Antiferromagnetic Ising model on the swedenborgite lattice
Buhrandt, Stefan; Fritz, Lars
2014-01-01
Geometrical frustration in spin systems often results in a large number of degenerate ground states. In this work, we study the antiferromagnetic Ising model on the three-dimensional swedenborgite lattice, which is a specific stacking of kagome and triangular layers. The model contains two exchange
Lattice distortion in disordered antiferromagnetic XY models
Li Peng-Fei; Cao Hai-Jing
2012-01-01
The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin-phonon coupling in the adiabatic limit.It is found that lattice distortion relies on the strength of the random modulation.For strong or weak enough spin-phonon couplings,the average lattice distortion may decrease or increase as the random modulation is strengthened.This may be the result of competition between the random magnetic modulation and the spin-phonon coupling.
Antiferromagnetic noise correlations in optical lattices
Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;
2009-01-01
We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...
Supersymmetry protected topological phases of isostatic lattices and kagome antiferromagnets
Lawler, Michael J.
2016-10-01
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 topological isostatic lattice state. Since ground states of magnetic systems also satisfy local constraint conditions (such as the vanishing of the total spin on a triangle), I identify a similar SUSY structure for many common models of antiferromagnets including the square, triangluar, kagome, pyrochlore nearest-neighbor antiferromagnets, and the J2=J1/2 square-lattice antiferromagnet. Remarkably, the kagome family of antiferromagnets is the analog of topological isostatic lattices among this collection of models. Thus, a solid-state realization of the theory of phonon topological band structure may be found in frustrated magnetic materials.
Correlations between Kondo clouds in nearly antiferromagnetic Kondo lattices
Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A
2004-05-01
We discuss a novel fluctuational mechanism explaining the physics of nearly antiferromagnetic Kondo lattices (KL). The effective action for KL model is expressed in terms of Bose operators responsible for paramagnetic excitations and semi-bosonic fields describing the dynamic Kondo clouds created by conduction electrons around local spin. The gauge invariant resonance valence bond theory of interacting Kondo clouds describes the spin liquid with strong critical fluctuations imitating itinerant fluctuation magnetism of Moriya type.
Fractional excitations in the square-lattice quantum antiferromagnet
Dalla Piazza, B.; Mourigal, M.; Christensen, N. B.; Nilsen, G. J.; Tregenna-Piggott, P.; Perring, T. G.; Enderle, M.; McMorrow, D. F.; Ivanov, D. A.; Rønnow, H. M.
2015-01-01
Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum square-lattice Heisenberg antiferromagnet, for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wavevector (π, 0). We use polarized neutron spectroscopy to fully characterize the magnetic fluctuations in the metal-organic compound Cu(DCOO)2.4D2O, a known realization of the quantum square-lattice Heisenberg antiferromagnet model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially extended pairs of fractional S = 1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wavevector, these fractional excitations are bound and form conventional magnons. Our results establish the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration.
Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice
Aoyama, Kazushi; Kawamura, Hikaru
2016-06-01
Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2 ,1/2 ,1/2 ) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.
Spin-Lattice-Coupled Order in Heisenberg Antiferromagnets on the Pyrochlore Lattice.
Aoyama, Kazushi; Kawamura, Hikaru
2016-06-24
Effects of local lattice distortions on the spin ordering are investigated for the antiferromagnetic classical Heisenberg model on the pyrochlore lattice. It is found by Monte Carlo simulations that the spin-lattice coupling (SLC) originating from site phonons induces a first-order transition into two different types of collinear magnetic ordered states. The state realized at the stronger SLC is cubic symmetric characterized by the magnetic (1/2,1/2,1/2) Bragg peaks, while that at the weaker SLC is tetragonal symmetric characterized by the (1,1,0) ones, each accompanied by the commensurate local lattice distortions. Experimental implications to chromium spinels are discussed.
Ferromagnetic and antiferromagnetic order in bacterial vortex lattices
Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.; Goldstein Lab Team
2013-11-01
In conventional electronic materials, spins can organize into ordered phases that give rise to ferromagnetic or antiferromagnetic behavior. Here, we report similar observations in a completely different system: a suspension of swimming bacteria. When a dense Bacillus subtilis suspension is confined to a small circular chamber, it can spontaneously form a stable vortex (``spin'') state that can persist for several minutes. By coupling up to 100 such chambers in microfluidic devices, we are able to realize bacterial spin lattices of different geometries. Depending on that geometry and the effective coupling strength between neighboring vortices, we observe the formation of stable ``antiferromagnetic'' and ``ferromagnetic'' bacterial vortex states, that appear to be controlled by the subtle competition between bacterial boundary layer flows and bulk dynamics.
The Heisenberg antiferromagnet on the square-kagomé lattice
J. Richter
2009-01-01
Full Text Available We discuss the ground state, the low-lying excitations as well as high-field thermodynamics of the Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. This magnetic system belongs to the class of highly frustrated spin systems with an infinite non-trivial degeneracy of the classical ground state as it is also known for the Heisenberg antiferromagnet on the kagomé and on the star lattice. The quantum ground state of the spin-half system is a quantum paramagnet with a finite spin gap and with a large number of non-magnetic excitations within this gap. We also discuss the magnetization versus field curve that shows a plateaux as well as a macroscopic magnetization jump to saturation due to independent localized magnon states. These localized states are highly degenerate and lead to interesting features in the low-temperature thermodynamics at high magnetic fields such as an additional low-temperature peak in the specific heat and an enhanced magnetocaloric effect.
Three-sublattice skyrmion crystal in the antiferromagnetic triangular lattice
Rosales, H. D.; Cabra, D. C.; Pujol, Pierre
2015-12-01
The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an antiferromagnetic skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated with the number of topological charges or skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.
Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices
Wellard, C J; Wellard, Cameron; Orus, Roman
2004-01-01
Motivated by its relation to an NP-hard problem we analyze the ground state properties of anti-ferromagnetic Ising-spin networks in planar cubic lattices under the action of homogeneous transverse and longitudinal magnetic fields. We consider different instances of the cubic geometry and find a set of quantum phase transitions for each one of the systems, which we characterize by means of entanglement behavior and majorization theory. Entanglement scaling at the critical region is in agreement with results arising from conformal symmetry, therefore even the simplest planar systems can display very large amounts of quantum correlation. No conclusion can be made as to the scaling behavior of the minimum energy gap, with the data allowing equally good fits to exponential and power law decays. Analysis of entanglement and especially of majorization instead of the energy spectrum proves to be a good way of detecting quantum phase transitions in highly frustrated configurations.
High magnetic field magnetization of a new triangular lattice antiferromagnet
Zhou, H. D. [Univ. of Tennessee, Knoxville, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Stritzinger, Laurel Elaine Winter [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Harrison, Neil [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-23
In CsV(MoO_{4})_{2}, the magnetic V^{3+} ions with octahedral oxygen-coordination form a geometrically frustrated triangular lattice. So fare, there is no magnetic properties reported on it. Recently, we successfully grew single crystals of CsV(MoO_{4})_{2} by using flux method. The susceptibility shows a sharp drop around 24 K, representing a long range magnetic ordering. To understand the physical properties of this new triangular lattice antiferromagnet (TLAF), we pursued high field magnetization measurements to answer two questions: (i) what is the saturation field, which will be very useful to calculate the exchange interaction of the system? (ii) Will it exhibit spin state transition, such as the up up down phase with 1/3-saturation moment as other TLAFs? Recently, we performed VSM measurements in Cell 8, Tallahassee, NHMFL, the results show that the magnetization reaches 0.38 MuB at 34 T, which is just 19% of the full moment of 2 MuB for V^{3+} (3d^{2}) ions. Apparently we need higher field to reach 1/3 value or full moment.
Evaluation of Watson-like integrals for a hyper bcc antiferromagnetic lattice
Radošević, S. M.; Pantić, M. R.; Kapor, D. V.; Pavkov-Hrvojević, M. V.; Škrinjar, M. G.
2010-04-01
Watson-like integrals for a d-dimensional bcc antiferromagnetic lattice, I_d (\\eta ) =\\frac{1}{\\pi ^d} \\prod _{i = 1}^d \\int _0^{\\pi } \\mathrm{d}x_i \\; \\frac{ \\eta }{\\sqrt{\\eta ^2 - \\prod \
Phase diagram of the triangular-lattice Potts antiferromagnet
Lykke Jacobsen, Jesper; Salas, Jesús; Scullard, Christian R.
2017-08-01
We study the phase diagram of the triangular-lattice Q-state Potts model in the real (Q, v) -plane, where v=e^J-1 is the temperature variable. Our first goal is to provide an obviously missing feature of this diagram: the position of the antiferromagnetic critical curve. This curve turns out to possess a bifurcation point with two branches emerging from it, entailing important consequences for the global phase diagram. We have obtained accurate numerical estimates for the position of this curve by combining the transfer-matrix approach for strip graphs with toroidal boundary conditions and the recent method of critical polynomials. The second goal of this work is to study the corresponding Ap-1 RSOS model on the torus, for integer p=4, 5, \\ldots, 8 . We clarify its relation to the corresponding Potts model, in particular concerning the role of boundary conditions. For certain values of p, we identify several new critical points and regimes for the RSOS model and we initiate the study of the flows between the corresponding field theories.
Masuda, Hiroshi; Okubo, Tsuyoshi; Kawamura, Hikaru
2012-08-03
Motivated by the recent experiment on kagome-lattice antiferromagnets, we study the zero-field ordering behavior of the antiferromagnetic classical Heisenberg model on a uniaxially distorted kagome lattice by Monte Carlo simulations. A first-order transition, which has no counterpart in the corresponding undistorted model, takes place at a very low temperature. The origin of the transition is ascribed to a cooperative proliferation of topological excitations inherent to the model.
Lapinskas, Saulius; Rosengren, Anders
1994-06-01
Using the cluster-variation method we study the phase diagram of the Blume-Emergy-Griffiths (BEG) model on simple cubic and face-centered cubic lattices. For the simple cubic lattice the main attention is paid to reentrant phenomena and ferrimagnetic phases occurring in a certain range of coupling constants. The results are in close agreement with Monte-Carlo data, available for parts of the phase diagram. Several ferrimagnetic phases are obtained in the vicinity of the line in parameter space, at which the model reduces to the antiferromagnetic three-state Potts model. Our results imply the existence of three phase transitions in the antiferromagnetic Potts model on the simple-cubic lattice. The phase diagrams for the BEG model on the face-centered cubic lattice are obtained in the region of antiquadrupolar ordering. Also the several ordered phases of the antiferromagnetic Potts model on this lattice are discussed.
Evidence for a bicritical point in the XXZ Heisenberg antiferromagnet on a simple cubic lattice.
Selke, Walter
2011-04-01
The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy (XXZ model) in a field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. We analyze, in particular, various staggered susceptibilities and Binder cumulants and present clear evidence for the triple point of the antiferromagnetic, spin-flop, and paramagnetic phases being a bicritical point with Heisenberg symmetry. Results are compared to previous predictions applying various theoretical approaches.
Evaluation of Watson-like Integrals for Hyper bcc Antiferromagnetic Lattice
Radosevic, S M; Kapor, D V; Pavkov-Hrvojevic, M V; Skrinjar, M G
2010-01-01
Watson-like integrals for a d-dimensional bcc antiferromagnetic lattice I_d(\\eta) and J_d(\\eta) and another two similar integrals are evaluated in an exact way in terms of generalized hypergeometric functions. A simple formula connecting Id and Jd+1 is given along with the differential equations for I_d(\\eta) and J_d(\\eta). An application of I_d and J_d in the theory of the Heisenberg antiferromagnet is discussed, together with possible generalizations to non-integer values of d. Corresponding integrals for sc lattices are also briefly reviewed.
Study of the Antiferromagnetic Blume-Capel Model on kagomé Lattice
Hwang, Chi-Ok; Park, Sojeong; Kwak, Wooseop
2016-09-01
We study the anti-ferromagnetic (AF) Ising model and the AF Blume-Capel (BC) model on the kagomé lattice. Using the Wang-Landau sampling method, we estimate the joint density functions for both models on the lattice, and we obtain the exact critical magnetic fields at zero temperature by using the micro-canonical analysis. We also show the patterns of critical lines for the models from micro-canonical analysis.
Spin superconductivity in the frustrated two-dimensional antiferromagnet in the square lattice
Lima, L. S.
2017-02-01
We use the SU(2) Schwinger boson formalism to study the spin transport in the two-dimensional S = 1 / 2 frustrated Heisenberg antiferromagnet in a square lattice, considering the second-neighbors interactions in the diagonal. We have obtained a spin superfluid behavior for the spin transport to this system similar to obtained recently to the triangular lattice. We consider an antiferromagnetic inter-chain coupling on the diagonal, J2 > 0 , and the nearest-neighbor coupling antiferromagnetic J1 > 0 . We also have in the critical temperature T0, where the correlation length ξ → 0 , that the system suffers a transition from an ordered ground state to a disordered ground state.
Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi
2011-07-22
Motivated by puzzling characteristics of spin-glass transitions widely observed in pyrochlore-based frustrated materials, we investigate the effects of coupling to local lattice distortions in a bond-disordered antiferromagnet on the pyrochlore lattice by extensive Monte Carlo simulations. We show that the spin-glass transition temperature T(f) is largely enhanced by the spin-lattice coupling and, furthermore, becomes almost independent of Δ in a wide range of the disorder strength Δ. The critical property of the spin-glass transition is indistinguishable from that of the canonical Heisenberg spin glass in the entire range of Δ. These peculiar behaviors are ascribed to a modification of the degenerate manifold from a continuous to semidiscrete one by spin-lattice coupling.
McLaughlin, A C; Sher, F; Attfield, J P
2005-08-11
The mechanism of high-transition-temperature (high-T(c)) superconductivity in doped copper oxides is an enduring problem. Antiferromagnetism is established as the competing order, but the relationship between the two states in the intervening 'pseudogap' regime has become a central puzzle. The role of the crystal lattice, which is important in conventional superconductors, also remains unclear. Here we report an anomalous increase of the distance between copper oxide planes on cooling, which results in negative thermal volume expansion, for layered ruthenium copper oxides that have been doped to the boundary of antiferromagnetism and superconductivity. We propose that a crossover between these states is driven by spin ordering in the ruthenium oxide layers, revealing a novel mechanism for negative lattice expansion in solids. The differences in volume and lattice strain between the distinct superconducting and antiferromagnetic states can account for the phase segregation phenomena found extensively in low-doped copper oxides, and show that Cooper pair formation is coupled to the lattice. Unusually large variations of resistivity with magnetic field are found in these ruthenium copper oxides at low temperatures through coupling between the ordered Ru and Cu spins.
The anti-ferromagnetic Ising model on the simplest pure Husimi lattice: An exact solution
Jurčišinová, E., E-mail: jurcisine@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Jurčišin, M., E-mail: jurcisin@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Bobák, A., E-mail: andrej.bobak@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)
2013-11-22
The anti-ferromagnetic spin-1/2 Ising model on the pure Husimi lattice with three sites in the elementary polygon (p=3) and the coordination number z=4 is investigated. It represents the simplest approximation of the anti-ferromagnetic Ising model on the two-dimensional kagome lattice which takes into account effects of frustration. The exact analytical solution of the model is found and discussed. It is proven that the model does not exhibit the first order as well as the second order phase transitions. A detailed analysis of the magnetization properties is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed.
Spin-1/2 Heisenberg Antiferromagnet on the Spatially Anisotropic Kagome Lattice
Schnyder, Andreas; Starykh, Oleg; Balents, Leon
2008-03-01
We study the quasi-one-dimensional limit of the Spin-1/2 quantum antiferromagnet on the Kagome lattice, a model Hamiltonian that might be of relevance for the mineral volborthite [1,2]. The lattice is divided into antiferromagnetic spin-chains (exchange J) that are weakly coupled via intermediate ``dangling'' spins (exchange J'). Using bosonization, renormalization group methods, and current algebra techniques we determine the ground state as a function of J'/J. The case of a strictly one-dimensional Kagome strip is also discussed. [1] Z. Hiroi, M. Hanawa, N. Kobayashi, M. Nohara, Hidenori Takagi, Y. Kato, and M. Takigawa, J. Phys. Soc. Japan 70, 3377 (2001). [2] F. Bert, D. Bono, P. Mendels, F. Ladieu, F. Duc, J.-C. Trumbe, and P. Millet, Phys. Rev. Lett. 95, 087203 (2005).
Solution of the antiferromagnetic Ising model on a tetrahedron recursive lattice.
Jurčišinová, E; Jurčišin, M
2014-03-01
We consider the antiferromagnetic spin-1/2 Ising model on the recursive tetrahedron lattice on which two elementary tetrahedrons are connected at each site. The model represents the simplest approximation of the antiferromagnetic Ising model on the real three-dimensional tetrahedron lattice which takes into account effects of frustration. An exact analytical solution of the model is found and discussed. It is shown that the model exhibits neither the first-order nor the second-order phase transitions. A detailed analysis of the magnetization of the model in the presence of the external magnetic field is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed. The existence of nontrivial singular ground states is proven and exact explicit expressions for them are found.
Monte Carlo Study of the Anisotropic Heisenberg Antiferromagnet on the Triangular Lattice
Stephan, W.; Southern, B. W.
1999-01-01
We report a Monte Carlo study of the classical antiferromagnetic Heisenberg model with easy axis anisotropy on the triangular lattice. Both the free energy cost for long wavelength spin waves as well as for the formation of free vortices are obtained from the spin stiffness and vorticity modulus respectively. Evidence for two distinct Kosterlitz-Thouless types of defect-mediated phase transitions at finite temperatures is presented.
Hida, Kazuo
1995-01-01
The ground state of the square lattice bilayer quantum antiferromagnet with nearest and next-nearest neighbour intralayer interaction is studied by means of the modified spin wave method. For weak interlayer coupling, the ground state is found to be always magnetically ordered while the quantum disordered phase appear for large enough interlayer coupling. The properties of the disordered phase vary according to the strength of the frustration. In the regime of weak frustration, the disordered...
Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation
2000-01-01
We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetisation, susceptibility, the autocorrelation function A(t) and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied a...
Yamagata, Atsushi
1994-01-01
We perform the Monte Carlo simulations of the hard-sphere lattice gas on the simple cubic lattice with nearest neighbour exclusion. The critical activity is estimated, $z_{\\rm c} = 1.0588 \\pm 0.0003$. Using a relation between the hard-sphere lattice gas and the antiferromagnetic Ising model in an external magnetic field, we conclude that there is no re-entrant phase transition of the latter on the simple cubic lattice.
Borovský, Michal; Weigel, Martin; Barash, Lev Yu.; Žukovič, Milan
2016-02-01
The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = -1). The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.
Borovský Michal
2016-01-01
Full Text Available The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = −1. The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.
Quantum phase transition of the randomly diluted heisenberg antiferromagnet on a square lattice
Kato; Todo; Harada; Kawashima; Miyashita; Takayama
2000-05-01
Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.
Quantum selection of order in an XXZ antiferromagnet on a Kagome lattice.
Chernyshev, A L; Zhitomirsky, M E
2014-12-05
Selection of the ground state of the kagome-lattice XXZ antiferromagnet by quantum fluctuations is investigated by combining nonlinear spin-wave and real-space perturbation theories. The two methods unanimously favor q=0 over sqrt[3]×sqrt[3] magnetic order in a wide range of the anisotropy parameter 0≤Δ≲0.72. Both approaches are also in accord on the magnitude of the quantum order-by-disorder effect generated by topologically nontrivial, looplike spin-flip processes. A tentative S-Δ phase diagram of the model is proposed.
Two-dimensional-lattice spin models with long-range antiferromagnetic interactions
Romano, S.
1991-10-01
We consider a classical system, consisting of m-component unit vectors (m=2,3), associated with a two-dimensional lattice \\{uk||k∈openZ2\\} and interacting via translationally and rotationally invariant antiferromagnetic pair potentials of the long-range form W=Wjk=ɛ||xj-xk||-puj.uk, p>2, where ɛ is a positive quantity, setting energy and temperature scales (i.e., T*=kBT/ɛ), and xk are the coordinates of the lattice sites. A spin-wave approach predicts orientational disorder (in the thermodynamic limit) at all finite temperatures and for all p>2 this agrees with available rigorous results for p>=4, whereas no such theorems are known in the literature when 22.
Frustrated antiferromagnet on generalized partial line graphs of a honeycomb lattice
Miyahara, Shin; Hotta, Chisa; Kubo, Kenn; Furukawa, Nobuo
2007-03-01
Recently we have proposed generalized partial line graphs on which tight binding models of electronic energy bands realize flat bands [1]. We study Heisenberg antiferromagnets on these structures, which are frustrated and may realize novel ground states. In this report, we focus on a generalized partial line graph created on a honeycomb lattice. The model is a honeycomb lattice composed of A and B-sublattice, where a triangle cluster sits on a site of A-sublattice and a single spin exists on a site of the B-sublattice. We assume the two-types of exchange coupling: J inside the triangle cluster and J' between the cluster and B-sublattice. In the limit J > J' and J J. Phys. Soc. Japan, 74 1918 (2005).
Order and excitations in large-S kagome-lattice antiferromagnets
Chernyshev, A. L.; Zhitomirsky, M. E.
2015-10-01
We systematically investigate the ground-state and the spectral properties of antiferromagnets on a kagomé lattice with several common types of the planar anisotropy: X X Z , single-ion, and out-of-plane Dzyaloshinskii-Moriya. Our main focus is on the role of nonlinear, anharmonic terms, which are responsible for the quantum order-by-disorder effect and for the corresponding selection of the ground-state spin structure in many of these models. The X X Z and the single-ion anisotropy models exhibit a quantum phase transition between the q =0 and the √{3 }×√{3 } states as a function of the anisotropy parameter, offering a rare example of the quantum order-by-disorder fluctuations favoring a ground state which is different from the one selected by thermal fluctuations. The nonlinear terms are also shown to be crucial for a very strong near-resonant decay phenomenon leading to the quasiparticle breakdown in the kagomé-lattice antiferromagnets whose spectra are featuring flat or weakly dispersive modes. The effect is shown to persist even in the limit of large spin values and should be common to other frustrated magnets with flat branches of excitations. Model calculations of the spectrum of the S =5 /2 Fe-jarosite with Dzyaloshinskii-Moriya anisotropy provide a convincing and detailed characterization of the proposed scenario.
Classical Heisenberg antiferromagnet on a garnet lattice: A Monte Carlo simulation
Petrenko, O. A.; Paul, D. McK.
2001-01-01
We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in gadolinium gallium garnet Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetization, susceptibility, the autocorrelation function A(t), and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied along the principal symmetry axes. A model, which includes only nearest-neighbor exchange J1, neither orders down to the lowest temperature nor does it show any tendency towards forming a short-range coplanar spin structure. This model, however, does demonstrate a magnetic field induced ordering below T~0.01J1. In order to reproduce the experimentally observed properties of GGG, the simulated model must include nearest-neighbor exchange interactions and also dipolar forces. The presence of weak next-to-nearest exchange interactions is found to be insignificant. In zero field S(Q) exhibits diffuse magnetic scattering around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
Zaharko, O.; Christensen, Niels Bech; Cervellino, A.
2011-01-01
We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks...
Zaharko, O.; Cervellino, A.; Tsurkan, V.
2010-01-01
Using neutron powder diffraction and Monte Carlo simulations we show that a spin-liquid regime emerges at all compositions in the diamond-lattice antiferromagnets Co(Al1−xCox)2O4. This spin-liquid regime induced by frustration due to the second-neighbor exchange coupling J2 is gradually superseded...
Magnetic excitation spectrum of the square lattice S=1/2 Heisenberg antiferromagnet K2V3O8
Lumsden, M.D.; Nagler, S.E.; Sales, B.C.;
2006-01-01
We have explored the magnetic excitation spectrum of the S=1/2 square lattice Heisenberg antiferromagnet, K2V3O8, using both triple-axis and time-of-flight inelastic neutron scattering. The long-wavelength spin waves are consistent with the previously determined Hamiltonian for this material...
Shuaibu, A. [Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia and Physics Department, Faculty of Science, Nigerian Defence Academy, P.M.B 2109, Kaduna (Nigeria); Rahman, M. M. [Physics Department, Faculty of Science, Nigerian Defence Academy, P.M.B 2109, Kaduna (Nigeria)
2014-03-05
We study the low temperature behavior of a triangular lattice quantum spin-1 Heisenberg antiferromagnet with single-site anisotropy by using coordinate Bethe ansatz method. We compute the standard two-particle Hermitian Hamiltonian, and obtain the eigenfunctions and eigenvalue of the system. The obtained results show a number of advantages in comparison with many results.
Hamer, C. J.
2009-06-01
The energy spectra of the two-magnon bound states in the Heisenberg-Ising antiferromagnet on the square lattice are calculated using series expansion methods. The results confirm an earlier spin-wave prediction of Oguchi and Ishikawa that the bound states vanish into the continuum before the isotropic Heisenberg limit is reached.
Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice
Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris
2016-04-01
We study the low-temperature physics of the SU(2)-symmetric spin-1 /2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T /J =1 /6 . The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T /J =1 /6 . The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.
Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice.
Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris
2016-04-29
We study the low-temperature physics of the SU(2)-symmetric spin-1/2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T/J=1/6. The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T/J=1/6. The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.
Bond operator theory for the frustrated anisotropic Heisenberg antiferromagnet on a square lattice
Pires, A.S.T., E-mail: antpires@fisica.ufmg.br [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, Cp 702, 30123-970 MG (Brazil)
2012-07-15
The quantum anisotropic antiferromagnetic Heisenberg model with single ion anisotropy, spin S=1 and up to the next-next-nearest neighbor coupling (the J{sub 1}-J{sub 2}-J{sub 3} model) on a square lattice, is studied using the bond-operator formalism in a mean field approximation. The quantum phase transitions at zero temperature are obtained. The model features a complex T=0 phase diagram, whose ordering vector is subject to quantum corrections with respect to the classical limit. The phase diagram shows a quantum paramagnetic phase situated among Neel, spiral and collinear states. - Highlights: Black-Right-Pointing-Pointer The quantum phase transition at zero temperature is studied. Black-Right-Pointing-Pointer The phase diagram up to the next-next-nearest neighbor coupling is calculated. Black-Right-Pointing-Pointer The energy gap is calculated in several regions of the phase diagram.
NMR study of pyrochlore lattice antiferromagnet, melanothallite Cu2OCl2
Nishiyama, Masahide; Oyamada, Akira; Itou, Tetsuaki; Maegawa, Satoru; Okabe, Hirotaka; Akimitsu, Jun
2011-09-01
The melanothallite Cu2OCl2 is a new example of pyrochlore-like antiferromagnet, which is composed of 3d transition metal electrons. We performed Cu- and Cl-NMR experiments on powder samples of Cu2OCl2 below transition temperature TN = 70 K and we observed six resonant peaks of Cu nuclei, which are composed of three symmetric peaks corresponding to 63Cu and three corresponding to 65Cu. The Cu nuclei feel the strong hyperfine fields because of ordered magnetic moments and the electric field gradients. We determined the spin structure by analyzing the Cu-NMR spectra. The melanothallite has an all-in-all-out spin structure. The spin lattice relaxation rates T1-1 of Cu- and Cl-NMR in the ordered phase are proportional to the temperature; This suggests that although long-range ordering occurs at rather high temperature, the large spin fluctuations caused by the geometrical frustration still remain.
Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki
2016-09-01
We study Heisenberg antiferromagnets on a diamond-like decorated square lattice perturbed by further neighbor couplings. The second-order effective Hamiltonian is calculated and the resultant Hamiltonian is found to be a square-lattice quantum-dimer model with a finite hopping amplitude and no repulsion, which suggests the stabilization of the plaquette phase. Our recipe for constructing quantum-dimer models can be adopted for other lattices and provides a route for the experimental realization of quantum-dimer models.
Melting of Three-Sublattice Order in Easy-Axis Antiferromagnets on Triangular and Kagome Lattices.
Damle, Kedar
2015-09-18
When the constituent spins have an energetic preference to lie along an easy axis, triangular and kagome lattice antiferromagnets often develop long-range order that distinguishes the three sublattices of the underlying triangular Bravais lattice. In zero magnetic field, this three-sublattice order melts either in a two-step manner, i.e., via an intermediate phase with power-law three-sublattice order controlled by a temperature-dependent exponent η(T)∈(1/9,1/4), or via a transition in the three-state Potts universality class. Here, I predict that the uniform susceptibility to a small easy-axis field B diverges as χ(B)∼|B|^{-[(4-18η)/(4-9η)]} in a large part of the intermediate power-law ordered phase [corresponding to η(T)∈(1/9,2/9)], providing an easy-to-measure thermodynamic signature of two-step melting. I also show that these two melting scenarios can be generically connected via an intervening multicritical point and obtain numerical estimates of multicritical exponents.
Optical Signatures of Antiferromagnetic Ordering of Fermionic Atoms in an Optical Lattice
Francisco Cordobes Aguilar
2014-09-01
Full Text Available We show how off-resonant light scattering can provide quantitative information on antiferromagnetic ordering of a two-species fermionic atomic gas in a tightly-confined two-dimensional optical lattice. We analyze the emerging magnetic ordering of atoms in the mean-field and in random phase approximations and show how the many-body static and dynamic correlations, evaluated in the standard Feynman-Dyson perturbation series, can be detected in the scattered light signal. The staggered magnetization reveals itself in the magnetic Bragg peaks of the individual spin components. These magnetic peaks, however, can be considerably suppressed in the absence of a true long-range antiferromagnetic order. The light scattered outside the diffraction orders can be collected by a lens with highly improved signal-to-shot-noise ratio when the diffraction maxima are blocked. The collective and single-particle excitations are identified in the spectrum of the scattered light. We find that the spin-conserving and spin-exchanging atomic transitions convey information on density, longitudinal spin, and transverse spin correlations. The different correlations and scattering processes exhibit characteristic angular distribution profiles for the scattered light, and e.g., the diagnostic signal of transverse spin correlations could be separated from the optical response by the scattering direction, frequency, or polarization. We also analyze the detection accuracy by estimating the number of required measurements, constrained by the heating rate that is determined by inelastic light-scattering events. The imaging technique could be extended to the two-species fermionic states in other regions of the phase diagram where the ground-state properties are still not fully understood.
Monte carlo simulation study of the square lattice S=1/2 quantum heisenberg antiferromagnet
Kim, J K
1999-01-01
For the two dimensional S= 1/2 isotopic quantum Heisenberg antiferromagnet on a square lattice, we report our results of an extensive quantum Monte Carlo simulation for various physical observables such as the correlation length xi, the staggered magnetic susceptibility chi sub S sub T , the structure factor peak value S(Q), the internal energy epsilon, and the uniform susceptibility chi sub u. We find that chi sub S sub T approx chi sup 2 T and S(Q) approx xi sup 2 T sup 2 , in agreement with the predictions of the conventional theory but in disagreement with recent experiments. Our estimate of the spin stiffness constant rho sub s and spin wave velocity c, from the low temperature behavior of the chi sub u is shown to be consistent with the theoretical prediction of the low temperature behavior of the epsilon, and of the xi provided an additional correction up to T sup 2. However, our data are definitely inconsistent with the scenario of the crossover for the xi.
Search for the Heisenberg spin glass on rewired cubic lattices with antiferromagnetic interaction
Surungan, Tasrief
2016-10-01
Spin glass (SG) is a typical magnetic system which is mainly characterized by a frozen random spin orientation at low temperatures. Frustration and randomness are considered to be the key ingredients for the existence of SGs. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)] found that the antiferromagnetic (AF) Ising spins on scale free network (SFN) exhibited SG behavior. This is purely AF system, a new type of SG different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely due to a topological factor and its randomness is brought by irregular connectivity. Recently, it was reported that the AF Heisenberg model on SFN exhibited SG behavior [Surungan et al., JPCS, 640, 012005 (2015)/doi:10.1088/1742-6596/640/1/012005]. In order to accommodate the notion of spatial dimension, we further investigated this type of system by studying an AF Heisenberg model on rewired cubic lattices, constructed by adding one extra bond randomly connecting each spin to one of its next-nearest neighbors. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.
Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction
Surungan, Tasrief; Bansawang B., J.; Tahir, Dahlang
2016-03-01
Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect, and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series, 640, 012001 (2015)] reported SG bahavior of AF Heisenberg model on SFN. We further investigate this type of system by studying an AF Heisenberg model on rewired square lattices. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.
Lattice and spin dynamics in a low-symmetry antiferromagnet NiWO4
Prosnikov, M. A.; Davydov, V. Yu.; Smirnov, A. N.; Volkov, M. P.; Pisarev, R. V.; Becker, P.; Bohatý, L.
2017-07-01
Lattice and magnetic dynamics of NiWO4 single crystals were studied with the use of polarized Raman spectroscopy in a wide temperature range of 10-300 K including the antiferromagnetic ordering temperature TN=62 K. Static magnetic measurements were used for characterizing the single crystals. All Raman-active phonons predicted by the group theory were observed and characterized. Magnetic symmetry analysis was used to determine possible magnetic space groups for NiWO4 which can be also applied to any other isostructural crystal with the same magnetic propagation vector k =(1 /2 ,0 ,0 ) . Although the magnetic structure of NiWO4 is relatively simple, a rich set of narrow and broad magnetic excitations with different polarization properties and temperature behavior in the very broad frequency range of 10-200 cm-1 was observed, with some modes surviving at temperatures much higher than TN up to 220 K. Part of the magnetic excitations were identified as acoustic and optical spin-wave branches which allowed us to construct exchange structure and estimate exchange and anisotropy constants with the use of linear spin-wave theory.
Spin dynamics of S = 1/2 kagome lattice antiferromagnets observed by high-field ESR
Ohta, Hitoshi [Molecular Photoscience Research Center, Kobe University, Kobe 657-8501 (Japan); Graduate School of Science, Kobe University, Kobe 657-8501 (Japan); Zhang, Wei-min [Graduate School of Science, Kobe University, Kobe 657-8501 (Japan); Okubo, Susumu; Fujisawa, Masashi [Molecular Photoscience Research Center, Kobe University, Kobe 657-8501 (Japan); Sakurai, Takahiro [Center for Supports to Research and Education Activities, Kobe University, Kobe 657-8501 (Japan); Okamoto, Yoshihiko; Yoshida, Hiroyuki; Hiroi, Zenji [Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581 (Japan)
2010-03-15
Due to the existence of strong spin frustration in a system, the spin dynamics of S = 1/2 kagome lattice antiferromagnet at low temperature has attracted much interest. High-field ESR has been measured on its model substances, Cu{sub 3}V{sub 2}O{sub 7}(OH){sub 2} . 2H{sub 2}O (volborthite) and BaCu{sub 3}V{sub 2}O{sub 3}(OH){sub 2} (vesignieite), down to 1.8 K using pulsed magnetic fields up to 16 T. The measurements are performed for 160 and 315 GHz using polycrys-talline samples. Although both samples showed the g-shift and the change of linewidth at low temperature, volborthite showed a small gap excitation of the order of 40 GHz (1.9 K) while vesignieite showed a paramagnetic behavior down to 1.9 K. Observed difference will be discussed in connection with the crystal structure, and the possible spin liquid state in vesignieite will be discussed. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Spin-1/2 Heisenberg J1-J2 antiferromagnet on the kagome lattice
Iqbal, Yasir; Poilblanc, Didier; Becca, Federico
2015-01-01
We report variational Monte Carlo calculations for the spin-1/2 Heisenberg model on the kagome lattice in the presence of both nearest-neighbor J1 and next-nearest-neighbor J2 antiferromagnetic superexchange couplings. Our approach is based upon Gutzwiller projected fermionic states that represent a flexible tool to describe quantum spin liquids with different properties (e.g., gapless and gapped). We show that, on finite clusters, a gapped Z2 spin liquid can be stabilized in the presence of a finite J2 superexchange, with a substantial energy gain with respect to the gapless U (1 ) Dirac spin liquid. However, this energy gain vanishes in the thermodynamic limit, implying that, at least within this approach, the U (1 ) Dirac spin liquid remains stable in a relatively large region of the phase diagram. For J2/J1≳0.3 , we find that a magnetically ordered state with q =0 overcomes the magnetically disordered wave functions, suggesting the end of the putative gapless spin-liquid phase.
GdPtPb: A noncollinear antiferromagnet with distorted kagome lattice
Manni, S.; Bud'ko, Sergey L.; Canfield, Paul C.
2017-08-01
In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb, which crystallizes in the ZrNiAl-type structure that has a distorted kagome lattice of Gd triangles. Single crystals were grown and investigated using structural, magnetic, transport, and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K, arguably with a planar, noncollinear structure. The high temperature magnetic susceptibility data reveal an "anti-frustration" behavior having a frustration parameter, |f | =|Θ | /TN=0.25 , which can be explained by mean field theory within a two-sublattice model. Study of the magnetic phase diagram down to T =1.8 K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that GdPtPb can serve as an example of a planar, noncollinear AF with a distorted kagome magnetic sublattice.
Control of the third dimension in copper-based square-lattice antiferromagnets
Goddard, Paul A.; Singleton, John; Franke, Isabel; Möller, Johannes S.; Lancaster, Tom; Steele, Andrew J.; Topping, Craig V.; Blundell, Stephen J.; Pratt, Francis L.; Baines, C.; Bendix, Jesper; McDonald, Ross D.; Brambleby, Jamie; Lees, Martin R.; Lapidus, Saul H.; Stephens, Peter W.; Twamley, Brendan W.; Conner, Marianne M.; Funk, Kylee; Corbey, Jordan F.; Tran, Hope E.; Schlueter, J. A.; Manson, Jamie L.
2016-03-01
Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)(2)]ClO4 [pyz = pyrazine], [CuL2(pyz)(2)](ClO4)(2) [L = pyO = pyridine-N-oxide and 4-phpy-O = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)(2)](2+) nearly square layers, but exhibit interlayer spacings that vary from 6.5713 to 16.777 angstrom, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed-and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)(2)(ClO4)(2). We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpy-O) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)(2)(ClO4)(2), the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S = 1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin-exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.
Yamane, Haruki; Kobayashi, Masanobu
2014-01-01
The influence of two-dimensional array structures (hexagonal anti-dot lattices) on magneto-optical (MO) properties was investigated in perpendicular antiferromagnetically coupled Co80Pt20 stacked films containing ZnO optical interference layers. Antiferromagnetic exchange coupling was generated in a [CoPt/Ru/CoPt] tri-layered structure, and anti-dot lattices were formed on both CoPt layers. The exchange coupling between the CoPt layers across a very thin 0.46-nm Ru interlayer was maintained even after nanofabrication. Characteristic MO hysteresis loops were measured by a 405-nm wavelength incident light on samples containing a 50-nm ZnO optical interference layer. The anti-dot lattice with a 200-nm diameter hole exhibited an increase in the residual Kerr rotation angle owing to the antiparallel magnetization alignment of the CoPt layers. Furthermore, compared with samples without the interference layer, the figure of merit for the anti-dot lattice with a 200-nm diameter hole was enhanced by inserting a 100-nm ZnO interference layer. These improvements are attributed to MO interference effects inside the stacked films.
Lima, L. S.
2017-04-01
We use the SU(N) Schwinger boson formalism to study the spin transport in the S=1 biquadratic frustrated Heisenberg antiferromagnetic model in the triangular lattice, considering the next-nearest-neighbors interactions J2. We have obtained a jump in the spin conductivity in the point of cusp of the phase diagram - η vs. - α of the model at T=0, which represents the force of the biquadratic coupling versus the next-nearest-neighbor coupling (K vs. J2). We have obtained also a superfluid behavior for the spin transport in the DC limit for this system similar to ones recently obtained for other two-dimensional frustrated spin systems. We consider all the couplings, first and second couplings as antiferromagnetic.
Inaba, Kensuke; Yamashita, Makoto
2010-10-22
We propose a simple method to detect the antiferromagnetic (AF) state of fermionic atoms in an optical lattice by combining a time-of-flight (TOF) imaging method and a Feshbach resonance. In this scheme, the nontrivial dynamics of fermionic atoms during the imaging process works as a probe with respect to the breaking of the translational symmetry in the AF state. Precise numerical simulations demonstrate that the characteristic oscillatory dynamics induced by the scattering process that transfers an AF ordering vector appears in TOF images, which can be easily observed experimentally.
Magnetic properties of the S =1/2 honeycomb lattice antiferromagnet 2 -Cl -3 ,6 -F2-V
Okabe, Toshiki; Yamaguchi, Hironori; Kittaka, Shunichiro; Sakakibara, Toshiro; Ono, Toshio; Hosokoshi, Yuko
2017-02-01
We successfully synthesized single crystals of the verdazyl radical 2 -Cl -3 ,6 -F2-V [=3-(2-chloro-3,6-difluorophenyl)-1,5-diphenylverdazyl], which is a rare model compound with an S =1/2 Heisenberg antiferromagnetic (HAF) honeycomb lattice. Ab initio molecular orbital calculations indicate two dominant AF interactions, forming a slightly distorted honeycomb lattice. We explain the magnetic susceptibility and the magnetization curve up to the saturation field based on the expected spin model using the quantum Monte Carlo method. In the low-temperature regions, we found a phase transition to an AF ordered state at about 0.77 K for the zero field and obtained the magnetic field-temperature phase diagram from the magnetic susceptibility and the specific heat for various magnetic fields. Through the analysis considering the effect of lattice distortion on magnetic behavior, we confirm that the lattice distortion of the present model is small enough that it does not affect the intrinsic behavior of the uniform S =1/2 HAF honeycomb lattice.
Photodynamic therapy for implanted VX2 tumor in rabbit brains
Li, Fei; Feng, Hua; Lin, Jiangkai; Zhu, Gang; Chen, Zhi; Li, Cong-yan
2005-07-01
To evaluate the therapeutic effect and the safety of single photodynamic therapy (PDT) with hematoporphyrin derivative produced in China, 60 New Zealand adult rabbits with VX2 tumor implanted into the brain were divided randomly into non-PDT-group and PDT-group. 36 rabbits of the PDT-group were performed photodynamic therapy. The survival time, neurological deteriorations, intracranial pressure (ICP), histology, pathology, tumor volume and brain water content were measured. Other 12 rabbits were received hematoporphyrin derivative and light irradiation of the normal brain. The ICP, histology, pathology, and brain water content were measured. The result indicated that Simple PDT may elongate the average survival time of the rabbits with VX2 tumors significantly; kill tumor cells; cause transient brain edema and increase ICP, but it is safe to be used in treating brain tumor.
Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9
Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang
2015-12-01
We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
Okubo, Tsuyoshi; Chung, Sungki; Kawamura, Hikaru
2012-01-06
Ordering of the frustrated classical Heisenberg model on the triangular lattice with an incommensurate spiral structure is studied under magnetic fields by means of a mean-field analysis and a Monte Carlo simulation. Several types of multiple-q states including the Skyrmion-lattice state is observed in addition to the standard single-q state. In contrast to the Dzyaloshinskii-Moriya interaction driven system, the present model allows both Skyrmions and anti-Skyrmions, together with a new thermodynamic phase where Skyrmion and anti-Skyrmion lattices form a domain state.
Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki
2017-01-01
We study the ground-state phase diagram of a Heisenberg model with spin S = 1/2 on a diamond-like-decorated square lattice. A diamond unit has two types of antiferromagnetic exchange interactions, and the ratio λ of the length of the diagonal bond to that of the other four edges determines the strength of frustration. It has been pointed out [https://doi.org/10.7566/JPSJ.85.033705" xlink:type="simple">J. Phys. Soc. Jpn 85, 033705 (2016)] that the so-called tetramer-dimer states, which are expected to be stabilized in an intermediate region of λc < λ < 2, are identical to the square-lattice dimer-covering states, which ignited renewed interest in high-dimensional diamond-like-decorated lattices. In order to determine the phase boundary λc, we employ the modified spin wave method to estimate the energy of the ferrimagnetic state and obtain λc = 0.974. Furthermore, our numerical diagonalization study suggests that other cluster states do not appear in the ground-state phase diagram.
Oh, Joosung; Le, Manh Duc; Jeong, Jaehong; Lee, Jung-hyun; Woo, Hyungje; Song, Wan-Young; Perring, T. G.; Buyers, W. J. L.; Cheong, S.-W.; Park, Je-Geun
2013-12-01
The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as “classical” can indeed break down.
Shimokawa, Tokuro; Kawamura, Hikaru
2016-11-01
Thermal properties of the S = 1/2 kagome Heisenberg antiferromagnet at low temperatures are investigated by means of the Hams-de Raedt method for clusters of up to 36 sites possessing a full symmetry of the lattice. The specific heat exhibits, in addition to the double peaks, the third and the fourth peaks at lower temperatures. With decreasing the temperature, the type of the magnetic short-range order (SRO) changes around the third-peak temperature from the √{3} × √{3} to the q = 0 states, suggesting that the third peak of the specific heat is associated with a crossover phenomenon between the spin-liquid states with distinct magnetic SRO. Experimental implications are discussed.
Jurčišinová, E.; Jurčišin, M.
2016-09-01
The antiferromagnetic spin-1 Ising model is studied on the Husimi lattice constructed from elementary triangles with coordination number z = 4. It is found that the model has a unique solution for arbitrary values of the magnetic field as well as for all temperatures. A detailed analysis of the magnetization is performed and it is shown that in addition to the standard plateau-like ground states, the model also contains well-defined single-point ground states related to definite values of the magnetic field. Exact values of the residual entropies for all ground states are found. The properties of the susceptibility and the specific heat of the model are also discussed. The existence of the Schottky-type behavior of the specific heat and the strong magnetocaloric effect for low enough temperatures and for the external magnetic field close to the values at which the single-point ground states exist are identified.
Oh, Joosung; Le, Manh Duc; Jeong, Jaehong; Lee, Jung-hyun; Woo, Hyungje; Song, Wan-Young; Perring, T G; Buyers, W J L; Cheong, S-W; Park, Je-Geun
2013-12-20
The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down.
Hirose, Yuhei; Miura, Shoma; Yasuda, Chitoshi; Fukumoto, Yoshiyuki
2017-08-01
Quantum Monte Carlo (QMC) simulations are performed to study ground-state properties of a mixed spin-1 and spin-1/2 Lieb-lattice Heisenberg antiferromagnet, in order to get further insight beyond the modified spin-wave (MSW) study reported in [https://doi.org/10.7566/JPSJ.86.014002" xlink:type="simple">J. Phys. Soc. Jpn. 86, 014002 (2017)]. It is confirmed that the MSW results are in good agreement with the QMC results. In particular, the scaling relation found in the MSW study, which argues that sublattice spin reductions are inversely proportional to the sublattice sizes, is observed in our QMC simulation. We present a rigorous proof for spontaneous sublattice magnetizations induced by an infinitesimal uniform magnetic field. The calculation process in the MSW theory is reexamined to clarify the mathematical structure behind the scaling relation for sublattice long-range orders.
A. B. Babaev
2015-01-01
Full Text Available Using Monte-Carlo simulations, we investigated phase transitions and frustrations in the three-state Potts model on a triangular lattice with allowance for antiferromagnetic exchange interactions between nearest- neighbors J1 and next- nearest- neighbors J2. The ratio of the next-nearest- neighbor and nearest- neighbor exchange constants r=J2/J1 is chosen within the 0÷2 range. Based on the analysis of the entropy, specific heat, system state density function, and fourth order Binder cumulants, the phase transitions in the Potts model with interactions J1<0 and J2<0 are shown to be found in value ranges of 0 r<0.2 and 1.0
Murtazaev, Akai K.; Babaev, Albert B.; Magomedov, Magomed A.; Kassan-Ogly, Felix A.; Proshkin, Alexey I.
2016-11-01
Using Monte Carlo simulations, we investigated phase transitions and frustrations in the three-state Potts model on a triangular lattice with allowance for antiferromagnetic exchange interactions between nearest-neighbors J1 and next-nearest-neighbors J2. The ratio of the next-nearest-neighbor and nearest-neighbor exchange constants r=J2/J1 is chosen within the range of 0≤r≤2. Based on the analysis of the entropy, specific heat, system state density function, and fourth order Binder cumulants, the phase transitions in the Potts model with interactions J1<0 and J2<0 are shown to be found in value ranges of 0≤r<0.2 and 1.25≤r≤2.0. In an intermediate range of 0.2≤r≤1.0 the phase transition fails and the frustrations are revealed.
Bishop, R. F.; Li, P. H. Y.; Zinke, R.; Darradi, R.; Richter, J.; Farnell, D. J. J.; Schulenburg, J.
2017-04-01
We use the coupled cluster method (CCM) to study the ground-state properties and lowest-lying triplet excited state of the spin-half XXZ antiferromagnet on the square lattice. The CCM is applied to it to high orders of approximation by using an efficient computer code that has been written by us and which has been implemented to run on massively parallelized computer platforms. We are able therefore to present precise data for the basic quantities of this model over a wide range of values for the anisotropy parameter Δ in the range - 1 ≤ Δ 1) regimes, where Δ → ∞ represents the Ising limit. We present results for the ground-state energy, the sublattice magnetization, the zero-field transverse magnetic susceptibility, the spin stiffness, and the triplet spin gap. Our results provide a useful yardstick against which other approximate methods and/or experimental studies of relevant antiferromagnetic square-lattice compounds may now compare their own results. We also focus particular attention on the behaviour of these parameters for the easy-axis system in the vicinity of the isotropic Heisenberg point (Δ = 1) , where the model undergoes a phase transition from a gapped state (for Δ > 1) to a gapless state (for Δ ≤ 1), and compare our results there with those from spin-wave theory (SWT). Interestingly, the nature of the criticality at Δ = 1 for the present model with spins of spin quantum number s =1/2 that is revealed by our CCM results seems to differ qualitatively from that predicted by SWT, which becomes exact only for its near-classical large-s counterpart.
Han, Tianheng; Chu, Shaoyan; Lee, Young S
2012-04-13
We report thermodynamic measurements of the S=1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2, a promising candidate system with a spin-liquid ground state. Using single crystal samples, the magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured. A small, temperature-dependent anisotropy has been observed, where χ(z)/χ(p)>1 at high temperatures and χ(z)/χ(p)kagome Heisenberg antiferromagnet model to the experiments on ZnCu3(OH)6Cl2.
Dipolar order by disorder in the classical Heisenberg antiferromagnet on the kagome lattice.
Chern, Gia-Wei; Moessner, R
2013-02-15
Ever since the experiments which founded the field of highly frustrated magnetism, the kagome Heisenberg antiferromagnet has been the archetypical setting for the study of fluctuation induced exotic ordering. To this day the nature of its classical low-temperature state has remained a mystery: the nonlinear nature of the fluctuations around the exponentially numerous harmonically degenerate ground states has not permitted a controlled theory, while its complex energy landscape has precluded numerical simulations at low temperature, T. Here we present an efficient Monte Carlo algorithm which removes the latter obstacle. Our simulations detect a low-temperature regime in which correlations asymptote to a remarkably small value as T→0. Feeding these results into an effective model and analyzing the results in the framework of an appropriate field theory implies the presence of long-range dipolar spin order with a tripled unit cell.
Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team
One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3
陈利平; 文天夫
2011-01-01
[目的]制作VX-2兔肝移植癌模型.[方法]新西兰白兔10只,采用VX-2瘤株动物自身接种传代.采用瘤组织块包埋法,均接种于肝左叶.[结果]2周后均顺利成瘤,该瘤在肝组织中呈浸润式生长.[结论]成功建立了兔VX-2移植性肝癌模型,为肝癌治疗的基础及临床研究提供了成熟的大型实验动物肝癌模型.%[Objective]To establish a metastatic rabbit VX-2 liver tumor model.[Methods]10 New-Zealand white rabbits were inoculated with VX-2 carcinoma in the left lobe of the liver by implantation.[Results]The tumor was successfully established two weeks later.The tumor grew in the liver tissue and infiltrated into the normal liver tissue.[Conclusion]It is successful to establish a modified metastatic rabbit VX-2 liver carcinma model, and it makes it possible to gain a reliable mature large animal model of tumor for the basic and clinical study of therapy of liver carcinoma.
Yarash K. Abuev; Albert B. Babaev; Pharkhat E. Esetov
2017-01-01
Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange...
Neto, Minos A., E-mail: minos@pq.cnpq.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Roberto Viana, J., E-mail: vianafisica@bol.com.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@edu.ufam.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, Manaus, 69077-000 AM (Brazil)
2012-08-15
In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter ({Delta}) and magnetic field (H), where {Delta}=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). The staggered m{sub s}=(m{sub A}-m{sub B})/2 and total m=(m{sub A}+m{sub B})/2 magnetizations are numerically calculated, where in the limit of m{sub s}{yields}0 the critical line T{sub N}(H,{Delta}) is obtained. The phase diagram in the T-H plane is discussed as a function of the parameter {Delta} for all values of H Element-Of [0,H{sub c}({Delta})], where H{sub c}({Delta}) correspond the critical field (T{sub N}=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=H{sub c}({Delta}){>=}H{sub c}({Delta}=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of {Delta} Element-Of [0,1]. This reentrant behavior increases with increase of the anisotropy parameter {Delta}. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: Black-Right-Pointing-Pointer In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. Black-Right-Pointing-Pointer Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. Black-Right-Pointing-Pointer We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.
Enhanced local lattice distortions with the antiferromagnetic transition in the multiferroic LuMnO3
Louca, Despina; Proffen, Thomas; Lee, Seung-Hun; Cheong, Sang-Wook
2009-03-01
The ferroelectric hexagonal manganite, LuMnO3, has been investigated via neutron scattering and the pair density function analysis to determine the nature of the local atomic distortions with the antiferromagnetic transition, TN, of the Mn ions. While in previously reported neutron diffraction data, it was shown that all atomic coordinates changed based on symmetry considerations with TN, we hereby show that it is the ferroelectric motion of the Lu ions coupled with O distortions that exhibits a strong temperature dependence below TN as reflected in the Lu-O bonds. This suggests an enhancement of the net electric polarization below TN. At the same time, the motion of the apical O1 and O2 ions distorts the MnO5 bipyramids, leading to more buckling of the ab-layers. However, the Mn ions do not appear to distort significantly away from their equilibrium position. The oxygen distortions induced with the spin reorientations below TN may be the cause for the Lu ion displacements through electrostatic interactions and this in turn produces coupling to the electric dipole moments.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F.; Mekhov, Igor B.
2016-08-01
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Mazzucchi, Gabriel; Caballero-Benitez, Santiago F; Mekhov, Igor B
2016-08-11
Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
The density of states for an antiferromagnetic Ising model on a triangular lattice
XIA Kai; YAO Xiao-yan; LIU Jun-ming
2007-01-01
The Wang-Landau algorithm is an efficient Monte Carlo approach to the density of states of a statistical mechanics system.The estimation of state density would allow the computation of thermodynamic properties of the system over the whole temperature range.We apply this sampling method to study the phase transitions in a triangular Ising model.The entropy of the lattice at zero temperature as well as other thermodynamic properties is computed.The calculated thermodynamic properties are explained in the context of the magnetic phase transition.
MR diffusion-weighted imaging of rabbit liver VX-2 tumor
You-Hong Yuan; Quan-Liang Shang; Wei-Zhou Hu; Su-Wen Yuan; En-Hua Xiao; Jun Xiang; Ke-Li Tang; Ke Jin; Shi-Jian Yi; Qiang Yin; Rong-Hua Yan; Zhong He
2005-01-01
AIM: To investigate the implanting method of rabbit liver VX-2 tumor and its MR diffusion-weighted imaging (DWI) characteristics.METHODS: Thirty-five New Zealand rabbits were included in the study. VX-2 tumor was implanted subcutaneously in 14 rabbits and intrahepatically in 6 for pre-experiments. VX-2 tumor was implanted intrahepatically in 12 rabbits for experiment and three were used as the control group. DWI, T1- and T2-weighted of MR1 were performed periodically in 15 rabbits for experiment before and after implantation. The distinction of VX-2 tumors on DWI was assessed by their apparent diffusion coefficient (ADC) values. The statistical significance was calculated byanalysis of variance (ANOVA) of the randomized block design using SPSS10.0 software. RESULTS: The successful rate of subcutaneous implantation of VX-2 tumor was 29% (4/14) while that of intrahepatic implantation of it was 33% (2/6) in the preexperiment. The successful rate of intrahepatic implantation of VX-2 tumor in the experiment was 83% (10/12) and 15 tumors grew in 10 successfully implanted rabbits. The DWT signal of VX-2 tumor was high and became lower when the b value increased step by step. The signal of VX-2 tumor on the map of ADC was low. When the b value was 100 or 300 s/mm2, the ADC value of normal group and VX-2 tumor group was respectively 2.57±0.26, 1.73±0.31, 1.87±0.25 and 1.57±0.23 mm2/s. Their distinction was significant (F= 43.26, P＜0.01), the tumor ADC value between b values 100 and 300 s/mm2 wassignificant (Tukey HSP, P＜0.05) and the ADC value between VX-2 tumor and normal liver was also significant (Tukey HSP, P＜0.01). VX-2 tumor developed quickly and metastasized early to all body, especially to the lung, liver, lymph nodes of mediastinum, etc.CONCLUSION: The DWI signal of rabbit VX-2 tumor has its characteristics on MR DWI and DWI plays an important role in diagnosing and discovering VX-2 tumor.
