uvarov who introduced the concept of polyphenism. Decades of research revealed that phase transition implies changes in morphometry, the color of the cuticle, behavior and several aspects of physiology. In particular, in the recent decade, quite a number of molecular studies have been undertaken to uncover phase-related differences.They resulted in novel insights into the role of corazonin, neuroparsins, some protease inhibitors, phenylacetonitrile and so on. The advent of EST-databases of locusts (e.g. Kang et al., 2004) is a most encouraging novel development in physiological and behavioral locust research. Yet, the answer to the most intriguing question, namely whether or not there is a primordial molecular inducer of phase transition, is probably not within reach in the very near future.
Thermal phase mixing during first order phase transitions
Borrill, J; Borrill, Julian; Gleiser, Marcelo
1995-01-01
The dynamics of first order phase transitions are studied in the context of (3+1)-dimensional scalar field theories. Particular attention is paid to the question of quantifying the strength of the transition, and how `weak' and `strong' transitions have different dynamics. We propose a model with two available low temperature phases separated by an energy barrier so that one of them becomes metastable below the critical temperature T_c. The system is initially prepared in this phase and is coupled to a thermal bath. Investigating the system at its critical temperature, we find that `strong' transitions are characterized by the system remaining localized within its initial phase, while `weak' transitions are characterized by considerable phase mixing. Always at T_c, we argue that the two regimes are themselves separated by a (second order) phase transition, with an order parameter given by the fractional population difference between the two phases and a control parameter given by the strength of the scalar fi...
The deconfinement phase transition in asymmetric matter
We study the phase transition of asymmetric hadronic matter to a quark-gluon plasma within the framework of a simple two-phase model. The analysis is performed in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws and Gibbs' criteria for phase equilibrium. The EOS is obtained in a separate description for the hadronic phase and for the quark-gluon plasma. For the hadrons, a relativistic mean-field model calibrated to the properties of nuclear matter is used, and a bag-model type EOS is used for the quarks and gluons. The model is applied to the deconfinement phase transition that may occur in matter created in ultra-relativistic collisions of heavy ions. Based on the two-dimensional coexistence surface (binodal), various phase separation scenarios and the Maxwell construction through the mixed phase are discussed. In the framework of the two-phase model the phase transition in asymmetric matter is continuous (second-order by Ehrenfest's definition) in contrast to the discontinuous (first-order) transition of symmetric systems. (orig.)
Contemporary Research of Dynamically Induced Phase Transitions
Hull, Lawrence
2015-06-01
Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions. Supported by the DoD/DOE Joint Munitions Technology Development Program.
An absorbing phase transition from a structured active particle phase
Lopez, Cristobal [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain); Ramos, Francisco [Departamento de Electromagnetismo y Fisica de la Materia and Instituto de Fisica Teorica y Computacional Carlos I, Facultad de Ciencias, Universidad de Granada, 18071 Granada (Spain); Hernandez-GarcIa, Emilio [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain)
2007-02-14
In this work we study the absorbing state phase transition of a recently introduced model for interacting particles with neighbourhood-dependent reproduction rates. The novelty of the transition is that as soon as the active phase is reached by increasing a control parameter a periodically arranged structure of particle clusters appears. A numerical study in one and two dimensions shows that the system falls into the directed percolation universality class.
Variational analysis of the deconfinement phase transition
We study the deconfining phase transition in 3+1 dimensional pure SU(N) Yang-Mills theory using a gauge invariant variational calculation. We generalize the variational ansatz to mixed states (density matrices) and minimize the free energy. For N ≥ 3 we find a first order phase transition with the transition temperature of Tc ≅450 MeV. Below Tc the Polyakov loop has vanishing expectation value, while above Tc , its average value is nonzero. According to the standard lore this corresponds to the deconfining transition. Within the accuracy of our approximation the entropy of the system in the low temperature phase vanishes. The latent heat is not small but, rather, is of the order of the nonperturbative vacuum energy. (author)
The Structural Phase Transition in Solid DCN
Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.
1975-01-01
Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase change from a tetragonal to an orthorhombic form at 160K is a first-order transition. A transverse acoustic phonon mode, which has the symmetry of the phase change, was observed at very low energies...
The Structural Phase Transition in Solid DCN
Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.
1975-01-01
Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase change from a tetragonal to an orthorhombic form at 160K is a first-order transition. A transverse acoustic phonon mode, which has the symmetry of the phase change, was observed at very low energie...