Wang, Wan-Sheng; Liu, Yuan-Chun; Xiang, Yuan-Yuan; Wang, Qiang-Hua
2016-07-01
We investigate the electronic instabilities in a kagome lattice with Rashba spin-orbital coupling by the unbiased singular-mode functional renormalization group. At the parent 1 /3 filling, the normal state is a quantum spin Hall system. Since the bottom of the conduction band is near the van Hove singularity, the electron-doped system is highly susceptible to competing orders upon electron interactions. The topological nature of the parent system enriches the complexity and novelty of such orders. We find 120∘-type intra-unit-cell antiferromagnetic order, f -wave superconductivity, and chiral p -wave superconductivity with increasing electron doping above the van Hove point. In both types of superconducting phases, there is a mixture of comparable spin singlet and triplet components because of the Rashba coupling. The chiral p -wave superconducting state is characterized by a Chern number Z =1 , supporting a branch of Weyl fermion states on each edge. The model bares close relevance to the so-called s d2 graphenes proposed recently.
Lattice distortion and stripelike antiferromagnetic order in Ca10(Pt3As8)(Fe2As2)5
Sapkota, Aashish [Ames Laboratory; Tucker, Gregory S [Ames Laboratory; Ramazanoglu, Mehmet [Ames Laboratory; Tian, Wei [Ames Laboratory; Ni, N [University of California; Cava, R J; McQueeney, Robert J [Princeton; Goldman, Alan I [Ames Laboratory; Kreyssig, Andreas [Ames Laboratory
2014-09-01
Ca10(Pt3As8)(Fe2As2)5 is the parent compound for a class of Fe-based high-temperature superconductors where superconductivity with transition temperatures up to 30 K can be introduced by partial element substitution. We present a combined high-resolution high-energy x-ray diffraction and elastic neutron scattering study on a Ca10(Pt3As8)(Fe2As2)5 single crystal. This study reveals the microscopic nature of two distinct and continuous phase transitions to be very similar to other Fe-based high-temperature superconductors: an orthorhombic distortion of the high-temperature tetragonal Fe-As lattice below TS=110(2) K followed by stripelike antiferromagnetic ordering of the Fe moments below TN=96(2) K. These findings demonstrate that major features of the Fe-based high-temperature superconductors are very robust against variations in chemical constitution as well as structural imperfection of the layers separating the Fe-As layers from each other and confirms that the Fe-As layers primarily determine the physics in this class of material.
Mi, Bin-Zhou
2017-02-01
The magnetic and thermodynamic properties of anisotropic frustrated spin-1 Heisenberg antiferromagnet on a body-centered cubic lattice for Néel phase (the region of weak frustration) are systematically investigated by use of the double-time Green's function method within the random phase approximation and the Anderson and Callen's decoupling. The zero-temperature sublattice magnetization and Néel temperature increase with spin anisotropy strength and single-ion anisotropy strength, and decrease with frustration strength. This indicates that quantum fluctuation is suppressed by spin anisotropy and single-ion anisotropy, by contrast, is strengthened by frustration. It is possible to tune the quantum fluctuations by the competition of anisotropy strength and frustration strength to change the ground state properties of magnetic materials. Although we find that both the spin anisotropy and the single-ion anisotropy suppress the quantum fluctuations, but their respective effects on the thermodynamic quantities, especially the internal energy and free energy, are different at zero temperature and finite temperature. Furthermore, when these two kinds of anisotropic coexist, the effect of the spin anisotropy on the sublattice magnetization and internal energy is larger than that of the single-ion anisotropy.
Large-N theory of the Sp(N) Heisenberg quantum antiferromagnet on an anisotropic triangular lattice
Chung, Chung-Hou; Marston, Brad
2000-03-01
The magnetic properties of the two-dimensional layered organic superconductors κ-(BEDT-TTF)_2X are modeled by a spin-1/2 Heisenberg quantum antiferromagnet on an anisotropic triangular lattice. The phase diagram is ascertained by means of a large-N expansion of the Sp(N) generalization of the physical SU(2) \\cong Sp(1) Heisenberg magnet.(S. Sachdev and N. Reed, Int. J. Mod. Phys. B5), 219 (1991). The phase diagram is presented in the two-dimensional parameter space of J_1/J_2, the ratio of the nearest to next-nearest neighbor Heisenberg exchange, and the ratio nb / N, which sets the strength of the quantum fluctuations. At large nb / N (equivalent to the large-spin limit of the physical SU(2) model) quantum effects are small, the ground states break global Sp(N) spin-rotational symmetry, and exhibit magnetic long-range-order (LRO). At small nb / N, however, quantum fluctuations overwhelm the tendency to order and there is only short-range magnetic order (SRO). The LRO and SRO phases can be further classified into two types depending on the size of the anisotropy: (i) ground states with commensurate, collinear, spin correlations; and (ii) ground states with incommensurate, coplanar, spin correlations. Finite-N corrections due to a Berry's phase term modify the character of the SRO phases, leading in the case of the commensurate state to spin-Peierls order and the confinement of spinons.
Babaev, A. B., E-mail: b-albert78@mail.ru; Magomedov, M. A.; Murtazaev, A. K. [Russian Academy of Sciences, Amirkhanov Institute of Physics, Dagestan Scientific Center (Russian Federation); Kassan-Ogly, F. A.; Proshkin, A. I. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2016-02-15
Phase transitions (PTs) and frustrations in two-dimensional structures described by a three-vertex antiferromagnetic Potts model on a triangular lattice are investigated by the Monte Carlo method with regard to nearest and next-nearest neighbors with interaction constants J{sub 1} and J{sub 2}, respectively. PTs in these models are analyzed for the ratio r = J{sub 2}/J{sub 1} of next-nearest to nearest exchange interaction constants in the interval |r| = 0–1.0. On the basis of the analysis of the low-temperature entropy, the density of states function of the system, and the fourth-order Binder cumulants, it is shown that a Potts model with interaction constants J{sub 1} < 0 and J{sub 2} < 0 exhibits a first-order PT in the range of 0 ⩽ r < 0.2, whereas, in the interval 0.2 ⩽ r ⩽ 1.0, frustrations arise in the system. At the same time, for J{sub 1} > 0 and J{sub 2} < 0, frustrations arise in the range 0.5 < |r| < 1.0, while, in the interval 0 ⩽ |r| ⩽ 1/3, the model exhibits a second-order PT.
Aoki, Dai; Paulsen, Carley; Kotegawa, Hisashi; Hardy, Frederic; Meingast, Christoph; Haen, Pierre; Boukahil, Mounir; Knafo, William; Ressouche, Eric; Raymond, Stephane; Flouquet, Jacques
2012-01-01
Doping Kondo lattice system CeRu2Si2 with Rh-8% (Ce(Ru0.92Rh0.08)2Si2) leads to drastic consequences due to the mismatch of the lattice parameters between CeRu2Si2 and CeRh2Si2. A large variety of experiments clarifies the unusual properties of the ground state induced by the magnetic field from longitudinal antiferromagnetic (AF) mode at H = 0 to polarized paramagnetic phase in very high magnetic field. The separation between AF phase, paramagnetic phase and polarized paramagnetic phase vary...
Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4
Ge, L.; Flynn, J.; Paddison, J. A. M.; Stone, M. B.; Calder, S.; Subramanian, M. A.; Ramirez, A. P.; Mourigal, M.
2017-08-01
Antiferromagnetic insulators on a diamond lattice are candidate materials to host exotic magnetic phenomena ranging from spin-orbital entanglement to degenerate spiral ground states and topological paramagnetism. Compared to other three-dimensional networks of magnetic ions, such as the geometrically frustrated pyrochlore lattice, the investigation of diamond-lattice magnetism in real materials is less mature. In this work, we characterize the magnetic properties of model A -site spinels CoRh2O4 (cobalt rhodite) and CuRh2O4 (copper rhodite) by means of thermomagnetic and neutron-scattering measurements, and we perform group theory analysis, Rietveld refinement, mean-field theory, and spin-wave theory calculations to analyze the experimental results. Our investigation reveals that cubic CoRh2O4 is a canonical S =3 /2 diamond-lattice Heisenberg antiferromagnet with a nearest-neighbor exchange J =0.63 meV and a Néel ordered ground state below a temperature of 25 K. In tetragonally distorted CuRh2O4 , competing exchange interactions between up to third-nearest-neighbor spins lead to the development of an incommensurate spin helix at 24 K with a magnetic propagation vector km=(0 ,0 ,0.79 ) . Strong reduction of the ordered moment is observed for the S =1 /2 spins in CuRh2O4 and captured by our 1 /S corrections to the staggered magnetization. Our work identifies CoRh2O4 and CuRh2O4 as reference materials to guide future work searching for exotic quantum behavior in diamond-lattice antiferromagnets.
Hu, Wen-Jun; Gong, Shou-Shu; Sheng, D. N.
2016-08-01
By using Gutzwiller projected fermionic wave functions and variational Monte Carlo technique, we study the spin-1 /2 Heisenberg model with the first-neighbor (J1), second-neighbor (J2), and additional scalar chiral interaction JχSi.(Sj×Sk) on the triangular lattice. In the nonmagnetic phase of the J1-J2 triangular model with 0.08 ≲J2/J1≲0.16 , recent density-matrix renormalization group (DMRG) studies [Zhu and White, Phys. Rev. B 92, 041105(R) (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403(R) (2015), 10.1103/PhysRevB.92.140403] find a possible gapped spin liquid with the signal of a competition between a chiral and a Z2 spin liquid. Motivated by the DMRG results, we consider the chiral interaction JχSi.(Sj×Sk) as a perturbation for this nonmagnetic phase. We find that with growing Jχ, the gapless U(1) Dirac spin liquid, which has the best variational energy for Jχ=0 , exhibits the energy instability towards a gapped spin liquid with nontrivial magnetic fluxes and nonzero chiral order. We calculate topological Chern number and ground-state degeneracy, both of which identify this flux state as the chiral spin liquid with fractionalized Chern number C =1 /2 and twofold topological degeneracy. Our results indicate a positive direction to stabilize a chiral spin liquid near the nonmagnetic phase of the J1-J2 triangular model.
Honda, Zentaro; Kodama, Takafumi; Hagiwara, Masayuki; Kida, Takanori; Okutani, Akira; Sakai, Masamichi; Fukuda, Takeshi; Kamata, Norihiko
2016-09-01
We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M2(pymca)3(ClO4), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.
Henriques, M. S.; Gorbunov, D. I.; Kriegner, D.; Vališka, M.; Andreev, A. V.; Matěj, Z.
2016-02-01
Structural changes through the first-order paramagnetic-antiferromagnetic phase transition of Dy3Ru4Al12 at 7 K have been studied by means of X-ray diffraction and thermal expansion measurements. The compound crystallizes in a hexagonal crystal structure of Gd3Ru4Al12 type (P63/mmc space group), and no structural phase transition has been found in the temperature interval between 2.5 and 300 K. Nevertheless, due to the spin-lattice coupling the crystal volume undergoes a small orthorhombic distortion of the order of 2×10-5 as the compound enters the antiferromagnetic state. We propose that the first-order phase transition is not driven by the structural changes but rather by the exchange interactions present in the system.
You-Hong Yuan; En-Hua Xiao; Jian-Bin Liu; Zhong He; Ke Jin; Cong Ma; Jun Xiang; Jian-Hua Xiao; Wei-Jian Chen
2008-01-01
AIM: To investigate the dynamic characteristics and the correlation between PCNA, Bax, nm23, E-cadherin expression and apparent diffusion coefficient (ADC)on MR diffusion-weighted imaging (DWI) after chemoembolization in rabbit liver VX-2 tumor model. METHODS: Forty New Zealand rabbit liver VX-2 tumor models were included in the study. DWI was carried out periodically after chemoembolization. All VX-2 tumor samples in each group were examined by histopathology and StTept Avidin-Biotin Complex (SABC)immunohistochemical staining. RESULTS" The PCNA expression index in VX-2 tumors was higher than in the normal parenchyma around the tumor (P＜0. 001). Nm23, Bax or E-caderin expression index in VX-2 tumors were lower than in the normal parenchyma around the tumor (all P＜0. 001). PCNA and nm23 expression in the VX-2 tumor periphery first increased and then decreased (P＜0. 001 and P=0. 03, respectively), while the expression of Bax and E-cadherin before and after chemoembolization was insignificant. When b-value was 100 s/mm2, there was a linear correlation between PCNA expression and ADC in the area of VX-2 tumor periphery (P＜0. 001), and PCNA expression in VX-2 tumor periphery influenced the ADC. CONCLUSION: The potential of VX-2 tumor infiltrating and metastasizing decreases, while its ability to proliferate increases for a short time after chemoembolization. To some degree, the ADC value indirectly reflects the proliferation of VX-2 tumor cells.
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
Lima, L. S.
2017-02-01
We have used the Dirac's massless quasi-particles together with the Kubo's formula to study the spin transport by electrons in the graphene monolayer. We have calculated the electric conductivity and verified the behavior of the AC and DC currents of this system, that is a relativistic electron plasma. Our results show that the AC conductivity tends to infinity in the limit ω → 0 , similar to the behavior obtained for the spin transport in the two-dimensional frustrated antiferromagnet in the honeycomb lattice. We have made a diagrammatic expansion for the Green's function and we have not gotten significative change in the results.
Aoki, Dai; Paulsen, Carley; Kotegawa, Hisashi; Hardy, Frédéric; Meingast, Christoph; Haen, Pierre; Boukahil, Mounir; Knafo, William; Ressouche, Eric; Raymond, Stephane; Flouquet, Jacques
2012-03-01
Doping Kondo lattice system CeRu2Si2 with Rh-8% (Ce(Ru0.92Rh0.08)2Si2) leads to drastic consequences due to the mismatch of the lattice parameters between CeRu2Si2 and CeRh2Si2. A large variety of experiments clarifies the unusual properties of the ground state induced by the magnetic field from longitudinal antiferromagnetic (AF) mode at H=0 to polarized paramagnetic phase in very high magnetic field. The separation between AF phase, paramagnetic phase and polarized paramagnetic phase varying with temperature, magnetic field and pressure is discussed on the basis of the experiments down to very low temperature. Similarities and differences between Rh and La substituted alloys are discussed with emphasis on the competition between transverse and longitudinal AF modes, and ferromagnetic fluctuations.
Huang, Ran; Gujrati, Purushottam D.
2017-01-01
An inhomogeneous 2-dimensional recursive lattice formed by planar elements has been designed to investigate the thermodynamics of Ising spin system on the surface/thin film. The lattice is constructed as a hybrid of partial Husimi square lattice representing the bulk and 1D single bonds representing the surface. Exact calculations can be achieved with the recursive property of the lattice. The model has an anti-ferromagnetic interaction to give rise to an ordered phase identified as crystal, and a solution with higher energy to represent the amorphous/metastable phase. Free energy and entropy of the ideal crystal and supercooled liquid state of the model on the surface are calculated by the partial partition function. By analyzing the free energies and entropies of the crystal and supercooled liquid state, we are able to identify the melting and ideal glass transition on the surface. The results show that due to the variation of coordination number, the transition temperatures on the surface decrease significantly compared to the bulk system. Our calculation qualitatively agrees with both experimental and simulation works on the thermodynamics of surfaces and thin films conducted by others. Interactions between particles farther than the nearest neighbor distance are taken into consideration, and their effects are investigated. Supported by the National Natural Science Foundation of China under Grant No. 11505110, the Shanghai Pujiang Talent Program under Grant No. 16PJ1431900, and the China Postdoctoral Science Foundation under Grant No. 2016M591666
Nunes, Wagner A; de Sousa, J Ricardo; Viana, J Roberto; Richter, J
2010-04-14
The ground state phase diagram of the quantum spin-1/2 Heisenberg antiferromagnet in the presence of nearest-neighbor (J(1)) and next-nearest-neighbor (J(2)) interactions (J(1)-J(2) model) on a stacked square lattice, where we introduce an interlayer coupling through nearest-neighbor bonds of strength J(), is studied within the framework of the differential operator technique. The Hamiltonian is solved by effective-field theory in a cluster with N=4 spins (EFT-4). We obtain the sublattice magnetization m(A) for the ordered phases: antiferromagnetic (AF) and collinear (CAF-collinear antiferromagnetic). We propose a functional for the free energy Ψ(μ)(m(μ)) (μ=A, B) to obtain the phase diagram in the λ-α plane, where λ=J()/J(1) and α=J(2)/J(1). Depending on the values of λ and α, we found different ordered states (AF and CAF) and a disordered state (quantum paramagnetic (QP)). For an intermediate region α(1c)(λ) α(2c)(λ), and below λ(1), we have the AF and CAF semi-classically ordered states, respectively. At α=α(1c)(λ) a second-order transition between the AF and QP states occurs and at α=α(2c)(λ) a first-order transition between the AF and CAF phases takes place. The boundaries between these ordered phases merge at the critical end point CEP≡(λ(1), α(c)), where α(c)≈0.56. Above this CEP there is again a direct first-order transition between the AF and CAF phases, with a behavior described by the point α(c) independent of λ ≥ λ(1).
Hu, Wen-Jun; Gong, Shou-Shu; Becca, Federico; Sheng, D. N.
2015-11-01
By using the variational Monte Carlo technique, we study the spin-1/2 XXZ antiferromagnetic model (with easy-plane anisotropy) on the kagome lattice. A class of Gutzwiller projected fermionic states with a spin Jastrow factor is considered to describe either spin liquids [with U (1 ) or Z2 symmetry] or magnetically ordered phases [with q =(0 ,0 ) or q =(4 π /3 ,0 ) ]. We find that the magnetic states are not stable in the thermodynamic limit. Moreover, there is no energy gain to break the gauge symmetry from U (1 ) to Z2 within the spin-liquid states, as previously found in the Heisenberg model. The best variational wave function is therefore the U (1 ) Dirac state, supplemented by the spin Jastrow factor. Furthermore, a vanishing S =2 spin gap is obtained at the variational level, in the whole regime from the X Y to the Heisenberg model.
Zhu, Rengui, E-mail: rgzhu@mail.ahnu.edu.cn; Hu, Gangsan
2013-06-15
A frustrated Heisenberg model on a stacked square lattice in a striped antiferromagnetic spin order is studied by the Green's function approach. Besides the intra- and inter-layer exchange couplings, the single-ion anisotropy (J{sub s}) is also considered. The expressions of the spin spectrum gap (Δ), the transition temperature (T{sub N}) and the zero-temperature average spin (〈S{sup z}〉{sub 0}) are derived analytically. Their dependences on the single-ion anisotropy are investigated. We find they are all increasing functions of J{sub s}. We make a further estimation of the magnitude of J{sub s} according to the experimental temperature T{sub N}=138K of the pure compound LaFeAsO.
Pires, A.S.T. [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, MG, CP 702, 30123-970 (Brazil); Lapa, R.S., E-mail: rodrigophc@gmail.com [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, MG, CP 702, 30123-970 (Brazil)
2013-08-15
We study the disordered phase of the J{sub 1}–J{sub 2} frustrated Heisenberg antiferromagnet with spin S=1 on a square lattice using a SU(3) Schwinger boson representation. In the approximation of Bose condensation and in a mean-field treatment of the four-operator terms, we calculate the gap as a function of J{sub 1}/J{sub 2}, and the quadrupole static structure factor at zero temperature. Our results indicate the existence of a nematic state in the paramagnetic phase. - Highlights: ► The disordered phase is studied. ► The energy gap in the paramagnetic phase is calculated. ► The static spin structure factor is calculated. ► The static quadrupole structure factor is calculated. ► The ground state energy is calculated.
Susuki, Takuya; Kurita, Nobuyuki; Tanaka, Takuya; Nojiri, Hiroyuki; Matsuo, Akira; Kindo, Koichi; Tanaka, Hidekazu
2013-06-28
We have performed high-field magnetization and electronic spin resonance (ESR) measurements on Ba3CoSb2O9 single crystals, which approximates the two-dimensional (2D) S=1/2 triangular-lattice Heisenberg antiferromagnet. For an applied magnetic field H parallel to the ab plane, the entire magnetization curve including the plateau at one-third of the saturation magnetization (Ms) is in excellent agreement with the results of theoretical calculations except a small step anomaly near (3/5)Ms, indicative of a theoretically undiscovered quantum phase transition. However, for H∥c, the magnetization curve exhibits a cusp near Ms/3 owing to the weak easy-plane anisotropy and the 2D quantum fluctuation. From a detailed analysis of the collective ESR modes observed in the ordered state, combined with the magnetization process, we have determined all the magnetic parameters including the interlayer and anisotropic exchange interactions.
Babkevich, P.; Katukuri, Vamshi M.; Fâk, B.; Rols, S.; Fennell, T.; Pajić, D.; Tanaka, H.; Pardini, T.; Singh, R. R. P.; Mitrushchenkov, A.; Yazyev, O. V.; Rønnow, H. M.
2016-12-01
Sr2 CuTeO6 presents an opportunity for exploring low-dimensional magnetism on a square lattice of S =1 /2 Cu2 + ions. We employ ab initio multireference configuration interaction calculations to unravel the Cu2 + electronic structure and to evaluate exchange interactions in Sr2 CuTeO6 . The latter results are validated by inelastic neutron scattering using linear spin-wave theory and series-expansion corrections for quantum effects to extract true coupling parameters. Using this methodology, which is quite general, we demonstrate that Sr2 CuTeO6 is an almost ideal realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV.
Matan, K., E-mail: kmatan@issp.u-tokyo.ac.j [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Helton, J.S. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Grohol, D. [The Dow Chemical Company, Core R and D, Midland, MI 48674 (United States); Nocera, D.G. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Wakimoto, S.; Kakurai, K. [Quantum Beam Science Directorate, Japanese Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); Lee, Y.S. [Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
2009-09-01
We report polarized neutron scattering studies of spin-wave excitations and spin fluctuations in the S=5/2 kagome{sup '} lattice antiferromagnet KFe{sub 3}(OH){sub 6}(SO{sub 4}){sub 2} (jarosite). Inelastic polarized neutron scattering measurements at 10 K on a single crystal sample reveal two spin gaps, associated with in-plane and out-of-plane excitations. The polarization analysis of quasi-elastic scattering at 67 K shows in-plane spin fluctuations with XY symmetry, consistent with the disappearance of the in-plane gap above the Neel temperature T{sub N}=65K. Our results suggest that jarosite is a promising candidate for studying the 2D XY universality class in magnetic systems.
Majumdar, Kingshuk; Datta, Trinanjan
2009-10-07
At zero temperature the sublattice magnetization of the quantum spin- 1/2 Heisenberg antiferromagnet on a body-centered cubic lattice with competing first and second neighbor exchange (J(1) and J(2)) is investigated using the non-linear spin wave theory. The zero temperature phases of the model consist of a two sublattice Néel phase for small J(2) (AF(1)) and a collinear phase at large J(2) (AF(2)). We show that quartic corrections due to spin wave interactions enhance the sublattice magnetization in both the AF(1) and the AF(2) phase. The magnetization corrections are prominent near the classical transition point of the model and in the J(2)>J(1) regime. The ground state energy with quartic interactions is also calculated. It is found that up to quartic corrections the first order phase transition (previously observed in this model) between the AF(1) and the AF(2) phase survives.
Thermochemical ablation therapy of VX2 tumor using a permeable oil-packed liquid alkali metal.
Ziyi Guo
Full Text Available Alkali metal appears to be a promising tool in thermochemical ablation, but, it requires additional data on safety is required. The objective of this study was to explore the effectiveness of permeable oil-packed liquid alkali metal in the thermochemical ablation of tumors.Permeable oil-packed sodium-potassium (NaK was prepared using ultrasonic mixing of different ratios of metal to oil. The thermal effect of the mixture during ablation of muscle tissue ex vivo was evaluated using the Fluke Ti400 Thermal Imager. The thermochemical effect of the NaK-oil mixture on VX2 tumors was evaluated by performing perfusion CT scans both before and after treatment in 10 VX2 rabbit model tumors. VX2 tumors were harvested from two rabbits immediately after treatment to assess their viability using trypan blue and hematoxylin and eosin (H.E. staining.The injection of the NaK-oil mixture resulted in significantly higher heat in the ablation areas. The permeable oil controlled the rate of heat released during the NaK reaction with water in the living tissue. Perfusion computed tomography and its parameter map confirmed that the NaK-oil mixture had curative effects on VX2 tumors. Both trypan blue and H.E. staining showed partial necrosis of the VX2 tumors.The NaK-oil mixture may be used successfully to ablate tumor tissue in vivo. With reference to the controlled thermal and chemical lethal injury to tumors, using a liquid alkali in ablation is potentially an effective and safe method to treat malignant tumors.
Yu, Houqiang; Wang, Wei; He, Xiaoling; Zhou, Qibing; Ding, Mingyue
2017-03-01
Ultrasound contrast agents (UCAs) such as SonoVue or Optison have been used widely in clinic for contrast-enhanced vascular imaging. However, microbubbles UCAs display limitations in tumor-targeted imaging due to the large sizes, nanoscaled UCAs has consequently attracted increasing attentions. In this work, we synthesized nanobubbles (NBs) by ultrasonic cavitation method, then a fluorescent marker of Alexa Fluor 680 was conjugated to the shell in order to observe the localization of NBs in tumor tissue. Measurement of fundamental characteristics showed that the NBs had homogeneous distribution of mean diameter of 267.9 +/- 19.2 nm and polydispersity index of 0.410 +/- 0.056. To assess in vivo tumor-selectivity of NBs, we established the rabbits VX2 hepatocellular carcinoma model though surgical implantation method. After the rabbits were intravenous administered of NBs, contrast-enhanced sonograms was observed in the surrounding of VX2 tumor, which showed there are rich capillaries in the tumor periphery. We additionally investigated the toxic of the NBs by hematoxylin-eosin staining. The results indicated that the NBs is a biocompatible non-toxic lipid system. Furthermore, the VX2 tumors and major organs were analyzed using ex vivo fluorescence imaging to confirm the targeted selectivity of NBs, and the results verified that the NBs were capable of targeting VX2 tumor. Confocal laser scanning microscopy examination showed that the NBs can traverse the VX2 tumor capillaries and target to the hepatocellular carcinoma tumor cells. All these results suggested that the newly prepared NBs have a potential application in molecular imaging and tumor-targeting therapy.
Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4
Zhao, Songrui; Dalmas de Réotier, P.; Yaouanc, A.; MacLaughlin, D. E.; Mackie, J. M.; Bernal, O. O.; Nambu, Y.; Higo, T.; Nakatsuji, S.
2012-08-01
Magnetic susceptibility and muon spin relaxation (μSR) experiments have been carried out on the quasi-2D triangular-lattice spin S=2 antiferromagnet FeGa2S4. The μSR data indicate a sharp onset of a frozen or nearly frozen spin state at T*=31(2) K, twice the spin-glass-like freezing temperature Tf=16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in μSR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate λd(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures, λd(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of λd(T) between the two compounds is observed from ˜Tf to ˜1.5T*. Although the μSR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly fluctuating “spin gel” regime between Tf and T*. Such a regime and the absence of a divergence in λd(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z2 vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.
Bera, A. K.; Yusuf, S. M.; Kumar, Amit; Ritter, C.
2017-03-01
The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet N a2C o2Te O6 have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below TN˜24.8 K . The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector k =(1 /2 0 0 ) , occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the c axis (perpendicular to the honeycomb layers in the a b planes) has been found even at 1.8 K, well below the TN˜24.8 K . The observed limited correlation along the c axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments mCo (1 )=2.77 (3 ) μB/C o2 + and mCo (2 )=2.45 (2 ) μB/C o2 + at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above TN˜24.8 K , the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers (a b plane) with a correlation length of ˜12 Å at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at T ≤TN . The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the TN and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is
Capponi, Sylvain
2017-01-01
We present numerical evidence that the spin-1/2 Heisenberg model on the two-dimensional checkerboard lattice exhibits several magnetization plateaus for m =0 , 1 /4 , 1 /2 , and 3 /4 , where m is the magnetization normalized by its saturation value. These incompressible states correspond to somewhat similar valence-bond crystal phases that break lattice symmetries, though they are different from the already established plaquette phase for m =0 . Our results are based on exact diagonalization as well as density-matrix renormalization-group large-scale simulations and interpreted in terms of simple parameter-free trial wave functions.
YAO Xiao-yan; LI Peng-lei; DONG Shuai; LIU Jun-ming
2007-01-01
A three-dimensional Ising-like model doped with anti-ferromagnetic (AFM) bonds is proposed to investigate the magnetic properties of a doped triangular spin-chain system by using a Monte-Carlo simulation. The simulated results indicate that a steplike magnetization behavior is very sensitive to the concentration of AFM bonds. A low concentration of AFM bonds can suppress the stepwise behavior considerably, in accordance with doping experiments on Ca3Co206. The analysis of spin snapshots demonstrates that the AFM bond doping not only breaks the ferromagnetic ordered linear spin chains along the hexagonal c-axis but also has a great influence upon the spin configuration in the ab-plane.
Antiferromagnetic spintronics.
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.
Metabolomic Analysis of Liver Tissue from the VX2 Rabbit Model of Secondary Liver Tumors
Ibarra, R.; Dazard, J-E.; Y. Sandlers; Rehman, F; Abbas, R.; Kombu, R.; Zhang, G-F; Brunengraber, H; Sanabria, J.
2014-01-01
Purpose. The incidence of liver neoplasms is rising in USA. The purpose of this study was to determine metabolic profiles of liver tissue during early cancer development. Methods. We used the rabbit VX2 model of liver tumors (LT) and a control group consisting of sham animals implanted with Gelfoam into their livers (LG). After two weeks from implantation, liver tissue from lobes with and without tumor was obtained from experimental animals (LT+/LT−) as well as liver tissue from controls (LG+...
Li Peijing; Zhu Mei; Xu Yali; Zhao Yang; Gao Shunji; Liu Zheng; Gao Yun-hua
2014-01-01
Background Intravascular microbubble-enhanced acoustic cavitation is capable of disrupting the vascular walls of capillaries and small vessels.This study was designed to investigate the impact of microbubble-enhanced,pulsed and focused ultrasound (MEUS) on the blood perfusion of subcutaneous VX2 tumors in rabbits.Methods Subcutaneous VX2 cancers in twenty New Zealand rabbits were treated by combining high-pressure amplitude,pulsed and focused therapeutic ultrasound (TUS) and intravenous microbubble injections.The TUS transducer was operated with a peak negative pressure of 4.6 MPa and a duty cycle of 0.41％.Controls were subcutaneous VX2 cancers treated with TUS or microbubbles only.Contrast-enhanced ultrasound (CEUS) and intravenous Evans Blue (EB) perfusion were performed to assess the tumor circulation.The tumor microvascular disruption was assessed by histological examination.Results CEUS showed that the tumor circulation almost vanished after MEUS treatment.The average peak grayscale value (GSV) of tumor CEUS dropped significantly from 84.1±22.4 to 15.8±10.8 in the MEUS-treated tumors but no significant GSV changes were found in tumors in the two control groups.The mean tumor EB content of the MEUS-treated tumors was significantly lower than that of the controls.Histological examination found scattered tumor microvascular disruption with intercellular edema after MEUS treatment.Conclusion The tumor circulation of VX2 cancers can be arrested or significantly reduced by MEUS due to microvascular disruption.
Sentinel Node Mapping of VX2 Carcinoma in Rabbit Thigh with CT Lymphography Using Ethiodized Oil
Lee, Yoon Jin; Kim, Young Hoon; Lee, Kyoung Ho; Park, Ji Hoon [Department of Radiology, Seoul National University Bundang Hospital, Seongnam 463-707 (Korea, Republic of); Lee, Hye Seung [Department of Pathology, Seoul National University Bundang Hospital, Seongnam 463-707 (Korea, Republic of); Jung, Seung Chai [Department of Radiology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-744 (Korea, Republic of); Joo, Seung-Moon [Department of Radiology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul 135-720 (Korea, Republic of)
2014-07-01
To assess the feasibility of computed tomography (CT) lymphography using ethiodized oil for sentinel node mapping in experimentally induced VX2 carcinoma in the rabbit thigh. This experiment received approval from the institutional animal use and care administrative advisory committee. Twenty-three rabbits with VX2 carcinoma in the thigh underwent CT before and after (1 hour, 2 hour) peritumoral injection of 2 mL ethiodized oil. After the CT examination, sentinel nodes were identified by peritumoral injection of methylene blue and subsequently removed. The retrieved sentinel and non-sentinel lymph nodes were investigated with radiographic and pathologic examinations. Based on the comparison of CT findings with those of radiographic and pathologic examinations, the diagnostic performance of CT for sentinel node identification was assessed. All 23 rabbits showed 53 ethiodized oil retention nodes on post-injection CT and specimen radiography, and 52 methylene blue-stained nodes at the right femoroiliac area. Of the 52 blue-stained sentinel nodes, 50 nodes demonstrated ethiodized oil retention. Thus, the sentinel node detection rate of CT was 96% (50 of 52). On pathologic examination, 28 sentinel nodes in 17 rabbits (nodes/rabbit, mean ± standard deviation, 1.7 ± 0.6) harbored metastasis. Twenty seven of the 28 metastatic sentinel nodes were found to have ethiodized oil retention. Computed tomography lymphography using ethiodized oil may be feasible for sentinel node mapping in experimentally induced VX2 carcinoma in the rabbit thigh.
Histotripsy and metastasis: Assessment in a renal VX-2 rabbit tumor model
Styn, Nicholas R.; Hall, Timothy L.; Fowlkes, J. Brian; Cain, Charles A.; Roberts, William W.
2012-10-01
Histotripsy is a non-invasive, pulsed ultrasound technology where controlled cavitation is used to homogenize targeted tissue. We sought to assess the possibility that histotripsy may increase metastatic spread of tumor by quantifying the number of lung metastasis apparent after histotripsy treatment of aggressive renal VX-2 tumor compared to nontreated controls. VX-2 tumor was implanted in the left kidneys of 28 New Zealand White rabbits. Twenty rabbits were treated with histotripsy (day 13 after implantation) while 8 served as controls. All rabbits underwent left nephrectomy (day 14) and then were euthanized (day 19). This study was powered to detect a doubling in metastatic rate. Homogenized tumor was seen in all treated nephrectomy specimens. Whole-mount, coronal lung sections were viewed to calculate number and density of metastases. Viable tumor was present in all 28 lungs examined. Histology confirmed fractionation of tumor in all treatment rabbits. There was not a statistical difference in total lung metastases (88.7 vs. 72.5; p=0.29) or metastatic density (8.9 vs. 7.0 mets/cm2; p=0.22) between treated and control rabbits. Further investigation is planned to validate these results in the VX-2 model and to assess metastatic rates in less aggressive tumors treated with histotripsy.
Cellular Imaging Using Equivalent Cross-Relaxation Rate Technique in Rabbit VX-2 Tumor Model.
Nishiofuku, Hideyuki; Matsushima, Shigeru; Taguchi, Osamu; Inaba, Yoshitaka; Yamaura, Hidekazu; Sato, Yozo; Tanaka, Toshihiro; Kichikawa, Kimihiko
2011-01-01
Equivalent cross-relaxation rate (ECR) imaging (ECRI) is a measurement technique that can be used to quantitatively evaluate changes in structural organization and cellular density by MRI. The aim of this study was to evaluate the correlation between the ECR value and cellular density in the rabbit VX2 tumor model. Five rabbits implanted with 10 VX2 tumors in the femur muscles were included in this study. We adopted the off-resonance technique with a single saturation transfer pulse frequency of 7 ppm downfield from water resonance. The ECR value was defined as the percentage of signal loss between the unsaturated and saturated images. ECR images were constructed based on the percentage of the ECR value. Pathological specimens were divided into 34 areas and classified into two groups: the viable group and the necrotic group. ECR values were measured and compared between groups. The correlation between the ECR value and cellular density was then determined. The mean ECR value was significantly higher in the viable group than in the necrotic group (61.2% vs. 35.8%). The area under the curve that calculated by receiver operating characteristic curve was 0.991 at 7 ppm. The regression graph showed a linear relationship between the ECR value and cellular density; the correlation coefficient (r) was 0.858. There is a strong association between the ECR value and cellular density in VX2 tumors and so ECRI could be a potentially useful technique for accurately depicting viable and necrotic areas.
无
2007-01-01
AIM: To investigate dynamic characteristics and pathological mechanism of signal in rabbit VX-2 tumor model on diffusion-weighted imaging (DWI) after chemoembolization.METHODS: Forty New Zealand rabbits were included in the study and forty-seven rabbit VX-2 tumor models were raised by implanting directly and intrahepatically after abdominal cavity opened. Forty VX-2 tumor models from them were divided into four groups. DWI was performed periodically and respectively for each group after chemoembolization. All VX-2 tumor samples of each group were studied by pathology. The distinction of VX-2tumors on DWI was assessed by their apparent diffusion coefficient (ADC) values. The statistical significance between different time groups, different area groups or different b-value groups was calculated by using SPSS12.0 software.RESULTS: Under b-value of 100 s/mm2, ADC values were lowest at 16 h after chemoembolization in area of VX-2 tumor periphery, central, and normal liver parenchyma around tumor, but turned to increase with further elongation of chemoembolization treatment. The distinction of ADC between different time groups was significant respectively (F = 7.325, P ＜ 0.001; F = 2.496,P ＜ 0.048; F = 6.856, P ＜ 0.001). Cellular edema in the area of VX-2 tumor periphery or normal liver parenchyma around tumor, increased quickly in sixteen h after chemoembolization but, from the 16th h to the 48th h, cellular edema in the area of normal liver parenchyma around tumor decreased gradually and that in the area of VX-2 tumor periphery decreased lightly at, and then increased continually. After chemoembolization, Cellular necrosis in the area of VX-2 tumor periphery was more significantly high than that before chemoembolization. The areas of dead cells in VX-2 tumors manifested low signal and high ADC value, while the areas of viable cells manifested high signal and low ADC value.CONCLUSION: DWI is able to detect and differentiate tumor necrotic areas from viable
Magnetic phases of the quasi-two-dimensional antiferromagnet CuCrO2 on a triangular lattice
Sakhratov, Yu. A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.
2016-09-01
We have carried out Cu,6563 NMR spectra measurements in a magnetic field up to about 45 T on a single crystal of a multiferroic triangular antiferromagnet CuCrO2. The measurements were performed for magnetic fields aligned along the crystal c axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H ≲15 T). At higher fields magnetic structures form within individual triangular planes whereas the spin directions of the magnetic ions from neighboring planes are not correlated. It is established that the 2D-3D transition is hysteretic in field and temperature. Line-shape analysis reveals several possible magnetic structures existing within individual planes for different phases of CuCrO2. Within certain regions on the magnetic H -T phase diagram of CuCrO2 a 3D magnetic ordering with tensor order parameter is expected.
Cun Liu; Ping Liang; Yang Wang; Pei Zhou; Xin Li; Zhi-Yu Han; Shao-Ping Liu
2008-01-01
AIM: To evaluate the feasibility and efficacy of percutaneous transhepatic lymphosonography (PTL) as a novel method for the detection of tumor lymphangiogenesis in hepatic VX2 of rabbits and to evaluate combined PTL and routine contrast-enhanced ultrasonographic imaging for the diagnosis of liver cancer.METHODS: Ten rabbits with VX2 tumor were included in this study.SonoVue (0.1 mL/kg) was injected into each rabbit v/a an ear vein for contrast-enhanced ultrasonographic imaging,and 0.5 mL SonoVue was injected into the normal liver parenchyma near the VX2 tumor for PTL.Images and/or movie clips were stored for further analysis.RESULTS: Ultrasonographic imaging showed VX2 tumors ranging 5-19 mm in the liver of rabbits.The VX2 tumor was hyperechoic and hypoechoic to liver parenchyma at the early and later phase,respectively.The hepatic lymph vessels were visualized immediately after injection of contrast medium and continuously visualized with SonoVue(R) during PTL.The boundaries of VX2 tumors were hyperechoic to liver parenchyma and the tumors.There was a significant difference in the values for the boundaries of VX2 tumors after injection compared with the liver normal parenchyma and the tumor parenchyma during PTL.CONCLUSION: PTL is a novel method for the detection of tumor lymphangiogenesis in hepatic VX2 of rabbits.Combined PTL and contrast-enhanced ultrasonographic imaging can improve the diagnosis of liver cancer.
Okubo, Susumu; Nakata, Ryohei; Ikeda, Shohei; Takahashi, Naoki; Sakurai, Takahiro; Zhang, Wei-Min; Ohta, Hitoshi; Shimokawa, Tokuro; Sakai, Tôru; Okuta, Koji; Hara, Shigeo; Sato, Hirohiko
2017-02-01
A single-crystal S = 3/2 perfect kagome lattice antiferromagnet, KCr3(OH)6(SO4)2 (Cr-jarosite), has been studied by X-band and high-frequency electron spin resonance (ESR). The g-values perpendicular to the kagome plane (c-axis) and in the plane were determined to be gc = 1.9704 ± 0.0002 and gξ = 1.9720 ± 0.0003, respectively, by high-frequency ESR observed at 265 K. Antiferromagnetic resonances (AFMRs) with an antiferromagnetic gap of 120 GHz were observed at 1.9 K, which is below TN = 4.5 K. The analysis of AFMR modes using the conventional molecular field theory gave dp = 0.27 K and dz = 0.07 K, where dp and dz are in-plane and out-of-plane components of d vector of the Dzyaloshinsky-Moriya (DM) interaction, respectively. On the basis of these results and the exchange interaction of J = 6.15 K estimated by Okuta et al., the ground state of Cr-jarosite was discussed in connection with the Monte Carlo simulation results with classical Heisenberg spins on the kagome lattice by Elhajal et al. Finally, the angular dependence of the linewidth and lineshape observed at 296 K by X-band ESR showed the typical behavior of a two-dimensional Heisenberg antiferromagnet, suggesting the good two-dimensionality of Cr-jarosite.
Yoshida, Hiroyuki; Noguchi, Naoya; Matsushita, Yoshitaka; Ishii, Yuto; Ihara, Yoshihiko; Oda, Migaku; Okabe, Hirotaka; Yamashita, Satoshi; Nakazawa, Yasuhiro; Takata, Atsushi; Kida, Takanori; Narumi, Yasuo; Hagiwara, Masayuki
2017-03-01
We have succeeded in preparing single crystals of CaCu3(OH)6Cl2 • 0.6H2O, a candidate for the S = 1/2 Kagome lattice antiferromagnet. Magnetic properties of the compound are dominated by the nearest neighbor antiferromagnetic interaction J1, and the next nearest neighbor ferromagnetic J2 and an antiferromagnetic Jd across a hexagon, which is different from related compounds Kapellasite and Haydeeite with ferromagnetic J1. Magnetic susceptibility exhibits a sudden increase below 13 K and a cusp anomaly at T* = 7.2 K in the ab-plane, whereas only a moderate enhancement is observed below T* along the c-axis. A tiny peak detected in heat capacity at T* indicates the occurrence of a magnetic phase transition. The low temperature magnetic heat capacity was reproduced by assuming a two-dimensional spin-wave component and a temperature-linear term. The spin-wave contribution suggests a magnon excitation in a short-range ordered region, whereas the relatively large T-linear term 5.9 mJ/(Cu-mol·K2) at H = 0 T of this insulating compound suggests the existence of an unusual quasi-particle excitation below T*. They apparently reveal the unconventionality of the ground state of this S = 1/2 Kagome lattice antiferromagnet.
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'Monte Carlo method. By calculating the Binder 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.
Kumar, Krishna; Changlani, Hitesh J.; Clark, Bryan K.; Fradkin, Eduardo
2016-10-01
We perform an exact-diagonalization study of the spin-1/2 XXZ Heisenberg antiferromagnet on the kagome lattice at finite magnetization m =2/3 with an emphasis on the X Y point (Jz=0 ) and in the presence of a small chiral term. Recent analytic work by Kumar et al. [K. Kumar, K. Sun, and E. Fradkin, Phys. Rev. B 90, 174409 (2014), 10.1103/PhysRevB.90.174409] on the same model, using a newly developed flux attachment transformation, predicts a plateau at this value of the magnetization described by a chiral spin liquid (CSL) with a spin Hall conductance of σx y=1/2 . Such a state is topological in nature, has a ground-state degeneracy, and exhibits fractional excitations. We analyze the degeneracy structure in the low-energy manifold, identify the candidate topological states, and use them to compute the modular matrices and Chern numbers, all of which strongly agree with expected theoretical behavior for the σx y=1/2 CSL. In the limit of zero chirality, we find on most (not all) clusters that the topological invariants are still those of a CSL.
Canted antiferromagnetism in KNi3[PO3(F,OH)]2[PO2(OH)2]F2 with a stair-case Kagomé lattice
Liu, Li-Chen; Ren, Wei-Jian; Huang, Ya-Xi; Pan, Yuanming; Mi, Jin-Xiao
2017-10-01
A new nickel phosphate KNi3[PO3(F,OH)]2[PO2(OH)2]F2 has been synthesized using a modified hydrothermal method. Structural characterizations show that it adopts a 3D framework structure with 2D layers of Ni octahedra in a stair-case Kagomé lattice. The Ni2 octahedron at the inversion center shares two trans-faces with Ni1 octahedra to form a linear trimer (Ni3O8F6) as the basic structural unit. The Ni-trimers are linked between themselves by sharing F-corners and to [PO3(F,OH)] tetrahedral groups by sharing O-corners to form 2D stair-case Kagomé layers, which are parallel to the (100) plane and are stacked along the a-axis. Successive Kagomé layers are combined together by [PO2(OH)2] tetrahedral groups and interstice cations K+. Magnetic measurements reveal that KNi3[PO3(F,OH)]2[PO2(OH)2]F2 exhibits a canted antiferromagnetic ordering with a ferromagnetic component at low temperatures.
Wang, Guangmei [Ruhr-Universitat Bochum; Valldor, Martin [Max Plank Institute for Chemical Physics of Solids, Dresden, Germany; Mallick, Bert [Ruhr Universitat Bochum; Mudring, Anja-Verena [Ames Laboratory
2014-01-01
Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron–oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2–4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AAi… and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4+ ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (Tc = 10 or 13 K for Co and Tc = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+.
Takashi Anayama; Takahiro Nakajima; Michael Dunne; Jinzi Zheng; Christine Allen; Brandon Driscoll; Douglass Vines; Shaf Keshavjee; David Jaffray; Kazuhiro Yasufuku
2013-01-01
BACKGROUND: The rabbit VX2 lung cancer model is a large animal model useful for preclinical lung cancer imaging and interventional studies. However, previously reported models had issues in terms of invasiveness of tumor inoculation, control of tumor aggressiveness and incidence of complications. PURPOSE: We aimed to develop a minimally invasive rabbit VX2 lung cancer model suitable for imaging and transbronchial interventional studies. METHODS: New Zealand white rabbits and VX2 tumors were u...
Shimokawa, Tokuro; Watanabe, Ken; Kawamura, Hikaru
2015-10-01
Inspired by the recent theoretical suggestion that the random-bond S =1 /2 antiferromagnetic Heisenberg model on the triangular and the kagome lattices might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the strength of the randomness exceeds a critical value, and that this "random-singlet state" might be relevant to the QSL behaviors experimentally observed in triangular organic salts κ -(ET) 2Cu2(CN) 3 and EtMe3Sb [Pd(dmit)2] 2 and in kagome herbertsmithite ZnCu3(OH) 6Cl2 , we further investigate the nature of the static and the dynamical spin correlations of these models. We compute the static and the dynamical spin structure factors, S (q ) and S (q ,ω ) , by means of an exact diagonalization method. In both triangular and kagome models, the computed S (q ,ω ) in the random-singlet state depends on the wave vector q only weakly, robustly exhibiting gapless behaviors accompanied by the broad distribution extending to higher energy ω . Especially in the strongly random kagome model, S (q ,ω ) hardly depends on q , and exhibits an almost flat distribution for a wide range of ω , together with a ω =0 peak. These features agree semiquantitatively with the recent neutron-scattering data on a single-crystal herbertsmithite. Furthermore, the computed magnetization curve agrees almost quantitatively with the experimental one recently measured on a single-crystal herbertsmithite. These results suggest that the QSL state observed in herbertsmithite might indeed be the randomness-induced QSL state, i.e., the random-singlet state.
The Characteristics of Vascular Growth in VX2 Tumor Measured by MRI and Micro-CT
X.-L. Qi
2012-01-01
Full Text Available Blood supply is crucial for rapid growth of a malignant tumor; medical imaging can play an important role in evaluating the vascular characterstics of tumors. Magnetic resonance imaging (MRI and micro-computed tomography (CT are able to detect tumors and measure blood volumes of microcirculation in tissue. In this study, we used MR imaging and micro-CT to assess the microcirculation in a VX2 tumor model in rabbits. MRI characterization was performed using the intravascular contrast agent Clariscan (NC100150-Injection; micro-CT with Microfil was used to directly depict blood vessels with diameters as low as 17 um in tissue. Relative blood volume fraction (rBVF in the tumor rim and blood vessel density (rBVD over the whole tumor was calculated using the two imaging methods. Our study indicates that rBVF is negatively related to the volume of the tumor measured by ultrasound (R=0.90. rBVF in the tissue of a VX2 tumor measured by MRI in vivo was qualitatively consistent with the rBVD demonstrated by micro-CT in vitro (R=0.97. The good correlation between the two methods indicates that MRI studies are potentially valuable for assessing characteristics or tumor vascularity and for assessing response to therapy noninvasively.
Electrical switching of an antiferromagnet.
Wadley, P; Howells, B; Železný, J; Andrews, C; Hills, V; Campion, R P; Novák, V; Olejník, K; Maccherozzi, F; Dhesi, S S; Martin, S Y; Wagner, T; Wunderlich, J; Freimuth, F; Mokrousov, Y; Kuneš, J; Chauhan, J S; Grzybowski, M J; Rushforth, A W; Edmonds, K W; Gallagher, B L; Jungwirth, T
2016-02-05
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Cho, Jin Han; Choi, Jong Cheol; Shin, Tae Beom; Park, Byeong Ho [Dong-A University, School of Medicine, Busan (Korea, Republic of)
2005-07-15
The purpose of this study was to develop a large animal (rabbit) model which has a proper solitary intrahepatic tumor with lower leakage rates through less traumatic methods. Consequently, we evaluated tumor progression following the intrahepatic inoculation of VX2 cells into New Zealand white rabbits to acquire baseline data on the progression of a VX2 tumor. Twenty New Zealand white rabbits, each weighting 2.5-3 kg, were selected for this study. A 1 mm{sup 3} VX2 tumor fragment was created and then minced to enable the particles to pass through a 21 G needle mounting in a tuberculin syringe with 0.1 ml of normal saline. The minced VX2 tumor particles were injected into the subcapsular parenchyma of the left hepatic lobe. A 21 G needle was used to avoid penetrating large hepatic vessels. In order to prevent hemorrhage or leakage of the VX2 tumor cells through the injection route, a purse-string suture around the puncture site was made using black silk 4-0. The tumor particles were then injected through the center of the suture. While removing the needle, the suture was tightened to prevent hemorrhage or leakage of the VX2 tumor cells through the injection route. Finally, the injection site was covered with a Surgical patch. The inoculated intrahepatic VX2 tumors were then imaged with a 16 channel multidetector CT every week for the duration of the study. The CT images covered from the lung apex to the pelvic floor. Two radiologists evaluated the size, location, and peritoneal seeding of the tumors as well as metastasis of other organs. Three rabbits were sacrificed as random beginning in the second week, and this process continued on a weekly basis for the duration of the study. The CT images and pathologic findings for the sacrificed rabbits were correlated. The inoculated intrahepatic VX2 tumors were not visible in the first week. By the second week 66.7% were visible on CT images and by the third week all tumors were visible. Of the twenty rabbits, three (15
Manson, J. L.; Warter, M. L.; Schlueter, J. A.; Lancaster, T.; Steele, A. J.; Blundell, S. J.; Pratt, F. L.; Singleton, J.; McDonald, R. D.; Lee, C.; Whangbo, M.-H.; Plonczak, A. (Materials Science Division); (Eastern Washington Univ.); (Oxford Univ.); (Rutherford Appleton Lab.); (LANL); (North Carolina State Univ.)
2011-01-14
The two-dimensional antiferromagnet [Cu(HF{sub 2}){sub 2}(pyz)]{sub n} (pyz=pyrazine) has a rectangular lattice (see picture) displaying two types of FHF{sup -} bridging modes. The spin exchange through Cu-(FHF){sub 2}-Cu is about 90% stronger than through Cu-pyz-Cu, and the {mu}{sub 1,1}-coordinated FHF{sup -}, which is close in nature to F{sup -}---HF, is largely responsible for the exchange. C black, Cu red, F green, H cyan.
Konya, Andras; Pelt, Carolyn S. Van; Wright, Kenneth C. [The University of Texas MD Anderson Cancer Center, Hoston (United States); Choi, Byung Gil [The Catholic University of Korea, Seoul (Korea, Republic of)
2007-04-15
We wanted to determine whether transcatheter Ethiodol-based capillary embolization in combination with carboplatin could improve the efficiency of a 1:1 Ethiodol-ethanol mixture (EEM) to ablate kidneys that been inoculated with VX-2 carcinoma. The right kidney in 34 New Zealand white rabbits were inoculated with fresh VX-2 tumor fragments. One week later, the kidneys were subjected to transarterial treatment (4-5 rabbits/group): Saline infusion (Group 1); carboplatin infusion (5 or 10 mg, Groups 2A and 2B); carboplatin- Ethiodol (CE) alone (Group 3) and followed by main renal artery occlusion with ethanol (RAO) (Group 4); carboplatin-EEM (C-EEM) followed by RAO (Group 5); carboplatin infusion followed by EEM plus RAO (Group 6); and EEM followed by RAO (Group 7). The animals were followed for up to 3-weeks. The treated kidneys were evaluated angiographically and macroscopically. The kidneys that showed successful embolization macroscopically were entirely cut into serial sections, and these were examined microscopically. Histologically, the kidneys were evaluated on the basis of the residual tumor found in the serial sections. The results obtained with carboplatin infusion alone (Groups 2A and 2B) and CE without RAO (Group 3) were similar to those of the control animals (Group 1). Kidneys from Groups 4-7 demonstrated macroscopically successful embolization with histologically proven complete renal parenchyma infarction; however, some residual tumor was evident in all but one animal. None of the Ethiodol-based modalities combined with locoregional carboplatin were more efficacious for tumor ablation than EEM alone.
Xiang, Zhiming; Liang, Qianwen; Liang, Changhong; Zhong, Guimian
2014-12-01
Our objective is to explore the value of liver cancer contrast-enhanced ultrasound (CEUS) and MRI perfusion quantitative analysis in liver cancer and the correlation between these two analysis methods. Rabbit VX2 liver cancer model was established in this study. CEUS was applied. Sono Vue was applied in rabbits by ear vein to dynamically observe and record the blood perfusion and changes in the process of VX2 liver cancer and surrounding tissue. MRI perfusion quantitative analysis was used to analyze the mean enhancement time and change law of maximal slope increasing, which were further compared with the pathological examination results. Quantitative indicators of liver cancer CEUS and MRI perfusion quantitative analysis were compared, and the correlation between them was analyzed by correlation analysis. Rabbit VX2 liver cancer model was successfully established. CEUS showed that time-intensity curve of rabbit VX2 liver cancer showed "fast in, fast out" model while MRI perfusion quantitative analysis showed that quantitative parameter MTE of tumor tissue increased and MSI decreased: the difference was statistically significant (P 0.05). However, the quantitative parameter of them were significantly positively correlated (P liver cancer lesion and surrounding liver parenchyma, and the quantitative parameters of them are correlated. The combined application of both is of importance in early diagnosis of liver cancer.
Sun, Yao; Xiong, Xiaobing; Pandya, Darpan; Jung, Youngkyoo; Mintz, Akiva; Hayasaka, Satoru; Wadas, Thaddeus J; Li, King C P
2017-06-28
High Intensity Focused Ultrasound (HIFU) is an emerging noninvasive, nonionizing physical energy based modality to ablate solid tumors with high power, or increase local permeability in tissues/tumors in pulsed mode with relatively low power. Compared with traditional ablative HIFU, nondestructive pulsed HIFU (pHIFU) is present in the majority of novel applications recently developed for enhancing the delivery of drugs and genes. Previous studies have demonstrated the capability of pHIFU to change tissue local permeability for enhanced drug delivery in both mouse tumors and mouse muscle. Further study based on bulk tissues in large animals and clinical HIFU system revealed correlation between therapeutic effect and thermal parameters, which was absent in the previous mouse studies. In this study, we further investigated the relation between the therapeutic effect of pHIFU and thermal parameters in bulky normal muscle tissues based on a rabbit model and a preclinical HIFU system. Correlation between therapeutic effect and thermal parameters was confirmed in our study on the same bulk tissues although different HIFU systems were used. Following the study in bulky normal muscle tissues, we further created bulky tumor model with VX2 tumors implanted on both hind limbs of rabbits and investigated the feasibility to enhance tumor permeability in bulky VX2 tumors in a rabbit model using pHIFU technique. A radiolabeled peptidomimetic integrin antagonist, (111)In-DOTA-IA, was used following pHIFU treatment in our study to target VX2 tumor and serve as the radiotracer for follow-up single-photon emission computed tomography (SPECT) scanning. The results have shown significantly elevated uptake of (111)In-DOTA-IA in the area of VX2 tumors pretreated by pHIFU compared with the control VX2 tumors not being pretreated by pHIFU, and statistical analysis revealed averaged 34.5% enhancement 24h after systematic delivery of (111)In-DOTA-IA in VX2 tumors pretreated by pHIFU compared
Sun HL
2013-10-01
Full Text Available Hongliang Sun,1 Linfeng Xu,1 Tianyuan Fan,2 Hongzhi Zhan,3 Xiaodong Wang,3 Yanfei Zhou,2 Ren-jie Yang3 1Department of Interventional Therapy, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, Guangzhou, 2Pharmacy School of Beijing University, Beijing, 3Department of Interventional Therapy, Peking University School of Oncology, Beijing Cancer Hospital and Institute, Beijing, People's Republic of China Background: The purpose of this study was to observe the effect and feasibility of hyperthermia and the influence of heat on surrounding organs in a VX2 rabbit liver model exposed to an alternating magnetic field after embolization with ferromagnetic nanoparticles. Methods: Forty rabbits containing implanted hepatic VX2 carcinomas were divided into four groups, each containing ten rabbits. Fourteen days after tumor transplantation, we opened the abdomen to observe the size and shape of the tumor. A transfemoral retrograde approach was then used for hepatic arterial catheterization in groups B, C, and D to perform angiography and embolization. The next day, three rabbits in group B and all rabbits in group D were exposed to an alternating magnetic field, and the temperature was recorded simultaneously in the center of the tumor, at the edge of the tumor, and in the normal liver parenchyma. On day 28, all animals was euthanized to observe changes in the implanted liver tumor and the condition of the abdomen. A pathologic examination was also done. Results: Before surgery, there was no significant difference in tumor volume between the four groups. Three different temperature points (center of the tumor, edge of the tumor, and in the normal liver parenchyma of group B under an alternating magnetic field were 37.2°C ± 1.1°C, 36.8°C ± 1.2°C, and 36.9°C ± 2.1°C, none of which were significantly different from pretreatment values. Three points basal temperature in group D showed no significant difference (F = 1.038, P = 0.413. Seven to 26
A spin-1 kagome antiferromagnet
Tovar, Mayra; Shtengel, Kirill; Refael, Gil
2010-03-01
We study a spin-1 antiferromagnet on the kagom'e lattice. We start by constructing a Klein-type SU(2) symmetric Hamiltonian which contains Heisenberg interactions between nearest and next-nearest neighbors as well as three-body terms. Our model Hamiltonian has an extensive degenerate ground state whose manifold is spanned by the AKLT-like valence bond states. We also perturb the parent Hamiltonian by introducing an enhancement to the nearest neighbor antiferromagnetic Heisenberg interactions. By projecting this perturbation onto the basis spanned by the unperturbed ground states, we derive an effective Hamiltonian which is dual to that of the transverse field antiferromagnetic Ising model on the triangular lattice. Based on the parameters of our model, we find it to be in the order-by-disorder phase. The ground state is a valence bond crystal stabilized by quantum fluctuations. We also discuss excitations, both magnetic and non-magnetic, and address their possible relevance to experiment.
Amaya, Naoki; Ono, Toshio; Oku, Yuta; Yamaguchi, Hironori; Matsuo, Akira; Kindo, Koichi; Nojiri, Hiroyuki; Palacio, Fernando; Campo, Javier; Hosokoshi, Yuko
2017-07-01
We have succeeded in synthesizing a new organic biradical F4BIPBNN [= 2,2'-(3,3',5,5'-tetrafluorobiphenyl-4,4'-diyl)bis(4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide)] which forms an S = 1/2 Heisenberg three-dimensional honeycomb antiferromagnet. Each site of a honeycomb layer alternately couples with upper or lower layers, which results in the unique three-dimensional honeycomb network with four nearest neighbors. At zero magnetic field, antiferromagnetic long-range order has been observed below TN = 2.7 K. Magnetic susceptibility in both paramagnetic and antiferromagnetic states and the magnetization curves are well reproduced by quantum Monte Carlo calculations with three antiferromagnetic interactions in the range of 4.3 to 6.6 K. From the concave shape of the magnetization curve, the shrinkage of spin due to spin fluctuations is evaluated to approximately 30% with respect to its classical value. The phase diagram of magnetic field versus temperature was determined by heat capacity and magnetization. In the field region below 3 T, a slight increase of TN was observed, which reflects the effect of spin fluctuations.
Functional CT imaging of angiogenesis in rabbit VX2 soft-tissue tumour
Purdie, Thomas G.; Henderson, Elizabeth; Lee, Ting-Yim
2001-12-01
Functional parameters such as blood flow (BF), microvessel permeability surface area product (PS), blood volume (BV) and mean transit time (MTT) are physiological markers related to the changes associated with angiogenesis. In the current study we present a functional CT technique for the simultaneous measurement of these four functional parameters and the display of each parameter as a functional image over an entire tissue slice. New Zealand White rabbits with implanted VX2 thigh tumours were scanned using CT with contrast media injection. The ex vivo method of radioactive microspheres was used to evaluate the accuracy of BF measurements with the functional CT technique. There was a significant linear correlation (R = 0.96) between regional CT and microsphere-measured BF values, with a slope not significantly different from unity (0.98 +/- 0.02, P precision of our CT technique was determined by the repeated scanning under steady-state conditions. The precision of CT-measured BF, PS, BV and MTT was 14%, 18%, 20% and 24%, respectively. In conclusion, BF can be measured accurately and BF, PS, BV and MTT reproducibly using our functional CT technique. Functional CT can be readily incorporated into existing imaging protocols to assess tumour angiogenesis.
Experimental Study of Multi-slice Spiral CT Perfusion Imaging in VX2 Soft-tissue Tumor of Rabbits
ZHANG Jingfeng; WANG Renfa; WANG Min; LI Yonggang; YANG Haitao
2006-01-01
An experimental animal model of malignant soft-tissue tumor was established to investigate the applied value of multi-slice spiral CT perfusion imaging preliminarily. Ten New Zealand white rabbits which were implanted with VX2 tumor in either proximal thigh were subjected to CT plain scan and perfusion scan two weeks later respectively, then the original perfusion images were transmitted to AW4.0 Workstation. The functional maps and perfusion parameters including blood flow (BF), blood volume (BV), mean transit time (MTT) and permeability surface (PS) were computed and analyzed. All the values of BF, BV and PS in VX2 soft-tissue tumors were obviously higher while the MTT-values were lower than those in the normal muscular tissues significantly. It was suggested that multi-slice spiral CT perfusion imaging is an accurate, convenient and relatively safe functional imaging technique, and can give a quantitative assessment to angiogenesis and blood perfusion of soft-tissue tumors.
Bioevaluation study of 32P-CP-PLLA particle brachytherapy in a rabbit VX2 lung tumor model.
Xu, Yu ping; Yang, Min; Pan, Dong hui; Wang, Li zhen; Liu, Lu; Huang, Peilin; Shao, Guoqiang
2012-04-01
The purpose of this study was to investigate the therapy effects of intratumoral administration of (32)P-CP-PLLA particles in a rabbit VX2 lung tumor model. 16 rabbits with tumors were randomly divided into 4 groups. 4 rabbits served as untreated controls, and others received intratumoral administration of (32)P-CP-PLLA particles with CT guidance. The total radioactivities in treated groups were as follows: a low activity was 93 MBq (n=4) (group 1), a medium activity was 185 MBq (n=4) (group 2) and a high activity was 370 MBq (n=4) (group 3). Brachytherapy treated VX2 tumors underwent (18)F-FDG PET/CT at 0 day, 3 day, 7 day and 14 day postinjection. In control group, (18)F-FDG PET/CT images were acquired at the same time points but without any treatment. Bremsstrahlung SPECT images were performed at 14 days after intratumoral brachytherapy in treated groups. After Bremsstrahlung SPECT and last (18)F-FDG PET/CT imagings, the rabbits were euthanized and the tumors were removed for histological examination. Bremsstrahlung SPECT images study indicated that there was no leakage of (32)P out of the injection site at 14 days after treatment. Compared with the control, the tumor volumes in treated groups significantly decreased, and (32)P-CP-PLLA particle produced a reduction in maximum or mean SUV of VX2 tumor (pCP-PLLA particle localized on the injecting sites. This novel brachytherapy device efficiently suppressed the growth of the VX2 tumors implanted in the rabbit. Copyright Â© 2012 Elsevier Ltd. All rights reserved.
Katayama, Kazuya; Kurita, Nobuyuki; Tanaka, Hidekazu
2015-06-01
We have systematically investigated the variation of the exchange parameters and the ground state in the S =1/2 kagome-lattice antiferromagnet (Rb1 -xCsx )2Cu3SnF12 via magnetic measurements using single crystals. One of the parent compounds, Rb2Cu3SnF12 , which has a distorted kagome lattice accompanied by four sorts of nearest-neighbor exchange interaction, has a disordered ground state described by a pinwheel valence-bond-solid state. The other parent compound, Cs2Cu3SnF12 , which has a uniform kagome lattice at room temperature, has an ordered ground state with the q =0 spin structure. The analysis of magnetic susceptibilities shows that with increasing cesium concentration x , the exchange parameters increase with the tendency to be uniform. It was found that the ground state is disordered for x 0.53 . The pseudogap observed for x 0.53 approach zero at xc≃0.53 . This is indicative of the occurrence of a quantum phase transition at xc.
Establishment of rabbit model with VX2 cell pyriformsinus grafting tumor%兔梨状隐窝VX2瘤模型的建立及解剖与影像学观察
韩秀丽; 陈万军; 王兆鹏
2012-01-01
Objective To establish a rabbit model with pyriformsinus carcinoma (PSC) grown from grafted VX2 tumor cells to serve as an animal research tool system for experimental study of hypolaryngeal carcinoma. Methods Grafting tumor was prepared with VX2 tumour cells among New Zealand rabbits for several generations at first, and then, grafting tumor was taken made into a suspension with the tissue pieces at a size of 1 mm3 or so. (in the cell density about 1～2× 106/ml cells). After that, the tissue suspension was injected into pyriformsinus mucosa of 17 rabbits under direct laryngoscope to grow PSC. Following tumor suspension injected, all these rabbits were given CT scanning regularly to detect the growing status, and tumor tissues were collected to do histological assays to identify if the grafting tumor model of VX2 cells established successfully based on the analysis of tumor growing rate and their behaviour characteristics. Results Two to four weeks late following the tumor tissue suspension injected, Grafting tumors were successfully grown in piriform recess among 16 rabbits, as confirmed by CT images and histological evidences meaning that the model was prepared successfully. The growing rate of grafting tumor was 94.1% (16/17), while 90% of the animals with PSC died in 4 weeks following tumour cells grafting. Conclusions It is suggested that the preparing procedures for PSC model are practicable by using tissue suspension, made from the grafting tumors of VX2 cells prepared among Zealand rabbits at first, injecting into the mucosa of piriform recess of rabbits under direct laryngoscope. This kind of animal model can be utilized in the research field of hypolaryngeal carcinoma.%目的 建立兔梨状隐窝VX2移植瘤模型.方法 先以VX2细胞在新西兰大白兔制备移植瘤并传代,再将兔移植瘤制备组织悬液(组织块约1mm3大小,约含1～2×106/ml个细胞),直达喉镜下接种于17只兔梨状隐窝,然后行影像学观察及瘤
You-Hong Yuan; En-Hua Xiao; Jian-Bin Liu; Zhong He; Ke Jin; Cong Ma; Jun Xiang; Jian-Hun Xiao; Wei-Jian Chen
2008-01-01
AIM: To investigate dynamical and image pathological characteristics of the liver on magnetic resonance (MR) diffusion-weighted imaging (DWI) in the rabbit VX-2 tumor model.METHODS: Forty New Zealand rabbits were included in the study and VX-2 tumor piece was implanted intrahepatically. Fifteen animals received two intrahepatic implantations while 25 had one intrahepatical implantation. DWI, T1-and T2-weighted of magnetic resonance imaging (MRI) were carried out on the 7th and the 14th d after implantation and DWI was conducted, respectively on the 21th d. Ten VX-2 tumor samples were studied pathologically.RESULTS: The rate of lump detected by DWI, T1WI and T2WI was 78.7%,10.7% and 53.5% (χ2= 32.61, P<0.001) on the 7th d after implantation and 95.8%,54.3% and 82.9% (χ2= 21.50, P<0.001) on the 14th d. The signal of most VX-2 tumors on DWI was uniform and it was equal on the map of apparent diffusion coefficient (ADC). The signal of VX tumors did not decrease on the 7th d after implantation, most of them slowly growing during the week following implantation without significant cell dying within the tumor. VX-2 tumors grew increasingly within 14 d after implantation but the signal of most VX-2 tumors on DWI or on the map of ADC was uniform or uneven and ADC of VX tumors decreased obscurely or slightly because tumor necrosis was still not obvious. On the 21th d after implantation, the signal of most VX-2 tumors on DWI or on the map of ADC was uneven because tumor necrosis was evident and ADC of VX-2 tumor necrotic areas decreased. The areas of viable cells in VX-2 tumors manifested a high signal on DWI and a low signal on the map of ADC. The areas of dead cells or necrosis in VX-2 tumors manifested low signals on DWI and low, equal or high signals on the map of ADC but they manifested high signals on DWI and on the map of ADC at the same time when the areas of necrotic tumor became liquefied or cystic. The border of tumors on DWI appeared gradually distinct and
MR DIFFUSION WEIGHTED IMAGING FOR EVALUATION OF RADIOTHERAPEUTIC EFFECTS ON RABBIT VX2 TUMOR MODEL
Shuo Li; Hua-dan Xue; Xin-hai Wang; Fei Sun; Bo Jiang; Dong Liu; Jing Lei; Zheng-yu Jin
2008-01-01
Objective To investigate the feasibility of magnetic resonance (MR) diffusion weighted imaging (DWI) for evaluation of radiotherapeutic effects on rabbit VX2 tumor model.Methods Sixteen New Zealand white rabbits received a subcutaneous implantation of VX2 tumor cdl suspension 0.5 mL (4× 107cells/mL) in their right thighs to set up tumor model. And 2 weeks later they were randomly divided into therapy group (Group T, n = 10) and control group (Group C, n = 6). Group T received radiotherapy at a single dose of 10 Gy. MR imaging (MRI) scan including short TI inversion recovery echo-planar imaging DWI, T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI) sequences were performed 1 day prior to as well as 1 day, 2 days, 3 days and 7 days after radiotherapy. Group C received only MRI scan at the same time points without any treatment. MRI appearance on T2WI, T1WI, and DWI images was compared and tumor volume was calculated. Apparent diffusion coefficient (ADC) values of the tumor were evaluated in all cases. HE staining was used for pathological study.Results Necrosis (n = 8) and hemorrhage (n = 2) were seen gradually on T2WI and T1WI images of Group T after time point of day 2 after irradiation. In Group C, no obvious necrosis was found until day 7. There was no significant difference in tumor volume between the two groups before radiotherapy. After radiotherapy, tumors in Group T showed a gradual growth but not as obvious as Group C. There was a significant difference in tumor volume between the two groups from day 2 on (P < 0.05). ADC value changed dramatically right from the 1st day after radio-therapy in Group T [(0.99 ± 0.15) ×10-3 mm2/s for 1 day before radiotherapy, (1.23 ± 0.08) ×10-3 , (1.45 ± 0.07) ×10-3 , (1.63 ± 0.06) ×10-3 , and (2.02 ± 0.18) ×10-3 mm2/s for day 1, 2, 3, and 7]; and ADC value had no significant changes after radiotherapy in Group C except day 7 [(1.07 ± 0.08) ×10-3 mm2/s for 1 day before radiotherapy, (1.03 ± 0.04) ×10
Xu, Xun; Okada, Kunihide; Fujii, Muneaki [Department of Physics, Kumamoto University, Kurokami 2-39-1, Kumamoto 860 (Japan); Kubo, Takeji [Department of Physics, Nara Education University, Takabatake, Nara 613 (Japan); Ajiro, Yoshitami [Department of Applied Physics, Fukui University, Bunkyo 3-9-1, Fukui 910 (Japan)
1996-05-27
The Br NMR in the triangular-lattice antiferromagnetic CsMnBr{sub 3} is investigated in the ordered state at low temperatures. Two distinct peaks of the Br NMR spin-echo spectrum were observed at 36.0 {+-} 0.5 MHz and 43.0 {+-} 0.5 MHz accompanied by a broad signal ranging from 34 to 55 MHz in zero field. The peak frequencies are independent of temperature and the ratio of the frequencies is the same as that of the quadrupole moments of {sup 81}Br and {sup 79}Br. This suggests that the quadrupole resonance of Br is perturbed by the distribution of the internal magnetic field. Theoretical results obtained under the assumption that the Mn spins have disordered structure in the c-plane due to the frustration effect agree with the experimental data. (author)
LI, HONG; Gong, Jian; Jiang, Xuyuan; Shao, Haibo
2013-01-01
Aim To investigate the role of tumor apoptosis-inhibitory protein survivin in arsenic trioxide-induced apoptosis in VX-2 carcinoma in the rabbit liver by means of transcatheter arterial chemoembolization. Methods Sixteen rabbits with 32 implanted hepatic VX-2 tumors were randomly divided into two groups. The experimental group received 2 mg of arsenic trioxide and 1 mL of ultra-fluid lipiodol co-injected via hepatic arterial cannulation and the control group received o...
Purdie, Thomas G [Department of Medical Biophysics, University of Western Ontario, London, ON (Canada); Lee, Ting-Yim [Department of Medical Biophysics, University of Western Ontario, London, ON (Canada)
2003-04-07
Tumour blood flow is one of the important factors limiting the efficacy of radiation therapy (hypoxic radioresistance), chemotherapy (drug delivery) and thermal therapy (heat dissipation) in treating cancer. The modification of tumour blood flow has been an area of intense investigation. In the current study, the arterial carbon dioxide tension (P{sub a}CO{sub 2}) was changed in order to investigate the tumour vascular response to carbon dioxide. Functional maps of blood flow, blood volume and mean transit time were generated at four P{sub a}CO{sub 2} levels in VX2 tumour in the rabbit thigh and normal soft tissue. The P{sub a}CO{sub 2} levels investigated were normocapnia (P{sub a}CO{sub 2} = 40.9 {+-} 1.2 mmHg), hypocapnia (27.2 {+-} 2.3 and 33.5 {+-} 2.3 mmHg) and hypercapnia (54.9 {+-} 4.4 mmHg). The carbon dioxide reactivity of the global tumour blood flow and mean transit time showed significant differences between normocapnia and the two levels of hypocapnia, but not between normocapnia and hypercapnia. The average fractional change of blood flow from normocapnia for the two levels of hypocapnia was -0.41 {+-} 0.06 and -0.29 {+-} 0.08, respectively (P < 0.05). In the case of mean transit time the fractional change was +0.39 {+-} 0.30 and +0.23 {+-} 0.24, respectively (P < 0.05). The fractional change of blood volume from normocapnia, however, was not significantly different at any capnic level, as was the case with respect to each of the functional parameters in normal tissue. The ability to reduce blood flow and increase mean transit time through hypocapnia has significant implications in thermal therapy, since heat dissipation is a major factor in limiting the effectiveness of treatment.
Winter, Jeff D; Cheng, Hai-Ling Margaret [Research Institute and Diagnostic Imaging, Hospital for Sick Children, Toronto M5G 1X8 (Canada); Akens, Margarete K, E-mail: Hai-Ling.Cheng@sickkids.ca [Division of Orthopaedic Surgery, Orthopaedic Biomechanics Laboratory, Sunnybrook Health Science, Toronto M4N 3M5 (Canada)
2011-03-07
Magnetic resonance imaging (MRI) relaxation times provide indirect estimates of tissue O{sub 2} for monitoring tumour oxygenation. This study provides insight into mechanisms underlying longitudinal (R{sub 1} = 1/T{sub 1}) and transverse effective (R{sub 2}* = 1/T{sub 2}*) relaxation rate changes during inhalation of 100% O{sub 2} and 3%, 6% and 9% CO{sub 2} (balanced O{sub 2}) in a rabbit tumour model. Quantitative R{sub 1}, R{sub 2}*, and dynamic contrast-enhanced (DCE) imaging was performed in six rabbits 12-23 days following implantation of VX2 carcinoma cells in the quadricep muscle. Invasive measurements of tissue partial pressure of O{sub 2} (pO{sub 2}) and perfusion were also performed, which revealed elevated pO{sub 2} levels in all tumour regions for all hyperoxic gases compared to baseline (air) and reduced perfusion for carbogen. During 100% O{sub 2} breathing, an R{sub 1} increase and R{sub 2}* decrease consistent with elevated pO{sub 2} were observed within tumours. DCE-derived blood flow was weakly correlated with R{sub 1} changes from air to 100% O{sub 2}. Further addition of CO{sub 2} (carbogen) did not introduce considerable changes in MR relaxation rates, but a trend towards higher R{sub 1} relative to breathing 100% O{sub 2} was observed, while R{sub 2}* changes were inconsistent. This observation supports the predominance of dissolved O{sub 2} on R{sub 1} sensitivity and demonstrates the value of R{sub 1} over R{sub 2}* for tissue oxygenation measures.
Rogério Saad Hossne
2002-08-01
Full Text Available Os estudos para a investigação de novas modalidades terapêuticas em biologia tumoral, deveriam passar por estudos experimentais prévios. Neste sentido dispõem-se hoje de uma grande variedade de modelos tumorais experimentais; em determinadas investigações faz-se necessária a adequação do modelo tumoral às necessidades biológicas, patológicas e experimentais dos estudos. Desta forma, em nosso serviço, buscávamos um modelo tumoral hepático para estudos experimentais que se adequasse às seguintes características: fácil manipulação, crescimento controlável, evolução e agressividade semelhantes aos seres humanos. Os dados da literatura nos levaram a busca do tumor hepático VX-2, em coelhos. Neste artigo discutimos as vantagens da utilização deste modelo experimental e a sua introdução em nosso país.Studies for investigation of new therapeutic modalities in tumoral biology should be based on previous experimental studies. Then, there are a great variety of tumoral experimental models today. Some investigations have been done necessary an adaptation of the tumoral model to the needing of the studies biological and pathological. So, in our laboratory, we looked for a tumoral hepatic model for experimental studies with the following characteristics: easy manipulation, control of growing, evolution and aggressiveness like to humans. Data of the literature took us the search of the hepatic tumor VX-2, in rabbits. In this article we discussed the advantages of use this experimental model and its introduction in our country. Experimental hepatic tumor (VX-2 in rabbit. Implantation of the model in Brazil.
Irinotecan Loaded in Eluting Beads: Preclinical Assessment in a Rabbit VX2 Liver Tumor Model
Rao, Pramod P.; Pascale, Florentina [Institute Gustave Roussy, Department of Interventional Radiology (France); Seck, Atman [Institute Gustave Roussy, UPRES EA 3535, Pharmacologie et Nouveaux Traitements du Cancer (France); Auperin, Anne [Institute Gustave Roussy, Department of Biostatistics and Epidemiology (France); Drouard-Troalen, Laurence [Institute Gustave Roussy, Department of Biology and Pathology (France); Deschamps, Frederic; Teriitheau, Christophe [Institute Gustave Roussy, Department of Interventional Radiology (France); Paci, Angelo [Institute Gustave Roussy, UPRES EA 3535, Pharmacologie et Nouveaux Traitements du Cancer (France); Denys, Alban; Bize, Pierre [Centre Hospitalier Universitaire Vaudois, Department of Interventional Radiology (Switzerland); Baere, Thierry de, E-mail: debaere@igr.fr [Institute Gustave Roussy, Department of Interventional Radiology (France)
2012-12-15
Purpose: The purpose of this study was to study the pharmacokinetics of irinotecan injected intravenously, intra-arterially, or loaded onto a delivery platform. Material and Methods: Fifty-four New Zealand White rabbits with VX2 liver tumor, divided in 3 groups of 17 rabbits, each received irinotecan either by intravenous (IV) route, intra-arterial hepatic (IA) route, or loaded on drug-eluting beads (DEBIRI). Animals were killed at 1, 6, and 24 h. Irinotecan and SN-38 concentrations were measured at different time points in serum, tumor, and normal liver.ResultsTwelve milligrams of irinotecan were injected IV and IA, whereas 6-16.5 mg were injected loaded onto DEBIRI. Normalized serum irinotecan reached a peak of 333 ng/ml (range 198.8-502.5) for IV, 327.1 ng/ml (range 277.1-495.6) for IA, and 189.7 ng/ml (range 111.1-261.9) for DEBIRI (P < 0.001) delivery. The area-under-the-curve value from 10 to 60 min of serum irinotecan concentration was significantly lower for DEBIRI (P = 0.0009). Tumor irinotecan levels for IV, IA, and DEBIRI (in ng/200 mg of tissue followed by ranges in parentheses) were, respectively, 23.6 (0.3-24.9), 36.5 (7.7-1914.1), and 20.2 (2.9-319) at 1 h; 4.2 (1-27.9), 99.3 (46.6-159.5), and 42.1 (11.3-189) at 6 h; and 2.7 (2.5-6.9), 18.3 (1.5-369.1), and 174.4 (3.4-5147.3) at 24 h (P = 0.02). At 24 h, tumor necrosis was 25% (10-30), 60% (40-91.25), and 95% (76.25-95) for IV, IA, and DEBIRI, respectively (P = 0.03). Conclusion: Compared with IV or IA, DEBIRI induces lower early serum levels of irinotecan, a high and prolonged intratumoral level of irinotecan, and a greater rate of tumor necrosis at 24 h. Further evaluation of the clinical benefit of DEBIRI is warranted.
Chen, Yuk-Kwan; Huang, Anderson Hsien-Cheng; Lin, Li-Min
2014-12-01
Previous studies have demonstrated that spheroid type cells grown under suspension culture conditions have cancer stem cell (CSC) traits in a number of cancers, but this phenomenon has not yet been reported in the VX2 rabbit oral cancer model. Hence, this study aimed to study the spheroid cells from VX2 rabbit buccal squamous cell carcinomas (SCCs) and assess their CSC characteristics. Five adult male New Zealand white outbred rabbits were used to generate VX2 rabbit buccal SCC. Sphere-forming cell culture was performed for the VX2 rabbit buccal SCC specimens. The self-renewal capability; cluster of designation (CD) 44, CD133, acetaldehyde dehydrogenase 1 (ALDH1), B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1), Nestin, octamer-binding transcription factor 4 (Oct4) and reduced expression protein-1 (Rex-1) expression with reverse transcription-polymerase chain reaction (RT-PCR); chemoresistance to cisplatin and 5-fluorouracil; and in vivo tumorigenicity of spheroid cell transplantation in nude mice were evaluated to determine the CSC characteristics of the resulting spheroid cells. We successfully obtained spheroid cells from the VX2 rabbit OSCC tissues. The spheroid cells exhibited CSC traits, including the expression of CSC and stem cell markers (CD44, Bmi-1, Nestin, Oct4 and Rex-1), capacity to generate new spheroid colonies within 1 week of reseeding from single-dissociated spheroid cells, chemoresistance capacity and generation of tumour xenografts (with histological features resembling those of the original VX2 rabbit buccal SCC) from the transplantation of 10(3) undifferentiated spheroid cells into nude mice. In summary, we demonstrated that spheroid cells with CSC cell traits can be derived from VX2 rabbit buccal SCCs, indicating that this animal cancer model is applicable for studying CSCs in human oral cancers.
Yuk-Kwan Chen; Anderson Hsien-Cheng Huang; Li-Min Lin
2014-01-01
Previous studies have demonstrated that spheroid type cells grown under suspension culture conditions have cancer stem cell (CSC) traits in a number of cancers, but this phenomenon has not yet been reported in the VX2 rabbit oral cancer model. Hence, this study aimed to study the spheroid cells from VX2 rabbit buccal squamous cell carcinomas (SCCs) and assess their CSC characteristics. Five adult male New Zealand white outbred rabbits were used to generate VX2 rabbit buccal SCC. Sphere-forming cell culture was performed for the VX2 rabbit buccal SCC specimens. The self-renewal capability;cluster of designation (CD) 44, CD133, acetaldehyde dehydrogenase 1 (ALDH1), B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1), Nestin, octamer-binding transcription factor 4 (Oct4) and reduced expression protein-1 (Rex-1) expression with reverse transcription-polymerase chain reaction (RT-PCR);chemoresistance to cisplatin and 5-fluorouracil;and in vivo tumorigenicity of spheroid cell transplantation in nude mice were evaluated to determine the CSC characteristics of the resulting spheroid cells. We successfully obtained spheroid cells from the VX2 rabbit OSCC tissues. The spheroid cells exhibited CSC traits, including the expression of CSC and stem cell markers (CD44, Bmi-1, Nestin, Oct4 and Rex-1), capacity to generate new spheroid colonies within 1 week of reseeding from single-dissociated spheroid cells, chemoresistance capacity and generation of tumour xenografts (with histological features resembling those of the original VX2 rabbit buccal SCC) from the transplantation of 103 undifferentiated spheroid cells into nude mice. In summary, we demonstrated that spheroid cells with CSC cell traits can be derived from VX2 rabbit buccal SCCs, indicating that this animal cancer model is applicable for studying CSCs in human oral cancers.
Zhang, Long Jiang, E-mail: kevinzhanglongjiang@yahoo.com.cn [Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 210002 (China); Wu, Shengyong, E-mail: cjr.wushengyong@vip.163.com [Institute of Tianjin Medical Imaging, Tianjin 300192 (China); Wang, Mei, E-mail: 281406196@qq.com [Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 210002 (China); Lu, Li, E-mail: xuzhoululi@163.com [Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 210002 (China); Chen, Bo, E-mail: chenbo1985@yahoo.com.cn [Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 210002 (China); Jin, Lixin, E-mail: lixin.jin@siemens.com [Siemens Healthcare, MR Collaboration NE Asia, Shanghai (China); Wang, Jiandong, E-mail: jdwang1216@163.com [Department of Pathology, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 200012 (China); Larson, Andrew C., E-mail: a-larson@northwestern.edu [Department of Radiology, Northwestern University, Chicago, IL (United States); Lu, Guang Ming, E-mail: cjr.luguangming@vip.163.com [Department of Medical Imaging, Jinling Hospital, Clinical School of Medical College, Nanjing University, 305 Zhongshan East Road, Xuanwu District, Nangjing, Jiangsu Province 210002 (China)
2012-08-15
Purpose: To evaluate the correlation between quantitative dual energy CT and perfusion CT measurements in rabbit VX2 liver tumors. Materials and methods: This study was approved by the institutional animal care and use committee at our institution. Nine rabbits with VX2 liver tumors underwent contrast-enhanced dual energy CT and perfusion CT. CT attenuation for the tumors and normal liver parenchyma and tumor-to-liver ratio were obtained at the 140 kVp, 80 kVp, average weighted images and dual energy CT iodine maps. Quantitative parameters for the viable tumor and adjacent liver were measured with perfusion CT. The correlation between the enhancement values of the tumor in iodine maps and perfusion CT parameters of each tumor was analyzed. Radiation dose from dual energy CT and perfusion CT was measured. Results: Enhancement values for the tumor were higher than that for normal liver parenchyma at the hepatic arterial phase (P < 0.05). The highest tumor-to-liver ratio was obtained in hepatic arterial phase iodine map. Hepatic blood flow of the tumor was higher than that for adjacent liver (P < 0.05). Enhancement values of hepatic tumors in the iodine maps positively correlated with permeability of capillary vessel surface (r = 0.913, P < 0.001), hepatic blood flow (r = 0.512, P = 0.010), and hepatic blood volume (r = 0.464, P = 0.022) at the hepatic arterial phases. The effective radiation dose from perfusion CT was higher than that from DECT (P < 0.001). Conclusions: The enhancement values for viable tumor tissues measured in iodine maps were well correlated to perfusion CT measurements in rabbit VX2 liver tumors. Compared with perfusion CT, dual energy CT of the liver required a lower radiation dose.
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^{'}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 ^{3}He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q_{2}, ρ, and C(T) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.
Liu, Junjie; Goddard, Paul A; Singleton, John; Brambleby, Jamie; Foronda, Francesca; Möller, Johannes S; Kohama, Yoshimitsu; Ghannadzadeh, Saman; Ardavan, Arzhang; Blundell, Stephen J; Lancaster, Tom; Xiao, Fan; Williams, Robert C; Pratt, Francis L; Baker, Peter J; Wierschem, Keola; Lapidus, Saul H; Stone, Kevin H; Stephens, Peter W; Bendix, Jesper; Woods, Toby J; Carreiro, Kimberly E; Tran, Hope E; Villa, Cecelia J; Manson, Jamie L
2016-04-01
The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]EF6 (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero-field splitting (ZFS) being observed. The magnetism of 1-4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J⊥) being slightly stronger than the intralayer interaction along Ni-pyz-Ni segments (J(pyz)) within the two-dimensional [Ni(pyz)2](2+) square planes. Regardless of X, J(pyz) is similar for the four compounds and is roughly 1 K.
兔Vx2肝癌改良模型的建立及其DSA影像分析%Vx2 carcinoma model and its DSA imagining features in rabbits
曹玮; 王执民; 张洪新; 王义清; 郭卫平; 李文献; 倪代会; 梁志会; 齐连君
2001-01-01
AIM To establish suitable metastatic rabbit Vx2 liver tumor model for experimental study, probe into different tumor transplanted methods and analyze the DSA (digital substract angiography) imagining features of the liver tumor. METHODS 60 male New Zealand white rabbits were divided into 3 groups at random, 20 in each group. 5×107 Vx2 carcinoma cells were injected via hepatic artery, pecutaneous into liver by syringe needle in the different 2 groups (control groups); the 3rd group (retrofit group) were transplanted tumor tissue mass (about 106～108 carcinoma cells) into liver. Then we observed: ①the success rate of implanting tumor; ②the volume change of tumor by ultrasonograpy (the growth rate of tumor was calculated); ③the biological features of tumor (histopathology and electronic microscope photographs); ④the DSA imagining features of tumor. RESULTS The success rates of transplanting tumor of 3 groups were 7/20, 10/20, 19/20; the retrofit group was the highest of 3 groups (P<0.05). The tumor grew as exponential curve. Histopathology and electronic microscope photographs indicated that tumor grew in the liver tissue and infiltrated into the normal liver tissue, and that it had the similar biological features of squamous cell carcinoma transplanted in other sites of rabbits. The DSA imagining of tumor indicated that the carcinoma had liberal blood vessels. CONCLUSION A retrofit metastatic rabbit Vx2 liver carcinoma model has successfully been set up, The success rate of the method by which tumor tissue mass transplanted is obviously higher than the other two methods. This makes it possible to gain a reliable mature large tumor animal model for study.%目的 建立可供实验研究的稳定的兔Vx2移植性肝癌模型，探讨不同植瘤方式的成功率，并分析该肿瘤的DSA影像特征. 方法 新西兰白兔60只，随机分3组，每组20只. 将Vx2瘤细胞（5×107个）经肝动脉或经肝包膜分别接种于2组兔的肝
Goto, Masato; Ueda, Hiroaki; Michioka, Chishiro; Matsuo, Akira; Kindo, Koichi; Yoshimura, Kazuyoshi
2016-09-01
We have investigated the crystal structure and magnetic properties of three kagome lattice antiferromagnets, Rb2Na Ti3F12 , Cs2Na Ti3F12 , and Cs2K Ti3F12 , using single crystals. These compounds represent a S =1 /2 kagome system consisting of magnetic Ti3 + ions, which is expected to have negligibly small Dzyaloshinsky-Moriya interaction. The structural analyses revealed that each of the three compounds has a slightly distorted kagome lattice. The distortion of the kagome lattice becomes small as the ionic radii of constituent alkali metals increase. All three compounds have nearly the same Weiss temperature of -45 K, and the ground states are disordered and strongly depend on the distortion. The ground states of Rb2Na Ti3F12 , Cs2Na Ti3F12 , and Cs2K Ti3F12 are found to be a two-component state including approximately 1/3 nearly free spins, a gapless disordered state, and a gapped disordered state, respectively. Our experimental results suggest that the ground state of the ideal S =1 /2 Heisenberg kagome lattice antiferromagnet is gapped. In addition, the magnetization curves of Cs2Na Ti3F12 and Cs2K Ti3F12 show anomalies at approximately 1/3 of the full magnetic moment of Ti3 +, which are a notable observation of signs of the theoretically proposed 1/3 magnetization plateau in S =1 /2 kagome antiferromagnets.
Suzuki, K; Tada, I; Okada, K; Kim, Y I; Kobayashi, M
1988-08-01
The effect of intra-arterial infusion of lipiodol-emulsion and local hyperthermia on tissue blood flow was examined in experimental hepatic tumor and normal liver of rabbits. VX-2 tumor was implanted in liver of rabbit. The tissue blood flow was estimated by hydrogen gas clearance method when the tumor grew to about 2 cm. Tissue blood flow in tumor (64.5 ml/min/100 g) was significantly less than in normal liver (90.8 ml/min/100 g) (p less than 0.005). The intra-arterial infusion of lipiodol-emulsion did not alter the flow in either tissue. However, the addition of hyperthermia induced a substantial rise of tissue blood flow in normal liver (35% increase, from 93.8 to 127 ml/min/100 g) when compared with in VX-2 tumor (8.9% increase, from 65.1 to 71.8 ml/min/100 g). These were accompanied by a selective heating of liver tumor; the tumor temperature rose to 43 degrees C, although that of normal liver remained at 38 degrees C. Our results suggested that a specific temperature rise of liver tumor after infusion of lipiodol-emulsion and local heating might be related to a different response of microcirculation in tumor and normal liver to the hyperthermia.
Xiaojuan, Ji; Jinqing, Li; Zhibiao, Wang; Jianzhong, Zou; Wenzhi, Chen; Jin, Bai
2007-05-01
Objective: To assess the value of sonographic appearance and to investigate the sonographic character of VX-2 liver tumor in rabbit treated by high intensity focused ultrasound (HIFU) combined with microbubble contrast agent. Methods: Forty-five rabbits bearing VX-2 tumors were randomly averagely assigned into three groups. In group A irradiation was sustained until the target region became hyperechoic. In group B therapy was stopped as soon as hyperecho occurred, and in group C irradiation time was prolonged to ensure the occurrence of coagulation necrosis. Results: Exposure duration for tumors treated purely with HIFU was the longest, whilst the use of microbubble contrast agent combined with HIFU shortened the exposure duration significantly. The gross examination and ultrasonogram coagulation necrosis area measurements correlated strongly (r=0.986,P<0.05) in the microbubble-enhanced HIFU group. Conclusion: It was feasible to enhance HIFU therapy with microbubble contrast agent. The characteristic change in the ultrasound images made it possible to assess the enhanced HIFU therapeutic efficacy in order to adjust the treatment program.
Pires, A. S. T.
2017-01-01
I present in details the SU(N) Schwinger boson formalism, also known as flavor wave theory, that has been used several times in the literature. I use the method to study the ferroquadrupolar phase of a quantum biquadratic Heisenberg model with spin S=1 on the triangular lattice with third-nearest-neighbor interactions. Results for the phase diagram at zero temperature and the static and dynamical quadrupolar structure factors are presented. In principle, the results could be applied to NiGa2S4.
Jin, Gong Yong; Han, Young Min; Lim, Yeong Su; Jang, Kyu Yun; Lee, Sang Yong; Chung, Gyung Ho [School of Medicine, Chonbuk National Univ., Chonju (Korea, Republic of)
2004-05-01
To evaluate the radiologic findings for complete and partial ablation after percutaneous CT-guided transthoracic radiofrequency ablation (RFA) of lung VX2 tumor implanted in rabbits. Thirteen rabbits with successfully implanted lung VX2 were used. Three rabbits as controls did not receive RFA while the other ten rabbits underwent RFA; 5 complete and 5 partial. RFA was performed using an internally cooled, 17-gauge electrode (Radionics, Burlington, MA) with a 1-cm active tip under CT guidance. Postprocedural CT was performed within 3 days, and we analyzed the ablated size, enhancement pattern, shape, margin, and complications of the complete and partial ablation groups. Rabbits were sacrificed after postprocedural CT with an overdose of ketamine, and pathologic findings of the ablated groups were compared with those of the control group. The size of the ablated lesions and the enhancement pattern differed between the completely and partially ablated groups on chest CT. The size of the ablated lesions was increased by 47.1% in the completely ablated group and by 2.1% in the partially ablated group. In the completely ablated group, VX2 tumor showed absolutely no enhancement, whereas only ablated pulmonary parenchyma outside VX2 showed mild enhancement on enhanced CT. In the partial ablated group, a part of VX2 became strongly enhanced on enhanced CT. On microscopic examination, the completely ablated group demonstrated that a viable tumor cell was not visible. In the partially ablated group, however, a viable tumor cell within the surrounding fibrous capsule on the peripheral area of the VX2 was observed. The important CT findings for evaluation of complete and partial RFA are the ablated size and enhancement pattern of the ablated lesion.
Gong, Shou-Shu; Zhu, W.; Sheng, D. N.; Yang, Kun
2017-05-01
The exotic normal state of iron chalcogenide superconductor FeSe, which exhibits vanishing magnetic order and possesses an electronic nematic order, triggered extensive explorations of its magnetic ground state. To understand its novel properties, we study the ground state of a highly frustrated spin-1 system with bilinear-biquadratic interactions using an unbiased large-scale density matrix renormalization group. Remarkably, with increasing biquadratic interactions, we find a paramagnetic phase between Néel and stripe magnetic ordered phases. We identify this phase as a candidate of nematic quantum spin liquid by the compelling evidences, including vanished spin and quadrupolar orders, absence of lattice translational symmetry breaking, and a persistent nonzero lattice nematic order in the thermodynamic limit. The established quantum phase diagram naturally explains the observations of enhanced spin fluctuations of FeSe in neutron scattering measurement and the phase transition with increasing pressure. This identified paramagnetic phase provides a possibility to understand the novel properties of FeSe.
Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid
2016-10-12
Using the modified spin wave method, we study the [Formula: see text] Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter [Formula: see text]: (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for [Formula: see text], (2) a magnetically gapped disordered state for [Formula: see text], preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for [Formula: see text]. We also explore the phase diagram of a distorted [Formula: see text] model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.
Ghorbani, Elaheh; Shahbazi, Farhad; Mosadeq, Hamid
2016-10-01
Using the modified spin wave method, we study the {{J}1}-{{J}2} Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For a symmetric S = 1/2 model, with the same couplings for all the equivalent neighbors, we find three phases in terms of the frustration parameter \\barα={{J}2}/{{J}1} : (1) a commensurate collinear ordering with staggered magnetization (Néel.I state) for 0≤slant \\barα≲ 0.207 , (2) a magnetically gapped disordered state for 0.207≲ \\barα≲ 0.369 , preserving all the symmetries of the Hamiltonian and lattice, which by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of the three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (Néel.II state), for 0.396≲ \\barα≤slant 1 . We also explore the phase diagram of a distorted {{J}1}-{{J}2} model with S = 1/2. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal phase in addition to the previous three phases found for the undistorted model.
Bhattacharjee, Suraka; Chaudhury, Ranjan
2016-11-01
The generalized spin stiffness constant for a doped quantum antiferromagnet has been investigated both analytically and numerically as a function of doping concentration at zero temperature, based on the strongly correlated t-J model on two-dimensional square lattice. The nature of the theoretical dependence of the stiffness constant on doping shows a striking similarity with that of the effective exchange constant, obtained from the combination of other theoretical and experimental techniques in the low doping region. This correspondence once again establishes that spin stiffness can very well play the role of an effective exchange constant even in the strongly correlated semi-itinerant systems. Our theoretical plot of the stiffness constant against doping concentration in the whole doping region exhibits the various characteristic features like a possible crossover in the higher doping regions and persistence of short range ordering even for very high doping with the complete vanishing of spin stiffness occurring only close to 100% doping. Our results receive very good support from various other theoretical approaches and also brings out a few limitations of some of them. Our detailed analysis highlights the crucial importance of the study of spin stiffness for the proper understanding of magnetic correlations in a semi-itinerant magnetic system described by the strongly correlated t-J model. Moreover, our basic formalism can also be utilized for determination of the effective exchange constant and magnetic correlations for itinerant magnetic systems, in general in a novel way.
Chowdhury, Rajeswari Roy; Dhara, Susmita; Bandyopadhyay, Bilwadal
2015-06-01
In PrCo2Si2 and NdCo2Si2, Co has been partially substituted by V. Vanadium having a larger atomic radius than cobalt, the substitution results in a negative pressure affecting the magnetic properties of the compound. The samples RE(Co1-xVx)2Si2 (RE = Pr, Nd; x = 0, 0.20, 0.35) were prepared by melting the corresponding elements in arc furnace and characterized using x-ray diffraction. Magnetometric measurements show that the parent compounds PrCo2Si2 and NdCo2Si2 are antiferromagnetic, as reported. With doping, ferrimagnetic behaviour is observed from temperature dependence of inverse susceptibility at about 50 K. At lower than 30 K, the magnetizations tend to saturate at high fields. From the field dependence of magnetization, the hysteresis loops and also coercive fields as observed, the samples exhibit ferromagnetism below ˜ 30 K. Exchange bias effect is also observed in the high V containing sample. The specific heat studies of the samples show transitions consistent with the magnetization data. Pr(Co0.65V0.35)2Si2 and Nd(Co0.65V0.35)2Si2 show magnetoresistance (MR) of ˜ 25% and 15%, respectively, at 4 K and 9 tesla.
周悦; 高剑波; 杨学华; 张永高; 岳松伟; 曲艳红
2011-01-01
Aim:To assess the diagnostic value of Muhi-slice CT perfusion for blood supply evaluation of the rabbits VX2 hepatic tumors. Methods: VX2 hepatic carcinoma mass were implanted into the left lobe of liver of 30 rabbits via laparotomic route. Multi-slice CT enhancement and perfusion were performed in these rabbits at twenty-one day after implantation. The CT imaging features of the tumors were observed and the perfusion parameters were measured in the rim of the tumor, non-tumorous regions nearby the tumor and the normal liver tissues. Results: Twenty-five (83％) rabbits were sucessfully implanted with the tumor. The tumors which has smooth border were demostrated itself as the round-shaped tumors with hypodensity on plain CT scan,significantly tinge-enhancement on arterial phase, relatively hypodensity on portal phase and no enhanced in the zone of necrosis. Blood flow, blood volume, permeability surface, hepatic arterial fraction, hepatic arterial perfusion increased and mean transit time decreased in the rim of the tumor compared with those of the non-normorous regions nearby the tumor and the normal liver ( P ＜ 0.05). Conclusion: Multi-slice CT perfusion could evaluate the blood supply station of hepatic tumors in vivo by perfusion parameters.%目的:探讨多排螺旋CT灌注成像对兔VX2肝癌血供的评价价值.方法:采用开腹瘤组织块直接包埋法将VX2肝癌移植瘤植入30只新西兰大白兔肝左叶,并于种植后第21天行多排螺旋CT增强及灌注扫描,观察其CT征象,并对比肿瘤边缘区、瘤旁肝组织以及对照肝组织的CT灌注参数(血流量、血容量、平均通过时间、表面通透性、肝动脉分数以及肝动脉灌注量).结果:25只(83%)大白兔种植成功.CT平扫肿瘤为类圆形低密度灶;增强动脉期病灶表现为边缘环状强化;门脉期呈相对低密度,中心见低密度坏死区,与周围组织界限较清.CT灌注成像结果:肿瘤边缘区、瘤旁肝组织及对照肝
Suh, B J
2000-01-01
A comprehensive analysis of the sup 3 sup 5 Cl nuclear magnetic resonance (NMR) relaxation data in Sr sub 2 CuO sub 2 Cl sub 2 single crystals is presented. Both the spin-lattice relaxation rate, T sub 1 sup - sup 1 (=2W), and the spin-spin relaxation rate, T sub 2 sup - sup 1 , show a crossover of the spin dimensionality well above the Neel temperature T sub N. The crossover is due to easy-plane anisotropy and is apparently signaled by the partial suppression of the Cu sup 2 sup + spin fluctuations along the tetragonal c-axis. By analyzing 2W for H ll c in terms of the critical behavior of the spin correlation length, we estimate the temperature for the crossover of the Cu sup 2 sup + spin correlations from Heisenberg to XY-like behavior to be T approx =290 K.
F Keshavarz
2017-02-01
Full Text Available In this study, the effect of four-spin exchanges between the nearest and next nearest neighbor spins of honeycomb lattice on the phase diagram of S=3/2 antiferomagnetic Heisenberg model is considered with two-spin exchanges between the nearest and next nearest neighbor spins. Firstly, the method is investigated with classical phase diagram. In classical phase diagram, in addition to Neel order, classical degeneracy is also seen. The existance of this phase in diagram phase is important because of the probability of the existence of quantum spin liquid in this region for such amount of interaction. To investigate the effect of quantum fluctuation on the stability of the obtained classical phase diagram, linear spin wave theory has been used. Obtained results show that in classical degeneracy regime, the quantum fluctuations cause the order by disorder in the spin system and the ground state is ordered
Yubao Liu
Full Text Available To evaluate the value of DWI in detecting the lesions of pre- and post-radiofrequency ablation (RFA of the rabbit liver VX2 tumors.Twenty-two New Zealand White rabbits were tested. The protocol was approved by the Committee on the Ethics of Animal Experiments. Twenty separate tumor fragments were implanted into the livers of 20 rabbits, the liver was exposed by performing midline laparotomy. 3.0T MR DWI (b = 0, 200, 400, 600, 800,1000 s/mm2 were performed 14-21 days after tumor implantation (mean, 17 days in the 18 tumor-bearing animals. Then RFA was performed in the 18 tumor-bearing animals and in the two healthy animals. 3.0T MR DWI was performed 7-10 days after RFA (mean, 8 days. Pathology exam was performed immediately after the completion of post- RFA MR imaging. Analyzing the features of MRI and ADC values in the pre- and post- RFA lesions of the VX2 tumors, and histopathologic results were compared with imaging findings.The difference of ADC value between viable tumor and normal liver parenchyma was significant (P<.001. After RFA, when b = 200, 400, 600, 800, 1000 s/mm2, the differences of ADC values of viable tumor, granulation tissue, necrosis, normal liver parenchyma were significant (P<.001. At the time the animals were sacrificed after RFA and MR imaging, histopathologic results of local viable tumors were found in 9 (50% of the 18 treated tumors. Macroscopic viable tumors were found at the RFA sites in 3 (17%, all 3 macroscopic viable tumors were visualized at the periphery of the RFA areas.3.0T MR DWI can be used to follow up the progress of the RFA lesion, it is useful in detecting different tissues after RFA, and it is valuable in the further clinical research.
Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F. L.; Chantrell, Roy W.; Jeng, Horng-Tay
2016-01-01
We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0 μB. The GGA plus on-site Coulomb interaction U (GGA + U) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics. PMID:27601195
Wen-Hua Du; Wei-Xiao Yang; Xiang Wang; Xiu-Qin Xiong; Yi Zhou; Tao Li
2003-01-01
AIM: To investigate the possible clinical application value of second harmonic imaging under low acoustic pressure.METHODS: Six New Zealand rabbits, averaging 2.7±0.4kg, were selected and operated upon to construct hepatic VX2 tumor carrier model. Hepatic VX2 tumors were imaged with B mode Ultrasonography (US), and second harmonic imaging (SHI) under high mechanic index (1.6) and low mechanic index (0.1). Echo agent was intravenously injected through ear vein at a dose of 0.01 mL/kg under B mode US and high MI SHI, and 0.05 mL/kg under low MI SHI, and then the venous channel was cleaned with sterilized saline.All the images were recorded by magnetic optics (MO),and they were analyzed further by at least two independent experienced sonographers.RESULTS: Totally 6 hypoechoic and 3 hyperechoic lesions were found in the six carrier rabbits with a mean size about 2.1±0.4 under B mode ultrasound, they were oval or round in shape with a clear outline or a hypoechoic halo at the margin of the lesions. Contrast agent could not change the echogenicity of the lesions under B mode US and SHI under high acoustic pressure. However, it could greatly increase the real time visualization sensitivity of the lesions with SHI under low acoustic pressure.CONCLUSION: Our results suggest that contrast enhanced SHI with low MI and a bubble non-destructive method would be much more helpful than conventional SHI in our future clinical applications.
The electronic structure of antiferromagnetic chromium
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...
Refaat, Tamer; West, Derek; El Achy, Samar; Parimi, Vamsi; May, Jasmine; Xin, Lun; Harris, Kathleen; Liu, William; Wanzer, Michael; Finney, Lydia; Maxey, Evan; Vogt, Stefan; Omary, Reed; Procissi, Daniele; Larson, Andrew; Paunesku, Tatjana; Woloschak, Gayle
2016-08-03
This work compares intravenous (IV) versus fluoroscopy-guided transarterial intra-catheter (IC) delivery of iron oxide core-titanium dioxide shell nanoparticles (NPs) in vivo in VX2 model of liver cancer in rabbits. NPs coated with glucose and decorated with a peptide sequence from cortactin were administered to animals with developed VX2 liver cancer. Two hours after NPs delivery tumors, normal liver, kidney, lung and spleen tissues were harvested and used for a series on histological and elemental analysis tests. Quantification of NPs in tissues was done both by bulk inductively coupled plasma mass spectrometry (ICP-MS) analysis and by hard X-ray fluorescence microscopy. Both IV and IC NPs injection are feasible modalities for delivering NPs to VX2 liver tumors with comparable tumor accumulation. It is possible that this is an outcome of the fact that VX2 tumors are highly vascularized and hemorrhagic, and therefore enhanced permeability and retention (EPR) plays the most significant role in accumulation of nanoparticles in tumor tissue. It is, however, interesting to note that IV delivery led to increased sequestration of NPs by spleen and normal liver tissue, while IC delivery lead to more NP positive Kupffer cells. This difference is most likely a direct outcome of blood flow dynamics. Armed with this knowledge about nanoparticle delivery, we plan to test them as radiosensitizers in the future.
Tamer Refaat
2016-08-01
Full Text Available This work compares intravenous (IV versus fluoroscopy-guided transarterial intra-catheter (IC delivery of iron oxide core-titanium dioxide shell nanoparticles (NPs in vivo in VX2 model of liver cancer in rabbits. NPs coated with glucose and decorated with a peptide sequence from cortactin were administered to animals with developed VX2 liver cancer. Two hours after NPs delivery tumors, normal liver, kidney, lung and spleen tissues were harvested and used for a series on histological and elemental analysis tests. Quantification of NPs in tissues was done both by bulk inductively coupled plasma mass spectrometry (ICP-MS analysis and by hard X-ray fluorescence microscopy. Both IV and IC NPs injection are feasible modalities for delivering NPs to VX2 liver tumors with comparable tumor accumulation. It is possible that this is an outcome of the fact that VX2 tumors are highly vascularized and hemorrhagic, and therefore enhanced permeability and retention (EPR plays the most significant role in accumulation of nanoparticles in tumor tissue. It is, however, interesting to note that IV delivery led to increased sequestration of NPs by spleen and normal liver tissue, while IC delivery lead to more NP positive Kupffer cells. This difference is most likely a direct outcome of blood flow dynamics. Armed with this knowledge about nanoparticle delivery, we plan to test them as radiosensitizers in the future.