Magnetic phase transitions in low dimension quantum spin systems
In this PhD thesis, three low dimensional spin systems are studied by means of elastic and inelastic neutron scattering. Macroscopic measurements in the DMACuCl3 compound indicate the coexistence of two kinds of dimers: antiferromagnetic and ferromagnetic. The magnetic structure determined by our neutron diffraction survey at H = 0 shows irrevocably the existence of these two kinds of dimers. It has been shown that the Ising-like compound BaCo2V2O8 should be the first realization of a system in which a longitudinal spin density wave (LSDW) magnetic order occurs when a magnetic field is applied. In a first time, we have determined the magnetic structure in zero magnetic field. Then, we focused on the effect of a magnetic field on the propagation vector, showing an entrance in the LSDW phase at Hc = 3.9 T. The magnetic structure refined above this critical field confirms that BaCo2V2O8 is the first compound in which occurs a LSDW phase. In the organic compound DF5PNN, it has been shown that this compound is well described at low temperature by spin chains with alternating couplings. However, the crystallographic structure determined at room temperature implies that the interactions are uniform. By means of neutron diffraction, we characterized a structural transition at low temperature (Tc = 450 mK) making the system evolve from C2/c space group to Pc. This transition explains the alternating behavior of the interactions. We have also evidenced a field-induced structural transition (Hc = 1.1 T). Above this field, the system is back to the C2/c space group, implying that the interactions are back to uniform. We have confirmed this by studying the magnetic excitations. (author)
Multiple phase transitions and magnetoresistance of HoFe{sub 4}Ge{sub 2}
Liu, J., E-mail: liujing@iastate.edu; Pecharsky, V.K.; Gschneidner, K.A.
2015-05-15
Highlights: • Three magnetic transitions at T{sub N} = 51 K, T{sub f1} = 42 K, and T{sub f2} = 15 K. • Kinetically arrested phase below a freezing point of ∼11 K. • First-order metamagnetic transition at critical field ∼22 kOe below 35 K. • A large magnetoresistance of ∼30% at a field change of 30 kOe near 15 K. - Abstract: A systematic study of the structural, magnetic, heat capacity, electrical resistivity and magnetoresistance properties of HoFe{sub 4}Ge{sub 2} has been performed. The temperature dependencies of the magnetization and heat capacity show three magnetic transitions at T{sub N} = 51 K, T{sub f1} = 42 K, and T{sub f2} = 15 K. The high temperature transition is antiferromagnetic ordering and the two low temperature phase transitions are due to rearrangements of the magnetic structure. A kinetically arrested phase is observed below a freezing point of ∼11 K. Below 35 K, the behavior of the isothermal magnetization reflects a first-order metamagnetic phase transition. Multiple phase transitions are also manifested in the electrical resistivity behavior. For a field change of 30 kOe, a large magnetoresistance of ∼30% is observed near T{sub f2} (15 K)
End point of the electroweak phase transition
Csikor, Ferenc; Heitger, J; Aoki, Y; Ukawa, A
1999-01-01
We study the hot electroweak phase transition (EWPT) by 4-dimensional lattice simulations on lattices with symmetric and asymmetric lattice spacings and give the phase diagram. A continuum extrapolation is done. We find first order phase transition for Higgs-boson masses $m_H<66.5 \\pm 1.4$ GeV. Above this end point a rapid cross-over occurs. Our result agrees with that of the dimensional reduction approach. It also indicates that the fermionic sector of the Standard Model (SM) may be included perturbatively. We get for the SM end point $72.4 the SM.
Thermochromic phase transitions in two aromatic tetrachlorocuprates
Mostafa, M. Fareed; Abdel-Kader, M. M.; Arafat, S. S.; Kandeel, E. M.
1991-06-01
Bis(para-toluidinium)2 tetrachlorocuprate and bis(para-chloroanilinium)2 tetrachlorocuprate crystallize in a perovskite-related layer structure. The former crystallizes in an orthorhombic unit cell with a = 6.911 Å, b = 7.052 Å and c = 33.182 Å. It undergoes a thermochromic first order phase transition from a yellow low temperature phase to a dark orange high temperature phase at T = 300 ± 3K with a 10° thermal hysteresis. The latter compound undergoes two thermochromic transitions expressed by the relation. Orange Phase (I) rightleftarrows294 K Yellow Phase (II) rightleftarrows214K Green Phase (III). Both compounds are ferromagnetic at low temperture with exchange interactions J/k = 17.5° and 20° for the two compounds respectively.