韩世龙; 朱晓黎; 张猛; 郭永团; 徐云华
2013-01-01
目的 观察臭氧局部注射治疗实体肿瘤的安全性、对肝肾功能的影响及所致的组织病理学改变.方法 建立兔VX2移植瘤模型24只,分为三组,A、B组均为9只,C组6只(假手术组).向A、B组瘤内分别注入40 μg/ml和70 μg/ml浓度臭氧,并于术前1d、术后1、3d抽静脉血.术后3d处死动物,取病理标本.观察术后动物生命体征、并发症及大体标本的组织学变化.结果 实验动物术后24 h内均出现活动减少、纳差,对刺激反应差,精神萎靡,24 h后恢复正常.A、B组各有1只荷瘤兔于术中或术后1h内死亡.术前1d,术后1、3d各组血清丙氨酸转氨酶、天冬氨酸转氨酶及肌酐比较无明显差异.肉眼及光镜下见A、B组坏死区大体标本无明显差异.C组镜下可见部分肿瘤细胞突破肌层向深处生长,肿瘤细胞排列紊乱,大量癌巢形成,细胞核大深染,核分裂,异性核.结论 VX2肿瘤内注入浓度为40 μg/ml和70μg/ml的医用臭氧安全、有效.%Objective To evaluate the safety and effectiveness of percutaneous medical ozone injection in treating solid transplanted VX2 tumors in rabbits, and to discuss the histopathological changes cause by ozone injection. Methods Transplanted VX2 tumor model was established in 24 rabbits. The rabbits were randomly divided into three groups. Rabbits in group A (n = 9) received medical ozone (40 μg/ ml) injection of the tumor. Rabbits in group B (n = 9) received medical ozone (70 μg/ml) injection of the tumor. Rabbits in group C (n = 6, used as sham group) received no treatment. The serum AIT, AST and Cr levels were determined at one day before and one, three days after the treatment. All the animals were sacrificed at three days after the treatment. The specimens were collected and sent for pathological examination. After the procedure, careful observation of animal's vital signs, complications was executed, and the pathological findings were recorded. Results After the treatment
崔磊; 龚沈初; 何书; 尹剑兵; 杨巨顺; 杨红
2011-01-01
Purpose To prospectively evaluate the reproducibility of CT perfusion parameters in rabbits with implanted VX2 lung tumors. Materials and Methods Perfusion CT was performed twice with 24-hour interval in 10 New Zealand White rabbits with implanted VX2 lung tumors. The volume, maximum diameter, blood volume (B V), Blood flow (BF), Time to peak (TTP), Permeability surface (PS), Patlak BV (PBV), Patlak R square (PatRsq) and Patlak Residual (PatRea) were measured, and reproducibility was evaluated using Bland-Altman statistics. Results CT perfusion parameters showed good agreement between two perfusion examinations. Intragroup correlation coefficients (ICCs) were all more than 0.6, within-subject coefficient of variation (WCV) was from 10.8% to 30.2%. The WCV of PS (10.8%) and PBV (12.3%) showed excellent agreement between studies comparable to the WCV of volume (8.5%) and maximum diameter (10.0%). Conclusion The trial confirms that lung tumor perfusion CT yields a good reproducibility and a range of reference values for CT perfusion parameters.%目的 前瞻性评估兔VX-2肺种植肿瘤CT灌注检查测量参数的可重复性.材料与方法 10只肺种植肿瘤的新西兰大白兔行2次CT灌注检查(间隔24h),分别测量肿瘤体积、最大径、血容量、血流量、达峰时间、表面通透性(PS)、Patlak血容量(PBV)、Patlak R方程(PatRsq)及Patlak残差(PatRes).使用Bland-Altman法分析2组CT测量数据的可重复性.结果 2次CT检查所有的CT灌注参数均显示较好的一致性,组内相关系数(ICC)均＞0.6,个体间变异系数(WCV) 10.8％～30.2％.其中,PS和PBV的WCV分别为10.8％和12.3％,与CT形态学指标体积及最大径相仿(8.5％和10.0％).结论 通过动物实验验证了肺种植肿瘤CT灌注的可重复性,初步确定了CT灌注参数变化的参考值范围,为进一步研究提供了实验数据.
Quantum Entanglement in Heisenberg Antiferromagnets
Subramanian, V
2004-01-01
Entanglement sharing among pairs of spins in Heisenberg antiferromagnets is investigated using the concurrence measure. For a nondegenerate S=0 ground state, a simple formula relates the concurrence to the diagonal correlation function. The concurrence length is seen to be extremely short. A few finite clusters are studied numerically, to see the trend in higher dimensions. It is argued that nearest-neighbour concurrence is zero for triangular and Kagome lattices. The concurrences in the maximal-spin states are explicitly calculated, where the concurrence averaged over all pairs is larger than the S=0 states.
兔VX2脑瘤血管生成的灌注CT研究%Experimental study on angiogenesis in rabbit VX2 brain tumor using perfusion CT
康立清; 张云亭; 孙世梅
2006-01-01
Objective: To study the perfusion CT features of rabbit VX2 brain tumor with correlation to MVD and VEGF, and to validate perfusion CT for reflection of tumor angiogenesis. Methods: Rabbit VX2 brain tumor model was established by injection of 100 μL viable tumor cells (107/mL) through a 2 mm-hole 5 mm to the right of the sagittal suture and 5 mm posterior to the coronal suture bored by dental drill. MRI was performed every 2 days after seven days of implantation to evaluate the growth of the tumor. Twenty New Zealand White rabbits with tumor size over 3 mm in diameter were randomly divided into 2 groups according to the tumor growth time with those less than 3 weeks as group 1 and those more than 3 weeks as group 2, and perfusion CT were performed accordingly. CT measurements of BV, BF and PS from tumor, peritumor and contralateral normal tissue regions were obtained. After that the animals were sacrificed and 2% Evans blue (2 mL/kg) was given intravenously in 16 of these animals 1 h prior to sacrifice to detect breakdown of the blood brain barrier. VEGF and MVD were evaluated in immunohistochemical examination of the specimens. Results: Tumor had significantly higher BV, BF and PS (P=0.000) than peritumor and normal tissue region. Tumor BV, BF and MVD in group 2 were significantly higher than that in group 1 (P＜0.01).Significant linear correlation was found between MVD and BV (t=0.915, P=0.000), MVD and BF (r=0.901, P=0.000), and MVD and PS (r=0.459, P=0.042). We also found a rank correlation between PS and blue stain of tumor (rs=0.861, P=0.000). Conclusion: Perfusion CT can distinguish tumor from peritumor and normal tissue clearly, reflect tumor angiogenesis accurately, and provide useful information for the evaluation of brain tumor.
Frustrated 3×3 Heisenberg antiferromagnets
Moustanis, P. N.
2016-08-01
The full energy spectrum and the exact thermodynamic results of the antiferromagnetic Heisenberg Hamiltonian of the 3×3 triangular and the frustrated square lattice with periodic boundary conditions and s=1/2 are obtained. To this end the method of hierarchy of algebras is employed. It was found that the ground state of the 3×3 frustrated square lattice is a Resonating Valence Bond (RVB) state. Thermodynamic properties, like the specific heat, magnetic susceptibility, the thermal average of the square of the total Sz and entropy, for these two lattices are presented.
Cao Wei [Department of Interventional Radiology, Tangdu Hospital, Fourth Military Medical University, No.1 Xinshi Road, Shaanxi Province, Xi' an 710038 (China)], E-mail: zjfurong2008@126.com; Wan Yi [Department of Health Statistics, Fourth Military Medical University, No. 17 West Changle Road, Xi' an 710032 (China); Liang Zhihui [Department of Radiology, Bethune International Peace Hospital, Shijiazhuang, Hebei Province 050082 (China); Duan Yunyou; Liu Xi [Department of Ultrasonography, Tangdu Hospital, Fourth Military Medical University, No. 1 Xinshi Road, Xi' an 710038 (China); Wang Zhimin; Liu Yiyong; Zhu Jia; Liu Xiongtao [Department of Interventional Radiology, Tangdu Hospital, Fourth Military Medical University, No.1 Xinshi Road, Shaanxi Province, Xi' an 710038 (China); Zhang Hongxin [Department of Interventional Radiology, Tangdu Hospital, Fourth Military Medical University, No.1 Xinshi Road, Shaanxi Province, Xi' an 710038 (China)], E-mail: cawe-001@163.com
2010-02-15
Purpose: To evaluate the therapeutic effect of heated (60 deg. C) lipiodol via hepatic artery administration in a rabbit model of VX2 liver cancer. Materials and methods: Thirty male New Zealand white rabbits were randomly divided into three groups with 10 rabbits assigned to each group. VX2 carcinoma cells were surgically implanted into the left hepatic lobe. The tumors were allowed to grow for 2 weeks, and studies were performed until the diameter of the tumors detected by ultrasonograph reached 2-3 cm. Under anesthesia, trans-catheter hepatic arterial embolization was performed and doxorubicin-lipiodol (37 deg. C) (1 mL), lipiodol (60 deg. C) (1 mL) or control (physiological saline (37 deg. C) (1 mL)) solution was injected into the hepatic arteries of animals in the three groups. One week later, the volume of the tumor was measured by ultrasonograph again. The serum of all rabbits was collected before injection and at 4 and 7 days after injection, and the level of aspartate aminotransferase (AST) was checked. The survival period of the three groups of rabbits after treatment was also recorded. During the last course of their disease, the rabbits were given analgesics to relieve suffering. Results: The tumor growth rate in the lipiodol (60 deg. C) group (0.92 {+-} 0.21, tumor volume from 1811 {+-} 435 to 1670 {+-} 564 mm{sup 3}) was significantly lower than that in the control group (3.48 {+-} 1.17, tumor volume from 1808 {+-} 756 to 5747 {+-} 1341 mm{sup 3}) (P < 0.05) and in the doxorubicin-lipiodol (37 deg. C) group (1.69 {+-} 0.26, tumor volume from 1881 {+-} 641 to 2428 {+-} 752 mm{sup 3}) (P < 0.05). Consequently, the survival period of the animals in the lipiodol (60 deg. C) group (41.0 {+-} 3.0 days) was significantly greater than that in the doxorubicin-lipiodol (37 deg. C) group (38.0 {+-} 2.5 days) (P < 0.05). On the other hand, there was no statistically significant difference in serum AST levels between the lipiodol (60 deg. C) group (148.2 {+-} 11
Vali, Mustafa; Vossen, Josephina A; Buijs, Manon; Engles, James M; Liapi, Eleni; Ventura, Veronica Prieto; Khwaja, Afsheen; Acha-Ngwodo, Obele; Ganapathy-Kanniappan, Shanmugasundaram; Shanmugasundaram, Ganapathy; Syed, Labiq; Wahl, Richard L; Geschwind, Jean-Francois H
2008-10-01
The aim of this study was to determine the biodistribution and tumor targeting ability of (14)C-labeled 3-bromopyruvate ([(14)C]3-BrPA) after i.a. and i.v. delivery in the VX2 rabbit model. In addition, we evaluated the effects of [(14)C]3-BrPA on tumor and healthy tissue glucose metabolism by determining (18)F-deoxyglucose (FDG) uptake. Last, we determined the survival benefit of i.a. administered 3-BrPA. In total, 60 rabbits with VX2 liver tumor received either 1.75 mM [(14)C]3-BrPA i.a., 1.75 mM [(14)C]3-BrPA i.v., 20 mM [(14)C]3-BrPA i.v., or 25 ml of phosphate-buffered saline (PBS). All rabbits (with the exception of the 20 mM i.v. group) received FDG 1 h before sacrifice. Next, we compared survival of animals treated with i.a. administered 1.75 mM [(14)C]3-BrPA in 25 ml of PBS (n = 22) with controls (n = 10). After i.a. infusion, tumor uptake of [(14)C]3-BrPA was 1.8 +/- 0.2% percentage of injected dose per gram of tissue (%ID/g), whereas other tissues showed minimal uptake. After i.v. infusion (1.75 mM), tumor uptake of [(14)C]3-BrPA was 0.03 +/- 0.01% ID/g. After i.a. administration of [(14)C]3-BrPA, tumor uptake of FDG was 26 times lower than in controls. After i.v. administration of [(14)C]3-BrPA, there was no significant difference in tumor FDG uptake. Survival analysis showed that rabbits treated with 1.75 mM 3-BrPA survived longer (55 days) than controls (18.6 days). Intra-arterially delivered 3-BrPA has a favorable biodistribution profile, combining a high tumor uptake resulting in blockage of FDG uptake with no effects on healthy tissue. The local control of the liver tumor by 3-BrPA resulted in a significant survival benefit.
Krijn P van Lienden; Lisette T Hoekstra; Jessica D van Trigt; Joris J Roelofs
2013-01-01
BACKGROUND: Portal vein embolization not only induces hypertrophy of the non-embolized liver, but also enhances tumor growth. The latter could be prevented by embolizing the hepatic arteries supplying the tumor-bearing liver segments. This study aimed to determine the effects of transcatheter arterial embolization (TAE) on tumor volume and liver regeneration in a rabbit VX2 tumor model. METHODS: Twenty-three rabbits underwent subcapsular tumor implantation with a VX2 tumor. Two weeks after implantation, 18 rabbits were used for TAE experiments, 5 were for sham controls. Tumor response and liver regeneration response of the embolized cranial and non-embolized caudal liver lobes were assessed by CT volumetry, liver to body weight index, and the amount of proliferating hepatocytes. RESULTS: All super-selective arterial tumor embolization procedures were performed successfully. Despite embolization, the tumor volume increased after an initial steady state. The tumor volume after embolization was smaller than that of the sham group, but this difference was not significant. Massive necrosis of the tumor, however, was seen after embolization, without damage of the surrounding liver parenchyma. There was a significant atrophy response of the tumor bearing cranial lobe after super-selective arterial embolization of the tumor with a concomitant hypertrophy response of the non-embolized, caudal lobe. This regeneration response was confirmed histologically by a
Treatment of (131)I-labeled anti-CD147 monoclonal antibody in VX2 carcinoma-induced liver tumors.
Niu, Huanzhang; Wang, Ruihua; Cheng, Jingliang; Gao, Shegan; Liu, Baoping
2013-07-01
Hepatocellular carcinoma (HCC) is a major health problem worldwide. CD147 has been reported to be overexpressed in HCC and blocking CD147 expression can decrease tumor growth. (131)I is often used in combination with other drugs to treat HCC and yields positive results. In this study, we combined the (131)I and CD147 monoclonal antibody to treat HCC in a rabbit VX2 animal model. In the (131)I-labeled CD147 antibody ((131)I-CD147-Ab) treatment group, the animals lived considerably longer than the animals in the other treatment groups. Metastasis and tumor growth in the (131)I-CD147-Ab treatment group were also inhibited. MMP2 and CD31 expression were significantly lower in the treatment group, whereas Tunel staining was overexpressed. These findings suggest that (131)I-CD147-Ab is a promising drug in the treatment of HCC, by inhibiting metastasis and growth and by decreasing the expression of MMP2 and CD31 or by inducing tumor necrosis. After testing the biochemical parameters, (131)I-CD147-Ab caused fewer side-effects in the animals.
Sera, A.; Kousaka, Y.; Akimitsu, J.; Sera, M.; Kawamata, T.; Koike, Y.; Inoue, K.
2016-12-01
We have performed the detailed investigations of the magnetization of the S =1/2 triangular-lattice antiferromagnets Ba3CoSb2O9 and CsCuCl3 with a 120∘ spin structure in the a b plane. In Ba3CoSb2O9 , the magnetic susceptibility (χ ) exhibits a broad maximum above the Néel temperature (TN) as is expected in the low-dimensional antiferromagnet (AFM). In CsCuCl3, χ exhibits a continuous increase down to TN as if it is the three-dimensional AFM. This is induced by the strong ferromagnetic (FM) interaction along the c axis. The magnetic phase diagrams are also very different. Although the transition field from the umbrella to the 2-1-coplanar phase (Hu -c) for H ∥c is almost independent of temperature in Ba3CoSb2O9 , it shows a considerable decrease with increasing temperature in CsCuCl3. The temperature independent Hu -c in Ba3CoSb2O9 originates from the magnetic anisotropy from the van Vleck contribution, which does not depend so much on the temperature. The temperature dependent Hu -c in CsCuCl3 originates from the magnetic anisotropy from the Dzyaloshinskii-Moriya (DM) interaction, which decreases with increasing temperature. For H ∥a b , the clear transition from the Y-coplanar to the up-up-down (u u d ) phase was observed in Ba3CoSb2O9 but not in CsCuCl3. While the reentrant behavior of TN originating from the thermal and quantum spin fluctuations is observed in both compounds, it is pronounced in Ba3CoSb2O9 but small in CsCuCl3. These differences originate from the existence or nonexistence of the DM interaction. The DM interaction in CsCuCl3 suppresses those fluctuations in the a b plane, leading to the less pronounced reentrant behavior of TN and the broad crossover in place of the phase transition. We analyzed the anisotropic magnetization of Ba3CoSb2O9 in the paramagnetic region by the mean field calculation. The spin-orbit (SO) coupling, the uniaxial crystalline electric field, and the isotropic exchange interaction were taken into account. We
Interferometric phase-contrast X-ray CT imaging of VX2 rabbit cancer at 35keV X-ray energy
Takeda, Tohoru; Wu, Jin; Tsuchiya, Yoshinori; Yoneyama, Akio; Lwin, Thet-Thet; Hyodo, Kazuyuki; Itai, Yuji
2004-05-01
Imaging of large objects at 17.7-keV low x-ray energy causes huge x-ray exposure to the objects even using interferometric phase-contrast x-ray CT (PCCT). Thus, we tried to obtain PCCT images at high x-ray energy of 35keV and examined the image quality using a formalin-fixed VX2 rabbit cancer specimen with 15-mm in diameter. The PCCT system consisted of an asymmetrically cut silicon (220) crystal, a monolithic x-ray interferometer, a phase-shifter, an object cell and an x-ray CCD camera. The PCCT at 35 keV clearly visualized various inner structures of VX2 rabbit cancer such as necrosis, cancer, the surrounding tumor vessels, and normal liver tissue. Besides, image-contrast was not degraded significantly. These results suggest that the PCCT at 35 KeV is sufficient to clearly depict the histopathological morphology of VX2 rabbit cancer specimen.
Jung Im Kim
2014-01-01
Full Text Available Objectives. To perform dual analysis of tumor perfusion and glucose metabolism using perfusion CT and FDG-PET/CT for the purpose of monitoring the early response to bevacizumab therapy in rabbit VX2 tumor models and to assess added value of FDG-PET to perfusion CT. Methods. Twenty-four VX2 carcinoma tumors implanted in bilateral back muscles of 12 rabbits were evaluated. Serial concurrent perfusion CT and FDG-PET/CT were performed before and 3, 7, and 14 days after bevacizumab therapy (treatment group or saline infusion (control group. Perfusion CT was analyzed to calculate blood flow (BF, blood volume (BV, and permeability surface area product (PS; FDG-PET was analyzed to calculate SUVmax, SUVmean, total lesion glycolysis (TLG, entropy, and homogeneity. The flow-metabolic ratio (FMR was also calculated and immunohistochemical analysis of microvessel density (MVD was performed. Results. On day 14, BF and BV in the treatment group were significantly lower than in the control group. There were no significant differences in all FDG-PET-derived parameters between both groups. In the treatment group, FMR prominently decreased after therapy and was positively correlated with MVD. Conclusions. In VX2 tumors, FMR could provide further insight into the early antiangiogenic effect reflecting a mismatch in intratumor blood flow and metabolism.
Li, Hong; Gong, Jian; Jiang, Xuyuan; Shao, Haibo
2013-02-01
To investigate the role of tumor apoptosis-inhibitory protein survivin in arsenic trioxide-induced apoptosis in VX-2 carcinoma in the rabbit liver by means of transcatheter arterial chemoembolization. Sixteen rabbits with 32 implanted hepatic VX-2 tumors were randomly divided into two groups. The experimental group received 2 mg of arsenic trioxide and 1 mL of ultra-fluid lipiodol co-injected via hepatic arterial cannulation and the control group received only 1 mL of lipiodol. Animals were sacrificed 3 weeks after trans-catheterial arterial chemoembolization. Tumor tissue and tumor-peripheral tissue were collected for analysis. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling staining was used to assess tumor cells apoptosis. Immunohistochemistry was used to assess the presence of survivin protein. Reverse transcription polymerase chain reaction was used to determine the expression of survivin gene. The number of apoptotic cells significantly increased in the tumor tissue (5.20 ± 0.60%) compared to tumor-peripheral tissue (1.29 ± 0.42%) of the arsenic trioxide-treated group. Survivin expression levels in the tumor tissue were significantly reduced in arsenic trioxide-treated group (7.68 ± 0.65) compared to the control group (35.30 ± 4.63). Transcatheter arterial chemoembolization with arsenic trioxide induced apoptosis of VX-2 carcinoma, in which tumor apoptosis-inhibitory protein survivin may have played a role.
Jingfeng Zhang; Renfa Wang; Min Wang; Jing Zhang; Jinmei Sang
2005-01-01
Objective: To perform a contrast investigation of multi-slice spiral CT (MSCT) perfusion imaging and pathological findings in VX2 soft-tissue tumor of rabbits, and discuss the applicative value of multi-slice spiral CT perfusion imaging in soft-tissue tumors. Methods: 8 Newzealand white rabbits were implanted with 0.1 ml VX2 tumor tissue suspension in bilateral proximal thighs. 14 days and 21 days later, CT plain scan and perfusion scan were performed on these rabbits respectively, then the images were transmitted to AW4.0 workstation, the functional maps and perfusion parameters including blood flow (BF), blood volume (BV), mean transit time(MTT) and permeability surface (PS) were computed and analyzed. Subsequently, the rabbits were sacrificed, the tumors of which were taken out for pathological examination. The correlation between MSCT functional parametric images and pathological findings was analyzed.Results: All the values of BF, BV and PS of VX2 soft-tissue tumors were obviously higher while the MTT-values were lower than those of the normal muscular tissues significantly ( P ＜ 0.001). Conclusion: Multi-slice spiral CT perfusion imaging is an accurate, convenient and relatively safe functional imaging technique, which can give a quantitative assessment to blood perfusion and angiogenesis of soft-tissue tumors.
Arterial embolization hyperthermia using As2O3 nanoparticles in VX2 carcinoma-induced liver tumors.
Hui Yu
Full Text Available BACKGROUND: Combination therapy for arterial embolization hyperthermia (AEH with arsenic trioxide (As(2O(3 nanoparticles (ATONs is a novel treatment for solid malignancies. This study was performed to evaluate the feasibility and therapeutic effect of AEH with As(2O(3 nanoparticles in a rabbit liver cancer model. The protocol was approved by our institutional animal use committee. METHODOLOGY/PRINCIPAL FINDINGS: In total, 60 VX(2 liver-tumor-bearing rabbits were randomly assigned to five groups (n = 12/group and received AEH with ATONs (Group 1, hepatic arterial embolization with ATONs (Group 2, lipiodol (Group 3, or saline (Group 4, on day 14 after tumor implantation. Twelve rabbits that received AEH with ATONs were prepared for temperature measurements, and were defined as Group 5. Computed tomography was used to measure the tumors' longest dimension, and evaluation was performed according to the Response Evaluation Criteria in Solid Tumors. Hepatic toxicity, tumor necrosis rate, vascular endothelial growth factor level, and microvessel density were determined. Survival rates were measured using the Kaplan-Meier method. The therapeutic temperature (42.5°C was obtained in Group 5. Hepatotoxicity reactions occurred but were transient in all groups. Tumor growth was delayed and survival was prolonged in Group 1 (treated with AEH and ATONs. Plasma and tumor vascular endothelial growth factor and microvessel density were significantly inhibited in Group 1, while tumor necrosis rates were markedly enhanced compared with those in the control groups. CONCLUSIONS: ATON-based AEH is a safe and effective treatment that can be targeted at liver tumors using the dual effects of hyperthermia and chemotherapy. This therapy can delay tumor growth and noticeably inhibit tumor angiogenesis.
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.
Spatially anisotropic Heisenberg kagome antiferromagnet
Apel, W.; Yavors'kii, T.; Everts, H.-U.
2007-04-01
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the {\\mathrm {Sp}}(\\mathcal {N}) symmetric generalization of this model in the large \\mathcal {N} limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.
Dong S
2013-10-01
Full Text Available Shengli Dong,1 Qibin Tang,2 Miaoyun Long,3 Jian Guan,4 Lu Ye,5 Gaopeng Li6 1Department of General Surgery, The Second Hospital of Shanxi Medical University, Shanxi Medical University, Taiyuan, Shanxi Province, 2Department of Hepatobiliopancreatic Surgery, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, Guangdong Province, 3Department of Thyroid and Vascular Surgery, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, Guangdong Province, 4Department of Radiology, First Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong Province, 5Infection Department, Guangzhou No 8 Hospital, Guangzhou, Guangdong Province, 6Department of Ultrasound, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, Guangzhou, Guangdong Province, People's Republic of China Background/aim: A local nanotherapy (LNT combining the therapeutic efficacy of trans-arterial embolization, nanoparticles, and p53 gene therapy has been previously presented. The study presented here aimed to further improve the incomplete tumor eradication and limited survival enhancement and to elucidate the molecular mechanism of the LNT. Methods: In a tumor-targeting manner, recombinant expressing plasmids harboring wild-type p53 and Rb were either co-transferred or transferred separately to rabbit hepatic VX2 tumors in a poly-L-lysine-modified hydroxyapatite nanoparticle nanoplex and Lipiodol® (Guerbet, Villepinte, France emulsion via the hepatic artery. Subsequent co-expression of p53 and Rb proteins within the treated tumors was investigated by Western blotting and in situ analysis by laser-scanning confocal microscopy. The therapeutic effect was evaluated by the tumor growth velocity, apoptosis and necrosis rates, their sensitivity to Adriamycin® (ADM, mitomycin C, and fluorouracil, the microvessel density of tumor tissue, and the survival time of animals. Eventually, real-time polymerase chain reaction and enhanced chemiluminescence Western blotting
Jin Huang
Full Text Available PURPOSE: This study was undertaken to establish a rabbit esophageal tumor model for mimicking human esophageal squamous carcinoma (ESC by endoscopic and surgical implantation of VX2 tumors. METHODS: Fragments of a VX2 tumour were endoscopically implanted in the submucosal layer of the thoracic esophagus of 32 New Zealand white rabbits, while 34 animals received surgical implantation into the muscular layer. Then, the animals were studied endoscopically and pathologically. The safety and efficiency of the two methods and the pathological features of the animal models were analyzed. RESULTS: Both the endoscopic and the surgical method had a relatively high success rate of tumor implantation [93.7% (30/32 vs. 97.1% (33/34] and tumor growth [86.7% (26/30 vs. 81.8% (27/33], and the variation in the results was not statistically significant (P>0.05. Compared with those produced by the surgical method, the models produced by the endoscopic method had a higher rate of severe esophageal stricture [61.5% (16/26 vs. 29.6% (8/27] and of intra-luminal tumor growth [73.1% (19/26 vs. 37.0% (10/27], and had a lower rate of tumor invasion of adjacent organs [53.8% (14/26 vs. 81.5% (22/27]; all of these results were statistically significant (P0.05. CONCLUSION: The endoscopic and surgical methods are both safe and effective for establishment of VX2 tumors in the rabbit esophagus. The models produced by the two methods have different pathologic features mimicking that of human ESC. We recommend the models for studies on surgical procedures and minimally invasive treatments.
Zheng Linfeng, E-mail: zhenglinfeng04@yahoo.com.cn [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Li Yujie, E-mail: yujieli01@yahoo.com.cn [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Wang Han, E-mail: bingowh@hotmail.com [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Zhao Jinglong, E-mail: jinglongz@yahoo.com [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Wang Xifu, E-mail: wangxiechen001@163.com [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Hu Yunsheng, E-mail: springmorninghu@163.com [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China); Zhang Guixiang, E-mail: guixiangzhang@sina.com [Department of Radiology, Shanghai First People' s Hospital, Medical College, Shanghai Jiaotong University, Hanning Road, 100, 200080 Shanghai (China)
2011-05-15
Purpose: To study the effects of combination of vascular endothelial growth factor (VEGF) antisense oligonucleotide therapy and radiotherapy on maxillofacial VX2 tumors in rabbits. Methods: We used 24 New Zealand white rabbits as a model to induce maxillofacial VX2 tumor. The rabbits were randomly divided into the following 4 groups: radiotherapy group (group A), treated with 16 Gy of radiotherapy; VEGF antisense oligonucleotide treatment group (group B), treated with an injection of 150 {mu}g of VEGF antisense oligonucleotide into the local tumor; VEGF antisense oligonucleotide combined with radiotherapy group (group C), treated with an injection of 150 {mu}g of VEGF antisense oligonucleotide into the local tumor immediately after 16 Gy of radiotherapy; and control group (group D), treated with an injection of 300 {mu}l 5% aqueous glucose solution into the local tumor. On days 3 and 14 after treatment, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed to calculate maximal enhancement ratio (MER), slope of enhancement (SLE), and tumor volume change. Rabbits were killed on day 14 to obtain samples for pathological examination and immunohistochemical staining for VEGF. Results: In group C, tumor volume was significantly reduced on day 14 after treatment, and the difference was statistically different as compared to that before treatment, on day 3 after treatment and other groups (P < 0.01). Values of both MER and SLE after treatment were significantly lower than the values before treatment (P < 0.05). Pathological specimen revealed tumor cell edema, bleeding, necrosis, vascular wall thickening and occlusion, and decreased VEGF expression. The immunohistochemical score (IHS) of group C was significantly different from groups A and D respectively (P < 0.05). Conclusion: Injecting the tumor with VEGF antisense oligonucleotide immediately after radiotherapy can enhance the curative effect on rabbit maxillofacial VX2 tumor, and DCE-MRI can serve
Cheng-Wen Zhou; Fa-Qi Li; Yan Qin; Chun-Mei Liu; Xiao-Lin Zheng; Zhi-Biao Wang
2008-01-01
AIM:To investigate the pathological characteristics of non-thermal damage induced by pulsed high intensity focused ultrasound (PHIFU) combined with ultrasound contrast agent (UCA),SonoVue (Bracco SpA,Milan,Italy) in rabbit liver VX2 tumor.METHODS:Liver VX2 tumor models were established in 20 rabbits,which were divided randomly into PHIFU combined with ultrasound contrast agent group (PHIFU + UCA group) and sham group.In the PHIFU + UCA group,0.2 mL of SonoVue was injected intravenously into the tumor,followed by ultrasound exposure of Isp 5900 W/cm2.The rabbits were sacrificed one day after ultrasound exposure.Specimens of the exposed tumor tissues were obtained and observed pathologically under light microscope and transmission electron microscope.The remaining tumor tissues were sent for 2,3,5-Triphenyltetrazolium chloride (TTC) staining.RESULTS:Before TTC staining,tumor tissues in both the sham and the PHIFU + UCA groups resembled gray fish meat.After TTC staining,the tumor tissues were uniformly stained red,with a clear boundary between tumor tissue and normal tissue.Histological examination showed signs of tumor cell injury in PHIFU + UCA group,with cytoplasmic vacuoles of various sizes,chromatin margination and karyopyknosis.Electron microscopic examination revealed tumor cell volume reduction,karyopyknosis,chromatin margination,intercellular space widening,the presence of high electron-density apoptotic bodies and vacuoles in cytoplasm.CONCLUSION:The non-thermal effects of PHIFU combined with UCA can be used to ablate rabbit liver VX2 tumors.
XIAO Hong; LIAO Qiong; CHENG Ming; LI Fei; XIE Bing; LI Mei; FENG Hua
2009-01-01
Background Complete tumour resection is important for improving the prognosis of brain tumour patients. However,extensive resection remains controversial because the tumour margin is difficult to be distinguished from surrounding brain tissue. It has been established that 5-amino-4-oxopentanoic acid (5-aminolevulinic acid, ALA) can be used as a photodynamic diagnostic marker and a photosensitizer for photodynamic therapy in surgical treatment of brain tumours. We investigated the efficacy of ALA photodynamically guided microsurgery and photodynamic therapy on VX2 brain tumour implanted in a rabbit model.Methods Eighty New Zealand rabbits implanted with VX2 brain tumours were randomly assigned to five groups: control, conventional white light microsurgery, a photodynamic therapy group, a photodynamically guided microsurgery group and a group in which guided microsurgery was followed by photodynamic therapy. The VX2 tumour was resected under a surgical microscope. The tumour resection was confirmed with histological analysis. All animals were examined with MRI for presence of any residual tumour tissue. The survival time of each rabbit was recorded.Results All treatment groups showed a significantly extended survival time compared with the control group.Photodynamically guided microsurgery combined with photodynamic therapy significantly prolonged survival time, compared with guided microsurgery alone. MRI and the autopsy results confirmed removal of most of the tumours.Conclusions Our results suggest that photodynamically guided surgery and photodynamic therapy significantly reduce or delay local recurrence, increase the effectiveness of radical resection and prolong the survival time of tumour bearing rabbits, Their combination has the potential to be used as a rapid and highly effective treatment of metastatic brain tumours.
Jao, Jo-Chi; Mac, Ka-Wai; Chang, Chiung-Yun; Wu, Yu-Chiuan; Hsiao, Chia-Chi; Chen, Po-Chou
2017-03-01
This study aimed to investigate the VX2 tumor growth in rabbit liver using T2-weighted imaging (T2WI) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Five New Zealand white (NZW) rabbits were implanted with VX2 cell suspension in liver. Afterwards, MRI was performed 7, 14, 21 and 28 days after tumor implantation. A 1.5T clinical MRI scanner was used to perform scans. After 3-plane localizer, T1 weighted imaging (T1WI), T2WI, and DCE-MRI using a three-dimensional gradient echo pulse sequence was performed. After 4 pre-contrast images were acquired, each rabbit was injected i.v. with 0.1 mmol/kg Dotarem. The total scan time after Dotarem administration was 30 minutes. All acquired images were analyzed using ImageJ software. Several regions of interest were selected from the rims of tumor, liver, and muscle. The enhancement ratio (ER) was calculated by dividing the MR signal after Dotarem injection to the MR signal before Dotarem injection. The maximum ER (ER_max) value of tumor for each rabbit was observed right after the Dotarem injection. The T2W MR signal intensities (T2W_SI) and the ER_max values obtained 7, 14, 21 and 28 days after tumor implantation were analyzed with a linear regression algorithm. Both T2W_SI and ER_max of tumors increased with time. The changes for T2W_SI and ER_max of tumors between 7 and 28 days after tumor implantation were 32.66% and 18.14%, respectively. T2W_SI is more sensitive than ER_max for monitoring the growth of VX2 tumor in a rabbit liver model.
YANG Hong-yan; XU Yi-kai; WU Yuan-kui; LIU Wen-yuan; L(U) Guo-shi; CAO Guo-hong
2008-01-01
Objective:To establish a rodent model of VX2 tumor of the spleen,to analyze relationship between the change of the signal intensity on superparamagnetic iron oxide enhanced magnetic resonance image(MRI)and pathologic change to evaluate the ability of superparamagnetic iron oxide enhanced MRI for detection of splenic metastases.Methods:8 rodent models of VX2 tumor of spleen were established successfully.The images were obtained before and after administration of superparamagnetic iron oxide.T1-weighted spin-echo(SE)pulse sequence with a repetition time(TR)of 450 msec,and echo time(TE)of 12 msec(TR/TE=450/12)was used.The imaging parameters Of T2-weighted SE pulse sequence were as follows:TR/TE=4000/128. Results:On plain MR scanning T1-weighted splenic VX2 tumor showed hypointensity or isointensity which approximated to the SI of splenic parenchyma.Therefore all lesions were not displayed clearly.On superparamagnetic iron oxide enhancement T2WI sequence the SI of splenic parenchyma decreased obviously with percentage of signal intensity loss(PSIL)of 55.04%,But the SI of tumor was not evidently changed with PSIL of 0.87%. Nevertheless the SNR of normal splenic parenchyma around the lesions had obvious difference(P＜0.001)comparatively.Therefore the contrast between tumor and spleen increased.and tumor displayed more clearly.Moreover the contrast-to-noise(CNR)between VX2 tumor and splenic parenchyma had an evident difference before and after admininstration of superparamagnetic iron oxide(P＜0.001).Conclusion:On superparamagnetic iron oxide enhancement T1WI sequence the contrast of tumor-to-spleen is poor.Therefore it is not sensitive to characterize the lesions in spleen.On superparamagnetie iron oxide enhanced T2WI the contrast degree of lesions increases obviously.Consequently, superparamagnetic iron oxide-enhanced T2WI MRI scanning can improve the rate of detection and characterization for lesions of spleen.
Park, Hee Sun; Chung, Jin Wook; Jae, Hwan Jun [Seoul National University College of Medicine, Seoul (Korea, Republic of)] (and others)
2007-06-15
We wanted to investigate the feasibility of using FDG-PET for evaluating the antitumor effect of intraarterial administration of a hexokinase II inhibitor, 3-bromopyruvate (3-BrPA), in a rabbit VX2 liver tumor model. VX2 carcinoma was grown in the livers of ten rabbits. Two weeks later, liver CT was performed to confirm appropriate tumor growth for the experiment. After tumor volume-matched grouping of the rabbits, transcatheter intraarterial administration of 3-BrPA was performed (1 mM and 5 mM in five animals each, respectively). FDG-PET scan was performed the day before, immediately after and a week after 3-BrPA administration. FDG uptake was semiquantified by measuring the standardized uptake value (SUV). A week after treatment, the experimental animals were sacrificed and the necrosis rates of the tumors were calculated based on the histopathology. The SUV of the VX2 tumors before treatment (3.87{+-}1.51 [mean SD]) was significantly higher than that of nontumorous liver parenchyma (1.72{+-}0.34) (p < 0.0001, Mann-Whitney U test). The SUV was significantly decreased immediately after 3-BrPA administration (2.05{+-}1.21) (p = 0.002, Wilcoxon signed rank test). On the one-week follow up PET scan, the FDG uptake remained significantly lower (SUV 1.41{+-}0.73) than that before treatment (p 0.002), although three out of ten animals showed a slightly increasing tendency for the FDG uptake. The tumor necrosis rate ranged from 50.00% to 99.90% (85.48%{+-}15.87). There was no significant correlation between the SUV or the SUV decrease rate and the tumor necrosis rate in that range. Even though FDG-PET cannot exactly reflect the tumor necrosis rate, FDG-PET is a useful modality for the early assessment of the antitumor effect of intraarterial administration of 3-BrPA in VX2 liver tumor.
Jun Hu; Zhi-Su Liu; Sheng-Li Tang; Yue-Ming He
2007-01-01
AIM:To evaluate the effect of hydroxyapatite nanoparticles (Nano HAP) by intravenous injection on the inhibition of implanted hepatic VX2 tumor growth in rabbits and cell p53/c-Myc protein expression.METHODS: 60 hepatic VX2 tumor-bearing rabbits was randomly divided into five groups. Nano HAP collosol 20 mg/kg, 40 mg/kg, 5-FU solutions 20 mg/mL, mixed liquor of 5-FU solution 20 mg/mL and Nano HAP collosol 20 mg/kg were infused by vein, normal saline conducted as the control. The general state, weight, liver function and gross tumor volume were detected dynamically.The expression of p53 and c-Myc gene protein in tumor tissue was detected by immunohistochemistry methods.RESULTS: The growth of implanted hepatic VX2 tumors was significantly inhibited in all therapy groups, 3 wk after the injection, the tumor control rates in Nano HAP collosol groups were 25.5% and 32.5% respectively,and the gross tumor volumes were obviously less than that of control group. (24.81 ± 5.17 and 22.73 ± 4.23vs 33.32 ± 5.26, P ＜ 0.05). The tumor control rate of 5-FU group was 43.7% (18.74 ± 4.40 vs 33.32 ± 5.26,P ＜ 0.05), but the general state of the animals after injection aggravated; and the adverse reaction in the drug combination group obviously decreased. Due to the effect of Nano HAP, the positive expression of tumor associated the mutated p53 and c-Myc in tumor tissue was decreased obviously compared with the control group.CONCLUSION: Nano HAP has evident inhibitory action on rabbit implanted hepatic VX2 tumor in vivo, which may be the result of decreasing the expression of the mutated p53 and c-myc, and drug combination can obviously decrease the adverse reaction of 5-FU.
Wen-Hua Du; Wei-Xiao Yang; Xiang Wang; Xiu-Qin Xiong; Yi Zhou; Tao Li
2003-01-01
AIM: To investigate the characteristics of the vascularity ofhepatic metastasis.METHODS: Six New Zealand rabbits, weighing averagely2.7±0.4 kg, were selected and operated to establish hepaticVX2 tumor carrier model. Hepatic VX2 tumors were thenimaged with conventional B mode US, second harmonicimaging (SHI), color Doppler flow imaging (CDFI), powerDoppler imaging (PDI) and harmonic PDI by a transducerS8 connected to HP-5 500 ultrasound system. A kind of selfmade echo contrast agent was intravenously injected at adose of 0.01 mL/kg through ear vein, and then the venouspassage was cleaned with sterilized saline.RESULTS: Totally, 6 hypoechoic lesions and 3 hyperechoiclesions were found in the six carrier rabbits with a mean sizeabout 2.1±0.4 cm under conventional B mode ultrasound, theywere oval or round in shape with a dear outline or a hypoechoichalo at the margin of the lesions. Contrast agent could notchange the echogenicity of the lesions under conventional Bmode and SHI, however, it could greatly increase the flowsensitivity of the lesions under PDI and harmonic PDI. Nutrientartery of these metastatic lesions might also be well depictedunder contrast enhanced PDI and harmonic PDI.CONCLUSION: Our result suggested that contrast enhancedPDI, especially harmonic PDI, was a promised method inthe detection of vascularity of hepatic tumor nodules.
Lv, Peijie; Liu, Jie; Yan, Xiaopeng; Chai, Yaru; Chen, Yan; Gao, Jianbo; Pan, Yuanwei; Li, Shuai; Guo, Hua; Zhou, Yue [The First Affiliated Hospital of Zhengzhou University, The Department of Radiology, Zhengzhou, Henan Province (China)
2017-03-15
The aim of this study was to evaluate the value of computed tomography (CT) spectral imaging in assessing the therapeutic efficacy of a vascular endothelial growth factor (VEGF) receptor inhibitor AG-013736 in rabbit VX2 liver tumours. Twenty-three VX2 liver tumour-bearing rabbits were scanned with CT in spectral imaging mode during the arterial phase (AP) and portal phase (PP). The iodine concentrations(ICs)of tumours normalized to aorta (nICs) at different time points (baseline, 2, 4, 7, 10, and 14 days after treatment) were compared within the treated group (n = 17) as well as between the control (n = 6) and treated groups. Correlations between the tumour size, necrotic fraction (NF), microvessel density (MVD), and nICs were analysed. The change of nICs relative to baseline in the treated group was lower compared to the control group. A greater decrease in the nIC of a tumour at 2 days was positively correlated with a smaller increase in tumour size at 14 days (P < 0.05 for both). The tumour nIC values in AP and PP had correlations with MVD (r = 0.71 and 0.52) and NF (r = -0.54 and -0.51) (P < 0.05 for all). CT spectral imaging allows for the evaluation and early prediction of tumour response to AG-013736. (orig.)
Antiferromagnetic Ising Model in Hierarchical Networks
Cheng, Xiang; Boettcher, Stefan
2015-03-01
The Ising antiferromagnet is a convenient model of glassy dynamics. It can introduce geometric frustrations and may give rise to a spin glass phase and glassy relaxation at low temperatures [ 1 ] . We apply the antiferromagnetic Ising model to 3 hierarchical networks which share features of both small world networks and regular lattices. Their recursive and fixed structures make them suitable for exact renormalization group analysis as well as numerical simulations. We first explore the dynamical behaviors using simulated annealing and discover an extremely slow relaxation at low temperatures. Then we employ the Wang-Landau algorithm to investigate the energy landscape and the corresponding equilibrium behaviors for different system sizes. Besides the Monte Carlo methods, renormalization group [ 2 ] is used to study the equilibrium properties in the thermodynamic limit and to compare with the results from simulated annealing and Wang-Landau sampling. Supported through NSF Grant DMR-1207431.
Antiferromagnetic order in hybrid electromagnetic metamaterials
Miroshnichenko, Andrey E.; Filonov, Dmitry; Lukyanchuk, Boris; Kivshar, Yuri
2017-08-01
We demonstrate experimentally a new type of order in optical magnetism resembling the staggered structure of spins in antiferromagnetic ordered materials. We study hybrid electromagnetic metasurfaces created by assembling hybrid meta-atoms formed by metallic split-ring resonators and dielectric particles with a high refractive index, both supporting optically-induced magnetic dipole resonances of different origin. Each pair (or ‘metamolecule’) is characterized by two interacting magnetic dipole moments with the distance-dependent magnetization resembling the spin exchange interaction in magnetic materials. By directly mapping the structure of the electromagnetic fields, we demonstrate experimentally that strong coupling between the optically-induced magnetic moments of different origin can flip the magnetisation orientation in a metamolecule creating an antiferromagnetic lattice of staggered optically-induced magnetic moments in hybrid metasurfaces.
Antiferromagnetic exchange mechanism of superconductivity in cuprates
Plakida, N M
2001-01-01
One examines theory of superconducting coupling resulted from antiferromagnetic exchange in terms of which one explains strong dependence of T sub c superconducting transition temperature on alpha lattice constant. Calculations are based on the Hubbard p-d two-region model within strong correlation limit. DELTA pd excitation high energy at antiferromagnetic exchange of two particles from different Hubbard subregions results in suppression o delay effects and in coupling of all particles in conductivity subregion with Fermi energy E sub F >= DELTA pd : T sub c approx = E sub F exp(-1/lambda), where lambda propor to J. T sub c (alpha) and isotopic effect are explained by J exchange interaction dependence on alpha and on zero oscillations of oxygen ions
李晓莉; 董诚; 李玉军; 陈海松; 吴增杰; 庞婧; 贾梦; 徐文坚
2016-01-01
目的：探讨 MRI 常用序列在判断恶性骨肿瘤骨髓内浸润范围及显示病变阳性率方面的应用价值。方法2010年6月—2012年3月选取兔龄8周、体质量2.0~3.0 kg 的雄性新西兰大白兔26只,1只制备荷瘤兔,25只接种 VX2肉瘤肿瘤组织块于兔右侧胫骨平台下2 cm 处的骨髓腔内,制备成恶性骨肿瘤模型兔。模型兔制备成功后,在全身麻醉状态下行 MRI 检查。选取肿瘤纵径最大层面,观察并测量 MR 自旋回波(SE) T1 WI、脂肪抑制 FSE T2 WI、短时间反转恢复序列(STIR)、脂肪抑制 SE T1 WI 增强序列图像中的髓内肿瘤浸润纵径。 MRI 检查完成后,处死模型兔,切取兔右下肢标本,用硬组织切片系统自 MR 扫描起始点间隔4 mm 连续切割,选取与 MRI 中骨髓内肿瘤纵径最大层面相对应的标本切片进行肿瘤髓内浸润纵径的测量和病理学观察。采用单因素方差分析和配对 t 检验,比较 MR 不同序列之间及 MR 不同序列和病理切片检查之间肿瘤髓内浸润纵径测量值的差异；并对 MR 不同序列间显示肿瘤髓内浸润的阳性率{[真阳性/(真阳性+假阳性)]×100%}进行χ2检验。结果成功制备21只模型兔。 MRI 中 SE T1 WI、脂肪抑制 FSE T2 WI、STIR、脂肪抑制 SE T1 WI 增强序列间肿瘤髓内浸润纵径的测量值分别为(44.5±10.8)mm、(41.0 ± 9.7) mm、(40.7 ± 9.4)mm、(40.3±9.5)mm,4种序列之间的差异无统计学意义(F =0.802,P >0.05)。 4种序列图像的肿瘤髓内浸润纵径测量值均大于病理标本测量值(39.3±9.3)mm,配对 t 检验分析差异均有统计学意义(t =7.053、6.334、6.445、8.150,P 值均 0. 05). The average value of group SE T1 WI, Fat-Sat FSE T2 WI, STIR and Fat-Sat SE T1 WI with contrast were (44. 5 ± 10. 8) mm, (41. 0 ± 9. 7) mm, (40. 7 ± 9. 4) mm and (40. 3 ± 9. 5) mm, respectively. The value of measuring tumor intraosseous extent in group SE T1 WI, Fat-Sat FSE T2 WI, STIR and group Fat
Singleton, John [Los Alamos National Laboratory; Mc Donald, R [Los Alamos National Laboratory; Sengupta, P [Los Alamos National Laboratory; Cox, S [Los Alamos National Laboratory; Manson, J [E WASHINGTON U; Southerland, H [E WASHINGTON U; Warter, M [E WASHINGTON U; Stone, K [STATE UNIV OF NY; Stephens, P [STATE UNIV OF NY; Lancaster, T [OXFORD U; Steele, A [OXFORD U; Blundell, S [OXFORD U; Baker, P [OXFORD U; Pratt, F [RUTHERFORD-APPLETON LAB; Lee, C [NCSU; Whangbo, M [NCSU
2009-01-01
X-ray powder diffraction and magnetic susceptibility measurements show that Ag(pyz){sub 2}(S{sub 2}O{sub 8}) consists of 2D square nets of Ag{sup 2+} ions resulting from the corner-sharing of axially elongated AgN{sub 4}O{sub 2} octahedra and exhibits characteristic 2D antiferromagnetism. Nevertheless, {mu}{sup +}Sr measurements indicate that Ag(pyz){sub 2}(S{sub 2}O{sub 8}) undergoes 3D magnetic ordering below 7.8(3) K.
Yi Wang; Xian-Qing Jin; Shan Wang; Qiao Wang; Qing Luo; Xiao-Ji Luo
2006-01-01
BACKGROUND: Malignant tumors are common diseases threatening to the health and life of human being. Clinically, the multidrug resistance of tumor cells and bone marrow depression caused by chemotherapeutic agents are the main obstacles to the treatment of tumors, and both are related to the mdr1 gene. The over expression of the mdr1 gene in tumor cells contributes to the multidrug resistance of malignant tumor cells. With little expression of the mdr1 gene, bone marrow cells particularly susceptible to multidrug resistance-sensitive agents, which cause serious toxicity in bone marrow. This study was undertaken to assess therapeutic efifcacy of transplantation of bone marrow mononuclear cells transferred with the mdr1 gene and over-dose chemotherapy with doxorubicin for VX2 hepatocarcinoma of rabbits. METHODS: The mdr1 gene was transferred into the bone marrow mononuclear cells of rabbits, which was co-cultured with retroviral vector-containing supernatant, and the cells were autotransplanted into a rabbit model with VX2 hepatocarcinoma. After chemotherapy with doxorubicin, the protective effects of the mdr1 gene and therapeutic efifcacy of over-dose chemotherapy were observed. RESULTS:The mdr1 gene was transferred successfully into the bone marrow mononuclear cells, with a transduction efifciency of 35%. After autotransplantation, the mdr1 gene was expressed functionally in bone marrow with a positive rate of 8%, indicating that the gene played an important role in bone marrow protection. The rabbits with VX2 hepatocarcinoma, which had received the mdr1 gene-transduced cells, survived after chemotherapy with a 3-fold dose of adriamycin, and their white blood cell counts were (4.26±1.03)×104/L. Since hepatocarcinoma cells were eradicated, the survival time (97.00±46.75 d) of the rabbits was extended (P CONCLUSIONS:The transferring of the mdr1 gene into bone marrow mononuclear cells could confer chemoprotection to bone marrow, and over-dose chemotherapy could be
Miao Zhu
Full Text Available Combination of percutaneous microwave ablation (PMWA and intravenous injection of 131I-hypericin(IIIH may bear potential as a mini-invasive treatment for tumor. The objective of this study was to assess the effect of PMWA and IIIH in breast tumor growth.Ten New Zealand White rabbits bearing VX2 breast carcinomas were randomly divided into two groups (each 5 examples and processed using PMWA followed by IIIH and IIIH alone. The IIIH activity was evaluated using planar scintigraphy, autoradiography and biodistribution analysis. The maximum effective safe dose of IIIH was found through 48 rabbits with VX2 breast tumor, which were randomized into six groups (n=8 per group. Subsequently, a further 75 rabbits bearing VX2 breast solid tumors were randomly divided into five groups (each 15 examples and treated as follows: A, no treatment group; B, PMWA alone; C, IIIH alone; D, PMWA+IIIH×1 (at 8 h post-PMWA; and E, PMWA+IIIH×2 (at 8 h and at 8 days post-PMWA. The therapeutic effect was assessed by measurement of tumor size and performation of positron emission tomography/computed tomograph (PET/CT scans, liver and renal function tests and Kaplan-Meier survival analysis.The planar scintigraphy findings suggested a significant uptake of 131I in necrotic tumor tissue. The autoradiography gray scales indicated higher selective uptake of IIIH by necrotic tissue, with significant differences between the groups with and those without necrotic tumor tissue (P<0.05. The maximum effective safe dose of IIIH was 1 mCi/kg. The PET/CT scans and tumor size measurement suggested improvements in treatment groups at all time points (P<0.01. Significant differences were detected among Groups A, B, D and E (P<0.05. Lower levels of lung metastasis were detected in Groups D and E (P<0.05. There were no abnormalities in liver and renal functions tests or other reported side effects.IIIH exhibited selective uptake by necrotic tumor tissue. Sequential therapy involving PMWA
Duan XH
2016-05-01
Full Text Available Xu-Hua Duan,1,2 Teng-Fei Li,2 Guo-Feng Zhou,1,* Xin-Wei Han,2,* Chuan-Sheng Zheng,1 Peng-fei Chen,2 Gan-Sheng Feng11Department of Interventional Radiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 2Department of Interventional Radiology, The First Affiliated Hospital, Zhengzhou University, Henan Province, Zhengzhou, People’s Republic of China*These authors contributed equally to this work Purpose: To evaluate the effect of transcatheter arterial embolization (TAE combined with radiofrequency ablation (RFA treatment (TAE + RFA on the expression of heat shock protein 70 (HSP70 in residual tumors and explore the relationship between the HSP70 and CD8+ T-cell infiltrate surrounding residual tumors in the rabbit VX2 liver tumor model.Materials and methods: Animals with VX2 liver tumors were randomized into four groups (control, TAE, RFA, and TAE + RFA with 15 rabbits in each group. Five rabbits in each group were sacrificed on days 1, 3, and 7 after treatment. HSP70 expression and infiltration of CD8+ T-cells in the liver and residual tumors surrounding the necrosis zone were detected by immunohistochemistry staining. The maximal diameters of tumor necrosis, numbers of metastases, and tumor growth rate were compared on day 7 after treatment.Results: TAE + RFA achieved larger maximal diameter of tumor necrosis, lower tumor growth rate, and fewer metastatic lesions, compared with other treatments on day 7. The number of CD8+ T-cells in the TAE + RFA group was significantly higher than in other groups on days 1, 3, and 7. There was a positive correlation between HSP70 expression level and infiltration of CD8+ T-cells surrounding the residual tumor on day 1 (r=0.9782, P=0.012, day 3 (r=0.93, P=0.021, and day 7 (r=0.8934, P=0.034.Conclusion: In the rabbit VX2 liver tumor model, TAE + RFA activated the highest number of CD8+ T-cells surrounding residual tumors. TAE + RFA appears to be a beneficial
Antiferromagnetic spin-orbitronics
Manchon, Aurelien
2015-05-01
Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.
Nanoparticles of antiferromagnetic materials
Madsen, Daniel Esmarch
2008-01-01
I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...
Donghui PAN
2011-01-01
Full Text Available Background and objective 32P-chromic phosphate-poly (L-lactic acid (32P-CP-PLLA microparticle is a novel potent brachytherapy implant, which has good biocompatibility and biodegradability. The aim of this study is to investigate the changes of pathology and PET/CT images in VX2 rabbit tumor after treatment with intratumorol administration of 32P-CP-PLLA microparticles, and to explore the effects and influence of tumor growth and apoptosis related proteins in VX2 lung tumor treatment with 32P-CP-PLLA microparticles. Methods Twenty-four tumor bearing rabbits were randomly divided into 4 groups (6 in each group. Group 1, 2 and 3 were treated groups; group 4 was the control. Under CT guidance, 32P-CPPLLA microparticles were implanted into tumors. Low, medium and high treatment doses were 93 MBq (group 1, 185 MBq (group 2 and 370 MBq (group 3, respectively. 18F-FDG PET/CT was performed at d0, d3, d7 and d14 after intratumoral administration. In the control group, 18F-FDG PET/CT images were acquired at the same time points but without treatment. The standardized uptake value (SUV of tumor regions were calculated. After last PET/CT imaging, the rabbits were euthanized and the tumors were removed for histological and immunohistochemical examination. The pathology and the expression of apoptosis related proteins (bcl-2, bax were compared. Results No significant difference of SUVmax was observed between the treatment groups and the control group at d0. At d14, the SUVmax values for group 1, 2 and 3 were 0.80±0.10, 1.1±0.19 and 2.85±0.15, respectively, and were significantly lower than that of the control group (5.61±0.50(P < 0.05. Significant dose-response relationship was observed in SUVmax between group 1 and group 2, and the SUV values gradually decreased from d7 to d14 after treatment. In group 3, SUVmax gradually increased and reached a peak at d7 then significantly decreased. The SUVmax values of group 3 were significantly lower than those of
Yang, C H; Lin, Y T; Hung, Y H; Liao, J W; Peir, J J; Liu, H M; Lin, Y L; Liu, Y M; Chen, Y W; Chuang, K S; Chou, F I
2015-12-01
Hepatoma is a malignant tumor that responds poorly to conventional therapies. Boron neutron capture therapy (BNCT) may provide a better way for hepatoma therapy. In this research, (10)B-enriched boric acid (BA, 99% (10)B) was used as the boron drug. A multifocal hepatic VX2 tumor-bearing rabbit model was used to study the mechanisms of BA-mediated BNCT. Autoradiography demonstrated that BA was selectively targeted to tumors and tumor vessels. Histopathological examination revealed the radiation damage to tumor-bearing liver was concentrated in the tumor regions during BNCT treatment. The selective killing of tumor cells and the destruction of the blood vessels in tumor masses may be responsible for the success of BA-mediated BNCT for liver tumors. Copyright © 2015 Elsevier Ltd. All rights reserved.