Phase transitions in warm, asymmetric nuclear matter
Müller, H; Mueller, Horst; Serot, Brian D
1995-01-01
A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature. An analysis is performed of the liquid-gas phase transition in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws, and Gibbs' criteria for phase equilibrium. For a binary system with two phases, the coexistence surface (binodal) is two-dimensional. The Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density. Moreover, because of the greater dimensionality of the binodal surface, the liquid-gas phase transition is continuous (second order by Ehrenfest's definition), rather than discontinuous (first order), as in familiar one-component systems. Using a mean-field equation of state calibrated to the properties of nuclear matter and finite nuclei, various phase-separation scenarios are considered. The model is th...
Phase transitions and entropies for synchronizing oscillators.
Bier, Martin; Lisowski, Bartosz; Gudowska-Nowak, Ewa
2016-01-01
We study a generic model of coupled oscillators. In the model there is competition between phase synchronization and diffusive effects. For a model with a finite number of states we derive how a phase transition occurs when the coupling parameter is varied. The phase transition is characterized by a symmetry breaking and a discontinuity in the first derivative of the order parameter. We quantitatively account for how the synchronized pulse is a low-entropy structure that facilitates the production of more entropy by the system as a whole. For a model with many states we apply a continuum approximation and derive a potential Burgers' equation for a propagating pulse. No phase transition occurs in that case. However, positive entropy production by diffusive effects still exceeds negative entropy production by the shock formation. PMID:26871059
Phase Transition Induced Fission in Lipid Vesicles
Leirer, C; Myles, V M; Schneider, M F
2010-01-01
In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>Tm) through the phase transition into the gel state (T
Random fields at a nonequilibrium phase transition.
Barghathi, Hatem; Vojta, Thomas
2012-10-26
We study nonequilibrium phase transitions in the presence of disorder that locally breaks the symmetry between two equivalent macroscopic states. In low-dimensional equilibrium systems, such random-field disorder is known to have dramatic effects: it prevents spontaneous symmetry breaking and completely destroys the phase transition. In contrast, we show that the phase transition of the one-dimensional generalized contact process persists in the presence of random-field disorder. The ultraslow dynamics in the symmetry-broken phase is described by a Sinai walk of the domain walls between two different absorbing states. We discuss the generality and limitations of our theory, and we illustrate our results by large-scale Monte Carlo simulations. PMID:23215170
Phase Transitions in Operational Risk
Kartik Anand; Reimer K\\"uhn
2006-01-01
In this paper we explore the functional correlation approach to operational risk. We consider networks with heterogeneous a-priori conditional and unconditional failure probability. In the limit of sparse connectivity, self-consistent expressions for the dynamical evolution of order parameters are obtained. Under equilibrium conditions, expressions for the stationary states are also obtained. The consequences of the analytical theory developed are analyzed using phase diagrams. We find co-exi...
Dimensional Reduction in Quantum Dipolar Antiferromagnets
Babkevich, P.; Jeong, M.; Matsumoto, Y.; Kovacevic, I.; Finco, A.; Toft-Petersen, R.; Ritter, C.; Mânsson, M.; Nakatsuji, S.; Rønnow, H. M.
2016-05-01
We report ac susceptibility, specific heat, and neutron scattering measurements on a dipolar-coupled antiferromagnet LiYbF4 . For the thermal transition, the order-parameter critical exponent is found to be 0.20(1) and the specific-heat critical exponent -0.25 (1 ) . The exponents agree with the 2D X Y /h4 universality class despite the lack of apparent two-dimensionality in the structure. The order-parameter exponent for the quantum phase transitions is found to be 0.35(1) corresponding to (2 +1 )D . These results are in line with those found for LiErF4 which has the same crystal structure, but largely different TN, crystal field environment and hyperfine interactions. Our results therefore experimentally establish that the dimensional reduction is universal to quantum dipolar antiferromagnets on a distorted diamond lattice.
Complete text of publication follows. Charge, antiferromagnetic and antiferromagnetic ordering in (Pr70Ca30)MnO3 have been studied using the Wide-Angle Neutron diffractometer (WAND) installed at the High Flux Isotope Reactor of ORNL. The WAND is equipped with a newly developed curved 3He one-dimensional position-sensitive detector which covers a 125 deg angular range, and can be used as a flat-cone geometry diffractometer and/or as a fast diffractometer. The phase transitions from the paramagnetic to the charge-ordering and antiferromagnetic states in zero field with decreasing temperature, and the further transition to the ferromagnetic state in magnetic fields up to ST have been clearly confirmed. Diffuse scattering observed over a wide reciprocal space around the fundamental reflections is significantly reduced upon cooling and under magnetic fields. The relaxation process from the metastable-ferromagnetic metal to the charge-ordered and antiferromagnetic insulator has been furthermore studied. The time-dependence of their intensities suggests that the system is percolatively phase-separated. All of these results are discussed in connection with the characteristic colossal magnetoresistance of this material. (author)
Classical and quantum anisotropic Heisenberg antiferromagnets
W. Selke
2009-01-01
Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.