Jae, Hwan Jun; Chung, Jin Wook; Park, Hee Sun; Lee, Min Jong; Lee, Ki Chang; Kim, Hyo Cheol; Yoon, Jung Hwan; Park, Jae Hyung [Seoul National University Hospital, Seoul (Korea, Republic of); Chung, He Son [Korea Institute of Science and Technology, Seoul (Korea, Republic of)
2009-12-15
The purpose of this study was to compare the antitumor effect and hepatotoxicity of an intraarterial delivery of low-dose and high-dose 3-bromopyruvate (3-BrPA) and those of a conventional Lipiodol-doxorubicin emulsion in a rabbit VX2 hepatoma model. This experiment was approved by the animal care committee at our institution. VX2 carcinoma was implanted in the livers of 36 rabbits. Transcatheter intraarterial administration was performed using low dose 3- BrPA (25 mL in a 1 mM concentration, n = 10), high dose 3-BrPA (25 mL in a 5 mM concentration, n = 10) and Lipiodol-doxorubicin emulsion (1.6 mg doxorubicin/ 0.4 mL Lipiodol, n = 10), and six rabbits were treated with normal saline alone as a control group. One week later, the proportion of tumor necrosis was calculated based on histopathologic examination. The hepatotoxicity was evaluated by biochemical analysis. The differences between these groups were statistically assessed with using Mann-Whitney U tests and Kruskal-Wallis tests. The tumor necrosis rate was significantly higher in the high dose group (93% +- 7.6 [mean +- SD]) than that in the control group (48% +- 21.7) (p = 0.0002), but the tumor necrosis rate was not significantly higher in the low dose group (62% +- 20.0) (p = 0.2780). However, the tumor necrosis rate of the high dose group was significantly lower than that of the Lipiodol-doxorubicin treatment group (99% +- 2.7) (p = 0.0015). The hepatotoxicity observed in the 3-BrPA groups was comparable to that of the Lipiodol-doxorubicin group. Even though intraarterial delivery of 3-BrPA shows a dose-related antitumor effect, single session treatment seems to have limited efficacy when compared with the conventional method
Park, Hee Sun [Dept. of Radiology, Konkuk University School of Medicine, Seoul (Korea, Republic of); Han, Joon Koo; Lee, Jeong Min; Woo, Sung Min; Choi, Byung Ihn [Seoul National University Hospital, Seoul (Korea, Republic of); Kim, Young Il [Dept. of Radiology, Sheikh Khalifa Specialty Hospital, Ras Al Khaimah (United Arab Emirates); Choi, Jin Young [Dept. of Radiology, Yonsei University College of Medicine, Seoul (Korea, Republic of)
2015-10-15
To evaluate the utility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using macromolecular contrast agent (P792) for assessment of vascular disrupting drug effect in rabbit VX2 liver tumor models. This study was approved by our Institutional Animal Care and Use Committee. DCE-MRI was performed with 3-T scanner in 13 VX2 liver tumor-bearing rabbits, before, 4 hours after, and 24 hours after administration of vascular disrupting agent (VDA), using gadomelitol (P792, n = 7) or low molecular weight contrast agent (gadoterate meglumine [Gd-DOTA], n = 6). P792 was injected at a of dose 0.05 mmol/kg, while that of Gd-DOTA was 0.2 mmol/kg. DCE-MRI parameters including volume transfer coefficient (Ktrans) and initial area under the gadolinium concentration-time curve until 60 seconds (iAUC) of tumors were compared between the 2 groups at each time point. DCE-MRI parameters were correlated with tumor histopathology. Reproducibility in measurement of DCE-MRI parameters and image quality of source MR were compared between groups. P792 group showed a more prominent decrease in Ktrans and iAUC at 4 hours and 24 hours, as compared to the Gd-DOTA group. Changes in DCE-MRI parameters showed a weak correlation with histologic parameters (necrotic fraction and microvessel density) in both groups. Reproducibility of DCE-MRI parameters and overall image quality was not significantly better in the P792 group, as compared to the Gd-DOTA group. Dynamic contrast-enhanced magnetic resonance imaging using a macromolecular contrast agent shows changes of hepatic perfusion more clearly after administration of the VDA. Gadolinium was required at smaller doses than a low molecular contrast agent.
Lei Zhen, E-mail: leizhen2004@163.com [Department of Anatomy, Chinese Medical University, No. 92, Beiermalu Road, Heping District, Shenyang, 110001 (China) and Department of Radiology, The First Hospital of Liaoning Medical College, No. 2, Wuduan, Renmin Street, Jinzhou, 121001 (China); Ma Heji, E-mail: maheji9831@sina.com [Department of Radiology, The First Hospital of Liaoning Medical College, No. 2, Wuduan, Renmin Street, Jinzhou, 121001 (China); Xu Na, E-mail: xuna821230@sohu.com [Department of Radiology, The First Hospital of Liaoning Medical College, No. 2, Wuduan, Renmin Street, Jinzhou, 121001 (China); Xi Huanjiu, E-mail: xihuanjiu2004@yahoo.cn [Anthropology Institute, Liaoning Medical College, No. 40, Sanduan, Songpo Rd, Jinzhou, 121001 (China)
2011-05-15
Objective: Investigate the benefit of functional multi-slice spiral computed tomography (f-MSCT) perfusion imaging in the non-invasive assessment of targeted anti-angiogenesis therapy on an implanted rabbit VX2 breast tumor model. Method: 69 female pure New Zealand white rabbits were randomly assigned to one of the 4 groups and received treatment accordingly: control (saline), Endostar, neoadjuvant chemotherapy (Cyclophosphamide, Epirubicin and 5-Fluorouracil, CEF), combination therapy (Endostar and CEF). After 2 weeks of treatment, f-MSCT perfusion scannings were performed for all rabbits and information about blood flow (BF), blood volume (BV), mean transit time (MTT) and surface permeability (SP) was collected. After perfusion imaging, tumor tissues were sampled for immunohistochemistry and the Western blot test of VEGF protein expression. Results: (1) The VEGF expression level, measured by immunohistochemistry and Western blot, decreased by treatment group (control > Endostar > CEF > combination therapy). The same was true for the mean BF, BV, MTT and PS, which decreased from the control group to the combination therapy group gradually. The mean MTT level increased in reverse order from the control to the combination therapy group. The difference between any 2 groups on these measures was statistically significant (P < 0.05). (2) There was moderate positive correlation between VEGF expression and BE, BV, or PS level (P < 0.05) and a negative correlation between VEGF expression and MTT level for all 4 groups (P < 0.05). Conclusion: Therefore, f-MSCT can be used as a non-invasive approach to evaluate the effect of anti-angiogenic therapy for implanted rabbit VX2 breast tumors.
Rogério Saad-Hossne
2006-06-01
Full Text Available PURPOSE: To analyze, in vitro, the effects of acetylsalicylic acid (aspirin and acetic acid solutions on VX2 carcinoma cells in suspension and to examine the correlation between these effects and neoplastic cell death. METHODS: The VX2 tumor cells (10(7 cells/ml were incubated in solutions containing differing concentrations (2.5% and 5% of either acetylsalicylic acid or acetic acid, or in saline solution (controls. Every five minutes, cell viability was tested (using the trypan blue test and analyzed under light microscopy. RESULTS: Tumor cell viability (in % decreased progressively and, by 30 minutes, neoplastic cell death had occurred in all solutions. CONCLUSION: Based on this experimental model and the methodology employed, we conclude that these solutions cause neoplastic cell death in vitro.OBJETIVO: Analisar os efeitos das soluções de ácido acetil salicílico (aspirina e de ácido acético, in vitro, sobre células em suspensão do carcinoma VX-2, verificando-se as mesmas causam a morte das células neoplásicas. MÉTODOS: Procedeu-se a incubação das células tumorais VX-2 (10(7 células/ml com diferentes concentrações do ácido acetil salicílico (2,5% e 5% e de ácido acético (2,5% e 5%, sendo estudada a viabilidade celular pelo teste do azul tripian a cada 5 minutos; procedeu-se à análise à microscopia ótica. RESULTADOS: Observou-se que o percentual de viabilidade das células tumorais foi progressivamente diminuindo, sendo que ao final de 30 minutos todas as células neoplásicas estavam inviáveis em todas as soluções e concentrações utilizadas. CONCLUSÃO: Com base neste modelo experimental e com a metodologia empregada, concluiu-se que in vitro, estas soluções causam a morte (inviabilidade das células neoplásicas.
Barlowite: A Spin-1/2 Antiferromagnet with a Geometrically Perfect Kagome Motif.
Han, Tian-Heng; Singleton, John; Schlueter, John A
2014-11-28
We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices-barlowite Cu_{4}(OH)_{6}FBr. Magnetic susceptibility gives θ_{CW}=-136 K, while long-range order does not happen until T_{N}=15 K with a weak ferromagnetic moment μkagome lattice makes charge doping promising.
Holes in Heisenberg antiferromagnets
Chen, Yang
1990-05-01
In this Brief Report we show that a recent model proposed by Shankar [Phys. Rev. Lett. 63, 203 (1989)], describing the motion of holes in quantum antiferromagnets is equivalent to the Schwinger model [Phys. Rev. 128, 2425 (1962)] in 1+1 dimensions. Some exact results are deduced. In addition to the superconducting long-range order found by Shankar, it is shown that there is a 2pF hole density wave existing with the superconducting pairing instability.
崔磊; 龚沈初; 何书; 尹剑兵; 杨巨顺; 杨红
2011-01-01
Objective To prospectively assess the reproducibility of CT perfusion parameters acquired with normal dose and low dose in rabbits with implanted VX2 lung tumours. Methods Two times of perfusion CT were performed with 24-hour interval in 10 New Zealand white rabbits with implanted VX2 lung tumours by means of using routine (120 kV, 100 mAs) and low (120 kV, 50 mAs) dose. The volume, maximum diameter, blood volume(BV) , blood flow(BF) , time to peak(TTP) , permeability surface (PS), patlak BV(PBV), Patlak R square (PatRsq) and Patlak residual ( PatR
孙昌进; 肖明勇; 阴俊; 于金明; 郞锦义; 王光辉; 李超; 李涛; 罗云秀; 吕海波; 张德康; 李彦; 黄建鸣
2013-01-01
Objective: To investigate the role of the 64-slice perfusion CT in the evaluation of the oxygen tension ( pO2 ) in the rabbit VX2 tumor model. Methods: Forty-five rabbit VX2 brain tumor model established successfully were examined with 64-detector row CT. Tumor specimens were assessed for the oxygen tension ( pO2 ) , perfusion, blood volume ( BV) , peak enhancement intensity ( PEI) and time to peak (TTP) , and Pearson correlation coefficients were conducted to represent the relationships between the perfusion parameters and pO2 of the tumor. pO2was measured by oxygen-sensitive electrodes guided by perfusion CT images. Results: Mean values for perfusion,BV,PEI, TTP and pO2 of the 45 tumors were 27. 102 ± 26. 723ml/min, 22. 1 96 ± 13. 680ml/100g,43. 456 ±28.73 HU, 38.823 ±14.759 sec,and 15.981 ± 14.815mmHg, respectively. BV,PEI, TTP were not significant correlated with pO2 (r =0.271, 0. 253 、- 0. 18 , P > 0. 05 ) , whereas positively correlation was found between perfusion with pO2 ( r = 0. 673, P = 0. 00 ). Conclusion: The perfusion value from 64-slice spiral CT perfusion imaging might to have ability to evaluate the tumor pO2%目的:利用64层灌注CT评价兔VX2肿瘤模型氧分压并与氧微电极法对照.方法:对45只成功建模兔VX2脑瘤模型行灌注CT检查.测量脑瘤兴趣区灌注值(perfusion)、血容量(blood volume,BV)、达峰时间(time to peak TTP)、最大峰值(peak enhancement intensity,PEI).结果与该兴趣区氧微电极法测得氧分压(PO2)对照.结果:45例成功建模兔VX2脑瘤兴趣区灌注值范围为1.3 ml/min～127.0 ml/min,平均为27.102 ml/min±26.723 ml/min;BV为1.2 ml/100g～53.1ml/100g,平均为22.196 ml/100g±13.680ml/100g,PEI为8.7 HU～124.6HU,平均为43.456 HU±28.73 HU; TTP为8.2 sec～62.5 sec,平均为38.823 sec±14.759 sec;对应区域PO2为0.14 mmHg～46.70mmHg,平均为15.981 mmHg±14.815mmHg.灌注值与对应区域PO2相关系数为0.673,有统计学意义(P=0.00).BV
王宇; 申锷; 胡兵
2011-01-01
Objective : To explore a noinvasive therapy of tumor by cavitation effect induced by microbuhbles mediated low frequency ultrasound radiation. Methods : VX2 tumor was implanted into the unilateral proximal thigh of 24 Newzealand white rabbits successfully. These rabbits were randomly divided into four groups, control group, simplicity microbubble group, simplicity ultrasound group, and ultrasound and microbubble group , when the tumors approached about 1. 0 centimeter in size, with 6 rabbits in each group. After treatment correspondently, measured the volume of gross tumor and observed the blood flow infusion by sonography for 2 weeks. Then, drew a growth curve and calculated the ratio of tumor growth,collected the tumor samples and histopathology damages were observed. Results: After treatment for two weeks , tumor volume and tumor growth ratio of ultrasound and microbubble group were significantly smaller than the other groups ( P ＜ 0. 01 ) , the blood flow reduction was observed by contrast enhanced ultrasonography. Necrosis was observed by histopathology. No statistical difference among control group, simplicity microbubble group and simplicity ultrasound group. Conclusion: Low frequency ultrasound radiation of 20kHz with microbubble sonoVue in vascular can inhibit the growth of VX2 soft - tissue tumors in rabbits. It might be the mechanism of the VX2 tumor microcirculation being selectively destroyed by microbubbles mediated ultrasound cavitation.%目的:探索低频超声辐照联合静脉注射微泡抑制肿瘤生长的非创伤性治疗肿瘤的新方法.方法:24只新西兰大白兔后腿肌肉内接种VX2肿瘤,瘤体长至1cm左右随机分为对照组、单纯微泡组、单纯超声组和超声微泡组.各组经相应处理后,超声检测肿瘤大小、观察瘤体内血流灌注情况,绘制肿瘤生长曲线,计算肿瘤增长百分率.病理学观察治疗后各组瘤体组织的病理学损伤.结果:治疗后2周结果显示超声微泡组
龚威; 查云飞; 闫力永; 邢栋; 王克军; 胡磊; 王娇; 刘昌盛
2015-01-01
Objective:To explore the feasibility of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI)based on the Reference-Region model for evaluating anti-tumor angiogenesis effect of endostar in rabbit VX2 bone tumor.Methods:20 rabbits with VX2 bone tumor (tumor size in soft tissue>1cm)were randomly divided into the control group (n= 10)and the experimental group (n= 10),and were accepted DCE-MRI examination before and 14 days after treatment (using saline in control group;using endostar with concentration of 1.5mg/8mL in experimental group).DCE-MRI parameters including microvascular permeability transfer constant (Ktrans )and microvascular permeability reflux con-stant (Kep )were acquired based on the Reference-Region model.All the rabbits were sacrificed after DCE-MRI scanning at the 14th day.MVD and VEGF expression were analyzed by immunohistochemical staining.Correlation analysis was per-formed between DCE-MRI parameters and immunohistochemistry results.Results:In the experimental group,the Ktrans , MVD and VEGF expression had statistical difference (P0.05)between the two regions.Before treatment,the Ktrans value of pe-ripheral region and central region of rabbit VX2 bone tumors in the control group were (32.58±3.10)and (28.5± 3.54)min-1 respectively;and were (27.7±4.75)and (23.9±4.40)min-1 in the experimental group;after treatment,they were (37.66±2.78)and (34.2±3.39)min-1 in control group,and were (22.2±4.29)and (18.3±4.23)min-1 in the ex-perimental group,respectively.In the experimental group,the Ktrans values of the peripheral region and central region of rab-bit VX2 bone tumors were correlated with the MVD and VEGF expression (r= 0.924,0.945,0.848 and 0.909,respective-ly;P0.01).Conclusion:The spatial distribution of blood perfusion in rabbit VX2 bone tumors has hetero-geneity.The Ktrans value in DCE-MRI based on the Reference-Region model can be applied to estimate the anti-tumor angio-genesis effect of endostar.%目的：
Magnetic and structural properties of antiferromagnetic VF{sub 3}
Reuvekamp, Patrick; Kremer, Reinhard; Eger, Roland [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Nenert, Gwilherm; Hansen, Thomas [Institut Laue-Langevin, 38042 Grenoble (France)
2013-07-01
We report on a magnetic and structural investigation of layered antiferromagnetic system vanadium (III) fluoride. VF{sub 3} crystallizes in a distorted ReO{sub 3} structure (R anti 3c) with rotated undistorted VF{sub 6} octahedra. The V{sup +3} cations are arranged in a triangular lattice with the possibility of exhibiting magnetic frustration. Polycrystalline samples of VF{sub 3} were investigated using heat capacity, dielectric, magnetic susceptibility and neutron powder diffraction methods. Combining our results, we confirmed that VF{sub 3} undergoes long-range antiferromagnetic order at ∝19 K in accordance with literature. The antiferromagnetic order results in a magnetic structure with the magnetic moments alternating between a parallel and b parallel alignments in the ab plane. A second phase transition can be seen at ∝120 K in the heat capacity and dielectric measurements possibly associated to a minute structural distortion.
Magnetic phase diagrams of classical triangular and kagome antiferromagnets
Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)
2011-04-27
We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.
Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase
Yamamoto, Seiji; Si, Qimiao
2006-03-01
We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.
Magnetic phase diagrams of classical triangular and kagome antiferromagnets.
Gvozdikova, M V; Melchy, P-E; Zhitomirsky, M E
2011-04-27
We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.
Role of the antiferromagnetic bulk spins in exchange bias
Schuller, Ivan K. [Center for Advanced Nanoscience and Physics Department, University of California San Diego, La Jolla, CA 92093 (United States); Morales, Rafael, E-mail: rafael.morales@ehu.es [Department of Chemical-Physics & BCMaterials, University of the Basque Country UPV/EHU (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Batlle, Xavier [Departament Física Fonamental and Institut de Nanociència i Nanotecnologia, Universitat de Barcelona, c/ Martí i Franqués s/n, 08028 Barcelona, Catalonia (Spain); Nowak, Ulrich [Department of Physics, University of Konstanz, 78464 Konstanz (Germany); Güntherodt, Gernot [Physics Institute (IIA), RWTH Aachen University, Campus RWTH-Melaten, 52074 Aachen (Germany)
2016-10-15
This “Critical Focused Issue” presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice. - Highlights: • We address the role of bulk antiferromagnetic spins in the exchange bias phenomenon. • Significant experiments on how bulk AFM spins determine exchange bias are highlighted. • We explain the model that accounts for experimental results.
Antiferromagnetic hedgehogs with superconducting cores
Goldbart, P.M.; Sheehy, D.E. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
1998-09-01
Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}
Yue-Yong Qi; Li-Guang Zou; Ping Liang; Dong Zhang
2007-01-01
AIM: To establish models of portal vein occlusion of hepatic VX2 tumor in rabbits and to evaluate the value of multi-slice CT.METHODS: Forty New Zealand rabbits were divided into 4 groups according to digital table: Immediate group (group A; transplantation of tumor immediately after the portal vein occlusion), 3-wk group (group B;transplantation of tumor at 3 wk after the portal vein occlusion), negative control group (group C) and positive control group (group D), 10 rabbits in each group.Hepatic VX2 tumor was transplanted with abdominal-embedding innoculation immediately after the portal vein occlusion and at 3 wk after the portal vein occlusion.Meanwhile, they were divided into negative control group (Left external branch of portal vein was occluded by sham-operation, and left exite was embedded and inoculated pseudoly) and positive control group (Transplanted tumor did not suffer from the portal vein occlusion). All rabbits were scanned with multi-slice CT.RESULTS: All 40 animals were employed in the final analysis without death. Tumor did not grow in both immediate group and 3-wk group. In 3-wk group, left endite was atrophied and growth of tumor was inhibited.The maximal diameter of tumor was significantly smaller than that in positive control group (2.55 ± 0.46 vs3.59 ± 0.37 cm, t = 5.57, P ＜ 0.001). Incidences of metastasis in the liver and lung were lower in 3-wk group than those in positive control group (10% vs 40%, and 90% vs 100%, respectively). The expression intensities of the vascular endothelium growth factor (VEGF) in groups A, B, C and D were 0.10 ± 0.06, 0.66 ± 0.21, 0.28± 0.09 and 1.48 ± 0.32, respectively. VEGF expression level in the test group A was significantly lower than that in the negative control group C (t = 5.07; P ＜ 0.001).In addition, VEGF expression in the test group B was significantly lower than that in the positive control group D (t = 6.38; P ＜ 0.001). Scanning with multi-slice CT showed that displaying rate of
阳红艳; 许乙凯; 吴元魁; 刘文源; 吕国士
2007-01-01
背景:CT和MRI对小于1 cm脾转移瘤结节的诊断的敏感度均不高,超顺磁性氧化铁粒子增强MR图像能否提高诊断敏感度有待研究.目的:建立大鼠脾脏转移瘤模型,结合特异的网状内皮系统对比剂超顺磁性氧化铁粒子行MRI扫描,探讨超顺磁性氧化铁粒子增强MR图像对脾转移瘤的诊断价值.设计:重复测量动物实验.单位:南方医科大学南方医院全军医学影像中心实验室.材料:实验于2005-05/2006-03在南方医科大学南方医院全军医学影像中心实验室完成,选用25只成年SD大鼠,雌雄不拘,体质量200～300 g,实验过程中动物的处置符合动物伦理学标准.摸球法将大鼠分为肿瘤组(n=20)及空白对照组(n=5).方法:制作脾脏荷VX2肿瘤模型鼠,注射超顺磁性氧化铁粒子后行MRI扫描,扫描序列采用T1加权成像(450/12 ms)和T2加权成像(4 000/128 ms).分析超顺磁性氧化铁粒子增强扫描前后MRI图像上不同组织的信号特点.空白对照组不制备模型,扫描序列与实验组相同.主要观察指标:超顺磁性氧化铁粒子增强扫描前后MRI图像上不同组织的信号特点.结果:纳入大鼠20只,肿瘤组8只死亡,其余12只与对照组5只均进入结果分析.肿瘤组行MR扫描发现有8只脾脏VX2肿瘤形成.①平扫SET1加权成像图像上正常脾实质相对于周围的肌肉及肝实质呈等信号,脾脏VX2肿瘤组织与周围的正常脾实质的信号强度对比较差,肿瘤-脾脏的对比噪声比极差,所有病灶均不能很好显示.②超顺磁性氧化铁粒子增强T2加权成像MR图像上正常脾实质信号强度与平扫时相比信号强度下降百分比为56.11%;脾脏VX2肿瘤信号强度与增强前比较无明显下降,信号强度下降百分比为1.90%,与正常脾实质的信号强度下降程度差异有显著性意义(P＜0.01).超顺磁性氧化铁粒子增强T2加权成像MR图像上脾VX2肿瘤信号强度无明显变化,而其周围正
江雄鹰; 张小萍; 黄金华; 罗荣光; 苗碧建; 王琰
2013-01-01
目的 探讨3-溴丙酮酸(3-BrPA)经肝动脉灌注对兔VX2肝肿瘤转移及荷瘤兔生存时间的影响.方法 18只新西兰大白兔肝左叶种植VX2肿瘤,随机分成3组,每组6只.PBS灌注组:在肿瘤种植14 d后行肝动脉PBS溶液灌注.3-BrPA 7和14 d灌注组:在肿瘤种植7/14 d后行肝动脉3-BrPA溶液灌注.在肿瘤种植28 d后每组处死3只兔,解剖探查有无肝内转移、肾转移、肺转移及腹腔转移.每组剩余的3只兔观察其生存时间并进行比较.结果 肿瘤种植28 d后,PBS灌注组均发现肝内及腹腔转移(3/3),肾转移2只(2/3),肺转移2只(2/3).3-BrPA 7 d灌注组实验兔肝内和肺转移各有1只(1/3),未发现有腹腔和肾转移(0/3).3-BrPA14 d灌注组实验兔有2只发现肝内转移(2/3),肺和腹腔转移各有1只(1/3),未发现肾转移(0/3).生存时间比较显示3-BrPA 14 d灌注组实验兔生存时间[(27±5)d]显著长于PBS溶液灌注组[(17±3)d](P=0.041).而3-BrPA 7 d灌注组实验兔生存时间[(42±6)d]显著长于3-BrPA 14 d灌注组实验兔[(27±5)d](P=0.007).结论 经肝动脉灌3-BrPA能够有效减少兔VX2肝肿瘤的转移,并可延长移植VX2肝肿瘤兔的生存时间,且灌注时间越早,治疗效果越好.%Objective To evaluate the metastasis and survival of an intra-arterial infusion of 3-bromopyruvate (3-BrPA) on hepatic VX2 tumor in rabbits.Methods VX2 tumor was implanted in left lateral lobe of liver of 18 white New Zealand rabbits.The animals were randomized into 3 groups (n =6 each) and underwent an intra-arterial infusion of phosphate-buffered saline or 3-BrPA via hepatic artery at 14 days post-implantation.At 28 days post-implantation,3 rabbits in each group were sacrificed.The abdomen of these rabbits was opened and inspected for metastases.Then the survival of the remaining rabbits was observed.Results At 28 days post-implantation,in PBS group,there were intrahepatic metastasis and abdominal cavity dissemination (n =3),renal metastases (n =2
Jiang Qing; Zhong Chonggui
2002-12-30
Soft-mode theory based on DIFFOUR model for ferroelectric interaction and the mean-field theory of high spin Ising model for antiferromagnetic interaction are used to investigate the ferroelectric, antiferromagnetic, magnetoelectric properties in ferroelectromagnetic lattice in which the ferroelectric order and antiferromagnetic order coexist simultaneously below a certain temperature. Ferroelectric polarization, spin moment, and magnetoelectric susceptibility as well, as a function of temperature for system, are calculated and compared with the different coupling coefficient. It is found that an anomaly appears in curve of the polarization susceptibility as a function of temperature due to the coupling between the ferroelectric and antiferromagnetic orders in the ferroelectromagnetic lattice. At the same time, we also considered the influence of magnetoelectric effect on polarization susceptibility by applying the external field including electric and magnetic.
Antiferromagnetic spin Seebeck effect.
Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-03
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.
Antiferromagnetic Spin Seebeck Effect
Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand
2016-03-01
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2 . A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm )/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T ) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.
Delemazure, A. S.; Salomir, R.; Grenier, N.; Palussière, J.; Deminière, C.; Mougenot, C.; Moonen, C. W.
2005-03-01
A significant number of patients with small renal tumours may get benefit from in situ thermo-ablation techniques. Focused ultrasound is a non-invasive approach which offers excellent flexibility. On the other hand, real time MR thermometry is a valuable tool for monitoring and controlling therapy. In this study, coupling of focused ultrasound with PRF-based, respiratory-gated MR thermometry was used to provide temperature feedback control for local hyperthermia in the rabbit kidney. Two heating protocols were initially used in healthy kidneys (medulla and cortex): 1. fixed focal point heating; 2. spiral trajectories of the focal point. Further, five VX2 renal carcinomas were treated with multiple focal point heating in each tumour. Post-treatment MRI follow up and post mortem histology were performed. The shape and size of the lesions (MRI, histology) were compared to the calculated thermal dose map. The standard deviation of the MR thermometry ranged from 0.5°C to 1°C. The temperature controller matched the objective curve with approximately 1°C precision (fixed focal point mode). Several technical and physiological difficulties for spiral heating could not be overcome with the available setup. Thermal ablation with temperature feedback control in healthy and tumour bearing kidney was demonstrated to be feasible and effective, despite specific challenges (deep seated organ, respiratory motion, high blood perfusion).
Hong, Tao [ORNL; Zhu, L. Y. [Argonne National Laboratory (ANL); Ke, X. [Michigan State University, East Lansing; Garlea, Vasile O [ORNL; Qiu, Y. [National Institute of Standards and Technol/University of Maryland, College Park; Nambu, Y. [Tohoku University, Sendai, Japan; Yoshizawa, H. [University of Tokyo, Tokyo, Japan; Zhu, M. [Michigan State University, East Lansing; Granroth, Garrett E [ORNL; Savici, Andrei T [ORNL; Gai, Zheng [ORNL; Zhou, H. D. [Department of Physics and Astronomy, University of Tennessee
2013-01-01
We report a comprehensive study of the DC susceptibility, specific heat, neutron diffraction, and inelastic neutron scattering measurements on the polycrystalline Ba3(Cr1-xVx)2O8 samples, where x=0, 0.06, 0.15, and 0.53. A Jahn-Teller structure transition occurs for x=0, 0.06, and 0.15 samples and the transition temperature is reduced upon vanadium substitution from 70(2) K at x=0 to 60(2) K at x=0.06 and 0.15. The structure becomes less distorted as x increases and such transition disappears at x=0.53. The observed magnetic excitation spectrum indicates that the singlet ground state remains unaltered and spin gap energy =1.3(1) meV is identical within the instrument resolution for all x. In addition, the dispersion bandwidth W decreases with increase of x. At x=0.53, W is reduced to 1.4(1) meV from 2.0(1) meV at x=0.
Huang, Lili; Shen, Ming; Li, Rongxin; Zhang, Xiangyu; Sun, Ying; Gao, Pei; Fu, Hao; Liu, Hongqiang; He, Yang; Du, Yuqing; Cao, Jun; Duan, Yourong
2016-11-08
Interventional embolization therapy is an effective, most widely used method for inoperable liver tumors. Blood-vessel-embolic agents were essential in transarterial embolization (TAE). In this work, thermo-sensitive composite hydrogels based on poloxamer 407, sodium alginate, hydroxymethyl cellulose and iodixanol (PSHI), together with Ca2+ (PSHI-Ca2+) were prepared as liquid embolic agents for TAE therapy to liver cancer. With increasing temperature, PSHI exhibited two phase states: a flowing sol and a shrunken gel. Rheology tests showed good fluidity and excellent viscoelastic behavior with a gelation temperature (GT) of 26.5°C. The studies of erosion indicated that PSHI had calcium ion-related erosion characteristics and showed a slow erosion rate in an aqueous environment. When incubated with L929 cells, the thermo-sensitive composite hydrogels had low cytotoxicity in vitro. The results of analyzing the digital subtraction angiography and computed tomography images obtained from in vitro and in vivo assays indicated a good embolic effect in the renal arteries of normal rabbits. Angiography and histological studies on VX2 tumor-bearing rabbits indicated that PSHI-Ca2+ successfully occluded the tumors, including the peripheral vessels. In conclusion, PSHI-Ca2+ was a promising embolic agent for transarterial embolization therapy.
Huang, Lili; Shen, Ming; Li, Rongxin; Zhang, Xiangyu; Sun, Ying; Gao, Pei; Fu, Hao; Liu, Hongqiang; He, Yang; Du, Yuqing; Cao, Jun; Duan, Yourong
2016-01-01
Interventional embolization therapy is an effective, most widely used method for inoperable liver tumors. Blood-vessel-embolic agents were essential in transarterial embolization (TAE). In this work, thermo-sensitive composite hydrogels based on poloxamer 407, sodium alginate, hydroxymethyl cellulose and iodixanol (PSHI), together with Ca2+ (PSHI-Ca2+) were prepared as liquid embolic agents for TAE therapy to liver cancer. With increasing temperature, PSHI exhibited two phase states: a flowing sol and a shrunken gel. Rheology tests showed good fluidity and excellent viscoelastic behavior with a gelation temperature (GT) of 26.5°C. The studies of erosion indicated that PSHI had calcium ion-related erosion characteristics and showed a slow erosion rate in an aqueous environment. When incubated with L929 cells, the thermo-sensitive composite hydrogels had low cytotoxicity in vitro. The results of analyzing the digital subtraction angiography and computed tomography images obtained from in vitro and in vivo assays indicated a good embolic effect in the renal arteries of normal rabbits. Angiography and histological studies on VX2 tumor-bearing rabbits indicated that PSHI-Ca2+ successfully occluded the tumors, including the peripheral vessels. In conclusion, PSHI-Ca2+ was a promising embolic agent for transarterial embolization therapy. PMID:27602579
Spatially frustrated S = 1 Heisenberg antiferromagnet with single ion anisotropy
Pires, A. S. T.
2016-10-01
Using the SU(3) Schwinger boson formalism, I study the S = 1 square lattice Heisenberg antiferromagnet, at zero temperature, with spatially anisotropic nearest-neighbor couplings frustrated by a next-nearest neighbor interaction and single ion anisotropy. The phase diagram at zero temperature is presented. My calculations show two magnetically ordered phases separated by a quantum-disordered region for all values of the anisotropy.
朱梅; 李佩倞; 钟渝; 梁红敏; 何利平; 刘政
2012-01-01
To investigate the blocking effect on microcirculation of rabbits VX2 tumors by low-intensity pulsed ultrasound combined with intravenous microbubble injection. Methods Thirty-six rabbits bearing subcutaneous VX2 tumors were randomly divided into 3 groups. For ultrasound combined with microbubbles group, pulsed ultrasound was delivered to the tumor surface for 10 min following intravenous infusion with microbubbles as ultrasound and microbubbles. For microbubbles group, only microbubbles were injected, while for ultrasound group, only exposure under pulsed ultrasound was performed. The tumor perfusion areas in CEUS were measured at 0, 30 min, 60 min. After treatment, 6 rabbits in each group were taken randomly to sacrifice for pathological observation. Results The contrast perfusion of tumors immediately vanished after treatment in ultrasound combined with microbubbles group, then recovered gradually at 30 min and 60 min. Pathological examination showed significant swell and hemorrhage, damages in the endothelia, abundance intercellular fluid, and in situ thrombosis in ultrasound combined with microbubbles group. There was no obvious change in CEUS and pathology in microbubbles group, nor in ultrasound group. Conclusion The tumor microcirculation can be blocked by microbubble associated with low energy ultrasound. The mechanism may be related to vessel wall injury caused by ultrasound cavitation, and tissue edema increases the resistance to the blood circulation of tumor areas.%目的 探讨低能量脉冲式超声联合微泡对兔VX2肿瘤微循环的阻断作用及其病理机制.方法 将36只皮下VX2荷瘤兔随机平均分成3组:超声微泡组注入0.2 ml/kg体质量微泡5ml,并辅以超声辐照10 min;单纯超声组注入生理盐水5 ml,辐照10 min;单纯微泡组仅注入0.2 ml/kg体质量微泡5 ml,不进行超声辐照.CEUS观察各组治疗前、治疗后0.30 min、60 min时血流灌注情况,比较各时间点的灌注面积.治
佟元涛
2015-01-01
Objective To evaluate the value of diagnosing rabbit VX2 peritoneal implantation metastasis tumor by 256 line CT JOG-H perfusion scan. Method The rabbits were induced into tumor models by injecting suspended particle, then CT perfusion scan were used to scan the abdomen of rabbit model. Pathological result was taken as gold standard to evaluate CT perfusion scan.Results CT perfusion scan was superior than CT enhanced scan in detecting the metastatic tumor less than 10mm,10-20 mm by CT enhanced scan.Conclusion CT perfusion scan was superior than CT enhanced scan in detecting the metastatic tumor less than 20 mm. In the focus greater than 20 mm, CT perfusion scan was equal to CT enhanced scan .%目的：评估CT灌注对腹腔内移植瘤的诊断价值。方法制作兔VX2腹膜腔移植瘤模型，对瘤兔腹部进行CT灌注扫描获得影像学结果，以病理结果为金标准评价CT增强加CT灌注的诊断价值。结果在对＜10 mm及对10~20 mm的腹腔种植瘤进行扫描对于病灶检出能力CT增强加CT灌注扫描要优于单纯CT增强扫描。结论对于20 mm以下的病灶CT增强加CT灌注扫描检出能力在敏感度、特异度、准确度方面优于单纯CT增强，而对于＞20 mm的病灶CT增强与CT增强加CT灌注检出结果相同均与病理结果一致。
易峰涛; 张永学; 王慧; 宋华志
2010-01-01
Objective To study the correlation of ~(18)F-fluorodeoxyglucose (FDG) PET/CT with pathological changes of the VX2 rabbit tumors after treatment of Ar-He knife,and to explore the evolution of the Ar-He knife curative effect for VX2 rabbit tumors.Methods Thirty-six Japanese white rabbits had successfully been implanted with VX2 tumors in thighs.Four weeks later,the rabbits with VX2 tumors were imaged with FDG PET/CT before they were treated with Ar-He cryoablation.The rabbits were evenly and randomly divided into 6 groups (6 rabbits in each group) and imaged with FDG PET/CT respectively on the first day,third day,seventh day,fourteenth day,thirtieth day and sixtieth day after cryoablation.The rabbits in each group were sacriftced after post-treatment FDG PET/CT imaging for pathology and immunohistochemistry studies.The standardized uptake value (SUV) of tumor regions were calculated and compared with pathology and immunohistochemistry findings in the cryoablative area in each group.Paired-samples t-test and bivariate correlation analysis were evaluated by statistical software SPSS 16.0.Results After ArHe cryoablation,pathological changes of "necrosis-inflammatory response→organization" were found.On CT imaging,the tumors enlarged during 3-14 d after treatment and then shrank gradually.On FDG PET imaging,the maximum SUV (SUV_(max)) dropped dramatically on the first day after the operation(from 2.54±1.12 to 0.67±0.12),and increased slightly on the third day (1.71±0.82),and then continually dropped to 0.51±0.32 (60 d afterthe operation).The differences of SUV_(max) between pre-and after cryoablationin each stage were significant,respectively (t=5.471,8.716,11.388,5.713,7.144 and 7.213,all P＜0.05).The size and SUV_(max) of the targeting area did not correlate with each other(r=0.259,P=0.675).The change of the MVD closely correlated with SUV_(max)(r=0.865,P=0.032).Conclusion FDG PET/CT can reveal the pathological change of tumor tissue after Ar-He cryoablation
Antiferromagnetic spin Seebeck Effect
Wu, SM; W. Zhang; Kc, A; Borisov, P.; Pearson, JE; Jiang, JS; Lederman, D.; Hoffmann, A.; Bhattacharya, A
2015-01-01
We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30 nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop t...
Topological gapless phases in nonsymmorphic antiferromagnets
Brzezicki, Wojciech; Cuoco, Mario
2017-04-01
We investigate the nature of the electronic states in a variety of nonsymmorphic collinear antiferromagnets with glide reflection symmetry, a combination of mirror and half-lattice translation. In particular, the study refers to a class of systems with two-band itinerant electrons that are spin-orbit coupled and interacting with a magnetic background having a zigzag pattern. We describe the symmetry properties of the model system by focusing on the role of nonsymmorphic transformations arising from the antiferromagnetic structure of the spin ordering. Gapless phases with Dirac points having different types of symmetry-protection as well as electronic structures with triple and quadruple band-crossing points are obtained. A glide semimetal is shown to be converted into a gapless phase with Dirac points protected by inversion and time-inversion symmetry combination. Interestingly, we find a relation between the states in the glide sectors that provides a general mechanism to get multiple band touching points. The split of the multiple Fermi points drives the transition from a point node to a line node semimetal or to a metal with nontrivial winding around the Fermi pockets and an electronic structure that is tied to the presence of glide symmetric Dirac points. Besides a new perspective of ordered states in complex materials, our findings indicate relevant paths to topological gapless phases and edge states in a wide class of magnetic systems.
Landau model for the multiferroic delafossite antiferromagnets
Ribeiro, J. L.; Perez-Mato, J. M.; Vieira, L. G.
2016-10-01
A symmetry based framework is used to describe the complex phase diagrams observed in the multiferroic delafossite compounds. A free energy Landau functional is derived from the analysis of the transformation properties of the most general incommensurate magnetic spin order parameter. A principle of maximal symmetry is invoked and the stability of each of the different higher symmetry phases considered. The competition between different potential ground states is analysed within the scope of a simplified model, which emphasizes the role of the symmetry allowed phase dependent biquadratic couplings. The cross-over between the different competing states is also discussed. The results show that the diverse set of phase diagrams that are experimentally observed in this class of triangular lattice antiferromagnets and, in particular, the stabilization of magnetically induced ferroelectric states, can be well interpreted and described within this integrated phenomenological approximation.
Transformation of spin current by antiferromagnetic insulators
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.
2016-06-01
It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current through the excitation of a pair of evanescent AFM spin wave modes. The spin current flowing through the AFM is not conserved due to the interaction between the excited AFM modes and the AFM lattice and, depending on the excitation conditions, can be either attenuated or enhanced. When the phase difference between the excited evanescent modes is close to π /2 , there is an optimum AFM thickness for which the output spin current reaches a maximum, which can significantly exceed the magnitude of the input spin current. The spin current transfer through the AFM depends on the ambient temperature and increases substantially when temperature approaches the Néel temperature of the AFM layer.
Probing the evolution of antiferromagnetism in multiferroics
Holcomb, M.; Martin, L.; Scholl, A.; He, Q.; Yu, P.; Yang, C.-H.; Yang, S.; Glans, P.-A.; Valvidares, M.; Huijben, M.; Kortright, J.; Guo,, J.; Chu, Y.-H.; Ramesh, R.
2010-06-09
This study delineates the evolution of magnetic order in epitaxial films of the room-temperature multiferroic BiFeO3 system. Using angle- and temperature-dependent dichroic measurements and spectromicroscopy, we have observed that the antiferromagnetic order in the model multiferroic BiFeO3 evolves systematically as a function of thickness and strain. Lattice-mismatch-induced strain is found to break the easy-plane magnetic symmetry of the bulk and leads to an easy axis of magnetization which can be controlled through strain. Understanding the evolution of magnetic structure and how to manipulate the magnetism in this model multiferroic has significant implications for utilization of such magnetoelectric materials in future applications.
von Reppert, A; Pudell, J; Koc, A; Reinhardt, M; Leitenberger, W; Dumesnil, K; Zamponi, F; Bargheer, M
2016-09-01
We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.
A. von Reppert
2016-09-01
Full Text Available We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.
Mao, Jingsong; Tang, Shunsong; Hong, Duo; Zhao, Fan; Niu, Meng; Han, Xiangjun; Qi, Ji; Bao, Han; Jiang, Yutian; Fu, Changhui; Long, Dan; Meng, Xianwei; Su, Hongying
2017-03-09
The use of nanomaterials as drug delivery systems shows good effects in treating tumors. However, the effective dose of drugs targeted to tumor tissues is very low because of the effect of the reticuloendothelial system (RES) in removing such foreign substances. In order to eliminate the RES effect, we developed mPEG-PLGA@ZrO2@(DOX + ILS) (mPEG-PLGA@ZrO2@[DOX + ILS]) drug-loaded microspheres. These microwave (MW)-sensitized microspheres directly embolized the blood-supply vessels of tumors to induce tumor ischemia and hypoxia, as well as to aggregate drugs within tumor tissues in a long-lasting manner. Additionally, combination with MW ablation can triple the effects for the inhibition of tumor growth. The MW sensitive ionic liquid (ILS) in microspheres can rapidly produce a high temperature in a MW field on the basis of MW sensitization, thus accelerating the degradation of microspheres to release DOX-loaded ZrO2 into the lesions to kill tumors. Microspheres can also prolong the pharmacological time and effect of drugs through the enhanced permeability and retention (EPR) effect of nanocarriers, as well as the sustained release of nanomaterials. Studies performed in vivo revealed that mPEG-PLGA@ZrO2@(DOX + ILS) showed good biosafety. We undertook sensitized microsphere embolism therapy using novel mPEG-PLGA@ZrO2@(DOX + ILS) microspheres in a rabbit VX2 liver tumor model. Three, 6 and 9 d after treatment, computed tomography indicated no significant change in tumor size, and diffusion weighted imaging showed a marked decrease of residual tumor tissues. With the multiple functions of inducing embolisms, sensitization, and the sustained release of chemotherapeutics, novel mPEG-PLGA@ZrO2@(DOX + ILS) microspheres can achieve good therapeutic efficacy, in combination with MW ablation and chemotherapy, while embolizing the blood vessels of arterial tumors.
Gholamrezanezhad, Ali; Mirpour, Sahar; Geschwind, Jean-Francois H; Rao, Pramod; Loffroy, Romaric; Pellerin, Olivier; Liapi, Eleni A
2016-10-01
To evaluate the pharmacokinetic profile (PK) and embolization effect of 70-150-μm doxorubicin eluting beads (DEBs) following intra-arterial injection (i.a.) in the rabbit liver VX2 tumour model. In this ACUC-approved study, 25 white New Zealand rabbits were randomly assigned into a small DEB group (SDB, n = 7, 70-150-μm DEBs), large DEB group (LDB, n = 7, 100-300-μm DEBs), untreated controls (n = 7), and doxorubicin controls (n = 4, without tumour, received i.a. 12.5 mg doxorubicin). Plasma PK was assessed up to 180 min post-injection. Drug tissue and liver enzyme levels, radiologic tumor response and histopathologic tumour necrosis were assessed at 7 days. Mean tumour doxorubicin concentrations were 922.83 nM (SD = 722.05) and 361.48 nM (SD = 473.23) for the SDB and LDB, respectively (p = 0.005). There was no statistically significant difference in tumour doxorubicinol, plasma doxorubicin and doxorubicinol PK values. More beads were observed in the SDB tumours (p = 0.01). Liver enzymes increased and gradually declined over the observation period, with significantly higher values in the SDB. In this preclinical study, plasma PK of i.a.-injected 70-150-μm DEBs was not different than that of 100-300-μm DEBs. More beads and higher tissue doxorubicin levels were observed in the SDB tumours. • Small and large doxorubicin-eluting beads show similar plasma pharmacokinetic profiles. • Higher tissue doxorubicin levels were observed in the small bead group. • Liver enzymes were overall significantly higher in the small bead group.
Kassner, Andrea; Thornhill, Rebecca E; Liu, Fang; Winter, Patrick M; Caruthers, Shelton D; Wickline, Samuel A; Lanza, Gregory M
2010-01-01
The purpose of this study was to evaluate the suitability of a macromolecular MRI contrast agent (paramagnetic nanoparticles, PNs) for the characterization of tumor angiogenesis. Our aim was to estimate the permeability of PNs in developing tumor vasculature and compare it with that of a low molecular weight contrast agent (Gd-DTPA) using dynamic contrast-enhanced MRI (DCE). Male New Zealand white rabbits (n = 5) underwent DCE MRI 12-14 days after Vx-2 tumor fragments were implanted into the left hind limb. Each contrast agent (PNs followed by Gd-DTPA) was evaluated using a DCE protocol and transendothelial transfer coefficient (K(i)) maps were calculated using a two-compartment model. Two regions of interest (ROIs) were located within the tumor core and hindlimb muscle and five ROIs were placed within the tumor rim. Comparisons were performed using repeated measures analysis of variance (ANOVA). The K(i) values estimated using PNs were significantly lower than those obtained for Gd-DTPA (p = 0.018). When PNs and Gd-DTPA data were analyzed separately, significant differences were identified among tumor rim ROIs for PNs (p < 0.0001), but not for Gd-DTPA data (p = 0.34). The mean K(i) for the tumor rim was significantly greater than that of either the core or the hindlimb muscle for both contrast agents (p < 0.05 for each comparison). In summary, the extravasation of Gd-DTPA was far greater than that of PNs, suggesting that PNs can reveal regional differences in tumor vascular permeability that are not otherwise apparent with clinical contrast agents such as Gd-DTPA. These results suggest that PNs show potential for the noninvasive delineation of tumor angiogenesis.
Superconductivity, antiferromagnetism, and neutron scattering
Tranquada, John M., E-mail: jtran@bnl.gov; Xu, Guangyong; Zaliznyak, Igor A.
2014-01-15
High-temperature superconductivity in both the copper-oxide and the iron–pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues. - Highlights: • High-temperature superconductivity is closely associated with antiferromagnetism. • Antiferromagnetic spin fluctuations coexist with the superconductivity. • Neutron scattering is essential for characterising the full spectrum of spin excitations.
齐劲松; 杨瑞民; 赵鹏; 张铭秋; 崔红凯
2013-01-01
Objective To observe the effect of interventional targeting administration of Ad-p53 combined with ultrasound irradiation in rabbit models of hepatic VX2 tumors, as well as its impact on VEGF and MMP2. Methods Forty-two Chinchilla rabbits were collected and VX2 cancer cells were injected into the left lobe of liver on the observation in rabbits. The growth of cancer was monitored by ultrasound. Thirty rabbit models were successfully made and divided into 3 groups (each n=10) randomly. Fourteen days after transplantation of cancer cells, Ad-p53 was administrated through hepatic artery (in Ad-p53 group) or combined with ultrasound wave irradiation (in Ad-p53 + US group), while the same amount of saline was given for rabbits in control group. Three days later, the tumor size was observed with ultrasound, and then all rabbits were sacrificed, the serum VEGF level was measured by ELISA, the hepatic tissue expression of p53, MMP2 and VEGF were detected respectively by immunohistochemistry, and expression level of wild type p53 was measured using Western blot. Results No difference of tumor size was found between 3 groups before therapy. All tumor sizes increased, but the tumors in Ad-p53 + US group were relatively smaller. The efficiency of Ad-p53 transfection was improved in Ad-p53 group compared with control group, which was the highest in Ad-p53 + US group. Furthermore, the serum VEGF level decreased in Ad-p53 + US group, so did the expression of MMP2 and VEGF in Ad-p53 group and Ad-p53 + US group, more obviously in Ad-p53 + US group. Conclusion Ad-p53 can suppress the growth of hepatic VX2 tumors in rabbit models. The therapeutic efficacy of Ad-p53 can be improved by interventional targeting administration combining with ultrasound irradiation.%目的 探讨介入导向下联合超声辐照对兔VX2肝癌模型Ad-p53转染效率及该基因对VEGF、MMP2的影响.方法 青紫蓝兔42只,直视下手术,将VX2肿瘤细胞种植于肝左叶,以超声检测
曹新山; 姜兴岳; 毛锡金; 王静; 秦东京
2012-01-01
目的 探讨磁共振背景信号抑制弥散加权成像( MR DWIBS)在评价磁标记负载肝癌抗原的树突状细胞疫苗活体内移植后对原发性肝癌的治疗作用.方法 用粒/巨细胞集落刺激因子(GM-CSF)和白细胞介素4(IL-4)诱导分化DC获得DC疫苗.并且用超顺磁性氧化铁标记.建立兔VX2肝癌模型,皮下注射磁标记的DC疫苗,观察DC疫苗的体内分布.运用DWIBS不同时间点活体检测肿瘤的大小、形态.结果 ①DC疫苗的体内分布.滏射树突状细胞疫苗后,兔肝细胞内可见较多蓝染铁颗粒沉着,而仅有少数Kupffer细胞内可见蓝染铁颗粒沉着；②肿瘤的DWIBS影像上,肝实质信号减低最显著,肿瘤边界清楚；③同时间点治疗组与对照组的凋亡指数(AI)情况:治疗后1周、2周治疗组分别与相应对照组凋亡指数差异有统计学意义(P＜0.05)；④不同时间点治疗组及对照组的ADC比值情况:治疗后1周、2周治疗组分别与相应对照组ADC比值差异有统计学意义(P＜0.05).结论 磁标记负载肝癌抗原的Dc疫苗体内能诱导产生明显的抑瘤作用.而用DWIBS成像技术则为原发性肝癌的免疫基因治疗提供了重要的形态学信息.%Objective To investigate the MRI DWIBS imaging in the evaluation of effectivenesse of magnetic labeled dendritic cell vaccine in treatment of rabbit liver VX2 tumor. Methods In this work, GM-CSF and IL-4 were employed to induce the differentiation of dendritic cell (DC) to gain DV vaccine, which was further labeled with superparamagnetic iron oxides. The rabbit VX2 liver cancer model was then established and the magnetic labeled DC vaccine was injected into this model. The electrical microscopy was used to prove DC vaccine distribution in vivo. The changes in tumor volume and shape were observed by MRI DWIBS at different time points. Results ①Distribution of DC vaccine in vivo: after the administration of DC vaccine, many blue iron deposits were seen in
Rogério Saad-Hossne
2007-08-01
Full Text Available PURPOSE: To analyze, in vitro, the effects of acetylsalicylic acid (aspirin and acetic acid solutions on VX2 carcinoma cells in the liver of rabbits with VX2 hepatic tumors; to determine the histolytic and anatomopathological characteristics of the solutions; and to evaluate the eventual biochemical and hepatic changes. METHODS: A total of 48 rabbits were evaluated. The animals were randomized into two groups, protocol 3 (study group and protocol 4 (controls, and each group was then subdivided into 3 subgroups. Four days after implantation of the tumor in the liver, median laparotomy was performed with a 0.4-ml injection of a solution of either aspirin (5.0%, acetic acid (5.0% or saline. The animals were sacrificed after 24 hours (protocol 3 or after 11 days (protocol 4. Body weight, clinical evolution and biochemical levels, as well as the abdominal and thoracic cavities, were evaluated, and liver microscopy was performed. RESULTS: No changes in clinical evolution, body weight or biochemical levels were reported. However, an increase in alkaline phosphatase was observed in protocol 4 (controls. The tumor was eliminated in both protocols. CONCLUSION: Acetylsalicylic acid and acetic acid solutions cause the destruction of experimental hepatic tumors.OBJETIVO: Analisar os efeitos das soluções de aspirina e de ácido acético, in vivo, em fígado de coelhos portadores de tumor hepático VX2, verificando o efeito histolítico e anatomo-patológico das soluções e eventuais alterações bioquímicas hepáticas. MÉTODOS: Utilizou-se 48 coelhos, divididos em 2 protocolos experimentais(3 e 4, subdivididos em 3 grupos cada. Após 4 dias da implantação do tumor no fígado, procedeu-se a laparotomia mediana, com injeção de 0,4 ml da solução de aspirina (5,0%, de ácido acético (5,0% e solução salina; o sacrifício ocorreu apos 24 horas (protocolo 3 e 11 dias (protocolo 4; avaliou-se o peso, evolução clinica, dosagens bioquímicas, cavidade
潘栋辉; 杨敏; 徐宇平; 王立振; 刘璐; 黄培林
2011-01-01
背景与目的 新型放射性植入剂32P-磷酸铬-聚-L-乳酸(32p-CP-PLLA)粒子具有良好的生物相容性和降解性,适用于实体肿瘤的近距离放射治疗.本研究旨在探讨兔VX2肺肿瘤经32P-CP-PLLA粒子瘤体间植入近距离治疗前后PET/CT显像及病理学的变化,分析32P-CP-PLLA粒子植入对荷VX2肺癌兔肿瘤生长及凋亡相关蛋白的影响.方法 24只荷瘤兔随机分成4组.每组6只.1组-3组为治疗组;4组为对照组.在CT导引下经皮穿刺将总放射性活度为93 MBq、185 MBq和370 MBq的32P-CP-PLLA粒子分别植入1组、2组和3组肿瘤组织内.对照组不做任何干预.分别在治疗后第0天、第3天、第7天和第14天进行18F-FDG PET/CT显像,观察标准摄取值(standardized uptake value,SUV)的变化.最后1次PET/CT显像后处死荷瘤兔,取出肿瘤组织,进行病理学检查和免疫组织化学分析,比较肿瘤细胞形态和凋亡基因(bd-2,bax)表达的变化.结果 第0天时,治疗组和对照组之间SUVmax无明显差异.治疗后第14天,1组、2组和3组SUVmax值分别为1.1±0.19、0.80±0.10和2.85±0.15,均较对照组(5.61±0.50)明显下降.第7天-第14天时,1组和2组SUVmax较第3天呈现持续下降趋势,且呈剂量效应关系(P＜0.05).治疗后第3天-第14天,3组SUVmax较第0天显著上升,并在第7天达到峰值,后明显下降.同期3组SUVmax明显低于对照组SUVmax.HE染色显示近粒子处的肿瘤细胞变性坏死,坏死程度随剂量的增加而严重.3组可见坏死组织周围有大量炎性细胞浸润,而1组-2组炎性细胞浸润不明显.免疫组化显示治疗组bcl-2表达强度低于对照组,bax表达强度高于对照组(P＜0.05).治疗组bd-2/bax比值明显下调(P＜0.05).凋亡基因的表达呈剂量效应关系.结论 32P-CP-PLLA粒子持续照射可直接杀伤VX2肿瘤细胞从而抑制其葡萄糖代谢功能.远离粒子处虽可见存活肿瘤细胞,但凋亡基因表达明显异于对照组.32P-CP-PLLA
刘曦; 罗小平; 曹闻挺; 邓昊
2012-01-01
目的 评价平阳霉素混合碘油经肿瘤滋养动脉化疗栓塞对兔VX2肝癌的肿瘤组织、滋养血管及血管新生的影响.方法 将28只新西兰大白兔采用移植法建立兔VX2肝癌模型,并随机均分为单纯碘油组(A组)、平阳霉素组(B组)、平阳霉素加碘油组(C组)和等渗盐水对照组(D组).模型均于建模后第14天行CT检查并计算肿瘤体积V1,然后对各组模型作相应处理:A组经肿瘤滋养动脉注入超液态碘油,B组经肿瘤滋养动脉注入平阳霉素,C组经肿瘤滋养动脉注入平阳霉素加超液态碘油,D组经肿瘤滋养动脉注入等渗盐水.7d后再行CT检查,计算肿瘤体积V2及肿瘤的生长率.处死实验兔进行病理学检查,计算血管内皮生长因子(VEGF)阳性表达率及微血管密度(MVD).组间数据的比较用单因素方差分析,多组的两两间比较用LSD法,两组间比较用成组t检验,对方差不齐者用秩和检验;VEGF表达与MVD值比较用双变量相关分析;阳性表达率的比较用精确概率法.结果 A、B、C、D组介入治疗前的肿瘤体积分别为(389.8±167.3) mm3、(404.1±184.9) mm3、(355.1±158.3) mm3和(378.1±189.0) mm3,差异无统计学意义(F=0.257,P＞0.05);术后肿瘤体积分别为(922.6±32.9) mm3、(665.9±99.9) mm3、(349.5±177.8) mm3和(1403.5±411.2) mm3,差异有统计学意义(F=26.23,P＜0.05),且B组和C组明显小于A组和D组;VEGF阳性表达率分别为57.1％、42.9％、28.6％和100％,差异有统计学意义(F=8.407,P＜0.05).D组残余肿瘤区MVD显著升高(36.4±3.7),与A组(22.4±3.9)、B组(18.7±2.6)和C组(14.1±2.3)比较,差异有统计学意义(t值分别为6.89、10.34和13.49,P值均＜0.05),且C组明显低于其他各组(t值分别为4.89、3.53和13.49,P值均＜0.05).VEGF阳性表达率与MVD存在正相关关系(r=0.743,P＜ 0.01).结论 平阳霉素对兔VX2肝癌有较好的治疗效果,联合超液态碘油经肝动脉化
韩璐; 罗文; 郭凯; 李轲; 刘海静; 慕喜喜; 周晓东
2015-01-01
目的 观察在亚高温场中载水飞蓟宾热敏脂质体——微泡复合体(STLMC)对兔肝VX2肿瘤的作用.方法 将40只VX2荷瘤兔的40个肝转移瘤随机分为4组,每组10只动物:微波亚高温辐照组(SHM)、水飞蓟宾载药微泡组(STLMC)、微波亚高温辐照联合水飞蓟宾载药微泡治疗组(SHM+STLMC)、空白对照组(BL).分别给予不同干预:微波热辐照、STLMC注射、微波热辐照联合STLMC注射、无辐照无注射.治疗后7d及21 d,采用二维灰阶超声、超声造影成像分别评价术后各组肿瘤体积和最大径的变化.透射电镜观察各组干预区超微结构变化.结果 SHM+STLMC组术后7d及21d肿瘤体积及最大径均明显小于同期其余各组(P＜0.05);电镜下各组均出现染色质异常、细胞器受损的巨噬细胞,SHM+STLMC组受损巨噬细胞数目较其余各组明显增多(P＜0.05).结论 在亚高温场中STLMC可造成肿瘤微环境中巨噬细胞形态破坏,抑制肿瘤生长.
Lattice effects in YVO3 single crystal
Marquina, C; Sikora, M; Ibarra, MR; Nugroho, AA; Palstra, TTM
2005-01-01
In this paper we report on the lattice effects in the Mott insulator yttrium orthovanadate (YVO3). Linear thermal expansion and magnetostriction experiments have been performed on a single crystal, in the temperature range from 5 K to room temperature. The YVO3 orders antiferromagnetically at T-N =
Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs.
Wadley, P; Novák, V; Campion, R P; Rinaldi, C; Martí, X; Reichlová, H; Zelezný, J; Gazquez, J; Roldan, M A; Varela, M; Khalyavin, D; Langridge, S; Kriegner, D; Máca, F; Mašek, J; Bertacco, R; Holý, V; Rushforth, A W; Edmonds, K W; Gallagher, B L; Foxon, C T; Wunderlich, J; Jungwirth, T
2013-01-01
Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.
Creation of an antiferromagnetic exchange spring
Scholl, A.; Liberati, M.; Arenholz, E.; Ohldag, H.; Stohr, J.
2004-04-06
We present evidence for the creation of an exchange spring in an antiferromagnet due to exchange coupling to a ferromagnet. X-ray magnetic linear dichroism spectroscopy on single crystal Co/NiO(001) shows that a partial domain wall is wound up at the surface of the antiferromagnet when the adjacent ferromagnet is rotated by a magnetic field. We determine the interface exchange stiffness and the antiferromagnetic domain wall energy from the field dependence of the direction of the antiferromagnetic axis, the antiferromagnetic pendant to a ferromagnetic hysteresis loop. The existence of a planar antiferromagnetic domain wall, proven by our measurement, is a key assumption of most exchange bias models.
Tian, Mei; Lu, Wei; Zhang, Rui; Xiong, Chiyi; Ensor, Joe; Nazario, Javier; Jackson, James; Shaw, Colette; Dixon, Katherine A.; Miller, Jennifer; Wright, Kenneth; Li, Chun; Gupta, Sanjay
2014-01-01
Purpose This study was designed to investigate the intratumoral uptake of hollow gold nanospheres (HAuNS) after hepatic intra-arterial (IA) and intravenous (IV) injection in a liver tumor model. Materials and Methods Fifteen VX2 tumor-bearing rabbits were randomized into five groups (N=3 in each group) that received either IV 64Cu-labeled PEG-HAuNS (IV-PEG-HAuNS), IA 64Cu-labeled PEG-HAuNS (IA-PEG-HAuNS), IV cyclic peptide (RGD)-conjugated 64Cu-labeled PEG-HAuNS (IV-RGD-PEG-HAuNS), IA RGD-conjugated 64Cu-labeled PEG-HAuNS (IA-RGD-PEG-HAuNS), or IA 64Cu-labeled PEG-HAuNS with lipiodol (IA-PEG-HAuNS-lipiodol). The animals underwent PET/CT 1 hour after injection, and uptake expressed as percentage of injected dose per gram of tissue (%ID/g) was measured in tumor and major organs. The animals were euthanized 24 hours after injection, and tissues were evaluated for radioactivity. Results At 1 hour after injection, animals in the IA-PEG-HAuNS-lipiodol group showed significantly higher tumor uptake (P < 0.001) and higher ratios of tumor-to-normal liver uptake (P < 0.001) than those in all other groups. The biodistribution of radioactivity 24 hours after injection showed that IA delivery of PEG-HAuNS with lipiodol resulted in the highest tumor uptake (0.33 %ID/g; P < 0.001) and tumor-to-normal liver ratio (P < 0.001) among all delivery methods. At 24 hours, the IA-RGD-PEG-HAuNS group showed higher tumor uptake than the IA-PEG-HAuNS group (0.20 %ID/g vs. 0.099 %ID/g; P < 0.001). Conclusion Adding iodized oil to IA-PEG-HAuNS maximizes nanoparticle delivery to hepatic tumors and therefore may be useful in targeted chemotherapy and photoablative therapy. PET/CT can be used to noninvasively monitor the biodistribution of radiolabeled HAuNS after IV or IA injection. PMID:23608932
Antiferromagnetic skyrmion crystals: Generation, topological Hall, and topological spin Hall effect
Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid
2017-08-01
Skyrmions are topologically nontrivial, magnetic quasiparticles that are characterized by a topological charge. A regular array of skyrmions, a skyrmion crystal (SkX), features the topological Hall effect (THE) of electrons, which, in turn, gives rise to the Hall effect of the skyrmions themselves. It is commonly believed that antiferromagnetic skyrmion crystals (AFM-SkXs) lack both effects. In this Rapid Communication, we present a generally applicable method to create stable AFM-SkXs by growing a two-sublattice SkX onto a collinear antiferromagnet. As an example we show that both types of skyrmion crystals, conventional and antiferromagnetic, exist in honeycomb lattices. While AFM-SkXs with equivalent lattice sites do not show a THE, they exhibit a topological spin Hall effect. On top of this, AFM-SkXs on inequivalent sublattices exhibit a nonzero THE, which may be utilized in spintronics devices. Our theoretical findings call for experimental realization.
Hida, Kazuo
1992-03-01
The quantum disordered state (QDOS) of the spin 1/2 double layer square lattice Heisenberg antiferromagnet is studied. Using the dimer expansion from the limit of the large interlayer coupling J', the staggered susceptibility χ, the antiferromagnetic structure factor Sπ and the antiferromagnetic correlation length ξ are calculated up to the 6-th order in the intralayer coupling J. The ratio analysis shows that the QDOS becomes unstable against the Néel ordering at J'/J≃2.56. The critical exponents are not inconsistent with the universality class of the 3-dimensional classical Heisenberg model, suggesting that our QDOS corresponds to that expected in the 2-dimensional square lattice Heisenberg antiferromagnet with unphysically small spin (<0.276). The results of the projector Monte Carlo simulation also confirms the dimer expansion results.
STUDIES OF FCC HEISENBERG ANTIFERROMAGNETS BY MONTE CARLO SIMULATION ON LARGE SPIN ARRAYS
Minor, W.; Giebultowicz, T.
1988-01-01
We report Monte Carlo studies of fcc Heisenberg antiferromagnets carried out on arrays with 108,000 spins. A lattice with only JNN ≠ 0 was found to exhibit a Type I AF order despite the disordered nature of its ground state. Contrary to previous reports, our data indicate in this case a first order phase transition.
Neutron-scattering cross section of the S=1/2 Heisenberg triangular antiferromagnet
Lefmann, K.; Hedegård, P.
1994-01-01
In this paper we use a Schwinger-boson mean-field approach to calculate the neutron-scattering cross section from the S = 1/2 antiferromagnet with nearest-neighbor isotropic Heisenberg interaction on a two-dimensional triangular lattice. We investigate two solutions for T = 0: (i) a state with long...
Improved lower bounds on the ground-state entropy of the antiferromagnetic Potts model.
Chang, Shu-Chiuan; Shrock, Robert
2015-05-01
We present generalized methods for calculating lower bounds on the ground-state entropy per site, S(0), or equivalently, the ground-state degeneracy per site, W=e(S(0)/k(B)), of the antiferromagnetic Potts model. We use these methods to derive improved lower bounds on W for several lattices.
Thermophoresis of an antiferromagnetic soliton
Kim, Se Kwon; Tchernyshyov, Oleg; Tserkovnyak, Yaroslav
2015-07-01
We study the dynamics of an antiferromagnetic soliton under a temperature gradient. To this end, we start by phenomenologically constructing the stochastic Landau-Lifshitz-Gilbert equation for an antiferromagnet with the aid of the fluctuation-dissipation theorem. We then derive the Langevin equation for the soliton's center of mass by the collective coordinate approach. An antiferromagentic soliton behaves as a classical massive particle immersed in a viscous medium. By considering a thermodynamic ensemble of solitons, we obtain the Fokker-Planck equation, from which we extract the average drift velocity of a soliton. The diffusion coefficient is inversely proportional to a small damping constant α , which can yield a drift velocity of tens of m/s under a temperature gradient of 1 K/mm for a domain wall in an easy-axis antiferromagnetic wire with α ˜10-4 .
Schwandt, David; Mambrini, Matthieu; Poilblanc, Didier
2010-06-01
We propose a general nonperturbative scheme that quantitatively maps the low-energy sector of spin-1/2 frustrated Heisenberg antiferromagnets to effective generalized quantum dimer models. We develop the formal lattice-independent frame and establish some important results on (i) the locality of the generated Hamiltonians, (ii) how full resummations can be performed in this renormalization scheme. The method is then applied to the much debated kagome antiferromagnet for which a fully resummed effective Hamiltonian—shown to capture the essential properties and provide deep insights on the microscopic model [D. Poilblanc, M. Mambrini, and D. Schwandt, Phys. Rev. B 81, 180402(R) (2010)]—is derived.
Superconductivity, antiferromagnetism, and neutron scattering
Tranquada, John M.; Xu, Guangyong; Zaliznyak, Igor A.
2014-01-01
High-temperature superconductivity in both the copper-oxide and the iron-pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues.
Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi; Tomiyasu, Keisuke
2011-07-01
Ultrasound velocity measurements of the orbitally frustrated spinel GeCo2O4 reveal unique elastic anomalies within the antiferromagnetic phase. Temperature dependence of shear moduli exhibits a minimum within the antiferromagnetic phase, suggesting the coupling of shear acoustic phonons to molecular spin-orbit excitations. Magnetic-field dependence of elastic moduli exhibits diplike anomalies, being interpreted as magnetic-field-induced metamagnetic and structural transitions. These elastic anomalies suggest that the survival of geometrical frustration, and the interplay of spin, orbital, and lattice degrees of freedom evoke a set of phenomena in the antiferromagnetic phase.
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.
Ferromagnetic and antiferromagnetic order in bacterial vortex lattices
Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.
2016-01-01
This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nphys3607 Despite their inherently non-equilibrium nature [1] , living systems can self-organize in highly ordered collective states [2,3] that share striking similarities with the thermodynamic equilibrium phases [4,5] of conventional condensed-matter and fluid systems. Examples range from the liquid-crystal-like arrangements of bacterial colonies [6,7], microb...
Fractional excitations in the square-lattice quantum antiferromagnet
Piazza, B. Dalla; Mourigal, M.; Christensen, Niels Bech
2015-01-01
Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum ...
罗仕华; 郑传胜; 冯敢生; 孙细梅; 周国锋; 梁惠民; 夏向文; 方建林
2010-01-01
Objective To evaluate the efficacy of recombinant human adenovirus p53 gene therapy (rAd-p53) in the rabbit VX2 liver cancer model using different interventional therapy approach. Methods Thirty New Zealand rabbits implanted with VX2 tumor in the liver were randomized into five groups with six of each. The tumor volumes (V1) were measured by MRI and CT scan 11 days after tumors implanted. The interventional therapy scheme performed as below: intraarterial 0.9% saline solution perfusion in group A, transcatheter arterial embolization with 0.5ml ultrafluid lipoidol in group B, intraarterial rAd-p53 gene perfusion in group C (1×106/VP); intraarterial rAd-p53 gene perfusion (1×107VP) in combination with transcatherter arterial etnbolization (ultrofluid lipiodol, 0.5 ml) in group D and intratumoral rAd-p53 gene (1 ×10/VP) injection in group E. The tumor volumes (V2) were measured by MRI and CT scan, and the tumor growth ratios were calculated 14 days after interventional procedures. Then all animals were sacrificed.The tumor tissues were explanted for irnrnunohistochemistry to observe the expressions of vascular endothelial cell growth factor (VEGF) and factor VIH. Microvessel density (MVD) of the tumor tissues was assessed by factor Ⅷ immunohistochemical analysis. In addition, apoptotic index was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Results The tumor volumes before therapy were (79.4 ±8.2), (75.3±7.8), (74.6±6.6), (78.7± 9.1), (75.8±8.4) mm3 respectively, without differences found among them (F = 12.248, P = 0.0636). But the tumor volumes after therapy were (564.7 ±96.7), (176.5 ±83.2), (239.6 ± 42.8), (159.8 ± 58.6), (334.7 ± 32.6) mm3 respectively (F= 24.537, P = 0.0218). The tumor growth ratios were 6.9, 2.6, 3.1,1.6 and 4.1 respectively. The mean apoptosis index were 12.0% ± 1.1%, 14.5%± 2.1%, 17.6% ± 2.3%, 18.6% ± 2.3% and 19.6% ± 2.5% respectively, with significant differences in group E in
Symmetry Reduction in the Quantum Kagome Antiferromagnet Herbertsmithite
Zorko, A.; Herak, M.; Gomilšek, M.; van Tol, J.; Velázquez, M.; Khuntia, P.; Bert, F.; Mendels, P.
2017-01-01
Employing complementary torque magnetometry and electron spin resonance on single crystals of herbertsmithite, the closest realization to date of a quantum kagome antiferromagnet featuring a spin-liquid ground state, we provide novel insight into different contributions to its magnetism. At low temperatures, two distinct types of defects with different magnetic couplings to the kagome spins are found. Surprisingly, their magnetic response contradicts the threefold symmetry of the ideal kagome lattice, suggesting the presence of a global structural distortion that may be related to the establishment of the spin-liquid ground state.
Quenching the haldane gap in spin-1 Heisenberg antiferromagnets.
Wierschem, Keola; Sengupta, Pinaki
2014-06-20
We consider a quasi-one-dimensional system of spin-1 Heisenberg antiferromagnetic chains in two-dimensional and three-dimensional hypercubic lattices with interchain coupling J and uniaxial single-ion anisotropy D. Using large-scale numerical simulations, we map out the J-D phase diagram and investigate the low-lying excitations of the Haldane phase in the J≪1 limit. We also provide direct evidence that the Haldane phase remains a nontrivial symmetry-protected topological state for small but finite J.
Density matrix renormalization group numerical study of the kagome antiferromagnet.
Jiang, H C; Weng, Z Y; Sheng, D N
2008-09-12
We numerically study the spin-1/2 antiferromagnetic Heisenberg model on the kagome lattice using the density-matrix renormalization group method. We find that the ground state is a magnetically disordered spin liquid, characterized by an exponential decay of spin-spin correlation function in real space and a magnetic structure factor showing system-size independent peaks at commensurate magnetic wave vectors. We obtain a spin triplet excitation gap DeltaE(S=1)=0.055+/-0.005 by extrapolation based on the large size results, and confirm the presence of gapless singlet excitations. The physical nature of such an exotic spin liquid is also discussed.
Phase transitions in antiferromagnets with a NaCl structure
Kassan-Ogly, F.A. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)]. E-mail: felix.kassan-ogly@imp.uran.ru; Filippov, B.N. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)
2006-05-15
A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Neel point.
Phase transitions in antiferromagnets with a NaCl structure
Kassan-Ogly, F. A.; Filippov, B. N.
2006-05-01
A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Néel point.
Z2 antiferromagnetic topological insulators with broken C4 symmetry
Bègue, Frédéric; Pujol, Pierre; Ramazashvili, Revaz
2017-04-01
A two-dimensional topological insulator may arise in a centrosymmetric commensurate Néel antiferromagnet (AF), where staggered magnetization breaks both the elementary translation and time reversal, but retains their product as a symmetry. Fang et al. [6] proposed an expression for a Z2 topological invariant to characterize such systems. Here, we show that this expression does not allow to detect all the existing phases if a certain lattice symmetry is lacking. We implement numerical techniques to diagnose topological phases of a toy Hamiltonian, and verify our results by computing the Chern numbers of degenerate bands, and also by explicitly constructing the edge states, thus illustrating the efficiency of the method.
贾飞鸽; 张晓东; 许乙凯; 孟卓
2009-01-01
目的 尝试合成肝脏靶向对比剂乳糖基白蛋白超顺磁氧化铁(Gal-BSA-SPIO),探讨Gal-BSA-SPIO对肝癌的检出及其诊断价值.材料和方法采用还原胺法合成Gal-BSA.Gal-BSA与SPIO混合后超声振荡.建立20只兔的、VX2肝癌模型,随机分为SPIO组和Gal-BSA-SPIO组,行MR平扫及增强.测定肝脏及肿瘤的T2值.对13例人肝脏标本(肝癌6例、肝硬化4例、正常肝组织3例)Gal-BSA-SPIO孵育后,Perl's染色,观察去唾液酸糖蛋白(ASG)受体分布.统计学方法:对增强前后各组的T2值进行t检验.结果 Gal-BSA-SPIO平均粒径34.4 nm.20只兔VX2肿瘤直径3～12 nm,T1WI肝实质呈中等信号,肿瘤呈低信号,T2WI肝实质低信号,病灶为略高信号;GRE T2*WI肝实质中等信号,肿瘤略高信号.增强扫描,SPIO组T2WI肝实质信号轻中度下降,与肿瘤对比提高;Gal-BSA-SPIO组T2WI肝实质信号显著下降,肿瘤呈明亮的"灯泡征".正常肝脏的SPIO组和Gal-BSA-SPIO组增强后T2值明显下降,与增强前有显著性差异.肿瘤的SPIO组和Gal-BSA-SPIO组增强后T2值无明显下降,与增强前无显著性差异.组织学检查SPIO组,Kupffer细胞内见蓝染的铁颗粒;Gal-BSA-SPIO组.肝细胞内见较多的蓝染的铁颗粒,两组的肿瘤内未见蓝染的铁颗粒.Gal-BSA-SPIO孵育后,正常肝组织可见大量蓝染色,肝硬化及癌旁肝硬化组织均可见蓝染色;肝细胞癌罕见蓝染色.结论 Gal-BSA-SPIO可以与肝细胞膜的ASG受体可特异性结合,通过受体介导的特异性对肝脏产生负向增强作用,明显提高肿瘤对比噪声比.
Lattice-Gas Automata for the Problem Of Kinetic Theory of Gas During Free Expansion
Khotimah, Siti Nurul; Arif, Idam; Liong, The Houw
The lattice-gas method has been applied to solve the problem of kinetic theory of gas in the Gay-Lussac-Joule experiment. Numerical experiments for a two-dimensional gas were carried out to determine the number of molecules in one vessel (Nr), the ratio between the mean square values of the components of molecule velocity (/line{vx2}//line{v_y^2}), and the change in internal energy (ΔU) as a function of time during free expansion. These experiments were repeated for different sizes of an aperture in the partition between the two vessels. After puncturing the partition, the curve for the particle number in one vessel shows a damped oscillation for about half of the total number. The oscillations do not vanish after a sampling over different initial configurations. The system is in nonequilibrium due to the pressure equilibration, and here the flow is actually compressible. The equilibration time (in time steps) decreases with decreased size of aperture in the partition. For very small apertures (equal or less than 9{√{3}}/{2} lattice units), the number of molecules in one vessel changes with time in a smooth way until it reaches half of the total number; their curves obey the analytical solution for quasi-static processes. The calculations on /line{vx2}//line{v_y^2} and ΔU also support the results that the equilibration time decreases with decreased size of aperture in the partition.
Chakrabarti, J; Bagchi, B; Chakrabarti, Jayprokas; Basu, Asis; Bagchi, Bijon
2000-01-01
Fermions on the lattice have bosonic excitations generated from the underlying periodic background. These, the lattice bosons, arise near the empty band or when the bands are nearly full. They do not depend on the nature of the interactions and exist for any fermion-fermion coupling. We discuss these lattice boson solutions for the Dirac Hamiltonian.
Large anomalous Hall effect in a half-Heusler antiferromagnet
Suzuki, T.; Chisnell, R.; Devarakonda, A.; Liu, Y.-T.; Feng, W.; Xiao, D.; Lynn, J. W.; Checkelsky, J. G.
2016-12-01
The quantum mechanical (Berry) phase of the electronic wavefunction plays a critical role in the anomalous and spin Hall effects, including their quantized limits. While progress has been made in understanding these effects in ferromagnets, less is known in antiferromagnetic systems. Here we present a study of antiferromagnet GdPtBi, whose electronic structure is similar to that of the topologically non-trivial HgTe (refs ,,), and where the Gd ions offer the possibility to tune the Berry phase via control of the spin texture. We show that this system supports an anomalous Hall angle ΘAH > 0.1, comparable to the largest observed in bulk ferromagnets and significantly larger than in other antiferromagnets. Neutron scattering measurements and electronic structure calculations suggest that this effect originates from avoided crossing or Weyl points that develop near the Fermi level due to a breaking of combined time-reversal and lattice symmetries. Berry phase effects associated with such symmetry breaking have recently been explored in kagome networks; our results extend this to half-Heusler systems with non-trivial band topology. The magnetic textures indicated here may also provide pathways towards realizing the topological insulating and semimetallic states predicted in this material class.
Neutron scattering studies of a frustrated spinel antiferromagnet in zero and high magnetic field
Matsuda, M [Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)
2006-11-15
A review is given of the neutron scattering studies on a frustrated spinel antiferromagnet CdCr{sub 2}O{sub 4}. As observed in ZnCr{sub 2}O{sub 4}, which has been most extensively studied in the Cr-based spinel oxides, CdCr{sub 2}O{sub 4} also shows an antiferromagnetic phase transition and a structural phase transition simultaneously, indicating a strong spin-lattice coupling. The magnetic structure of CdCr{sub 2}O{sub 4}was determined by neutron scattering studies. The neutron scattering study in magnetic field up to 10 T indicates an orientation of magnetic domains.
Zhang, N.G.; Henley, C.L.; Rischel, C.;
2002-01-01
We study the low-lying eigenenergy clustering patterns of quantum antiferromagnets with p sublattices (in particular p = 4). We treat each sublattice as a large spin, and using second-order degenerate perturbation theory, we derive the effective (biquadratic) Hamiltonian coupling the p large spins....... In order to compare with exact diagonalizations, the Hamiltonian is explicitly written for a finite-size lattice, and it contains information on energies of excited states as well as the ground state. The result is applied to the face-centered-cubic Type-I antiferromagnet of spin 1/2, including second...
Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime
2001-01-01
Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of coupled alternating chains on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that, in contrast with the site-diluted system having an infinitesimal critical concentration, the bond-diluted system has a finite critical concentration of diluted bonds, $x_{c}$, above which the system is in an antiferromagnetic (AF) long-range ordered phase. In the disordered phase below $x_{c}$...
Topological Weyl semimetals in the chiral antiferromagnetic materials Mn3Ge and Mn3Sn
Yang, Hao; Sun, Yan; Zhang, Yang; Shi, Wu-Jun; Parkin, Stuart S. P.; Yan, Binghai
2017-01-01
Recent experiments revealed that Mn3Sn and Mn3Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect.
Giant electrothermal conductivity and spin-phonon coupling in an antiferromagnetic oxide.
Chiorescu, C; Neumeier, J J; Cohn, J L
2008-12-19
The application of weak electric fields ( less, similar 100 V/cm) is found to dramatically enhance the lattice thermal conductivity of the antiferromagnetic insulator CaMnO3 over a broad range of temperature about the Néel ordering point (125 K). The effect is coincident with field-induced detrapping of bound electrons, suggesting that phonon scattering associated with short- and long-ranged antiferromagnetic order is suppressed in the presence of the mobilized charge. This interplay between bound charge and spin-phonon coupling might allow for the reversible control of spin fluctuations using weak external fields.
Gammelmark, Søren; Eckardt, André
2013-01-01
We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials...... felt by the two species. Using numerical simulations we predict that a finite parabolic potential can assist the adiabatic preparation of the antiferromagnet. The optimal strength of the parabolic inhomogeneity depends sensitively on the number imbalance between the two species. We also find...
Nonequilibrium antiferromagnetic mixed-spin Ising model.
Godoy, Mauricio; Figueiredo, Wagner
2002-09-01
We studied an antiferromagnetic mixed-spin Ising model on the square lattice subject to two competing stochastic processes. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T, and the exchange of energy with the heat bath occurs via one-spin flip (Glauber dynamics). Besides, the system interacts with an external agency of energy, which supplies energy to it whenever two nearest neighboring spins are simultaneously flipped. By employing Monte Carlo simulations and a dynamical pair approximation, we found the phase diagram for the stationary states of the model in the plane temperature T versus the competition parameter between one- and two-spin flips p. We observed the appearance of three distinct phases, that are separated by continuous transition lines. We also determined the static critical exponents along these lines and we showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.
Antiferromagnetic Skyrmion: Stability, Creation and Manipulation
Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko
2016-04-01
Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.
Landau model for the multiferroic delafossite antiferromagnets
Ribeiro, J.L, E-mail: jlr@fisica.uminho.pt [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal); Perez-Mato, J.M [Dpto. de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao (Spain); Vieira, L.G [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal)
2016-10-15
A symmetry based framework is used to describe the complex phase diagrams observed in the multiferroic delafossite compounds. A free energy Landau functional is derived from the analysis of the transformation properties of the most general incommensurate magnetic spin order parameter. A principle of maximal symmetry is invoked and the stability of each of the different higher symmetry phases considered. The competition between different potential ground states is analysed within the scope of a simplified model, which emphasizes the role of the symmetry allowed phase dependent biquadratic couplings. The cross-over between the different competing states is also discussed. The results show that the diverse set of phase diagrams that are experimentally observed in this class of triangular lattice antiferromagnets and, in particular, the stabilization of magnetically induced ferroelectric states, can be well interpreted and described within this integrated phenomenological approximation. - Highlights: • Symmetry considerations are used to analyze the phase diagrams of the compounds. • The competition between possible ground states is discussed. • The field induced transitions between competing states are described.
Terada, N; Suzuki, H S; Kitazawa, H [National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, 305-0047 (Japan); Kaneko, K; Metoki, N [Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195 (Japan); Awaka, J [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 (Japan); Nagata, S, E-mail: terada.noriki@nims.go.j [Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido, 050-8585 (Japan)
2010-01-01
We have investigated the magnetic orderings and the magnetic interactions in garnet antiferromagnets AgCa{sub 2}M{sub 2}V{sub 3}O{sub 12}(M=Mn, Co, Ni) and NaPb{sub 2}Mn{sub 2}V{sub 3}O{sub 12}, using the powder neutron diffraction and magnetization measurements. In the neutron diffraction measurements, we revealed that the magnetic structures in all samples measured are simple two sublattice antiferromagnetic structures with collinear magnetic moments. We also determined the exchange interactions from the critical magnetic fields H{sup sat} observed in the high field magnetization processes up to 30 T.
李艳; 尹立雪; 李文华
2013-01-01
Objective To investigate the value of contrast-enhanced ultrasonography (CEUS) for the detection of sentinel lymph node (SLN) in breast cancer.Methods Eighteen VX2 breast cancer lymph node metastasis models in rabbit were established .Experimental methods:(1)Conventional two-dimensional, color and energy Doppler images and Doppler velocity tracings of axillary lymph nodes were obtained after injection of tumor cell suspension for 4 to 5 weeks;(2)After injected subcutaneously with SonoVue around the tumor,nodes perfusion images were collected;(3) Methylene blue tracer was subcutaneously injected around the tumor;(4)Axillary lymph nodes resected for pathological examination .Results Fifteen VX2 breast cancer lymph node metastasis models in rabbit were successfully established .A total of 39 lymph nodes were resected for pathologic examination and 30 were metastasis.(1)A total of 35 lymph nodes were detected by gray-scale ultrasound,of which,23 metastasized and 12 non-metastasized.The results showed that metastatic lymph nodes were mostly with rounded shape ( aspect ratio 0.05].The detection accuracy,sensitivity,specificity rate of metastatic lymph node by CEUS was higher than that by gray-scale ultrasound,but there was no statistically significant differences (χ2 =0.36,P>0.05;Fisher′s exact test,P=0.05).The detection accuracy rate of metastatic lymph node by CEUS was lower than that by gray-scale ultrasound,and there was no statistically significant differences too (Fisher′s exact test,P=0.08).Conclusions CEUS can be used for real-time observing both lymphatic perfusion and lymph node metastasis,and for non-invasive localization of SLN.It has the potential ability to determine lymph node metastases.CEUS has similar detection rate ,accuracy and sensitivity to blue dye test .It is suggested that the CEUS-guided method using SonoVue may be a novel useful method for SLN identification .% 目的探讨经皮超声造影在实验兔VX2乳腺癌前哨淋巴结
Spin diffusion and torques in disordered antiferromagnets
Manchon, Aurelien
2017-02-01
We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.
Thermoinduced magnetization in nanoparticles of antiferromagnetic materials
Mørup, Steen; Frandsen, Cathrine
2004-01-01
We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has...... the consequence that antiferromagnetism is nonexistent in nanoparticles at finite temperatures and it explains magnetic anomalies, which recently have been reported in a number of studies of nanoparticles of antiferromagnetic materials....
Yarash K. Abuev
2017-01-01
Full Text Available Abstract. Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange interactions between the nearest J1 and second J2 neighbours. The main goal of the computer simulation was to elucidate the effects of ground state and areas of frustration on the thermodynamic and magnetic properties of antiferromagnetic structures described by the lowdimensional Potts model. Method The computer simulation is based on the Monte Carlo method. This method is implemented using the Metropolis algorithm in combination with the Wolff claster algorithm. The computer simulation was carried out for low-dimensional systems with periodic boundary conditions and linear dimensions L = 24124. Results On the basis of heat capacity and entropy analysis, phase transitions were observed in the considered model to possess exchange interaction parameters J1 <0 and J2 <0 in the variation intervals 0r<0.2 and 1.0
Large magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4.
Hemberger, J; von Nidda, H-A Krug; Tsurkan, V; Loidl, A
2007-04-06
A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at TN=21 K. Specific heat and thermal expansion exhibit sharp first-order anomalies at the antiferromagnetic transition. TN is shifted to lower temperatures by external magnetic fields and finally is fully suppressed by a field of 65 kOe. The relative length change DeltaL/L(T) is unusually large and exhibits negative thermal expansion alpha below 75 K down to TN indicating strong frustration of the lattice. Magnetostriction DeltaL/L(H) reveals large values comparable to giant magnetostrictive materials. These results point to a spin-driven origin of the structural instability at TN explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions.
Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets
Železný, J.
2014-10-06
We predict that a lateral electrical current in antiferromagnets can induce nonequilibrium Néel-order fields, i.e., fields whose sign alternates between the spin sublattices, which can trigger ultrafast spin-axis reorientation. Based on microscopic transport theory calculations we identify staggered current-induced fields analogous to the intraband and to the intrinsic interband spin-orbit fields previously reported in ferromagnets with a broken inversion-symmetry crystal. To illustrate their rich physics and utility, we consider bulk Mn2Au with the two spin sublattices forming inversion partners, and a 2D square-lattice antiferromagnet with broken structural inversion symmetry modeled by a Rashba spin-orbit coupling. We propose an antiferromagnetic memory device with electrical writing and reading.
Indications of c-axis Charge Transport in Hole Doped Triangular Antiferromagnets
LIANG Ying; LIU Bin; FENG Shi-Ping
2004-01-01
The c-axis charge transport of the hole doped triangular antiferromagnet is investigated within the tJ model by considering the incoherent interlayer hopping.It is shown that the c-axis charge transport of the hole doped triangular antiferromagnet is essentially determined by the scattering from the in-plane fluctuation.The c-axis conductivity spectrum shows a lov-energy peak and the unusual high-energy broad band,while the c-axis resistivity is characterized by a crossover from the high temperature metallic-like behavior to the Iow temperature insulating-like behavior,which is qualitatively consistent with those of the hole doped square lattice antiferromagnet.
Ziyi Guo
Full Text Available To investigate the intravoxel incoherent motion diffusion weighted imaging (IVIM-DWI as a potential valuable marker to monitor the therapy responses of VX2 to radiofrequency ablation (RF Ablation.The institutional animal care and use committee approved this study. In 10 VX2 tumor-bearing rabbits, IVIM-DWI examinations were performed with a 3.0T imaging unit by using 16 b values from 0 to 800 sec/mm2. The true diffusion coefficient (D, pseudodiffusion coefficient (D* and perfusion fraction (f of tumors were compared between before and instantly after RF Ablation treatment. The differences of D, D* and f and conventional perfusion parameters (from perfusion CT and dynamic enhanced magnetic resonance imaging, DCE-MRI in the coagulation necrosis area, residual unablated area, untreated area, and normal control had been calculated by compared t-test. The correlation between f or D* with perfusion weighted CT including blood flow, BF (milliliter per 100 mL/min, blood volume, BV (milliliter per 100 mL/min, and capillary permeability-surface area, PMB (as a fraction or from DCE-MRI: transfer constant (Ktrans, extra-vascular extra-cellular volume fraction (Ve and reflux constant (Kep values had been analyzed by region-of-interest (ROI methods to calculate Pearson's correlation coefficients.In the ablated necrosis areas, f and D* significantly decreased and D significantly increased, compared with residual unblazed areas or untreated control groups and normal control groups (P < 0.001. The IVIM-DWI derived f parameters showed significant increases in the residual unablated tumor area. There was no significant correlations between f or D* and conventional perfusion parameters.The IVIM-DW derived f, D and D* parameters have the potential to indicate therapy response immediately after RF Ablation treatment, while no significant correlations with classical tumor perfusion metrics were derived from DCE-MRI and perfusion-CT measurements.
Kageyama, Ken, E-mail: kageyamaken0112@gmail.com; Yamamoto, Akira, E-mail: loveakirayamamoto@gmail.com; Okuma, Tomohisa, E-mail: o-kuma@msic.med.osaka-cu.ac.jp; Hamamoto, Shinichi, E-mail: hamashin_tigers1975@yahoo.co.jp; Takeshita, Toru, E-mail: takeshita3595@view.ocn.ne.jp; Sakai, Yukimasa, E-mail: sakaiy@trust.ocn.ne.jp; Nishida, Norifumi, E-mail: norifumin@med.osaka-cu.ac.jp; Matsuoka, Toshiyuki, E-mail: tmatsuoka@msic.med.osaka-cu.ac.jp; Miki, Yukio, E-mail: yukio.miki@med.osaka-cu.ac.jp [Osaka City University, Department of Radiology, Graduate School of Medicine (Japan)
2013-10-15
Purpose: To evaluate survival and distant tumor growth after radiofrequency ablation (RFA) and local OK-432 injection at a single tumor site in a rabbit model with intra- and extrahepatic VX2 tumors and to examine the effect of this combination therapy, which we termed immuno-radiofrequency ablation (immunoRFA), on systemic antitumor immunity in a rechallenge test. Methods: Our institutional animal care committee approved all experiments. VX2 tumors were implanted to three sites: two in the liver and one in the left ear. Rabbits were randomized into four groups of seven to receive control, RFA alone, OK-432 alone, and immunoRFA treatments at a single liver tumor at 1 week after implantation. Untreated liver and ear tumor volumes were measured after the treatment. As the rechallenge test, tumors were reimplanted into the right ear of rabbits, which survived the 35 weeks and were followed up without additional treatment. Statistical significance was examined by log-rank test for survival and Student's t test for tumor volume. Results: Survival was significantly prolonged in the immunoRFA group compared to the other three groups (P < 0.05). Untreated liver and ear tumor sizes became significantly smaller after immunoRFA compared to controls (P < 0.05). In the rechallenge test, the reimplanted tumors regressed without further therapy compared to the ear tumors of the control group (P < 0.05). Conclusion: ImmunoRFA led to improved survival and suppression of distant untreated tumor growth. Decreases in size of the distant untreated tumors and reimplanted tumors suggested that systemic antitumor immunity was enhanced by immunoRFA.
祁克信; 劳群; 贾玉柱
2013-01-01
Objective To explore the diagnostic value of the dual-energy technique with dual-source in the evaluation of therapeutic effect of interventional therapy for hepatocarcinoma.Methods 8 rabbits with tumor growing well were treated with intervention operation,paralleled with double energy CT scan and focal area image,CT and color order change were measured by dual energy liver OVERLAY workstation.Meanwhile,The necrosis and survival of tumor were evaluated by dual energy CT after hepatocarcinoma intervention therapy.Results Taking pathologic diagnosis as gold standard,compared with imaging and pathological results in the order of black,red,orange and red,accuracies were 87.2％,72.3％,71.5％ and 83.6％ respectively.Sensitivities were 95.1％,37.4％,54.7％ and 63.8％ respectively.Specificities were 85.4％,86.3％,81.5％ and 85.8％ respectively.Positive predictives value were 61.4％,54.2％,62.4％ and 55.6％ respectively.Negative predictive values were 96.3％,76.2％,79.7％ and 91.3 ％ respectively.According to the Spearman relevance analysis,there was strong positive correlation between survival of tumor cells and image color scale (r =12.35,P ＜ 0.05).Conclusion The necrosis and survival of tumor cells in rabbit VX2 liver tumor model can be preliminarily reflected by dual source CT dual energy enhancement scanning.The results provide good reference to the application of dual-source and dual-energy in clinical diagnosis and treatment.%目的 探讨双源双能量CT评价肝癌介入治疗疗效的价值.方法 8只生长良好的荷瘤兔,行介入手术,并进行双源双能量CT扫描,利用双源工作站OVERLAY信息图像,测量病灶区CT值,并记录其色阶变化,探讨双能量CT在肝癌介入治疗后肿瘤存活与坏死情况.结果 以全部的病理诊断为金标准,经过病理和影像对照分析,按黑色、暗红色、红色、橘红色顺序,色阶准确度分别为87.2％、72.3％、71.5％、83.6％,敏感度分别为95.1
Motome, Yukitoshi; Penc, Karlo; Shannon, Nic
2005-01-01
The antiferromagnetic Heisenberg model on a pyrochlore lattice under external magnetic field is studied by classical Monte Carlo simulation. The model includes bilinear and biquadratic interactions; the latter effectively describes the coupling to lattice distortions. The magnetization process shows a half-magnetization plateau at low temperatures, accompanied with strong suppression of the magnetic susceptibility. Temperature dependence of the plateau behavior is clarified. Finite-temperatur...
Quasiparticle excitations in frustrated antiferromagnets
Trumper, Adolfo E. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: trumper@ifir.edu.ar; Gazza, Claudio J. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina); Manuel, Luis O. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: manuel@ifir.edu.ar
2004-12-31
We have computed the quasiparticle wave function corresponding to a hole injected in a triangular antiferromagnet. We have taken into account multi-magnon contributions within the self-consistent Born approximation. We have found qualitative differences, under sign reversal of the integral transfer t, regarding the multi-magnon components and the own existence of the quasiparticle excitations. Such differences are due to the subtle interplay between magnon-assisted and free hopping mechanisms. We conclude that the conventional quasiparticle picture can be broken by geometrical frustration without invoking spin liquid phases.
Wang, Da-Wei; Zhu, Shi-Yao; Scully, Marlan O
2014-01-01
We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in the momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on an electromagnetically induced transparency (EIT) system. For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective electric field. The quantum behaviours of electrons in lattices, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing and dynamic localization can be observed in the SL. The SL can be extended to two, three and even higher dimensions where no analogous real space lattices exist and new physics are waiting to be explored.
Spin dynamics in charge doped antiferromagnets : a Li-7 NMR study in Ni1-xLixO
Tedoldi, F; Marini, S; Corti, M
1997-01-01
The effects of heterovalent substitutions causing itinerant holes in strongly correlated 3d electron systems are studied by means of Li-7 NMR in lithium-doped antiferromagnetic NiO. The spin-lattice relaxation rates, driven by the fluctuation of Ni2+ (S = 1) ions, in the temperature range 10 K
Magnetic correlations in the 2D S=5/2 honeycomb antiferromagnet MnPS_{3}
Rønnow, H.M.; Wildes, A.R.; Bramwell, S.T.
2000-01-01
MnPS3 is a quasi-2D S = 5/2 antiferromagnet on a honeycomb lattice. Using an energy integrating neutron scattering technique, we have measured the structure factor S(k) of the instantaneous magnetic fluctuations. The temperature dependence of the correlation length xi follows the Kosterlitz...
Spin dynamics in charge doped antiferromagnets : a Li-7 NMR study in Ni1-xLixO
Tedoldi, F; Marini, S; Corti, M
1997-01-01
The effects of heterovalent substitutions causing itinerant holes in strongly correlated 3d electron systems are studied by means of Li-7 NMR in lithium-doped antiferromagnetic NiO. The spin-lattice relaxation rates, driven by the fluctuation of Ni2+ (S = 1) ions, in the temperature range 10 K
Spin dynamics in charge doped antiferromagnets : a Li-7 NMR study in Ni1-xLixO
Tedoldi, F; Marini, S; Corti, M
1997-01-01
The effects of heterovalent substitutions causing itinerant holes in strongly correlated 3d electron systems are studied by means of Li-7 NMR in lithium-doped antiferromagnetic NiO. The spin-lattice relaxation rates, driven by the fluctuation of Ni2+ (S = 1) ions, in the temperature range 10 K
Zitzler, R.; Pruschke, Th.; Bulla, R.
2004-05-01
We discuss the magnetic phase diagram for the Hubbard model with magnetic frustration obtained within the dynamical mean-field theory. Most interesting is the appearance of a first-order paramagnetic metal to antiferromagnetic insulator transition for the magnetically frustrated lattice at half filling. For finite doping the antiferromagnetic phase is susceptible to phase separation and competes with an itinerant ferromagnetic phase (Nagaoka ferromagnetism), leading to an unexpectedly rich magnetic phase diagram.
Zitzler, R.; Pruschke, Th. E-mail: pruschke@theorie.physik.uni-goettingen.de; Bulla, R
2004-05-01
We discuss the magnetic phase diagram for the Hubbard model with magnetic frustration obtained within the dynamical mean-field theory. Most interesting is the appearance of a first-order paramagnetic metal to antiferromagnetic insulator transition for the magnetically frustrated lattice at half filling. For finite doping the antiferromagnetic phase is susceptible to phase separation and competes with an itinerant ferromagnetic phase (Nagaoka ferromagnetism), leading to an unexpectedly rich magnetic phase diagram.
Purely antiferromagnetic magnetoelectric random access memory
Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys
2017-01-01
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics.
Phase transition in Heisenberg stacked triangular antiferromagnets: end of a controversy.
Ngo, V Thanh; Diep, H T
2008-09-01
By using the Wang-Landau flat-histogram Monte Carlo (MC) method for very large lattice sizes never simulated before, we show that the phase transition in the frustrated Heisenberg stacked triangular antiferromagnet is of first order, contrary to results of earlier MC simulations using old-fashioned methods. Our result lends support to the conclusion of a nonperturbative renormalization group performed on an effective Hamiltonian. It puts an end to a 20-year -long controversial issue.
Yasuda, Shinya; Todo, Synge
2013-12-01
We present a method that optimizes the aspect ratio of a spatially anisotropic quantum lattice model during the quantum Monte Carlo simulation, and realizes the virtually isotropic lattice automatically. The anisotropy is removed by using the Robbins-Monro algorithm based on the correlation length in each direction. The method allows for comparing directly the value of the critical amplitude among different anisotropic models, and identifying the universality more precisely. We apply our method to the staggered dimer antiferromagnetic Heisenberg model and demonstrate that the apparent nonuniversal behavior is attributed mainly to the strong size correction of the effective aspect ratio due to the existence of the cubic interaction.
Z Jalali mola
2011-12-01
Full Text Available The Ising model is one of the simplest models describing the interacting particles. In this work, we calculate the high temperature series expansions of zero field susceptibility of ising model with ferromagnetic, antiferromagnetic and one antiferromagnetic interactions on two dimensional kagome lattice. Using the Pade´ approximation, we calculate the susceptibility of critical exponent of ferromagnetic ising model γ ≈ 1.75, which is consistent with universality hypothesis. However, antiferromagnetic and one antiferromagnetic interaction ising model doesn’t show any transition at finite temperature because of the effect of magnetic frustration.
Femtosecond optomagnetism in dielectric antiferromagnets
Bossini, D.; Rasing, Th
2017-02-01
Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.
Antiferromagnetic topological nodal line semimetals
Wang, Jing
2017-08-01
We study three-dimensional nodal line semimetals (NLSMs) with magnetic ordering and strong spin-orbit interaction. Two distinct classes of magnetic NLSMs are proposed. The first class is band-inversion NLSM where the accidental line node is induced by band inversion and locally protected by glide mirror plane and the combined time-reversal and inversion symmetries. This can be viewed as a trivial stacking of the two-dimensional antiferromagnetic Dirac semimetals. The second class is essential NLSM where the nodal features are filling enforced by specific magnetic symmetry group. We further provide two concrete tight-binding models for magnetic NLSMs which belong to these two different classes, respectively. We conclude with a brief discussion on the possible material venues and the experimental implications for such phases.
Striped spin liquid crystal ground state instability of kagome antiferromagnets.
Clark, Bryan K; Kinder, Jesse M; Neuscamman, Eric; Chan, Garnet Kin-Lic; Lawler, Michael J
2013-11-01
The Dirac spin liquid ground state of the spin 1/2 Heisenberg kagome antiferromagnet has potential instabilities. This has been suggested as the reason why it does not emerge as the ground state in large-scale numerical calculations. However, previous attempts to observe these instabilities have failed. We report on the discovery of a projected BCS state with lower energy than the projected Dirac spin liquid state which provides new insight into the stability of the ground state of the kagome antiferromagnet. The new state has three remarkable features. First, it breaks spatial symmetry in an unusual way that may leave spinons deconfined along one direction. Second, it breaks the U(1) gauge symmetry down to Z(2). Third, it has the spatial symmetry of a previously proposed "monopole" suggesting that it is an instability of the Dirac spin liquid. The state described herein also shares a remarkable similarity to the distortion of the kagome lattice observed at low Zn concentrations in Zn-paratacamite and in recently grown single crystals of volborthite suggesting it may already be realized in these materials.
Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet
Žukovič Milan
2014-07-01
Full Text Available Low-temperature magnetization processes and magnetocaloric properties of a geometrically frustrated spin-1 Blume-Capel model on a triangular lattice are studied by Monte Carlo simulations. The model is found to display qualitatively different behavior depending on the sign of the single-ion anisotropy D. For positive values of D we observe two magnetization plateaus, similar to the spin-1/2 Ising antiferromagnet, and negative isothermal entropy changes for any field intensity. For a range of small negative values of D there are four magnetization plateaus and the entropy changes can be either negative or positive, depending on the field. If D is negative but large in absolute value then the entropy changes are solely positive.
Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide
Baierl, S.; Mentink, J. H.; Hohenleutner, M.; Braun, L.; Do, T.-M.; Lange, C.; Sell, A.; Fiebig, M.; Woltersdorf, G.; Kampfrath, T.; Huber, R.
2016-11-01
Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism—information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.
Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet.
Zaletel, Michael P; Zhu, Zhenyue; Lu, Yuan-Ming; Vishwanath, Ashvin; White, Steven R
2016-05-13
The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.
Magnetic Orders and Fluctuations in the Dipolar Pyrochlore Antiferromagnet
Cepas, Olivier; Shastry, B. Sriram
2005-03-01
While the classical Heisenberg antiferromagnet on the pyrochlore lattice does not order, we will discuss, from a theoretical standpoint, possible magnetic phases induced by the dipole-dipole interactions. Such interactions play a role in systems such as Gd2Ti2O7 or Gd2Sn2O7 in stabilizing exotic forms of magnetic order, a subject of current debate. We will also argue that the external magnetic field induces multiple transitions, one of which is associated with no obvious broken symmetry, but can be characterized by a disorder parameter. Finally, Monte-Carlo simulations and Landau-Ginzburg expansion show that the dipolar Heisenberg model exhibits a fluctuation-induced first-order transition, thanks to the frustration and a continuous set of soft modes.
Potassium tantalate substrates for neutron experiments on antiferromagnetic perovskite films
Christen, H M; MacDougall, G J; Kim, H-S; Kim, D H; Boatner, L A; Bennett, C J Callender; Zarestky, J L; Nagler, S E, E-mail: christenhm@ornl.gov
2010-11-01
For the study of antiferromagnetism in thin-film materials, neutron diffraction is a particularly important tool, especially since magnetometry experiments are often complicated by the substrate's strong diamagnetic or paramagnetic contribution. However, the substrate, by necessity, has a lattice parameter that is very similar to that of the film, and in most cases is over 1000 times more massive than the film. Therefore, even weak structural distortions in the substrate crystal may complicate the analysis of magnetic scattering from the film. Here we show that in contrast to most other perovskite substrates (including SrTiO{sub 3}, LaAlO{sub 3}, etc.), KTaO3 provides a uniquely appropriate substrate platform for magnetic diffraction experiments on epitaxial oxide films.
Spin-phonon interaction in antiferromagnetics
Grigorashchuk, I.M.; Nitsovich, V.M.; Tovstyuk, K.D.
1975-01-01
The vibrational spectrum and the sound velocity in antiferromagnetics are obtained in the general form in pseudoharmonic approximation with allowance for the anharmonisms of all orders. Starting from experimentally defined dependence of the Debye-Waller factor on the temperature a corollary is put forward that in some antiferromagnetics under the temperature lower than T/subN/ the appearance of the narrow band of paramagnetic states is possible. In antiferromagnetics where the transition metal-dielectric described by the Habbard model is possible this results in the appearance of the additional transition dielectric-metal-dielectric. (auth)
Hu Jing-Guo; Stamps R L
2006-01-01
The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.
Wills, A. S.; Zhitomirsky, M. E.; Canals, B.; Sanchez, J. P.; Bonville, P.; Dalmas de Réotier, P.; Yaouanc, A.
2006-01-01
Low-temperature powder neutron diffraction measurements are performed in the ordered magnetic state of the pyrochlore antiferromagnet Gd2Sn2O7. Symmetry analysis of the diffraction data indicates that this compound has the ground state predicted theoretically for a Heisenberg pyrochlore antiferromagnet with dipolar interactions. The difference in the magnetic structure of Gd2Sn2O7 andof nominally analogous Gd2Ti2O7 is found to be determined by a specific type of third-neighbour superexchange interaction on the pyrochlore lattice between spins across empty hexagons.
Dynamic rotor mode in antiferromagnetic nanoparticles
Lefmann, Kim; Jacobsen, H.; Garde, J.
2015-01-01
We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K...
Donnellan, Thomas; Maxwell, E A; Plumpton, C
1968-01-01
Lattice Theory presents an elementary account of a significant branch of contemporary mathematics concerning lattice theory. This book discusses the unusual features, which include the presentation and exploitation of partitions of a finite set. Organized into six chapters, this book begins with an overview of the concept of several topics, including sets in general, the relations and operations, the relation of equivalence, and the relation of congruence. This text then defines the relation of partial order and then partially ordered sets, including chains. Other chapters examine the properti
Charge dynamics of the antiferromagnetically ordered Mott insulator
Han, Xing-Jie; Liu, Yu; Liu, Zhi-Yuan; Li, Xin; Chen, Jing; Liao, Hai-Jun; Xie, Zhi-Yuan; Normand, B.; Xiang, Tao
2016-10-01
We introduce a slave-fermion formulation in which to study the charge dynamics of the half-filled Hubbard model on the square lattice. In this description, the charge degrees of freedom are represented by fermionic holons and doublons and the Mott-insulating characteristics of the ground state are the consequence of holon-doublon bound-state formation. The bosonic spin degrees of freedom are described by the antiferromagnetic Heisenberg model, yielding long-ranged (Néel) magnetic order at zero temperature. Within this framework and in the self-consistent Born approximation, we perform systematic calculations of the average double occupancy, the electronic density of states, the spectral function and the optical conductivity. Qualitatively, our method reproduces the lower and upper Hubbard bands, the spectral-weight transfer into a coherent quasiparticle band at their lower edges and the renormalisation of the Mott gap, which is associated with holon-doublon binding, due to the interactions of both quasiparticle species with the magnons. The zeros of the Green function at the chemical potential give the Luttinger volume, the poles of the self-energy reflect the underlying quasiparticle dispersion with a spin-renormalised hopping parameter and the optical gap is directly related to the Mott gap. Quantitatively, the square-lattice Hubbard model is one of the best-characterised problems in correlated condensed matter and many numerical calculations, all with different strengths and weaknesses, exist with which to benchmark our approach. From the semi-quantitative accuracy of our results for all but the weakest interaction strengths, we conclude that a self-consistent treatment of the spin-fluctuation effects on the charge degrees of freedom captures all the essential physics of the antiferromagnetic Mott-Hubbard insulator. We remark in addition that an analytical approximation with these properties serves a vital function in developing a full understanding of the
Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3
Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.
2017-02-01
Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.
Large topological Hall effect in the non-collinear phase of an antiferromagnet.
Sürgers, Christoph; Fischer, Gerda; Winkel, Patrick; Löhneysen, Hilbert V
2014-03-05
Non-trivial spin arrangements in magnetic materials give rise to the topological Hall effect observed in compounds with a non-centrosymmetric cubic structure hosting a skyrmion lattice, in double-exchange ferromagnets and magnetically frustrated systems. The topological Hall effect has been proposed to appear also in presence of non-coplanar spin configurations and thus might occur in an antiferromagnetic material with a highly non-collinear and non-coplanar spin structure. Particularly interesting is a material where the non-collinearity develops not immediately at the onset of antiferromagnetic order but deep in the antiferromagnetic phase. This unusual situation arises in non-cubic antiferromagnetic Mn5Si3. Here we show that a large topological Hall effect develops well below the Néel temperature as soon as the spin arrangement changes from collinear to non-collinear with decreasing temperature. We further demonstrate that the effect is not observed when the material is turned ferromagnetic by carbon doping without changing its crystal structure.