Phase transitions in the pseudo-binary compounds Ho1-xTbxB2C2
We have performed specific heat experiments on Ho1-xTbxB2C2 (0 ≤ x ≤ 1.0) in order to clarify the similarity and difference between anomalous antiferromagnetic phases of HoB2C2 and TbB2C2. HoB2C2 undergoes an antiferromagnetic (AFM) transition at TN=5.9 K and an antiferroquadrupolar (AFQ) transition at TQ=4.5 K. TbB2C2 shows only an AFM transition at TN=21.7 K. Although TN changes gradually with increasing x, TQ hardly decreases up to x=0.6. This unusual result indicates that the Tb atoms seem to support the AFQ order in HoB2C2. However, judging from an entropy change at TQ, it is supposed that the Tb atoms do not participate in the AFQ order. (author)
Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao
2012-10-01
The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.
Phase transitions in warm, asymmetric nuclear matter
A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature. An analysis is performed of the liquid-gas phase transition in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws, and Gibbs' criteria for phase equilibrium. For a binary system with two phases, the coexistence surface (binodal) is two dimensional. The Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density. Moreover, because of the greater dimensionality of the binodal surface, the liquid-gas phase transition is continuous (second order by Ehrenfest's definition), rather than discontinuous (first order), as in familiar one-component systems. Using a mean-field equation of state calibrated to the properties of nuclear matter and finite nuclei, various phase-separation scenarios are considered. The model is then applied to the liquid-gas phase transition that may occur in the warm, dilute matter produced in energetic heavy-ion collisions. In asymmetric matter, instabilities that produce a liquid-gas phase separation arise from fluctuations in the proton concentration (chemical instability), rather than from fluctuations in the baryon density (mechanical instability)
Critical behavior in the electroweak phase transition
Gleiser, Marcello
1993-01-01
We examine the behavior of the standard-model electroweak phase transition in the early Universe. We argue that close to the critical temperature it is possible to estimate the {\\it effective} infrared corrections to the 1-loop potential using well known $\\varepsilon$-expansion results from the theory of critical phenomena in 3 spatial dimensions. The theory with the $\\varepsilon$-corrected potential exhibits much larger fluctuations in the spatial correlations of the order parameter, considerably weakening the strength of the transition.
Quantum phase transitions with dynamical flavors
Bea, Yago; Ramallo, Alfonso V
2016-01-01
We study the properties of a D6-brane probe in the ABJM background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and non-vanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at non-zero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number $N_f$ of unquenched quarks of the background.
The diamagnetic phase transition in Magnetars
Wang, Zhaojun; Zhu, Chunhua; Wu, Baoshan
2016-01-01
Neutron stars are ideal astrophysical laboratories for testing theories of the de Haas-van Alphen (dHvA) effect and diamagnetic phase transition which is associated with magnetic domain formation. The "magnetic interaction" between delocalized magnetic moments of electrons (the Shoenberg effect), can result in an effect of the diamagnetic phase transition into domains of alternating magnetization (Condon's domains). Associated with the domain formation are prominent magnetic field oscillation and anisotropic magnetic stress which may be large enough to fracture the crust of magnetar with a super-strong field. Even if the fracture is impossible as in "low-field" magnetar, the depinning phase transition of domain wall motion driven by low field rate (mainly due to the Hall effect) in the randomly perturbed crust can result in a catastrophically variation of magnetic field. This intermittent motion, similar to the avalanche process, makes the Hall effect be dissipative. These qualitative consequences about magne...
Non-equilibrium dynamics and phase transitions
Janik, Romuald A; Soltanpanahi, Hesam
2015-01-01
We study the poles of the retarded Green's functions of strongly coupled field theories exhibiting a variety of phase structures from a crossover up to a first order phase transition. These theories are modeled by a dual gravitational description. The poles of the holographic Green's functions appear at the frequencies of the quasinormal modes of the dual black hole background. We establish that near the transition, in all cases considered, the applicability of a hydrodynamic description breaks down already at lower momenta than in the conformal case. We establish the appearance of the spinodal region in the case of the first order phase transition at temperatures for which the speed of sound squared is negative. An estimate of the preferential scale attained by the unstable modes is also given. We additionally observe a novel diffusive regime for sound modes for a range of wavelengths.