Competing antiferromagnetic and spin-glass phases in a hollandite structure
Crespo, Y.; Andreanov, A.; Seriani, N.
2013-07-01
We introduce a simple lattice model with Ising spins as a zeroth-order approximation of the hollandite-type magnetic compounds. We argue that geometrical frustration of the lattice in combination with nearest-neighbor antiferromagnetic (AFM) interactions are responsible for the appearance of a spin-glass phase in presence of disorder. We investigate this system numerically using parallel tempering. The model reproduces magnetic transitions present in some oxides with hollandite structure and displays a rich phenomenology: in the absence of disorder we have identified five different ground states, depending on the relative strength and sign of the interactions: one ferromagnetically ordered, three antiferromagnetically ordered, and one disordered, macroscopically degenerate ground state. Remarkably, for the sets of AFM couplings having an AFM ground state in the clean system, there exists a critical value of the disorder above which the ground state becomes a spin glass while maintaining all the couplings antiferromagnetically. This model presents this kind of transition with nearest-neighbor frustrated AFM interactions. We argue that this model is useful for understanding the relation between AFM coupling, disorder, and appearance of spin-glass phases.
Antiferromagnetic domain wall motion driven by spin-orbit torques
Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M.; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin
2016-01-01
We theoretically investigate dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet/heavy metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin-waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets. PMID:27588878
Purely antiferromagnetic magnetoelectric random access memory
Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys
2017-01-01
Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics. PMID:28045029
Brackett, Jeremy; Newman, Joseph; De Silva, Theja N.
2016-10-01
We study an effective fermion model on a square lattice to investigate the cooperation and competition of superconductivity and anti-ferromagnetism. In addition to particle tunneling and on-site interaction, a bosonic excitation mediated attractive interaction is also included in the model. We assume that the attractive interaction is mediated by spin fluctuations and excitations of Bose-Einstein condensation (BEC) in electronic systems and Bose-Fermi mixtures on optical lattices, respectively. Using an effective mean-field theory to treat both superconductivity and anti-ferromagnetism at equal footing, we study a single effective model relevant for both systems within the Landau energy functional approach and a linearized theory. Within our approaches, we find possible co-existence of superconductivity and anti-ferromagnetism for both electronic and cold-atomic models. Our linearized theory shows while spin fluctuations favor d-wave superconductivity and BEC excitations favor s-wave superconductivity.
Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.
Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S
2015-11-06
The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.
Magnetostriction and Magnetostructural Domains in Antiferromagnetic YBa2Cu3O6.
Náfrádi, B; Keller, T; Hardy, F; Meingast, C; Erb, A; Keimer, B
2016-01-29
We use high-resolution neutron Larmor diffraction and capacitative dilatometry to investigate spontaneous and forced magnetostriction in undoped, antiferromagnetic YBa_{2}Cu_{3}O_{6.0}, the parent compound of a prominent family of high-temperature superconductors. Upon cooling below the Néel temperature T_{N}=420 K, Larmor diffraction reveals the formation of magnetostructural domains of characteristic size ∼240 nm. In the antiferromagnetic state, dilatometry reveals a minute (4×10^{-6}) orthorhombic distortion of the crystal lattice in external magnetic fields. We attribute these observations to exchange striction and spin-orbit coupling induced magnetostriction, respectively, and show that they have an important influence on the thermal and charge transport properties of undoped and lightly doped cuprates.
P. Sahebsara
2006-09-01
Full Text Available The self-energy-functional approach is a powerful many-body tool to investigate different broken symmetry phases of strongly correlated electron systems. We use the variational cluster perturbation theory (also called the variational cluster approximation to investigate the interplay between the antiferromagnetism and d-wave superconductivity of κ-(ET2 X conductors. These compounds are described by the so-called dimer Hubbard model, with various values of the on-site repulsion U and diagonal hopping amplitude t. At strong coupling, our zero-temperature calculations show a transition from Néel antiferromagnetism to a spin-liquid phase with no long range order, at around t ~ 0.9. At lower values of U, we find d-wave superconductivity. Taking into account the point group symmetries of the lattice, we find a transition between dx2-y2 and dxy pairing symmetries, the latter happening for smaller values of U.
DMRG studies of the frustrated kagome antiferromagnets and the application to volborthite
Gong, Shou-Shu; Sheng, D. N.; Yang, Kun
Motivated by the recent magnetization measurements on the high-quality single crystals of the kagome antiferromagnet volborthite, we study the ground state and magnetization properties of two kagome models proposed from the electronic structure simulations, which treat the volborthite as either the coupled trimers or the coupled frustrated chains on the kagome lattice. We study the models using density-matrix renormalization group on the cylinder geometry with the system width up to 4 legs. We find a quantum phase diagram of the models with changing couplings, and identify the magnetic properties of each phase. In the antiferromagnetic phases, we also study the magnetization curve and the different phases in the magnetic field. Finally, we compare the magetization properties of the models with the experimental observations of volborthite. NSF DMR-1157490, DMR-1408560, and the State of Florida.
Weak antiferromagnetic order and superconductivity in UPt 3 studied by neutron scattering
van Dijk, N. H.; Rodière, P.; Fåk, B.; Huxley, A.; Flouquet, J.
2002-07-01
The heavy-fermion superconductor UPt 3 is one of the best-studied examples of systems that show unconventional superconductivity. Below a transition temperature of Tc=0.55 K a complex phase diagram with three different superconducting phases is observed as a function of temperature, magnetic field, and pressure. The weak antiferromagnetic order ( TN=6 K) with an ordered moment of only 0.02 μB/U atom is believed to play a crucial role in the existence of multiple superconducting phases, as it can act as a symmetry-breaking field for the vector order parameter of the unconventional superconductivity. We review recent progress in neutron scattering measurements on the weak antiferromagnetic order as a function of magnetic field, pressure, and Pd doping and on the superconducting flux-line lattice. The relation between the magnetic and superconducting properties is discussed.
Potts Model on Maple Leaf Lattice with Pure Three-Site Interaction
WANG Zhou-Fei; CHEN Li
2005-01-01
We use Monte Carlo method to study three-state Potts model on maple leaf lattice with pure three-site interaction. The critical behavior of both ferromagnetic and antiferromagnetic cases is studied. Our results confirm that the critical behavior of the ferromagnetic model is independent of the lattice details and lies in the universality class of the three-state ferromagnetic Potts model. For the antiferromagnetic case the transition is of the first order. We have calculated the energy jump and critical temperature in this area. We find there is a tricritical point separating the first order and second order phases for this system.
Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing
2016-11-01
These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.
Paramagnetic and Antiferromagnetic Spin Seebeck Effect
Wu, Stephen
We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.
Frustrated Magnetism in Low-Dimensional Lattices
Tovar, Mayra
2011-12-01
In this dissertation we present the results of a theoretical investigation of spin models on two-dimensional and quasi one-dimensional lattices, all unified under the concept of quantum frustrated antiferromagnetism, and all discussing various aspects of the antiferromagnetic Heisenberg model on the kagome lattice. In the Introduction (Chapter 1), we discuss at some length such concepts as frustration and superexchange, among others, which are of common relevance in the rest of the chapters. In Chapter 2, we study the effect of Dzyaloshinskii-Moriya (DM) interactions on the zero-temperature magnetic susceptibility of systems whose low energy can be described by short-range valence bond states. Our work shows that this treatment is consistent with the experimentally observed non-vanishing susceptibility---in the specified temperature limit---of the spin-1/2 kagome antiferromagnetic compound ZnCu3(OH)6Cl2, also known as herbertsmithite. Although the objective of this work is explaining the aforementioned characteristic of the experimental system, our methods are more general and we apply them to the checkerboard and Shastry-Sutherland lattices as well. In Chapter 3, we discuss our findings in the study of ghost-mediated domain wall interactions in the diamondback ladder. These domain walls are the the spin excitations---the kinks and the antikinks---separating the ground states along one chain of the ladder. While as individual entities an antikink is energy costly and a kink energy free, our study finds that both interact via the ghosts that they produce in the opposite side of the ladder from where they are located. Through the study of these ghosts, we find that domain walls proliferate in the system above a critical value of the system's coupling constants. It is this proliferation that makes their treatment as free, non-interacting particles impossible, so we study here their interactions both quantitatively and qualitatively, in a region where the latter are
Spin-wave multiple excitations in nanoscale classical Heisenberg antiferromagnets
Hou, Zhuofei [University of Georgia, Athens; Landau, David P [University of Georgia, Athens; Stocks, George Malcolm [ORNL; Brown, G. [Florida State University, Tallahassee
2015-02-17
Monte Carlo and spin dynamics techniques have been used to perform large-scale simulations of the dynamic behavior of a nanoscale, classical, Heisenberg antiferromagnet on a simple-cubic lattice with linear sizes L≤ 40 at a temperature below the Neel temperature. In this study, nanoparticles are modeled with completely free boundary conditions, i.e., six free surfaces, and nanofilms are modeled with two free surfaces in the spatial z direction and periodic boundaries parallel to the surfaces in the xy direction, which are compared to the infinite system with periodic boundary conditions. The temporal evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a fast spin dynamics algorithm with the fourth-order Suzuki-Trotter decomposition of exponential operators, with initial spin configurations generated by Monte Carlo simulations. The local dynamic structure factor S(q,ω) was calculated from the local space- and time-displaced spin-spin correlation function. Multiple excitation peaks for wave vectors within the first Brillouin zone appear in the spin-wave spectra of the transverse component of dynamic structure factor S^{T} (q,ω) in the nanoscale classical Heisenberg antiferromagnet, which are lacking if periodic boundary conditions are used. With the assumption of q-space spin-wave reflections with broken momentum conservation due to free-surface confinements, we successfully explained those spectra quantitatively in the linear dispersion region. Meanwhile, we also observed two unexpected quantized spin-wave excitation modes in the spatial z direction in nanofilms for S^{T} (q,ω) not expected in bulk systems. In conclusion, the results of this study indicate the presence of unexpected forms of spin-wave excitation behavior that have yet to be observed experimentally but could be directly tested through neutron scattering experiments on nanoscale RbMnF_{3} particles or
Lattice effects on Laughlin wave functions and parent Hamiltonians
Glasser, Ivan; Cirac, J. Ignacio; Sierra, Germán; Nielsen, Anne E. B.
2016-12-01
We investigate lattice effects on wave functions that are lattice analogs of bosonic and fermionic Laughlin wave functions with number of particles per flux ν =1 /q in the Landau levels. These wave functions are defined analytically on lattices with μ particles per lattice site, where μ may be different than ν . We give numerical evidence that these states have the same topological properties as the corresponding continuum Laughlin states for different values of q and for different fillings μ . These states define, in particular, particle-hole symmetric lattice fractional quantum Hall states when the lattice is half filled. On the square lattice it is observed that for q ≤4 this particle-hole symmetric state displays the topological properties of the continuum Laughlin state at filling fraction ν =1 /q , while for larger q there is a transition towards long-range ordered antiferromagnets. This effect does not persist if the lattice is deformed from a square to a triangular lattice, or on the kagome lattice, in which case the topological properties of the state are recovered. We then show that changing the number of particles while keeping the expression of these wave functions identical gives rise to edge states that have the same correlations in the bulk as the reference lattice Laughlin states but a different density at the edge. We derive an exact parent Hamiltonian for which all these edge states are ground states with different number of particles. In addition this Hamiltonian admits the reference lattice Laughlin state as its unique ground state of filling factor 1 /q . Parent Hamiltonians are also derived for the lattice Laughlin states at other fillings of the lattice, when μ ≤1 /q or μ ≥1 -1 /q and when q =4 also at half filling.
Long-range interactions in lattice field theory
Rabin, J.M.
1981-06-01
Lattice quantum field theories containing fermions can be formulated in a chirally invariant way provided long-range interactions are introduced. It is established that in weak-coupling perturbation theory such a lattice theory is renormalizable when the corresponding continuum theory is, and that the continuum theory is indeed recovered in the perturbative continuum limit. In the strong-coupling limit of these theories one is led to study an effective Hamiltonian describing a Heisenberg antiferromagnet with long-range interactions. Block-spin renormalization group methods are used to find a critical rate of falloff of the interactions, approximately as inverse distance squared, which separates a nearest-neighbor-antiferromagnetic phase from a phase displaying identifiable long-range effects. A duality-type symmetry is present in some block-spin calculations.
Magnetic remanent states in antiferromagnetically coupled multilayers
Kiselev, N.S., E-mail: m.kyselov@ifw-dresden.d [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Donetsk Institute for Physics and Technology, 83114 Donetsk (Ukraine); Roessler, U.K.; Bogdanov, A.N. [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Hellwig, O. [San Jose Research Center, Hitachi Global Storage Technologies, San Jose, CA 95135 (United States)
2010-05-15
In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these 'ferroband' defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.
Direct measurement of antiferromagnetic domain fluctuations.
Shpyrko, O. G.; Isaacs, E. D.; Logan, J. M.; Feng, Y.; Aeppli, G.; Jaramillo, R.; Kim, H. C.; Rosenbaum, T. F.; Zschack, P.; Sprung, M.; Narayanan, S.; Sandy, A.; Univ. of Chicago; Univ. College London
2007-05-03
Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago1, and have underpinned much science and technology2, 3. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometer-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometer distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value--consistent with quantum fluctuations--on cooling below 40 K.
Antiferromagnetism in chromium alloy single crystals
Bjerrum Møller, Hans; Trego, A.L.; Mackintosh, A.R.
1965-01-01
The antiferromagnetism of single crystals of dilute alloys of V, Mn and Re in Cr has been studied at 95°K and 300°K by neutron diffraction. The addition of V causes the diffraction peaks to decrease in intensity and move away from (100), while Mn and Re cause them to increase and approach (100) so...
Antiferromagnet-long-period structure phase transition in RMn2O5 oxides
Men'shenin, V. V.; Nikolaev, V. V.; Dmitriev, A. V.
2011-07-01
An analysis of the magnetic phase transition from an antiferromagnetic into an incommensurate phase in oxides RMn2O5 has been performed. It has been shown that this is a second-order phase transition and that it can occur through one of complete irreducible representations of the space group Pbam, i.e., without a decrease in the symmetry of the crystal lattice. It has been established that the decrease in the electric polarization of the oxides in this transition is due to the development of long-period magnetic ordering.
Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2
Wawrzynska, E.; Coldea, R.; Wheeler, E M; Mazin, I. I.; Johannes, M. D.; Sorgel, T.; Jansen, M; Ibberson, R. M.; Radaelli, P. G.
2007-01-01
We report a high-resolution neutron diffraction study on the orbitally-degenerate spin-1/2 hexagonal antiferromagnet AgNiO2. A structural transition to a tripled unit cell with expanded and contracted NiO6 octahedra indicates root(3) x root(3) charge order on the Ni triangular lattice. This suggests charge order as a possible mechanism of lifting the orbital degeneracy in the presence of charge fluctuations, as an alternative to Jahn-Teller distortions. A novel magnetic ground state is observ...
Wawrzynska, E.; Coldea, R.; Wheeler, E M; Sorgel, T.; Jansen, M; Ibberson, R. M.; Radaelli, P. G.; Koza, M. M.
2007-01-01
We report a high-resolution neutron diffraction study of the crystal and magnetic structure of the orbitally-degenerate frustrated metallic magnet AgNiO2. At high temperatures the structure is hexagonal with a single crystallographic Ni site, low-spin Ni3+ with spin-1/2 and two-fold orbital degeneracy, arranged in an antiferromagnetic triangular lattice with frustrated spin and orbital order. A structural transition occurs upon cooling below 365 K to a tripled hexagonal unit cell containing t...
Néel temperature of quasi-low-dimensional Heisenberg antiferromagnets.
Yasuda, C; Todo, S; Hukushima, K; Alet, F; Keller, M; Troyer, M; Takayama, H
2005-06-03
The Néel temperature T(N) of quasi-one- and quasi-two-dimensional antiferromagnetic Heisenberg models on a cubic lattice is calculated by Monte Carlo simulations as a function of interchain (interlayer) to intrachain (intralayer) coupling J(')/J down to J(')/J approximately = 10(-3). We find that T(N) obeys a modified random-phase approximationlike relation for small J(')/J with an effective universal renormalized coordination number, independent of the size of the spin. Empirical formulas describing T(N) for a wide range of J(') and useful for the analysis of experimental measurements are presented.
Gammelmark, Søren; Eckardt, André
2013-01-01
We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials f...... that during the preparation finite size effects will play a crucial role for a system of realistic size. The experiment that we propose can be realized, for example, using atomic mixtures of rubidium 87 with potassium 41, or ytterbium 168 with ytterbium 174....
Quantum phase transitions in the Heisenberg J1-J2 triangular antiferromagnet in a magnetic field
Ye, Mengxing; Chubukov, Andrey V.
2017-01-01
We present the zero-temperature phase diagram of a Heisenberg antiferromagnet on a frustrated triangular lattice with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions, in a magnetic field. We show that the classical model has an accidental degeneracy for all J2/J1 and all fields, but the degeneracy is lifted by quantum fluctuations. We show that at large spin S , for J2/J11 , the transition remains first order, with a finite hysteresis width, but for S =1 /2 and, possibly, S =1 , there appears a new intermediate phase without a quasiclassical long-range order.
Emergent Power-Law Phase in the 2D Heisenberg Windmill Antiferromagnet: A Computational Experiment.
Jeevanesan, Bhilahari; Chandra, Premala; Coleman, Piers; Orth, Peter P
2015-10-23
In an extensive computational experiment, we test Polyakov's conjecture that under certain circumstances an isotropic Heisenberg model can develop algebraic spin correlations. We demonstrate the emergence of a multispin U(1) order parameter in a Heisenberg antiferromagnet on interpenetrating honeycomb and triangular lattices. The correlations of this relative phase angle are observed to decay algebraically at intermediate temperatures in an extended critical phase. Using finite-size scaling we show that both phase transitions are of the Berezinskii-Kosterlitz-Thouless type, and at lower temperatures we find long-range Z(6) order.
Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet
Lima, L. S.
2017-01-01
We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.
Frustrated diamond-chain quantum XXZ Heisenberg antiferromagnet in a magnetic field
Richter, Johannes, E-mail: Johannes.Richter@Physik.Uni-Magdeburg.DE [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Krupnitska, Olesia [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Krokhmalskii, Taras [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Derzhko, Oleg [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, I-34151 Trieste (Italy)
2015-04-01
We consider the antiferromagnetic spin-1/2 XXZ Heisenberg model on a frustrated diamond-chain lattice in a z- or x-aligned external magnetic field. We use the strong-coupling approach to elaborate an effective description in the low-temperature strong-field regime. The obtained effective models are spin-1/2 XY chains which are exactly solvable through the Jordan–Wigner fermionization. We perform exact-diagonalization studies of the magnetization curves to test the quality of the effective description. The results may have relevance for the description of the azurite spin-chain compound.
Large off-diagonal magnetoelectric coupling in the quantum paraelectric antiferromagnet EuTiO3
Shvartsman, V. V.; Borisov, P.; Kleemann, W.; Kamba, S.; Katsufuji, T.
2010-02-01
The third-order E2H2 -type magnetoelectric (ME) response of polycrystalline EuTiO3 changes sign under magnetic bias and shows a large anomaly at the antiferromagnetic (AF)-paramagnetic phase boundary below TN≈5.3K . It is attributed to critical fluctuations of the AF order parameter reinforced by quantum paraelectric polar correlations. The underlying biquadratic spin-lattice coupling involves electric field induced Dzyaloshinskii-Moriya interaction as described within mean-field approximation. Single domaining by ME annealing (or cooling) significantly enhances the response by additional EH and EH2 effects.
Macroscopic anisotropy and symmetry breaking in the pyrochlore antiferromagnet Gd2Ti2O7
Hassan, A. K.; Lévy, L. P.; Darie, C.; Strobel, P.
2003-06-01
In the Heisenberg antiferromagnet Gd2Ti2O7, the exchange interactions are geometrically frustrated by the pyrochlore lattice structure. This ESR study reveals a strong temperature dependent anisotropy with respect to a [111] body diagonal below a temperature TA=80 K, despite the spin only nature of the Gd3+ ion. Anisotropy and symmetry breaking can nevertheless appear through the superexchange interaction. In the presence of anisotropic exchanges, short range planar correlations restricted to specific Kagomé planes are sufficient to explain the two ESR modes studied in this work.
Unusual finite size effects on critical temperature in fcc Ising antiferromagnets
Pommier, J.; Diep, H. T.; Ghazali, A.; Lallemand, P.
1988-04-01
A new multispin coding technique is presented for Monte Carlo simulation of antiferromagnetic Ising spin systems on an fcc lattice. The nearest- and next-nearest-neighbor interactions J1 and J2 are included. This technique allows a considerable gain in CPU time and computer memory. As a first application, we have studied samples of 4L3 spins with L up to 48. An unusual behavior of the critical temperature with increasing L is found in the case of nearest-neighbor interaction in zero field. Finite size effects on the locations of tricrical points in the (T,J2/J1) plane are discussed.
Dual Lattice of ℤ-module Lattice
Futa Yuichi
2017-07-01
Full Text Available In this article, we formalize in Mizar [5] the definition of dual lattice and their properties. We formally prove that a set of all dual vectors in a rational lattice has the construction of a lattice. We show that a dual basis can be calculated by elements of an inverse of the Gram Matrix. We also formalize a summation of inner products and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL(Lenstra, Lenstra and Lovász base reduction algorithm and cryptographic systems with lattice [20], [10] and [19].
Optimized resonating valence bond state in square lattice: correlations & excitations
Z Nourbakhsh
2009-09-01
Full Text Available We consider RVB state as a variational estimate for the ground state of Heisenberg antiferromagnet in square lattice. We present numerical calculation of energy, spin-spin correlation function and spin excitation spectrum. We show, that the quantum flactuations reduce of magnetization respect to Neel order. Our results are in good agreement with other methods such as spin-wave calculation and series expansions.
Possible form of multi-polar interaction in cubic lattice
Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki
2003-05-01
The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection.
Spin Waves in 2D ferromagnetic square lattice stripe
Ahmed, Maher Z.
2011-01-01
In this work, the area and edges spin wave calculations were carried out using the Heisenberg Hamiltonian and the tridiagonal method for the 2D ferromagnetic square lattice stripe, where the SW modes are characterized by a 1D in-plane wave vector $q_x$. The results show a general and an unexpected feature that the area and edge spin waves only exist as optic modes. This behavior is also seen in 2D Heisenberg antiferromagnetic square lattice. This absence of the acoustic modes in the 2D square...
Possible form of multi-polar interaction in cubic lattice
Sakai, Osamu; Shiina, Ryousuke; Shiba, Hiroyuki
2003-05-01
The invariant form of interaction between multi-poles, including the octupole, is studied for the simple cubic (SC), body centered and face centered cubic lattices. The coupling terms can be arranged in a way similar to that of the hopping matrix between the LCAO's. A table for SC by Shiina et al. (J. Phys. Soc. Japan 66 (1997) 1741) is generalized for the general wave number case of the three types of lattice. Recent experimental result of TmTe is thereby analyzed. The development of the ferromagnetic moment below the anti-ferromagnetic transition under the anti-ferro quadrupolar order phase is discussed in this connection.
New statistical lattice model with double honeycomb symmetry
Naji, S.; Belhaj, A.; Labrim, H.; Bhihi, M.; Benyoussef, A.; El Kenz, A.
2014-04-01
Inspired from the connection between Lie symmetries and two-dimensional materials, we propose a new statistical lattice model based on a double hexagonal structure appearing in the G2 symmetry. We first construct an Ising-1/2 model, with spin values σ = ±1, exhibiting such a symmetry. The corresponding ground state shows the ferromagnetic, the antiferromagnetic, the partial ferrimagnetic and the topological ferrimagnetic phases depending on the exchange couplings. Then, we examine the phase diagrams and the magnetization using the mean field approximation (MFA). Among others, it has been suggested that the present model could be localized between systems involving the triangular and the single hexagonal lattice geometries.
Spin-lattice coupling in iron jarosite
Buurma, A.J.C.; Handayani, I.P. [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Mufti, N. [Max Planck Institute for Chemical Physics of Solids, Noethnitzer Str. 40, 01187 Dresden (Germany); Blake, G.R.; Loosdrecht, P.H.M. van [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Palstra, T.T.M., E-mail: t.t.m.palstra@rug.nl [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)
2012-11-15
We have studied the magnetoelectric coupling of the frustrated triangular antiferromagnet iron jarosite using Raman spectroscopy, dielectric measurements and specific heat. Temperature dependent capacitance measurements show an anomaly in the dielectric constant at T{sub N}. Specific heat data indicate the presence of a low frequency Einstein mode at low temperature. Raman spectroscopy confirms the presence of a new mode below T{sub N} that can be attributed to folding of the Brillouin zone. This mode shifts and sharpens below T{sub N}. We evaluate the strength of the magnetoelectric coupling using the symmetry unrestricted biquadratic magnetoelectric terms in the free energy. - Graphical abstract: Sketch of two connected triangles formed by Fe{sup 3+} spins (red arrows) in the hexagonal basal plane of potassium iron jarosite. An applied magnetic field (H) below the antiferromagnetic ordering temperature induces shifts of the hydroxy ligands, giving rise to local electrical dipole moments (blue arrows). These electric displacements cancel out in pairwise fashion by symmetry. Ligand shifts are confined to the plane and shown by shadowing. Highlights: Black-Right-Pointing-Pointer Evidence has been found for spin-lattice coupling in iron jarosite. Black-Right-Pointing-Pointer A new optical Raman mode appears below T{sub N} and shifts with temperature. Black-Right-Pointing-Pointer The magnetodielectric coupling is mediated by superexchange. Black-Right-Pointing-Pointer Symmetry of Kagome magnetic lattice causes local electrical dipole moments to cancel.
Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order
Goswami, Pallab; Si, Qimiao
2017-06-01
In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this paper, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of magnetic quantum phase transition, when the antiferromagnetic order-parameter field can be described by a dilute gas of hedgehogs and antihedgehogs. We show how the precise nature of emergent singlet order is determined by the overlap between dynamic fermion zero modes of opposite chirality, localized on the hedgehogs and antihedgehogs. For a Kondo-Heisenberg model on the honeycomb lattice, we demonstrate the competition between spin Peierls order and Kondo singlet formation, thereby elucidating its global phase diagram. We also discuss other physical problems that can be addressed within this general framework.
Relief of frustration in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7
Hallas, A. M.; Sharma, A. Z.; Cai, Y.; Munsie, T. J.; Wilson, M. N.; Tachibana, M.; Wiebe, C. R.; Luke, G. M.
2016-10-01
The gadolinium pyrochlores Gd2B2O7 are among the best realizations of antiferromagnetically coupled Heisenberg spins on a pyrochlore lattice. We present a magnetic characterization of Gd2Pt2O7 , a unique member of this family. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements show that Gd2Pt2O7 undergoes an antiferromagnetic ordering transition at TN=1.6 K. This transition is strongly first order, as indicated by the sharpness of the heat capacity anomaly, thermal hysteresis in the magnetic susceptibility, and a nondivergent relaxation rate in μ SR . The form of the heat capacity below TN suggests that the ground state is an anisotropic collinear antiferromagnet with an excitation spectrum that is gapped by 0.245(1) meV. The ordering temperature in Gd2Pt2O7,TN=1.6 K, is a substantial 160% increase from other gadolinium pyrochlores, which are all known to order at 1 K or lower. We attribute this enhancement in TN to the B -site cation, platinum. Despite being nonmagnetic, platinum has a filled 5 d t2 g orbital and an empty 5 d eg orbital that can facilitate superexchange. Thus, the magnetic frustration in Gd2Pt2O7 is partially "relieved," thereby promoting magnetic order.
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
Murtazaev, A. K.; Babaev, A. B.; Ataeva, G. Ya.
2017-01-01
The thermodynamic properties and phase transitions in a two-dimensional strongly diluted threevertex antiferromagnetic Potts model on a triangular lattice have been investigated using the Monte Carlo method. The systems with linear dimensions of L × L = N, where L = 18-48, have been considered. It has been shown using the method of fourth-order Binder cumulants that, upon the introduction of nonmagnetic impurities into the spin system described by the two-dimensional antiferromagnetic Potts model, the firstorder phase transition changes to a second-order phase transition.
Insight into the antiferromagnetic structure manipulated by electronic reconstruction
Cui, B.; Li, F.; Song, C.; Peng, J. J.; Saleem, M. S.; Gu, Y. D.; Li, S. N.; Wang, K. L.; Pan, F.
2016-10-01
Antiferromagnetic (AFM) materials, with robust rigidity to magnetic field perturbations and ultrafast spin dynamics, show great advantages in information storage and have developed into a fast-emerging field of AFM spintronics. However, a direct characterization of spin alignments in AFM films has been challenging, and their manipulation by lattice distortion and magnetic proximity is inevitably accompanied by "ferromagnetic" features within the AFM matrix. Here we resolve the G -type AFM structure of SrCo O2.5 and find that the interfacial AFM structure could be modulated intrinsically from in plane to out of plane with a canted angle of 60∘ by the charge transfer and orbital reconstruction in SrCo O2.5/L a2 /3S r1 /3Mn O3 heterostructures both experimentally and theoretically. Such an interfacial AFM reconfiguration caused by electronic reconstruction does not cause the ferromagnetic feature and changes the magnetization switching process of L a2 /3S r1 /3Mn O3 from in plane to perpendicular to the plane, in turn. Our study not only reveals the coupling between charge, orbital, and AFM structure, but also provides a unique approach to manipulating AFM structure.
Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides.
Gu, Mingqiang; Rondinelli, James M
2016-04-29
We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.
Spin-dynamics simulations of the triangular antiferromagnetic XY model*
Nho, Kwangsik; Landau, D. P.
2003-03-01
Using Monte Carlo and spin-dynamics methods, we have studied the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. We calculated the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_KT (Kosteritz-Thouless transition), both the in-plane (S^xx) and out-of-plane (S^zz) components exhibit very strong and sharp spin-wave peaks. Well above T_KT, S^xx and S^zz apparently display a central peak, and spin-wave signatures are still seen in S^zz. In addition, we also observed an almost dispersionless domain-wall peak at high w below Tc (Ising transition), where long-range order appears in the staggered chirality[1]. We found that our results demonstrate the consistency of the dynamic finite-size scaling theory for the characteristic frequency wm and S(q,w). *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)
Spin-dynamics simulations of the antiferromagnetic triangular XY model*
Nho, Kwangsik; Landau, D. P.
2002-03-01
Using Monte Carlo and spin-dynamics methods, we have simulated the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. From space-and time-displaced spin-spin correlation functions and their space-time Fourier transforms we obtained the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_c, where long-range order appears in the staggered chirality[1], S(q,w) exhibits very strong and sharp spin-wave peaks in the in-plane-component S^xx. We also observe two-spin-wave peaks at low w and an almost dispersionless domain-wall peak at high w. Above T_c, a weak spin-wave peak persists but the domain-wall peak disappears for all q. We have calculated the dispersion relation and the linewidth of the spin-wave peak in S^xx by fitting the line shape to simple Lorentzians. *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)
Three-dimensional antiferromagnetic CP(N-1) models.
Delfino, Francesco; Pelissetto, Andrea; Vicari, Ettore
2015-05-01
We investigate the critical behavior of three-dimensional antiferromagnetic CP(N-1) (ACP(N-1)) models in cubic lattices, which are characterized by a global U(N) symmetry and a local U(1) gauge symmetry. Assuming that critical fluctuations are associated with a staggered gauge-invariant (Hermitian traceless matrix) order parameter, we determine the corresponding Landau-Ginzburg-Wilson (LGW) model. For N=3 this mapping allows us to conclude that the three-component ACP(2) model undergoes a continuous transition that belongs to the O(8) vector universality class, with an effective enlargement of the symmetry at the critical point. This prediction is confirmed by numerical analyses of the finite-size scaling behaviors of the ACP(2) and the O(8) vector models, which show the same universal features at their transitions. We also present a renormalization-group (RG) analysis of the LGW theories for N≥4. We compute perturbative series in two different renormalization schemes and analyze the corresponding RG flow. We do not find stable fixed points that can be associated with continuous transitions.
Inducing spin-dependent tunneling to probe magnetic correlations in optical lattices
Pedersen, Kim-Georg; Andersen, Brian; Syljuåsen, Olav;
2012-01-01
We suggest a simple experimental method for probing antiferromagnetic spin correlations of two-component Fermi gases in optical lattices. The method relies on a spin selective Raman transition to excite atoms of one spin species to their first excited vibrational mode where the tunneling is large...
Monte Carlo study of the double and super-exchange model with lattice distortion
Suarez, J R; Vallejo, E; Navarro, O [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Mexico D. F. (Mexico); Avignon, M, E-mail: jrsuarez@iim.unam.m [Institut Neel, Centre National de la Recherche Scientifique (CNRS) and Universite Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France)
2009-05-01
In this work a magneto-elastic phase transition was obtained in a linear chain due to the interplay between magnetism and lattice distortion in a double and super-exchange model. It is considered a linear chain consisting of localized classical spins interacting with itinerant electrons. Due to the double exchange interaction, localized spins tend to align ferromagnetically. This ferromagnetic tendency is expected to be frustrated by anti-ferromagnetic super-exchange interactions between neighbor localized spins. Additionally, lattice parameter is allowed to have small changes, which contributes harmonically to the energy of the system. Phase diagram is obtained as a function of the electron density and the super-exchange interaction using a Monte Carlo minimization. At low super-exchange interaction energy phase transition between electron-full ferromagnetic distorted and electron-empty anti-ferromagnetic undistorted phases occurs. In this case all electrons and lattice distortions were found within the ferromagnetic domain. For high super-exchange interaction energy, phase transition between two site distorted periodic arrangement of independent magnetic polarons ordered anti-ferromagnetically and the electron-empty anti-ferromagnetic undistorted phase was found. For this high interaction energy, Wigner crystallization, lattice distortion and charge distribution inside two-site polarons were obtained.
Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets
HU Hui; LO Rong; ZHU Jia-Lin; XIONG Jia-Jiong
2001-01-01
The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.
Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets
HUHui; LURong; 等
2001-01-01
The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model.On the basis of instanton technique in the spin-coherent-state path-integral representation,both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained.We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys.Rev.Lett.80(1998)169),but also have great influence on the intensity of the ground-state tunnel splitting.Those features clearly have no analogue in the ferromagnetic molecular magnets.We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets.The analytical results are complemented by exact diagonalization calculation.
Shape-induced anisotropy in antiferromagnetic nanoparticles
H. Gomonay; Kondovych, S.; Loktev, V.
2013-01-01
High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magn...
Spin-Mechanical Inertia in Antiferromagnet
2016-01-01
The conservation of angular momentum has served as a guiding principle in the coupled dynamics of quantum spins and mechanical rotations. However, in an antiferromagnet with vanishing magnetization, new fundamental rules are required to properly describe spin-mechanical phenomena. Here we demonstrate that the Neel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperat...
Spin Transport in Ferromagnetic and Antiferromagnetic Textures
Akosa, Collins A.
2016-12-07
In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.
Multipartite Entanglement of a Tetrahedron Lattice
ZHANG Rong; ZHU Shi-Qun; HAO Xiang
2006-01-01
Three-dimensional Heiscnberg model in the form of a tetrahedron lattice is investigated. The concurrence and multipartite entanglement are calculated through 2-concurrence C and 4-concurrence C4. The concurrence C and multipartite entanglement C4 depend on different coupling strengths Ji and are decreased when the temperature T is increased. For a symmetric tetraledron lattice, the concurrence C is symmetric about J1 when J2 is negative while the multipartite entanglement C4 is symmetric about J1 wlen J2 ＜ 2. For a regular tetrahedron lattice, the concurrence C of ground state is 1/3 for ferromagnetic case while C=0 for antiferromagnetic case. However, there is no multipartite entanglement since C4=0 in a regular tetraledron lattice. The external magnetic field B can increase the maximum value of the concurrence CB and induce two or three peaks in CB. There is a peak in the multipartite entanglement C4B when C4B is varied as a function of the temperature T. This peak is mainly induced by the magnetic field B.
Spin transfer in antiferromagnets (Conference Presentation)
Moriyama, Takahiro
2016-10-01
Since antiferromagnets (AFMs) have no spontaneous magnetization unlike ferromagnetic materials, it is not easy to manipulate the magnetic moments in AFMs by external magnetic field. However, recent theoretical studies suggest that it is possible to manipulate the magnetization in AFMs by spin-transfer-torque in a similar manner to ferromagnetic materials. In this study, we perform spin-toque ferromagnetic resonance (ST-FMR) measurements on FeNi/NiO/Pt multilayers to experimentally investigate the interaction between the spin current and the magnetic moments of antiferromagnetic NiO. The spin current is injected to the NiO by the spin Hall effect in Pt. The monotonous change in the FMR linewidth of this system with respect to the spin current can be interpreted in a way that the spin current is transferred through the NiO and interacts with the FeNi. This intriguing spin current transport can be explained by the angular momentum transfer mediated by the antiferromagnetic magnons. The results assure that the spin current exerts a torque on the NiO magnetic moments and excites their dynamics. In the talk, recent results will be also discussed.
Spin Seebeck Effect Signals from Antiferromagnets
Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph
The Longitudinal Spin Seebeck Effect (LSSE), in which a heat current stimulates spin propagation across an interface between a magnetic material and a normal metal, is well established and observed in ferromagnetic systems. Data have been presented indicating that antiferromagnetic systems could also give rise to LSSE signals. We report here on LSSE signal measured on the Pt/NiO/YIG structure, where NiO is an antiferromagnet. This system is reported to exhibit antiferromagnonic transport. We explore the dependence of the signal on the thickness of the NiO and YIG layers. We also report its temperature dependence, which was not explored before. The results are interpreted in terms of the temperature dependence of the magnon density of states. It appears that magnon modes with energies below about 40 K are most involved in the process, as was the case to the LSSE on YIG itself. Preliminary results using other antiferromagnets and other inverse spin-Hall layers look promising and will also be reported Work supported by ARO- MURI W911NF-14-1-0016.
Model calculation of thermal conductivity in antiferromagnets
Mikhail, I.F.I., E-mail: ifi_mikhail@hotmail.com; Ismail, I.M.M.; Ameen, M.
2015-11-01
A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl{sub 2}. - Highlights: • The Boltzmann equations of phonons and magnons in antiferromagnets have been studied. • Model operators have been used to represent the magnon–phonon and three-phonon interactions. • The models possess the same important properties as the exact operators. • A new expression for the thermal conductivity has been derived. • The results showed a good quantitative agreement with the experimental data of FeCl{sub 2}.
B. Zhang; X. Lu; Z.X. Qin; H.B. Chang; X.Y. Ruan
2002-01-01
The aims of the work were to study the effect of Ge (0-6wt. %) on the paramagnetic-antiferromagnetic transition and martensitic transformation of Fe-Mn alloy using the susceptibility, microstructure examination, X-ray diffraction (XRD) and lattice parameter measurement. Ge lowers the Neel temperature, TN, and enhances the mag-netic susceptibility X, changing the Pauli paramagnetism above TN to paramagnetism state obeying the Curie Weiss law, which is essentially similar to that of γ-Fe-Mn alloys containing Al or Si; Ge depresses γ → ε martensitic transformation, which attribute to Ge increasing the stacking fault energy; Moreover, Ge increases the lat-tice parameter of 7 phase, and low content Ge increases the lattice parameter of γphase more than that of high Ge content. Comparing Ge(4s2 4p2 ) with Si(3s2 3p2 ) and Al(3s2 3p1), which have the same outer-shell of electron structures, we found that their effects on the martensitic transformation of Fe-Mn alloy are completely different. The result suggests the outer-shell of electron is not the main factor of governing the Ms temperature of Fe-Mn alloy although it is essential in the alloy's antiferromagnetic transition. The relation among the Ms temperature, stacking fault energy and lattice parameter of austenite, has been discussed in brief.
Coalescence-driven magnetic order of the uncompensated antiferromagnetic Co doped ZnO
Ney, V.; Henne, B.; Lumetzberger, J.; Wilhelm, F.; Ollefs, K.; Rogalev, A.; Kovacs, A.; Kieschnick, M.; Ney, A.
2016-12-01
The evolution of the structural and magnetic properties of Co doped ZnO has been investigated over an unprecedented concentration range above the coalescence limit. ZnO films with Co concentrations from 20% to 60% of the cationic lattice have been grown by reactive magnetron sputtering. The wurtzite crystal structure was maintained even for these high dopant concentrations. By measuring the x-ray absorption at the near edge and the linear and circular dichroism of the films at the Zn and Co K edge, it could be shown that Co substitutes predominantly for Zn in the lattice. No indications of metallic Co have been found in the samples. At low Co concentrations, the films are paramagnetic, but with increasing Co content, the films become antiferromagnetically ordered with increasing order temperature. Uncompensated spins, coupled to the antiferromagnetic dopant configurations, lead to a vertical exchange-bias-like effect, which increases with increasing Co concentration. In parallel, the single-ion anisotropy is gradually lost.
Santocanale, Luigi
2002-01-01
A μ-lattice is a lattice with the property that every unary polynomial has both a least and a greatest fix-point. In this paper we define the quasivariety of μ-lattices and, for a given partially ordered set P, we construct a μ-lattice JP whose elements are equivalence classes of games in a preor...
Spinor bose gases in cubic optical lattice
Mobarak, Mohamed Saidan Sayed Mohamed
2014-01-27
In recent years the quantum simulation of condensed-matter physics problems has resulted from exciting experimental progress in the realm of ultracold atoms and molecules in optical lattices. In this thesis we analyze theoretically a spinor Bose gas loaded into a three-dimensional cubic optical lattice. In order to account for different superfluid phases of spin-1 bosons with a linear Zeeman effect, we work out a Ginzburg-Landau theory for the underlying spin-1 Bose-Hubbard model. To this end we add artificial symmetry-breaking currents to the spin-1 Bose-Hubbard Hamiltonian in order to break the global U (1) symmetry. With this we determine a diagrammatic expansion of the grand-canonical free energy up to fourth order in the symmetry-breaking currents and up to the leading non-trivial order in the hopping strength which is of first order. As a cross-check we demonstrate that the resulting grand-canonical free energy allows to recover the mean-field theory. Applying a Legendre transformation to the grand-canonical free energy, where the symmetry-breaking currents are transformed to order parameters, we obtain the effective Ginzburg-Landau action. With this we calculate in detail at zero temperature the Mott insulator-superfluid quantum phase boundary as well as condensate and particle number density in the superfluid phase. We find that both mean-field and Ginzburg-Landau theory yield the same quantum phase transition between the Mott insulator and superfluid phases, but the range of validity of the mean-field theory turns out to be smaller than that of the Ginzburg-Landau theory. Due to this finding we expect that the Ginzburg-Landau theory gives better results for the superfluid phase and, thus, we restrict ourselves to extremize only the effective Ginzburg-Landau action with respect to the order parameters. Without external magnetic field the superfluid phase is a polar (ferromagnetic) state for anti-ferromagnetic (ferromagnetic) interactions, i.e. only the
Robust spin transfer torque in antiferromagnetic tunnel junctions
Saidaoui, Hamed Ben Mohamed
2017-04-18
We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the Néel antiferromagnetic order parameter is out of plane, ∼n×p, while the torque competing with the antiferromagnetic exchange is in plane, ∼n×(p×n). Here, p and n are the Néel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.
Emergent lattices with geometrical frustration in doped extended Hubbard models
Kaneko, Ryui; Tocchio, Luca F.; Valentí, Roser; Gros, Claudius
2016-11-01
Spontaneous charge ordering occurring in correlated systems may be considered as a possible route to generate effective lattice structures with unconventional couplings. For this purpose we investigate the phase diagram of doped extended Hubbard models on two lattices: (i) the honeycomb lattice with on-site U and nearest-neighbor V Coulomb interactions at 3 /4 filling (n =3 /2 ) and (ii) the triangular lattice with on-site U , nearest-neighbor V , and next-nearest-neighbor V' Coulomb interactions at 3 /8 filling (n =3 /4 ). We consider various approaches including mean-field approximations, perturbation theory, and variational Monte Carlo. For the honeycomb case (i), charge order induces an effective triangular lattice at large values of U /t and V /t , where t is the nearest-neighbor hopping integral. The nearest-neighbor spin exchange interactions on this effective triangular lattice are antiferromagnetic in most of the phase diagram, while they become ferromagnetic when U is much larger than V . At U /t ˜(V/t ) 3 , ferromagnetic and antiferromagnetic exchange interactions nearly cancel out, leading to a system with four-spin ring-exchange interactions. On the other hand, for the triangular case (ii) at large U and finite V', we find no charge order for small V , an effective kagome lattice for intermediate V , and one-dimensional charge order for large V . These results indicate that Coulomb interactions induce [case (i)] or enhance [case(ii)] emergent geometrical frustration of the spin degrees of freedom in the system, by forming charge order.
Ghosh, Pratyay; Verma, Akhilesh Kumar; Kumar, Brijesh
2016-01-01
A spin-1 Heisenberg model on trimerized kagome lattice is studied by doing a low-energy bosonic theory in terms of plaquette triplons defined on its triangular unit cells. The model considered has an intratriangle antiferromagnetic exchange interaction J (set to 1) and two intertriangle couplings J'>0 (nearest neighbor) and J″ (next nearest neighbor; of both signs). The triplon analysis performed on this model investigates the stability of the trimerized singlet ground state (which is exact in the absence of intertriangle couplings) in the J'-J″ plane. It gives a quantum phase diagram that has two gapless antiferromagnetically ordered phases separated by the spin-gapped trimerized singlet phase. The trimerized singlet ground state is found to be stable on J″=0 line (the nearest-neighbor case), and on both sides of it for J″≠0 , in an extended region bounded by the critical lines of transition to the gapless antiferromagnetic phases. The gapless phase in the negative J″ region has a coplanar 120∘ antiferromagnetic order with √{3 }×√{3 } structure. In this phase, all the magnetic moments are of equal length, and the angle between any two of them on a triangle is exactly 120∘. The magnetic lattice in this case has a unit cell consisting of three triangles. The other gapless phase, in the positive J″ region, is found to exhibit a different coplanar antiferromagnetic order with ordering wave vector q =(0 ,0 ) . Here, two magnetic moments in a triangle are of the same magnitude, but shorter than the third. While the angle between two short moments is 120∘-2 δ , it is 120∘+δ between a short and the long one. Only when J″=J' , their magnitudes become equal and the relative angles 120∘. The magnetic lattice in this q =(0 ,0 ) phase has the translational symmetry of the kagome lattice with triangular unit cells of reduced (isosceles) symmetry. This reduction in the point-group symmetry is found to show up as a difference in the intensities of
Ground state configurations in antiferromagnetic ultrathin films with dipolar anisotropy
Leon, H., E-mail: hleon@imre.oc.uh.cu [Instituto de Ciencia y Tecnologia de Materiales, Universidad de La Habana, Zapata e/ Mazon y G. Vedado, 10400 La Habana (Cuba)
2013-02-15
The formalism developed in a previous work to calculate the dipolar energy in quasi-two-dimensional crystals with ferromagnetic order is now extended to collinear antiferromagnetic order. Numerical calculations of the dipolar energy are carried out for systems with tetragonally distorted fcc [001] structures, the case of NiO and MnO ultrathin film grown in non-magnetic substrates, where the magnetic phase is a consequence of superexchange and dipolar interactions. The employed approximation allows to demonstrate that dipolar coupling between atomic layers is responsible for the orientation of the magnetization when it differs from the one in a single layer. The ground state energy of a given NiO or MnO film is found to depend not only on the strain, but also on how much the interlayer separation and the 2D lattice constant are changed with respect to the ideal values corresponding to the non-distorted cubic structure. Nevertheless, it is shown that the orientation of the magnetization in the magnetic phase of any of these films is determined by the strain exclusively. A striped phase with the magnetization along the [112{sup Macron }] direction appears as the ground state configuration of NiO and MnO ultrathin films. In films with equally oriented stripes along the layers this magnetic phase is twofold degenerate, while in films with multidomain layers it is eightfold degenerate. These results are not in contradiction with experimentally observed out-of-plane or in-plane magnetization of striped phases in NiO and MnO ultrathin films. - Highlights: Black-Right-Pointing-Pointer Dipolar energy in collinear antiferromagnetic ultrathin films is calculated. Black-Right-Pointing-Pointer Numerical results are presented for distorted fcc [001] structures. Black-Right-Pointing-Pointer The lowest energy of a system depends on how the tetragonal distortion is achieved. Black-Right-Pointing-Pointer A striped phase with magnetization in the [112{sup Macron }] direction is the
Spin-S kagome quantum antiferromagnets in a field with tensor networks
Picot, Thibaut; Ziegler, Marc; Orús, Román; Poilblanc, Didier
2016-02-01
Spin-S Heisenberg quantum antiferromagnets on the kagome lattice offer, when placed in a magnetic field, a fantastic playground to observe exotic phases of matter with (magnetic analogs of) superfluid, charge, bond, or nematic orders, or a coexistence of several of the latter. In this context, we have obtained the (zero-temperature) phase diagrams up to S =2 directly in the thermodynamic limit owing to infinite projected entangled pair states, a tensor network numerical tool. We find incompressible phases characterized by a magnetization plateau versus field and stabilized by spontaneous breaking of point group or lattice translation symmetry(ies). The nature of such phases may be semiclassical, as the plateaus at the 1/3th ,(1-2/9S)th, and (1-1/9S)th of the saturated magnetization (the latter followed by a macroscopic magnetization jump), or fully quantum as the spin-1/2 1/9 plateau exhibiting a coexistence of charge and bond orders. Upon restoration of the spin rotation U (1 ) symmetry, a finite compressibility appears, although lattice symmetry breaking persists. For integer spin values we also identify spin gapped phases at low enough fields, such as the S =2 (topologically trivial) spin liquid with no symmetry breaking, neither spin nor lattice.
B K Sahoo; B N Panda
2011-10-01
The effect of hybridization of conduction electrons and f-level on superconductivity (SC) and antiferromagnetism (AFM) in the coexistent phase of rare-earth nickel borocarbide superconductors (Ni2B2C) is reported. The Hamiltonian of the system is a mean ﬁeld one and has been solved by writing equations of motion for the single-particle Green functions. It is assumed that superconductivity arises due to BCS pairing mechanism in the presence of antiferromagnetism in nickel lattices of Ni2B2 plane. The expressions for superconducting and antiferromagnetic order parameters are derived using double time electron Green functions. The quasiparticle energy bands are plotted and the nature of band dispersion of the quasiparticles is studied.
Akamatsu, Hirofumi; Kumagai, Yu; Oba, Fumiyasu; Fujita, Koji; Murakami, Hideo; Tanaka, Katsuhisa; Tanaka, Isao
2011-06-01
A superexchange mechanism between Eu2+ 4f spins via the 3d states of nonmagnetic Ti4+ ions is proposed through first-principles calculations based on a hybrid Hartree-Fock density functional approach to explain G-type antiferromagnetism in EuTiO3. This mechanism is supported by systematic calculations for related Eu2+-based perovskite oxides. In EuTiO3, the competition between the antiferromagnetic superexchange and an indirect ferromagnetic exchange via the Eu 5d states leads to a delicate balance between antiferromagnetic and ferromagnetic phases. The superexchange mechanism involving the Ti 3d states hints at the microscopic origin of the strong spin-lattice coupling in EuTiO3.
Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles
Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.
2016-08-01
The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.
Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect
Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang
2016-10-01
Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.
V.V. Kulish
2015-06-01
Full Text Available The paper investigates the antiferromagnetic vector distribution in an antiferromagnetic film with a system of antidots. A static distribution of the antiferromagnetic vector is written and a method – based on the minimization of the antiferromagnet energy – that allows reducing the number of boundary conditions required for finding the constants of this distribution is proposed. Equations for the distribution constants are obtained for the both cases of minimizing the antiferromagnet energy by one and by two distribution constants that enter the expression for the antiferromagnet energy. The method is illustrated on a system of one isolated antidot. For such system, one additional condition – for the case when two boundary conditions on the surface of the antidot are given – and two additional conditions – for the case when one boundary condition on the surface of the antidot is given – on the distribution constants are written.
Dynamic scaling of the restoration of rotational symmetry in Heisenberg quantum antiferromagnets
Weinberg, Phillip; Sandvik, Anders W.
2017-08-01
We apply imaginary-time evolution with the operator e-τ H to study relaxation dynamics of gapless quantum antiferromagnets described by the spin-rotation-invariant Heisenberg Hamiltonian H . Using quantum Monte Carlo simulations to obtain unbiased results, we propagate an initial state with maximal order parameter msz (the staggered magnetization) in the z spin direction and monitor the expectation value 〈ms〉 as a function of imaginary time τ . Results for different system sizes (lengths) L exhibit an initial essentially size independent relaxation of 〈ms〉 toward its value in the infinite-size spontaneously symmetry broken state, followed by a strongly size dependent final decay to zero when the O (3 ) rotational symmetry of the order parameter is restored. We develop a generic finite-size scaling theory that shows the relaxation time diverges asymptotically as Lz, where z is the dynamic exponent of the low-energy excitations. We use the scaling theory to develop a practical way of extracting the dynamic exponent from the numerical finite-size data, systematically eliminating scaling corrections. We apply the method to spin-1 /2 Heisenberg antiferromagnets on two different lattice geometries: the standard two-dimensional (2D) square lattice and a site-diluted 2D square lattice at the percolation threshold. In the 2D case we obtain z =2.001 (5 ) , which is consistent with the known value z =2 , while for the site-diluted lattice we find z =3.90 (1 ) or z =2.056 (8 ) Df , where Df=91 /48 is the fractal dimensionality of the percolating system. This is an improvement on previous estimates of z ≈3.7 . The scaling results also show a fundamental difference between the two cases; for the 2D square lattice, the data can be collapsed onto a common scaling function even when 〈ms〉 is relatively large, reflecting the Anderson tower of quantum rotor states with a common dynamic exponent z =2 . For the diluted 2D square lattice, the scaling works well only for
Switching of antiferromagnetic chains with magnetic pulses
Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.
2016-04-01
Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.
High-Tc spin superfluidity in antiferromagnets.
Bunkov, Yu M; Alakshin, E M; Gazizulin, R R; Klochkov, A V; Kuzmin, V V; L'vov, V S; Tagirov, M S
2012-04-27
We report the observation of the unusual behavior of induction decay signals in antiferromagnetic monocrystals with Suhl-Nakamura interactions. The signals show the formation of the Bose-Einstein condensation (BEC) of magnons and the existence of spin supercurrent, in complete analogy with the spin superfluidity in the superfluid (3)He and the atomic BEC of quantum gases. In the experiments described here, the temperature of the magnon BEC is a thousand times larger than in the superfluid (3)He. It opens a possibility to apply the spin supercurrent for various magnetic spintronics applications.
Spin liquid nature in the Heisenberg J1-J2 triangular antiferromagnet
Iqbal, Yasir; Hu, Wen-Jun; Thomale, Ronny; Poilblanc, Didier; Becca, Federico
2016-04-01
We investigate the spin-1/2 Heisenberg model on the triangular lattice in the presence of nearest-neighbor J1 and next-nearest-neighbor J2 antiferromagnetic couplings. Motivated by recent findings from density-matrix renormalization group (DMRG) claiming the existence of a gapped spin liquid with signatures of spontaneously broken lattice point group symmetry [Zhu and White, Phys. Rev. B 92, 041105 (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403 (2015), 10.1103/PhysRevB.92.140403], we employ the variational Monte Carlo (VMC) approach to analyze the model from an alternative perspective that considers both magnetically ordered and paramagnetic trial states. We find a quantum paramagnet in the regime 0.08 ≲J2/J1≲0.16 , framed by 120∘ coplanar (stripe collinear) antiferromagnetic order for smaller (larger) J2/J1 . By considering the optimization of spin-liquid wave functions of a different gauge group and lattice point group content as derived from Abrikosov mean-field theory, we obtain the gapless U(1 ) Dirac spin liquid as the energetically most preferable state in comparison to all symmetric or nematic gapped Z2 spin liquids so far advocated by DMRG. Moreover, by the application of few Lanczos iterations, we find the energy to be the same as the DMRG result within error bars. To further resolve the intriguing disagreement between VMC and DMRG, we complement our methodological approach by the pseudofermion functional renormalization group (PFFRG) to compare the spin structure factors for the paramagnetic regime calculated by VMC, DMRG, and PFFRG. This model promises to be an ideal test bed for future numerical refinements in tracking the long-range correlations in frustrated magnets.
Measuring spin correlations in optical lattices using superlattice potentials
Pedersen, Kim Georg Lind; Andersen, Brian Møller; Bruun, Georg Morten;
2011-01-01
We suggest two experimental methods for probing both short- and long-range spin correlations of atoms in optical lattices using superlattice potentials. The first method involves an adiabatic doubling of the periodicity of the underlying lattice to probe neighboring singlet (triplet) correlations...... for fermions (bosons) by the occupation of the resulting vibrational ground state. The second method utilizes a time-dependent superlattice potential to generate spin-dependent transport by any number of prescribed lattice sites, and probes correlations by the resulting number of doubly occupied sites....... For experimentally relevant parameters, we demonstrate how both methods yield large signatures of antiferromagnetic correlations of strongly repulsive fermionic atoms in a single shot of the experiment. Lastly, we show how this method may also be applied to probe d-wave pairing, a possible ground-state candidate...
Parente, Walter E.F.; Pacobahyba, J.T.M.; Araújo, Ijanílio G. [Departamento de Física, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo. CEP: 69300-000 Boa Vista, Roraima (Brazil); Neto, Minos A., E-mail: minos@pq.cnpq.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Akinci, Ümit [Department of Physics, Dokuz Eylül University, Tr-35160 Izmir (Turkey)
2014-04-15
In this paper we study 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. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagrams in the H−T and D−T planes on a simple cubic lattice (z=6). We have only observed second order phase transitions for values between Δ∈[0,1], where the cases were analysed: Ising (Δ=1), anisotropic Heisenberg (Δ=0.6) and isotropic Heisenberg (Δ=0). - Highlights: • Anisotropic Heisenberg antiferromagnet on a simple cubic lattice. • Effective-field theory. • Dzyaloshinskii–Moriya interaction.
Study of magnetic properties of spin-dependent Falicov-Kimball model on a triangular lattice
Kumar, Sant; Yadav, Umesh K.; Maitra, Tulika; Singh, Ishwar
2013-02-01
Numerical diagonalization technique and Monte-Carlo simulation algorithm is used to study the ground state properties of spin-dependent Falicov-Kimball model (FKM) on a triangular lattice for 1/3 filling of itinerant (d) and localized (f) electrons. We have found that the ground state configurations are of long range Neel ordered antiferromagnetic, ferromagnetic or mixture of anti-ferromagnetic and ferromagnetic type for different values of exchange correlation (J). The magnetization of d and f-electrons increases with increasing the exchange correlation (J) between d and f-electrons and then decreases with further increasing the value of J.
Antiferromagnetic phase diagram of the cuprate superconductors
Nunes, L. H. C. M.; Teixeira, A. W.; Marino, E. C.
2017-02-01
Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa2Cu3O6+x compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.
Campos, R G; Campos, Rafael G.; Tututi, Eduardo S.
2002-01-01
It is shown that the nonlocal Dirac operator yielded by a lattice model that preserves chiral symmetry and uniqueness of fields, approaches to an ultralocal and invariant under translations operator when the size of the lattice tends to zero.
New integrable lattice hierarchies
Pickering, Andrew [Area de Matematica Aplicada, ESCET, Universidad Rey Juan Carlos, c/ Tulipan s/n, 28933 Mostoles, Madrid (Spain); Zhu Zuonong [Departamento de Matematicas, Universidad de Salamanca, Plaza de la Merced 1, 37008 Salamanca (Spain) and Department of Mathematics, Shanghai Jiao Tong University, Shanghai 200030 (China)]. E-mail: znzhu2@yahoo.com.cn
2006-01-23
In this Letter we give a new integrable four-field lattice hierarchy, associated to a new discrete spectral problem. We obtain our hierarchy as the compatibility condition of this spectral problem and an associated equation, constructed herein, for the time-evolution of eigenfunctions. We consider reductions of our hierarchy, which also of course admit discrete zero curvature representations, in detail. We find that our hierarchy includes many well-known integrable hierarchies as special cases, including the Toda lattice hierarchy, the modified Toda lattice hierarchy, the relativistic Toda lattice hierarchy, and the Volterra lattice hierarchy. We also obtain here a new integrable two-field lattice hierarchy, to which we give the name of Suris lattice hierarchy, since the first equation of this hierarchy has previously been given by Suris. The Hamiltonian structure of the Suris lattice hierarchy is obtained by means of a trace identity formula.
Charge Stripes and Antiferromagnetism in Copper-Oxide Superconductors
Tranquada, J.M.
1997-12-31
Superconducting cuprate compounds are obtained by doping holes into antiferromagnetic insulators. Neutron scattering studies have provided evidence that the doped holes tend to segregate into charge stripes, which act like domain walls between antiferromagnetic regions. The interaction between the spatially segregated holes and the magnetic domains may be responsible for the strong pairing interaction found in the cuprates.
Nematic antiferromagnetic states in bulk FeSe
Liu, Kai; Lu, Zhong-Yi; Xiang, Tao
2016-05-01
The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.
Sober Topological Molecular Lattices
张德学; 李永明
2003-01-01
A topological molecular lattice (TML) is a pair (L, T), where L is a completely distributive lattice and r is a subframe of L. There is an obvious forgetful functor from the category TML of TML's to the category Loc of locales. In this note,it is showed that this forgetful functor has a right adjoint. Then, by this adjunction,a special kind of topological molecular lattices called sober topological molecular lattices is introduced and investigated.
Classical Spin Liquid on the Maximally Frustrated Honeycomb Lattice
Rehn, J.; Sen, Arnab; Damle, Kedar; Moessner, R.
2016-10-01
We show that the honeycomb Heisenberg antiferromagnet with J1/2 =J2=J3, where J1 , J2 , and J3 are first-, second-, and third-neighbor couplings, respectively, forms a classical spin liquid with pinch-point singularities in the structure factor at the Brillouin zone corners. Upon dilution with nonmagnetic ions, fractionalized degrees of freedom carrying 1 /3 of the free moment emerge. Their effective description in the limit of low temperature is that of spins randomly located on a triangular lattice, with a frustrated sublattice-sensitive interaction of long-ranged logarithmic form. The X Y version of this magnet exhibits nematic thermal order by disorder. This comes with a clear experimental diagnostic in neutron scattering, which turns out to apply also to the case of the celebrated planar order by disorder of the kagome Heisenberg antiferromagnet.
Bilinear-biquadratic anisotropic Heisenberg model on a triangular lattice
Pires, A.S.T., E-mail: antpires@fisica.ufmg.br
2013-08-15
Motivated by the fact that the study of disordered phases at zero temperature is of great interest, I study the spin-one quantum antiferromagnet with a next-nearest neighbor interaction on a triangular lattice with bilinear and biquadratic exchange interactions and a single ion anisotropy, using a SU(3) Schwinger boson mean-field theory. I calculate the critical properties, at zero temperature, for values of the single ion anisotropy parameter D above a critical value D{sub C}, where a quantum phase transition takes place from a higher D disordered phase to a lower D ordered phase. - Highlights: • The quantum phase transition of the bilinear-biquadratic anisotropic antiferromagnet is studied. • The effect of competing interaction is analyzed. • The zero temperature phase diagram is obtained.
Tailoring exchange couplings in magnetic topological-insulator/antiferromagnet heterostructures
He, Qing Lin; Kou, Xufeng; Grutter, Alexander J.; Yin, Gen; Pan, Lei; Che, Xiaoyu; Liu, Yuxiang; Nie, Tianxiao; Zhang, Bin; Disseler, Steven M.; Kirby, Brian J.; Ratcliff, William, II; Shao, Qiming; Murata, Koichi; Zhu, Xiaodan; Yu, Guoqiang; Fan, Yabin; Montazeri, Mohammad; Han, Xiaodong; Borchers, Julie A.; Wang, Kang L.
2017-01-01
Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a platform for the realization of versatile time-reversal symmetry-breaking physics. By constructing heterostructures exhibiting Néel order in an antiferromagnetic CrSb and ferromagnetic order in Cr-doped (Bi,Sb)2Te3, we realize emergent interfacial magnetic phenomena which can be tailored through artificial structural engineering. Through deliberate geometrical design of heterostructures and superlattices, we demonstrate the use of antiferromagnetic exchange coupling in manipulating the magnetic properties of magnetic topological insulators. Proximity effects are shown to induce an interfacial spin texture modulation and establish an effective long-range exchange coupling mediated by antiferromagnetism, which significantly enhances the magnetic ordering temperature in the superlattice. This work provides a new framework on integrating topological insulators with antiferromagnetic materials and unveils new avenues towards dissipationless topological antiferromagnetic spintronics.
Takashi Yanagisawa
2015-01-01
Full Text Available We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsion U. We show that the antiferromagnetic correlation is suppressed as U is increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction.
Atkinson, D; van Steenwijk, F.J.
The resistance between two arbitrary nodes in an infinite square lattice of:identical resistors is calculated, The method is generalized to infinite triangular and hexagonal lattices in two dimensions, and also to infinite cubic and hypercubic lattices in three and more dimensions. (C) 1999 American
Lattice Regularization and Symmetries
Hasenfratz, Peter; Von Allmen, R; Allmen, Reto von; Hasenfratz, Peter; Niedermayer, Ferenc
2006-01-01
Finding the relation between the symmetry transformations in the continuum and on the lattice might be a nontrivial task as illustrated by the history of chiral symmetry. Lattice actions induced by a renormalization group procedure inherit all symmetries of the continuum theory. We give a general procedure which gives the corresponding symmetry transformations on the lattice.
Superconductivity in the Kondo lattice model
Bodensiek, Oliver; Pruschke, Thomas [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Zitko, Rok [Institute for Theoretical Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)
2011-07-01
We study the Kondo lattice model with an additional attractive interaction among the conduction-band electrons by means of dynamical mean-field theory in combination with the numerical renormalization group method. In the normal phase we observe a strong dependency of the low-energy scale on the attractive interaction. Thus, there exists a delicate interplay between the attractive interaction and the antiferromagnetic Kondo exchange, which results in a critical interaction, above of which the Fermi surface collapses because the spins become effectively decoupled from the conduction electrons. Additionally, we allow for a s-wave superconducting phase, which appears to be split at the point of the underlying Fermi surface collapse. We discuss the interplay between attractive interaction an Kondo exchange and its pertinence to phonons in heavy fermion physics.
Lattice parameters guide superconductivity in iron-arsenides
Konzen, Lance M. N.; Sefat, Athena S.
2017-03-01
The discovery of superconducting materials has led to their use in technological marvels such as magnetic-field sensors in MRI machines, powerful research magnets, short transmission cables, and high-speed trains. Despite such applications, the uses of superconductors are not widespread because they function much below room-temperature, hence the costly cooling. Since the discovery of Cu- and Fe-based high-temperature superconductors (HTS), much intense effort has tried to explain and understand the superconducting phenomenon. While no exact explanations are given, several trends are reported in relation to the materials basis in magnetism and spin excitations. In fact, most HTS have antiferromagnetic undoped ‘parent’ materials that undergo a superconducting transition upon small chemical substitutions in them. As it is currently unclear which ‘dopants’ can favor superconductivity, this manuscript investigates crystal structure changes upon chemical substitutions, to find clues in lattice parameters for the superconducting occurrence. We review the chemical substitution effects on the crystal lattice of iron-arsenide-based crystals (2008 to present). We note that (a) HTS compounds have nearly tetragonal structures with a-lattice parameter close to 4 Å, and (b) superconductivity can depend strongly on the c-lattice parameter changes with chemical substitution. For example, a decrease in c-lattice parameter is required to induce ‘in-plane’ superconductivity. The review of lattice parameter trends in iron-arsenides presented here should guide synthesis of new materials and provoke theoretical input, giving clues for HTS.
Gofryk, K. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Jaime, M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab)
2014-12-01
Our preliminary magnetostriction measurements have already shown a strong interplay of lattice dynamic and magnetism in both antiferromagnetic and paramagnetic states, and give unambiguous evidence of strong spin- phonon coupling in uranium dioxide. Further studies are planned to address the puzzling behavior of UO_{2} in magnetic and paramagnetic states and details of the spin-phonon coupling.
Zhang, Yu-Jun; Chen, Jia-Hui; Li, Liang-Liang; Ma, Jing; Nan, Ce-Wen; Lin, Yuan-Hua
2017-05-01
Electric field manipulation of magnetic properties has attracted a lot of research interest recently in solid-state physics. However, ferroelectric strain modulation of antiferromagnetic (AFM) layer is rarely studied in ferromagnet/antiferromagnet/ferroelectric heterostructures. In this paper, we prepared a Ni/NiO(001) heterostructure on ferroelectric Pb (Mg1/3N b2 /3 ) 0.7T i0.3O3(001 ) substrates and observed an out-of-plane electric field modulation of exchange bias and magnetic anisotropy in the Ni layer. The exchange bias was easily eliminated by an electric field cycle, which was due to the AFM domain switching induced by piezoelectric strain in the NiO layer. Synchrotron x ray linear dichroism results confirmed the AFM moment alignment induced by ferroelectric strain as well. Our work showed a promising strategy to manipulate AFM moments and domains, serving the blooming AFM spintronics.
Maeter, H; Zvyagin, A A; Luetkens, H; Pascua, G; Shermadini, Z; Saint-Martin, R; Revcolevschi, A; Hess, C; Büchner, B; Klauss, H-H
2013-09-11
We report zero and longitudinal magnetic field muon spin relaxation (μSR) measurements of the spin S = 1/2 antiferromagnetic Heisenberg chain material SrCuO2. We find that in a weak applied magnetic field B0 the spin-lattice relaxation rate λ follows a power law λ is proportional to B(0)(-n) with n = 0.9(3). This result is temperature independent for 5 K ≤ T ≤ 300 K. Within conformal field theory and using the Müller ansatz we conclude ballistic spin transport in SrCuO2.
Sousa, Griffith Mendonça A., E-mail: griffith_mas@hotmail.com; Pires, A.S.T.
2014-03-15
The Neel and collinear ordered phases of the two-dimensional S=1 antiferromagnet with next and next near neighbor exchange interactions and easy axis single ion anisotropy, on the square lattice, are studied at low temperature using a Modified Spin Wave Theory. We calculate the low-temperature quantities as a function of the temperature, frustration and anisotropy. We calculate also the phase diagram at T=0. We found a disordered phase separating the Neel and collinear phases. - Highlights: • The phase diagrams in zero temperature. • The critical temperature was studied as a function of frustration and D. • The sublattice magnetizations and the gap were studied.
Fractal dimension in percolating Heisenberg antiferromagnets
Itoh, S. [Neutron Science Laboratory, High Energy Accelerator Research Organization, Tsukuba 305-0810 (Japan)]. E-mail: shinichi.itoh@kek.jp; Kajimoto, R. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai 319-1195 (Japan); Adams, M.A. [ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX (United Kingdom); Bull, M.J. [ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX (United Kingdom); Iwasa, K. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Aso, N. [Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, Tokai 319-1106 (Japan); Yoshizawa, H. [Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, Tokai 319-1106 (Japan); Takeuchi, T. [Low Temperature Center, Osaka University, Toyonaka 560-0043 (Japan)
2007-03-15
We investigated static and dynamical properties in the three-dimensional percolating Heisenberg antiferromagnets, RbMn{sub c}Mg{sub 1-c}F{sub 3}, with the magnetic concentration close to the percolation threshold, c{sub P}=0.312, around the superlattice point well below T{sub N}. In neutron diffraction experiment, the wave number dependence of the elastic scattering component was well fitted to q{sup -x}. Magnetic fractons were also studied using inelastic neutron scattering, and the observed fractons showed the dispersion relation of q{sup z}. The determined exponents, x=2.43+/-0.05 and z=2.5+/-0.1, were in good agreement with the fractal dimension (D{sub f}=2.48)
Magnetic Properties of Nanoparticles of Antiferromagnetic Materials
Mørup, Steen; Frandsen, Cathrine; Bødker, Franz
2003-01-01
The magnetic properties of antiferromagnetic nanoparticles have been studied by Mossbauer spectroscopy and neutron scattering. Temperature series of Mossbauer spectra of non-interacting, superparamagnetic hematite nanoparticles were fitted by use of the Blume-Tjon relaxation model. It has been...... found that the magnetic anisotropy energy constant increases significantly with decreasing particle size. Neutron scattering experiments on similar samples give new information on both superparamagnetic relaxation and collective magnetic excitations. There is good agreement between the values...... of the parameters obtained from Mossbauer spectroscopy and neutron scattering. In samples of interacting hematite nanoparticles, the relaxation was significantly suppressed. The Mossbauer data for these samples are in accordance with a mean field model for an ordered state of strongly interacting particles. Mixing...
Antiferromagnetic spin wave and the superconductivity
Koh, Shun-ichiro
2000-07-01
The neutron scattering of UPd 2Al 3 showed that a sharp peak, which is absent in the normal phase, appears in the superconducting phase (Metoki et al., J. Phys. Soc. Japan 66 (1997) 2560; Bernhoeft et al., Phys. Rev. Lett. 81 (1998) 4244). Assuming this excitation to be an antiferromagnetic (AFM) spin-wave, this paper deals with its enhancement by the superconductivity. Applying the slave-boson formalism, we consider the AFM ordering as a spin-density-wave (Koh, Phys. Lett. A 253 (1999) 98). Above Tc, the spin-wave suffers an energy dissipation due to the conduction electron. Below Tc, the superconductivity suppresses the dissipation, resulting in the growth of the AFM spin-wave.
Spin dynamics in geometrically frustrated antiferromagnetic pyrochlores
Gardner, J. S.; Ehlers, G.; Bramwell, S. T.; Gaulin, B. D.
2004-03-01
We have studied the spin dynamics of several antiferromagnetic pyrochlore oxides. These magnets are geometrically frustrated and only reach their ground states at temperatures much lower than that expected from mean field theory. Here we present data on the magnetic nature, especially the spin dynamics of Tb2Ti2O7, Gd2Ti2O7 and Y2Mo2O7. In these systems the ground states are found to be very different. Y2Mo2O7 freezes completely into a spin glass-like state, Tb2Ti2O7 is a cooperative paramagnetic and remains dynamic down to 15 mK and Gd2Ti2O7 enters a unique partially ordered state at {\\sim }1 K.
Quasiparticle bandstructure of antiferromagnetic EuTe
Mathi Jaya, S.; Nolting, W.
1997-11-01
The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor EuTe is derived by use of a combination of a many-body model procedure with a tight-binding - `linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d - f model for a single band electron (`test electron') being exchange coupled to the antiferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d - f model are taken from a TB - LMTO calculation for paramagnetic EuTe. The d - f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice - quasiparticle bandstructure (S - QBS) and sublattice - quasiparticle density of states (S - QDOS) of the unoccupied 5d - 6s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles (`magnetic polarons') are worked out in detail. The temperature dependence of the S - QDOS and S - QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from 0953-8984/9/47/012/img1 to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5d - 6s) conduction band electrons and localized 4f moments.
Electrically tunable transport in antiferromagnetic Sr3Ir2O7
Seinige, Heidi; Wang, Cheng; Cao, Gang; Zhou, Jianshi-S.; Goodenough, John B.; Tsoi, Maxim
Recently we demonstrated experimentally the existence of interconnections between magnetic state and transport currents in antiferromagnetic (AFM) Mott insulator Sr2IrO4. We found a very large anisotropic magnetoresistance and demonstrated a reversible resistive switching driven by high-density currents/high electric fields. These results support the feasibility of AFM spintronics, where antiferromagnets are used in place of ferromagnets, however a low Néel temperature of this material (240 K) questions any practical applications. Here we present a comparative electrical transport study of its sister compound Sr2IrO4 which has a higher transition temperature (285 K). Similar to the case of Sr2IrO4, we find a continuous reduction in the resistivity of Sr3Ir2O7 as a function of increasing electrical bias and abrupt reversible changes above a threshold bias current. We explain these results by a reduction of activation energy associated with a field-driven lattice distortion. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, and by NSF Grants DMR-1207577, DMR-1265162, and DMR-1122603.
Excitation-Gap Scaling near Quantum Critical Three-Dimensional Antiferromagnets.
Lohöfer, M; Wessel, S
2017-04-07
By means of large-scale quantum Monte Carlo simulations, we examine the quantum critical scaling of the magnetic excitation gap (the triplon gap) in a three-dimensional dimerized quantum antiferromagnet, the bicubic lattice, and identify characteristic multiplicative logarithmic scaling corrections atop the leading mean-field behavior. These findings are in accord with field-theoretical predictions that are based on an effective description of the quantum critical system in terms of an asymptotically free field theory, which exhibits a logarithmic decay of the renormalized interaction strength upon approaching the quantum critical point. Furthermore, using bond-based singlet spectroscopy, we identify the amplitude (Higgs) mode resonance within the antiferromagnetic region. We find a Higgs mass scaling in accord with field-theoretical predictions that relate it by a factor of sqrt[2] to the corresponding triplon gap in the quantum disordered regime. In contrast to the situation in lower-dimensional systems, we observe in this three-dimensional coupled-dimer system a distinct signal from the amplitude mode also in the dynamical spin structure factor. Its width is observed to vanish proportional to the Higgs mass in the accessible proximity to the quantum critical point.
Strongly Coupled Systems: From Quantum Antiferromagnets To Unified Models For Superconductors
Chudnovsky, V
2002-01-01
I discuss the significance of the antiferromagnetic Heisenberg model (AFHM) in both high-energy and condensed-matter physics, and proceed to describe an efficient cluster algorithm used to simulate the AFHM. This is one of two algorithms with which my collaborators and I were able to obtain numerical results that definitively confirm that chiral perturbation theory, corrected for cutoff effects in the AFHM, leads to a correct field-theoretical description of the low- temperature behavior of the spin correlation length in various spin representations S. Using a finite-size-scaling technique, we explored correlation lengths of up to 105 lattice spacings for spins S = 1 and 5/2. We show how the recent prediction of cutoff effects by P. Hasenfratz is approached for moderate correlation lengths, and smoothly connects with other approaches to modeling the AFHM at smaller correlation lengths. I also simulate and discuss classical antiferromagnetic systems with simultaneous SO(M) and SO( N) symmetries, which have bee...
Strongly Coupled Systems From Quantum Antiferromagnets To Unified Models For Superconductors
Chudnovsky, V
2002-01-01
I discuss the significance of the antiferromagnetic Heisenberg model (AFHM) in both high-energy and condensed-matter physics, and proceed to describe an efficient cluster algorithm used to simulate the AFHM. This is one of two algorithms with which my collaborators and I were able to obtain numerical results that definitively confirm that chiral perturbation theory, corrected for cutoff effects in the AFHM, leads to a correct field-theoretical description of the low- temperature behavior of the spin correlation length in various spin representations S. Using a finite-size-scaling technique, we explored correlation lengths of up to 105 lattice spacings for spins S = 1 and 5/2. We show how the recent prediction of cutoff effects by P. Hasenfratz is approached for moderate correlation lengths, and smoothly connects with other approaches to modeling the AFHM at smaller correlation lengths. I also simulate and discuss classical antiferromagnetic systems with simultaneous SO(M) and SO( N) symmetries, which have bee...
Frustrated antiferromagnet YbAgGe under magnetic fields and pressures
Kubo, Hirokazu; Umeo, Kazunori; Takabatake, Toshiro [ADSM, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Katoh, Kenichi [Department of Applied Physics, National Defense Academy, Yokosuka 239-8686 (Japan); Ochiai, Akira, E-mail: khirokazu@hiroshima-u.ac.j [Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)
2010-01-15
We present a detailed study of the field (B)- temperature (T) phase diagram under pressures (P) up to 2.7 GPa for the heavy-fermion antiferromagnet YbAgGe that crystallizes in the hexagonal ZrNiAl-type structure with a quasi-kagome lattice of Yb ions. This compound undergoes two magnetic transitions at T{sub M1} = 0.8 K and T{sub M2} = 0.65 K in zero field at ambient pressure. In the ground state, M(B) shows a metamagnetic transition at B{sub M} = 4.6 T for the easy magnetization direction B || a. This transition field decreases to 3.3 T as P is increased to 2.2 GPa. At 2.7 GPa, {rho}(B) exhibits successive transitions at 5.0, 6.0, 7.5, and 9.0 T. On the other hand, for the hard direction B || c, T{sub M} increases with applied field in the P range above 0.5 GPa. This increase of T{sub M}(B) is opposite to the decrease of T{sub M}(B) for a conventional antiferromagnetic phase. These findings suggest that the application of pressure releases in part the magnetic frustration in YbAgGe.
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.
Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang
2016-07-01
Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .
Crucial role of interlayer distance for antiferromagnet-induced perpendicular magnetic anisotropy
Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Cheng, Pei-Yu; Wei, Der-Hsin
2015-12-01
Antiferromagnetic (AFM) thin films were recently proposed to be an alternative to conventional materials for achieving perpendicular magnetic anisotropy (PMA) in ferromagnetic thin films, because AFM thin films exhibit an advantage of flexible control. Here, we report that antiferromagnet-induced PMA is highly sensitive to interfacial moments of AFM thin films as well as the magnetic interaction of such moments with volume moments, determined according to the vertical interlayer distance. Magnetic hysteresis loops and x-ray magnetic domain imaging revealed the establishment of perpendicular magnetization on face-centered tetragonal (fct)-like Mn/Co/Ni films when covered with monolayered Mn films. A cover of Mn films that exhibit contracted fct- [vertical-to-in-plane lattice constant ratio (c /a )=0.95 ] and expanded fct-like (c /a =1.05 ) structures at different thickness levels induced in-plane magnetic anisotropy and PMA in Co/Ni films, respectively, confirming that the interlayer distance is a crucial parameter for establishing perpendicular magnetization.
Chiral Spin Liquid on a Kagome Antiferromagnet Induced by the Dzyaloshinskii-Moriya Interaction
Messio, Laura; Bieri, Samuel; Lhuillier, Claire; Bernu, Bernard
2017-06-01
The quantum spin liquid material herbertsmithite is described by an antiferromagnetic Heisenberg model on the kagome lattice with a non-negligible Dzyaloshinskii-Moriya interaction (DMI). A well-established phase transition to the q =0 long-range order occurs in this model when the DMI strength increases, but the precise nature of a small-DMI phase remains controversial. Here, we describe a new phase obtained from Schwinger-boson mean-field theory that is stable at small DMI, and which can explain the dispersionless spectrum seen in the inelastic neutron scattering experiment by Han et al. [Nature (London) 492, 406 (2012), 10.1038/nature11659]. It is a time-reversal symmetry breaking Z2 spin liquid, with the unique property of a small and constant spin gap in an extended region of the Brillouin zone. The phase diagram as a function of DMI and spin size is given, and dynamical spin structure factors are presented.
Anomalous curie response of impurities in quantum-critical spin-1/2 Heisenberg antiferromagnets.
Höglund, Kaj H; Sandvik, Anders W
2007-07-13
We consider a magnetic impurity in two different S=1/2 Heisenberg bilayer antiferromagnets at their respective critical interlayer couplings separating Néel and disordered ground states. We calculate the impurity susceptibility using a quantum Monte Carlo method. With intralayer couplings in only one of the layers (Kondo lattice), we observe an anomalous Curie constant C*, as predicted on the basis of field-theoretical work [S. Sachdev, Science 286, 2479 (1999)10.1126/science.286.5449.2479]. The value C* = 0.262 +/- 0.002 is larger than the normal Curie constant C=S(S+1)/3. Our low-temperature results for a symmetric bilayer are consistent with a universal C*.
Theoretical reconsideration of antiferromagnetic Fermi surfaces in URu{sub 2}Si{sub 2}
Yamagami, Hiroshi, E-mail: yamagami@cc.kyoto-su.ac.jp [Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555 (Japan)
2011-01-01
In an itinerant 5f-band model, the antiferromagnetic (AFM) Fermi surfaces of URu{sub 2}Si{sub 2} are reconsidered using a relativistic LAPW method within a local spin-density approximation, especially taking into account the lattice parameters dependent on pressures. The reduction of the z-coordinate of the Si sites results in the effect of flattening the Ru-Si layers of URu{sub 2}Si{sub 2} crystal structure, thus weakening a hybridization/mixing between the U-5f and Ru-4d states in the band structure. Consequently the 5f bands around the Fermi level are more flat in the dispersion with decreasing the z-coordinate, thus producing three closed Fermi surfaces like 'curing-stone', 'rugby-ball' and 'ball'. The origins of de Haas-van Alphen branches can be qualitatively interpreted from the obtained AFM Fermi surfaces.
Nishimoto, Satoshi; Shibata, Naokazu; Hotta, Chisa
2013-01-01
Quantum spin-1/2 kagome Heisenberg antiferromagnet is the representative frustrated system possibly hosting a spin liquid. Clarifying the nature of this elusive topological phase is a key challenge in condensed matter; however, even identifying it still remains unsettled. Here we apply a magnetic field and discover a series of spin-gapped phases appearing at five different fractions of magnetization by means of a grand canonical density matrix renormalization group, an unbiased state-of-the-art numerical technique. The magnetic field dopes magnons and first gives rise to a possible Z₃ spin liquid plateau at 1/9 magnetization. Higher field induces a self-organized super-lattice unit, a six-membered ring of quantum spins, resembling an atomic orbital structure. Putting magnons into this unit one by one yields three quantum solid plateaus. We thus find that the magnetic field could control the transition between various emergent phases by continuously releasing the frustration.
Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2 Ti2 O7
Petrenko, O. A.; Lees, M. R.; Balakrishnan, G.; Paul, D. Mck
2004-07-01
Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice, where apart from the Heisenberg exchange the spins also interact via dipole-dipole forces. We report on low-temperature specific heat measurements performed on single crystals of Gd2Ti2O7 for three different directions of an applied magnetic field. The measurements reveal the strongly anisotropic behavior of Gd2Ti2O7 in a magnetic field despite the apparent absence of a significant single-ion anisotropy for Gd3+ . The H-T phase diagrams are constructed for H∥[111] , H∥[110] , and H∥[112] . The results indicate that further theoretical work beyond a simple mean-field model is required.
Solitary Magnons in the S =5/2 Antiferromagnet CaFe2O4
Stock, C.; Rodriguez, E. E.; Lee, N.; Green, M. A.; Demmel, F.; Ewings, R. A.; Fouquet, P.; Laver, M.; Niedermayer, Ch.; Su, Y.; Nemkovski, K.; Rodriguez-Rivera, J. A.; Cheong, S.-W.
2016-07-01
CaFe2O4 is a S =5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c -axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ˜1 ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ˜1 - 2 c -axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A +B orders as well as localization of spin excitations in a classical magnet.
Revealing hidden antiferromagnetic correlations in doped Hubbard chains via string correlators
Hilker, Timon A.; Salomon, Guillaume; Grusdt, Fabian; Omran, Ahmed; Boll, Martin; Demler, Eugene; Bloch, Immanuel; Gross, Christian
2017-08-01
Topological phases, like the Haldane phase in spin-1 chains, defy characterization through local order parameters. Instead, nonlocal string order parameters can be employed to reveal their hidden order. Similar diluted magnetic correlations appear in doped one-dimensional lattice systems owing to the phenomenon of spin-charge separation. Here we report on the direct observation of such hidden magnetic correlations via quantum gas microscopy of hole-doped ultracold Fermi-Hubbard chains. The measurement of nonlocal spin-density correlation functions reveals a hidden finite-range antiferromagnetic order, a direct consequence of spin-charge separation. Our technique, which measures nonlocal order directly, can be readily extended to higher dimensions to study the complex interplay between magnetic order and density fluctuations.
Fermi surface evolution and checker-board block-spin antiferromagnetism in AxFe2-ySe2
Tai, Yuan-Yen; Zhu, Jian-Xin; Graf, Matthias J.; Ting, C. S.
2012-10-01
We develop an effective multiorbital mean-field t-J Hamiltonian with realistic tight-binding and exchange parameters to describe the electronic and magnetic structures of iron-selenide based superconductors AxFe2-ySe2 for iron vacancy doping in the range 0≤y≤0.4. The Fermi surface topology extracted from the spectral function of angle-resolved photoemission spectroscopy (ARPES) experiments is adequately accounted for by a tight-binding lattice model with random vacancy disorder. Since introducing iron vacancies breaks the lattice periodicity of the stochiometric compound, it greatly affects the electronic band structure. With changing vacancy concentration, the electronic band structure evolves, leading to a reconstruction of the Fermi surface topology. For intermediate doping levels, the realized stable electronic structure is a compromise between the solutions for the perfect lattice with y=0 and the vacancy stripe-ordered lattice with y=0.4, which results in a competition between vacancy random disorder and vacancy stripe order. A multiorbital hopping model is parameterized by comparing Fermi surface topologies to ARPES experiments, from which we construct a mean-field t-J lattice model to study the paramagnetic and antiferromagnetic (AFM) phases of K0.8Fe1.6Se2. In the AFM phase the calculated spin magnetization of the t-J model leads to a checker-board block-spin structure in good agreement with neutron scattering experiments and abinitio calculations.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.
Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D
2015-11-03
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.
2015-01-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
Computational design of a robust two-dimensional antiferromagnetic semiconductor
Chabungbam, Satyananda; Sen, Prasenjit
2017-07-01
Using density functional theory calculations, we establish the hitherto unknown compound CrCTe3 to be a stable antiferromagnetic semiconductor in the R 3 ¯ crystal structure with an indirect fundamental gap. Successive layers in the bulk compound are weakly bound by van der Waals forces so that individual layers can be easily exfoliated. A monolayer of CrCTe3 is also an antiferromagnetic semiconductor. The monolayer is structurally stable over a large range of compressive and tensile strains, and the antiferromagnetic state is robust over this strain range. Band gap of the monolayer can be tuned by as much as 50% by applying strain in this range.
Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain
Wang, Weiwei; Gu, Chenjie; Zhou, Yan; Fangohr, Hans
2017-07-01
We theoretically investigate the spin-wave (magnon) excitations in a classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a Dirac-like equation by linearizing the Landau-Lifshitz-Gilbert equation in this antiferromagnetic system, in contrast to the ferromagnetic system in which a Schrödinger-type equation is derived. The Hamiltonian operator in the Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin chain by measuring the expectation values of the wave-packet position.
Critical quasiparticles in single-impurity and lattice Kondo models
Vojta, M.; Bulla, R.; Wölfle, P.
2015-07-01
Quantum criticality in systems of local moments interacting with itinerant electrons has become an important and diverse field of research. Here we review recent results which concern (a) quantum phase transitions in single-impurity Kondo and Anderson models and (b) quantum phase transitions in heavy-fermion lattice models which involve critical quasiparticles. For (a) the focus will be on impurity models with a pseudogapped host density of states and their applications, e.g., in graphene and other Dirac materials, while (b) is devoted to strong-coupling behavior near antiferromagnetic quantum phase transitions, with potential applications in a variety of heavy-fermion metals.
Bowlan, P.; Trugman, S. A.; Bowlan, J.; Zhu, J.-X.; Hur, N. J.; Taylor, A. J.; Yarotski, D. A.; Prasankumar, R. P.
2016-09-01
We demonstrate an approach for directly tracking antiferromagnetic (AFM) spin dynamics by measuring ultrafast changes in a magnon resonance. We test this idea on the multiferroic HoMnO3 by optically photoexciting electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced change in the magnon line shape that builds up over 5-12 picoseconds, which we show to be the spin-lattice thermalization time, indicating that electrons heat the spins via phonons. We compare our results to previous studies of spin-lattice thermalization in ferromagnetic manganites, giving insight into fundamental differences between the two systems. Our work sheds light on the microscopic mechanism governing spin-phonon interactions in AFMs and demonstrates a powerful approach for directly monitoring ultrafast spin dynamics.
Enjalran, Matthew; Del Maestro, Adrian; Gingras, Michel J. P.
2008-03-01
The rare-earth pyrochlore gadolinium titanate, Gd2Ti2O7, represents an excellent experimental realization of a Heisenberg antiferromagnet (AFM) in a frustrated geometry with weak long-range dipole-dipole interactions (approximately 20% of nearest neighbor AFM exchange). Experiments on Gd2Ti2O7 in a magnetic field reveal a complex phase diagram associated with the breaking of spatial symmetries of the pyrochlore lattice as the field is applied along select symmetry directions. We study a model of classical Heisenberg spins (O(3) symmetry) on a pyrochlore lattice with exchange and dipolar interactions within mean-field theory. Using parameters relevant to the material system, we develop phase diagrams in finite magnetic fields. Our results our compared to experiments on Gd2Ti2O7 (and Gd2Sn2O7).
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-01-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a...
On Traveling Waves in Lattices: The Case of Riccati Lattices
Dimitrova, Zlatinka
2012-09-01
The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.
Shindler, A. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2007-07-15
I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)
Long-range interactions in antiferromagnetic quantum spin chains
Bravo, B.; Cabra, D. C.; Gómez Albarracín, F. A.; Rossini, G. L.
2017-08-01
We study the role of long-range dipolar interactions on antiferromagnetic spin chains, from the classical S →∞ limit to the deep quantum case S =1 /2 , including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization, and density matrix renormalization group (DMRG). We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation in both phases, and also close to zero field in the antiferromagnetic phase. In the extreme quantum limit S =1 /2 , extensive DMRG computations show that the main phases remain present with transition lines to saturation significatively shifted to lower fields, in agreement with the bosonization analysis. The overall picture maintains a close analogy with the phase diagram of the anisotropic XXZ spin chain in a transverse field.
Experimental and theoretical studies of nanoparticles of antiferromagnetic materials
Mørup, Steen; Madsen, Daniel Esmarch; Frandsen, Cathrine;
2007-01-01
The magnetic properties of nanoparticles of antiferromagnetic materials are reviewed. The magnetic structure is often similar to the bulk structure, but there are several examples of size-dependent magnetic structures. Owing to the small magnetic moments of antiferromagnetic nanoparticles...... measurements, Mössbauer spectroscopy and neutron scattering. Below the blocking temperature, the magnetic dynamics in nanoparticles is dominated by thermal excitations of the uniform mode. In antiferromagnetic nanoparticles, the frequency of this mode is much higher than in ferromagnetic and ferrimagnetic...... nanoparticles, but it depends crucially on the size of the uncompensated moment. Excitation of the uniform mode results in a so-called thermoinduced moment, because the two sublattices are not strictly antiparallel when this mode is excited. The magnetic dipole interaction between antiferromagnetic...
Characterization of the Dilute Ising Antiferromagnet
Wiener, T.
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi{sub 2}Ge{sub 2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi{sub 2}Ge{sub 2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of concentration s for which a spin
Characterization of the Dilute Ising Antiferromagnet
Wiener, Timothy [Iowa State Univ., Ames, IA (United States)
2000-09-12
A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi_{2}Ge_{2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi_{2}Ge_{2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of
Reversal of exchange bias in nanocrystalline antiferromagnetic-ferromagnetic bilayers
Prados, C; Hernando, A; Montone, A
2002-01-01
The sign of the exchange bias in field cooled nanocrystalline antiferromagnetic-ferromagnetic bilayers (Co-O and Ni-O/permalloy) is reversed at temperatures approaching the antiferromagnetic (AFM) blocking temperature. A similar phenomenon is observed after magnetic training processes at similar temperatures. These effects can be explained assuming that the boundaries of nanocrystalline grains in AFM layers exhibit lower transition temperatures than grain cores.
Antiferromagnetic and Orbital Ordering on a Diamond Lattice Near Quantum Criticality
Plumb, K. W.; Morey, J. R.; Rodriguez-Rivera, J. A.; Wu, Hui; Podlesnyak, A. A.; McQueen, T. M.; Broholm, C. L.
2016-10-01
We present neutron scattering measurements on powder samples of the spinel FeSc2S4 that reveal a previously unobserved magnetic ordering transition occurring at 11.8(2) K. Magnetic ordering occurs subsequent to a subtle cubic-to-tetragonal structural transition that distorts Fe coordinating sulfur tetrahedra and lifts the orbital degeneracy. The orbital ordering is not truly long ranged, but occurs over finite-sized domains that limit magnetic correlation lengths. The application of 1 GPa hydrostatic pressure appears to destabilize this Néel state, reducing the transition temperature to 8.6(8) K and redistributing magnetic spectral weight to higher energies. The relative magnitudes of ordered ⟨m ⟩2=3.1 (2 ) μB2 and fluctuating moments ⟨δ m ⟩=13 (1 ) μB2 show that the magnetically ordered state of FeSc2 S4 is drastically renormalized and close to criticality.
Magnetic order-disorder transitions on a one-third-depleted square lattice
Guo, H.-M.; Mendes-Santos, T.; Pickett, W. E.; Scalettar, R. T.
2017-01-01
Quantum Monte Carlo simulations are used to study the magnetic and transport properties of the Hubbard model, and its strong coupling Heisenberg limit, on a one-third-depleted square lattice. This is the geometry occupied, after charge ordering, by the spin-1/2 Ni1 + atoms in a single layer of the nickelate materials La4Ni3O8 and (predicted) La3Ni2O6 . Our model is also a description of strained graphene, where a honeycomb lattice has bond strengths which are inequivalent. For the Heisenberg case, we determine the location of the quantum critical point (QCP) where there is an onset of long range antiferromagnetic order (LRAFO), and the magnitude of the order parameter, and then compare with results of spin wave theory. An ordered phase also exists when electrons are itinerant. In this case, the growth in the antiferromagnetic structure factor coincides with the transition from band insulator to metal in the absence of interactions.
Quantum disordered insulating phase in the frustrated cubic-lattice Hubbard model
Laubach, Manuel; Joshi, Darshan G.; Reuther, Johannes; Thomale, Ronny; Vojta, Matthias; Rachel, Stephan
2016-01-01
In the quest for quantum spin liquids in three spatial dimensions (3D), we study the half-filled Hubbard model on the simple cubic lattice with hopping processes up to third neighbors. Employing the variational cluster approach (VCA), we determine the zero-temperature phase diagram: In addition to a paramagnetic metal at small interaction strength U and various antiferromagnetic insulators at large U , we find an intermediate-U antiferromagnetic metal. Most interestingly, we also identify a nonmagnetic insulating region, extending from intermediate to strong U . Using VCA results in the large-U limit, we establish the phase diagram of the corresponding J1-J2-J3 Heisenberg model. This is qualitatively confirmed—including the nonmagnetic region—using spin-wave theory. Further analysis reveals a striking similarity to the behavior of the J1-J2 square-lattice Heisenberg model, suggesting that the nonmagnetic region may host a 3D spin-liquid phase.
Thermally activated repolarization of antiferromagnetic particles: Monte Carlo dynamics
Soloviev, S. V.; Popkov, A. F.; Knizhnik, A. A.; Iskandarova, I. M.
2017-02-01
Based on the equation of motion of an antiferromagnetic moment, taking into account a random field of thermal fluctuations, we propose a Monte Carlo (MC) scheme for the numerical simulation of the evolutionary dynamics of an antiferromagnetic particle, corresponding to the Langevin dynamics in the Kramers theory for the two-well potential. Conditions for the selection of the sphere of fluctuations of random deviations of the antiferromagnetic vector at an MC time step are found. A good agreement with the theory of Kramers thermal relaxation is demonstrated for varying temperatures and heights of energy barrier over a wide range of integration time steps in an overdamped regime. Based on the developed scheme, we performed illustrative calculations of the temperature drift of the exchange bias under the fast annealing of a ferromagnet-antiferromagnet structure, taking into account the random variation of anisotropy directions in antiferromagnetic grains and their sizes. The proposed approach offers promise for modeling magnetic sensors and spintronic memory devices containing heterostructures with antiferromagnetic layers.
Robust ferromagnetism carried by antiferromagnetic domain walls
Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji
2017-02-01
Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.
Room-temperature antiferromagnetic memory resistor.
Marti, X; Fina, I; Frontera, C; Liu, Jian; Wadley, P; He, Q; Paull, R J; Clarkson, J D; Kudrnovský, J; Turek, I; Kuneš, J; Yi, D; Chu, J-H; Nelson, C T; You, L; Arenholz, E; Salahuddin, S; Fontcuberta, J; Jungwirth, T; Ramesh, R
2014-04-01
The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.
The mean field study of phase transitions in two dimensional Kagome lattice under local anisotropy
S. Mortezapour
2007-06-01
Full Text Available In this work we investigated the critical properties of the anti-ferromagnetic XY model on a two dimensional Kagome lattice under single-ion easy-axes anisotropy. Employing the mean field theory, we found that this model shows a second order phase transition from disordered to all-in all-out state for any value of anisotropy.
Magnetic order and Mott transition on the checkerboard lattice
Swain, Nyayabanta; Majumdar, Pinaki
2017-03-01
The checkerboard lattice, with alternating ‘crossed’ plaquettes, serves as the two dimensional analog of the pyrochlore lattice. The corner sharing plaquette structure leads to a hugely degenerate ground state, and no magnetic order, for classical spins with short range antiferromagnetic interaction. For the half-filled Hubbard model on this structure, however, we find that the Mott insulating phase involves virtual electronic processes that generate longer range and multispin couplings. These couplings lift the degeneracy, selecting a ‘flux like’ state in the Mott insulator. Increasing temperature leads, strangely, to a sharp crossover from this state to a ‘120 degree’ correlated state and then a paramagnet. Decrease in the Hubbard repulsion drives the system towards an insulator-metal transition—the moments reduce, and a spin disordered state wins over the flux state. Near the insulator-metal transition the electron system displays a pseudogap extending over a large temperature window.
Simulations of Quantum Spin Models on 2D Frustrated Lattices
Melko, Roger
2006-03-01
Algorithmic advances in quantum Monte Carlo techniques have opened up the possibility of studying models in the general class of the S=1/2 XXZ model (equivalent to hard-core bosons) on frustrated lattices. With an antiferromagnetic diagonal interaction (Jz), these models can be solved exactly with QMC, albeit with some effort required to retain ergodicity in the near-degenerate manifold of states that exists for large Jz. The application of the quantum (ferromagnetic off-diagonal) interaction to this classically degenerate manifold produces a variety of intriguing physics, including an order-by-disorder supersolid phase, novel insulating states, and possible exotic quantum critical phenomena. We discuss numerical results for the triangular and kagome lattices with nearest and next-nearest neighbor exchange interactions, and focus on the relevance of the simulations to related areas of physics, such as experiments of cold trapped atomic gasses and the recent theory of deconfined quantum criticality.
Sarkar, Subhajit; Chaudhury, Ranjan; Paul, Samir K.
2017-01-01
The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1/2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1/2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like MnPS3 however follows the conventional theory quite well.
Seabra, Luis; Sindzingre, Philippe; Momoi, Tsutomu; Shannon, Nic
2016-02-01
A large part of the interest in magnets with frustrated antiferromagnetic interactions comes from the many new phases found in applied magnetic field. In this article, we explore some of the new phases which arise in a model with frustrated ferromagnetic interactions, the J1-J2-J3 Heisenberg model on a square lattice. Using a combination of classical Monte Carlo simulation and spin-wave theory, we uncover behavior reminiscent of some widely studied frustrated antiferromagnets, but with a number of new twists. We first demonstrate that, for a suitable choice of parameters, the phase diagram as a function of magnetic field and temperature is nearly identical to that of the Heisenberg antiferromagnet on a triangular lattice, including the celebrated 1 /3 -magnetization plateau. We then examine how this phase diagram changes when the model is tuned to a point where the classical ground state is highly degenerate. In this case, two new phases emerge: a classical, finite-temperature spin liquid, characterized by a "ring" in the spin structure factor S (q ) ; and a vortex crystal, a multiple-Q state with finite magnetization, which can be viewed as an ordered lattice of magnetic vortices. All of these new phases persist for a wide range of magnetic fields. We discuss the relationship between these results and published studies of frustrated antiferromagnets, together with some of the materials where these new phases might be observed in experiment.
Epelbaum E.
2010-04-01
Full Text Available We review recent progress on nuclear lattice simulations using chiral eﬀective ﬁeld theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb eﬀects, and the binding energy of light nuclei.
Golubeva, Anna; Sotnikov, Andrii; Hofstetter, Walter
2015-10-01
We study the effects of anisotropic hopping amplitudes on quantum phases of ultracold fermions in optical lattices described by the repulsive Fermi-Hubbard model. In particular, using dynamical mean-field theory (DMFT) we investigate the dimensional crossover between the isotropic square and the isotropic cubic lattice. We analyze the phase transition from the antiferromagnetic to the paramagnetic state and observe a significant change in the critical temperature: depending on the interaction strength, the anisotropy can lead to both a suppression or increase. We also investigate the localization properties of the system, such as the compressibility and double occupancy. Using the local-density approximation in combination with DMFT we conclude that density profiles can be used to detect the mentioned anisotropy-driven transitions.
Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin
2016-08-01
This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.
Spin glass behavior of the antiferromagnetic Heisenberg model on scale free network
Surungan, Tasrief; Zen, Freddy P.; Williams, Anthony G.
2015-09-01
Randomness and frustration are considered to be the key ingredients for the existence of spin glass (SG) phase. In a canonical system, these ingredients are realized by the random mixture of ferromagnetic (FM) and antiferromagnetic (AF) couplings. The study by Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)] who observed the presence of SG phase on the AF Ising model on scale free network (SFN) is stimulating. It is a new type of SG system where randomness and frustration are not caused by the presence of FM and AF couplings. To further elaborate this type of system, here we study Heisenberg model on AF SFN and search for the SG phase. The canonical SG Heisenberg model is not observed in d-dimensional regular lattices for (d ≤ 3). We can make an analogy for the connectivity density (m) of SFN with the dimensionality of the regular lattice. It should be plausible to find the critical value of m for the existence of SG behaviour, analogous to the lower critical dimension (dl) for the canonical SG systems. Here we study system with m = 2, 3, 4 and 5. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter. We observed SG phase for each value of m and estimated its corersponding critical temperature.
Spin dynamics and magnetic correlation length in two-dimensional quantum heisenberg antiferromagnets
Carretta; Ciabattoni; Cuccoli; Mognaschi; Rigamonti; Tognetti; Verrucchi
2000-01-10
The correlated spin dynamics and temperature dependence of the correlation length xi(T) in two-dimensional quantum (S = 1/2) Heisenberg antiferromagnets (2DQHAF) on a square lattice are discussed in light of experimental results of proton spin lattice relaxation in copper formiate tetradeuterate. In this compound the exchange constant is much smaller than the one in recently studied 2DQHAF, such as La2CuO4 and Sr2CuO2Cl2. Thus the spin dynamics can be probed in detail over a wider temperature range. The NMR relaxation rates turn out to be in excellent agreement with a theoretical mode-coupling calculation. The deduced temperature behavior of xi(T) is in agreement with high-temperature expansions, quantum Monte Carlo simulations, and the pure quantum self-consistent harmonic approximation. Contrary to the predictions of the theories based on the nonlinear sigma model, no evidence of crossover between different quantum regimes is observed.
臧汉杰; 冯耀良; 余超; 祖庆泉; 马明; 顾宁
2012-01-01
Objective To investigate the effects of high volume hemofiltration(HVHF) on high mobility group box chromosomal protein 1 ( HMGB1), TNF-a, IL-6 in serum and live, lung, kidney tissues of sepsis dog model with acute kidney failure. Methods The bilateral ureters of twelve male Beagle dogs were ligated and lipopolysaccharide( LPS) 1.0 mg/kg was injected to establish the sepstic dog models with acute kidney failure. The dogs were equally randomized to model group and HVHF group( treated with HVHF for 24 h after injection of LPS immediately). Venous blood was collected to check blood routine, liver and kidney functions and electrolytes before and at 2,4,8,16,24 h after injection of LPS. Arterial blood gas analysis was performed before and at 24 h after injection of LPS. EILSA was used to determine the concentrations of HMGB1, TNF-a, IL-6 in serum at different time points above and in supernatant of liver, lung and kidney tissues at 24 h after injection of LPS. Results Compared with model group, the levels of HMGB1, TNF-o, IL-6 in serum and liver, lung, kidney tissues were decreased, peak time of HMGB1 level in serum was delayed, liver, lung and kidney functions were improved in HVHF group (P<0. 05). Conclusion HVHF therapy can decrease the concentrations of HMGB1,TNF-a and IL-6 in serum and liver,lung and kidney tissues and protect the liver, lung and kidney functions of septic dog with acute kidney failure.%目的 探讨交变磁场介导的二巯基丁二酸(DMSA)-Fe3O4纳米磁流体热疗治疗兔VX2肿瘤的疗效.方法 建立20只兔后肢VX2软组织肿瘤模型,随机分为4组:A组(对照组)、B组(磁流体局部注射组十热疗)、C组(磁流体动脉灌注组十热疗)、D组(磁流体静脉注射组十热疗),每组5只.成瘤2周后CT测量肿瘤大小.结果 B组和C组的肿瘤中心区[(46.01±1.97)℃和(40.38±1.50)℃]和肿瘤边缘区[(40.35±1.36)℃和(42.57±1.80)℃]的温度显著高于正常肌肉组织[(35.73±1.32)℃和(35.37±1.55)
乔璐; 朱梅; 高文宏; 张莉; 李露; 刘政
2013-01-01
Objective To observe the sonorelease of fluresence ricrobubbles to the lymph nodes metastasis of rabbits VX2 breast cancer by ultrasound excitation.Methods DiO-labeled microbubbles were prepared with lipid microbubbles and mixed Dimethyl sulfoxide (DMSO) dissolved DiO.The fluorescence microbubbles were made by high speed mechanical agitation.Rabbits models of VX2 breast carcinoma were established by means of injection of tissue mass suspension and were divided into fluorescent microbubbles combined ultrasonic cavitation group and fluorescence of microbubbles group (each n=8).In fluorescent microbubbles combined ultrasonic cavitation group,the fluorescent microbubbles (total 1 ml) were injected subcutaneously around tumor and massaged to drainage of lymph nodes The lymph nodes were exposured to pulse ultrasound intermittent treatment for 5 times,total 30 min.In fluorescence of microbubbles group,the same injection without ultrasound irradiation was performed.Laser confocal microscope was used to observe the deposition of green fluorescein in a small portion of frozen section lymph node tissues and to analyze the fluorescence of the area integrated optical density (IOD) and average optical density (AOD).Results Compared with fluorescence of microbubbles group,the fluorescence area,IOD and AOD of lymph node were higher in fluorescent microbubbles combined ultrasonic cavitation group (all P＜0.05).Condusion Flurescence microbubbles can not only enter lymph vessel to make lymph node development,but also deliver a high concentration of fluorescence microbubbles in the regional lymph node by lowpressure ultrasound in rabbit models.%目的 观察超声激励荧光微泡空化对兔乳腺癌转移淋巴结的荧光释放作用.方法 使用二甲基亚砜(DMSO)溶解绿色细胞膜荧光分子探针(DiO),抽取少量溶解液与脂质微泡混和,通过高速机械振荡制成荧光微泡.选取16只荷VX2乳腺癌的新西兰大白兔随机分成荧光微
Quasiparticle band structure of antiferromagnetic Eu Te
Mathi Jaya, S.; Nolting, W. [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Lehrstuhl Festkoerpertheorie, Invalidenstrasse 110, D-10115 Berlin (Germany)
1997-11-24
The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor Eu Te is derived by use of a combination of a many-body model procedure with a tight-binding-'linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d-f model for a single band electron ('test electron') being exchange coupled to the anti ferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d-f model are taken from a TB-LMTO calculation for paramagnetic Eu Te. The d-f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice-quasiparticle band structure (S-QBS) and sublattice-quasiparticle density of states (S-QDOS) of the unoccupied 5 d-6 s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles ('magnetic polarons') are worked out in detail. The temperature dependence of the S-QDOS and S-QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from T{sub N} to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5 d-6 s) conduction band electrons and localized 4 f moments. (author)
Von Smekal, L; Sternbeck, A; Williams, A G
2007-01-01
We propose a modified lattice Landau gauge based on stereographically projecting the link variables on the circle S^1 -> R for compact U(1) or the 3-sphere S^3 -> R^3 for SU(2) before imposing the Landau gauge condition. This can reduce the number of Gribov copies exponentially and solves the Gribov problem in compact U(1) where it is a lattice artifact. Applied to the maximal Abelian subgroup this might be just enough to avoid the perfect cancellation amongst the Gribov copies in a lattice BRST formulation for SU(N), and thus to avoid the Neuberger 0/0 problem. The continuum limit of the Landau gauge remains unchanged.
Jammed lattice sphere packings.
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Lipstein, Arthur E
2014-01-01
We formulate the theory of a 2-form gauge field on a Euclidean spacetime lattice. In this approach, the fundamental degrees of freedom live on the faces of the lattice, and the action can be constructed from the sum over Wilson surfaces associated with each fundamental cube of the lattice. If we take the gauge group to be $U(1)$, the theory reduces to the well-known abelian gerbe theory in the continuum limit. We also propose a very simple and natural non-abelian generalization with gauge group $U(N) \\times U(N)$, which gives rise to $U(N)$ Yang-Mills theory upon dimensional reduction. Formulating the theory on a lattice has several other advantages. In particular, it is possible to compute many observables, such as the expectation value of Wilson surfaces, analytically at strong coupling and numerically for any value of the coupling.
Root lattices and quasicrystals
Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.
1990-10-01
It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.
ORGINOS,K.
2003-01-07
I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.