Institute of Scientific and Technical Information of China (English)
JI An-Chun; TIAN Guang-Shan
2006-01-01
In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.
International Nuclear Information System (INIS)
The competition among spin glass (SG), antiferromagnetism (AF) and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising SG model with a local BCS pairing interaction in the presence of a transverse magnetic field Γ. The spins in different sublattices interact with Gaussian random couplings with an antiferromagnetic mean. The problem is formulated in a Grassmann path integral formalism. The static ansatz and the replica symmetry are used to obtain the half-filling thermodynamic potential. The results are shown in phase diagrams that exhibit a complex transition line separating the PAIR phase from the others. This line is second order at high temperature which ends in a tricritical point. The presence of Γ affects deeply the transition lines
Engelsberg, M.; Albino O. de Aguiar, J.
1985-04-01
The results of measurements on the magnetic field and temperature dependences of the 19F nuclear-spin lattice relaxation time T1 in KNiF3 for TKNiF3. Some similarities in the behavior of both systems suggest that a common mechanism may be responsible for spin-lattice relaxation in either case. We discuss the possibility that this mechanism may involve a diffusive mode below TN with a central peak in the relevant magnetic-ion spin correlation function.
Fujihala, M.; Zheng, X. G.; Oohara, Y.; Morodomi, H.; Kawae, T.; Matsuo, Akira; Kindo, Koichi
2012-01-01
Spin fluctuations and spin-liquid behaviors of frustrated kagome antiferromagnets have received intense recent attention. Although most severe frustration was predicted for an Ising kagome antiferromagnet, a real material system of undistorted kagome lattice has not been found so far. Here we report the frustrated magnetism of a new Ising kagome antiferromagnet, MgCo3(OH)6Cl2, which can be viewed as a Co version of the intensively researched quantum kagome antiferromagnet of Herbertsmithite ZnCu3(OH)6Cl2. Experiments of magnetization, heat capacity, μSR, and neutron scattering demonstrated a partially frozen state with persistent spin fluctuations below around T = 2.7 K. The present study has provided a real material system to study the Ising spin behaviors on undistorted kagome lattice.
Simple model for non-Fermi-liquid behavior induced by antiferromagnetic spin fluctuations
International Nuclear Information System (INIS)
We consider a simple model for itinerant antiferromagnetism consisting of an electron pocket and a hole pocket separated by a wave vector Q. The nesting of the Fermi surfaces leads to a spin-density wave instability for repulsive Hubbard coupling and to charge-density waves for an attractive interaction. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as TN→0. In the disordered phase perturbative corrections are logarithmic in the external frequency or the temperature. We investigate the renormalization-group flow of the model in leading and next-to-leading logarithmic order. The linear-response correlation functions for spin-density and charge-density waves are calculated. The specific-heat γ coefficient and the uniform magnetic-field susceptibility increase on a logarithmic scale when the temperature is lowered. The Wilson ratio is temperature dependent and nonuniversal. The Fermi-liquid picture breaks down at the ordering temperature TN or at a quantum critical point. Our results are valid in the disordered phase for weak and intermediate coupling, but not in the critical region. The results are discussed in the context of non-Fermi-liquid behavior found in some heavy fermion compounds (the two pockets are then part of the Fermi surface of the heavy electron bands). copyright 1999 The American Physical Society
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.
Antiferromagnetic spin Seebeck effect.
Energy Technology Data Exchange (ETDEWEB)
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.
Spin Dynamics and Critical Fluctuations in a Two-Dimensional Random Antiferromagnet
DEFF Research Database (Denmark)
Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.; Shirane, G.
1975-01-01
A comprehensive elastic- and inelastic-neutron-scattering study of the binary mixed antiferromagnet Rb2Mn0.5Ni0.5F4 has been carried out. The pure materials, Rb2MnF4 and Rb2NiF4 are [2d] near-Heisenberg antiferromagnets of the K2NiF4 type. Elastic-scattering experiments demonstrate that the Mn......++ and Ni++ ions are randomly distributed on a plane square lattice. At ∼ 64 K the system undergoes a second-order phase transition to two distinct [3d] antiferromagnetic structures, with both structures being composed of simple [2d] square antiferromagnetic arrays. All properties are found to be...... cluster model while the over-all dispersion is correctly given by the Walker mean-crystal model. The above calculations involve only interaction constants taken from the pure materials and JMn-Ni=(JMn-MnJNi-Ni)1/2 so that there are no adjustable parameters. At higher temperatures it is found that the gap...
Directory of Open Access Journals (Sweden)
V.M. Loktev
2008-09-01
Full Text Available We analyze the spectral properties of a phenomenological model for a weakly doped two-dimensional antiferromagnet, in which the carriers move within one of the two sublattices where they were introduced. Such a constraint results in the free carrier spectra with the maxima at k=(± π/2 , ± π/2 observed in some cuprates. We consider the spectral properties of the model by taking into account fluctuations of the spins in the antiferromagnetic background. We show that such fluctuations lead to a non-pole-like structure of the single-hole Green's function and these fluctuations can be responsible for some anomalous "strange metal" properties of underdoped cuprates in the nonsuperconducting regime.
Quantum fluctuations of the antiferro-antiferromagnetic double-layer
Institute of Scientific and Technical Information of China (English)
Jiang Wei; Zhu Cheng-Bo; Yu Gui-Hong; Lo Veng-Cheong
2009-01-01
This paper stuides the magnetization and quantum fluctuations of an antiferro-antiferromagnetic (AF-AF) doublelayer at zero temperature.It is found that the exchanges and anisotropy constants affect the quantum fluctuations of spins. If the anisotropy exists,there will be no acoustic energy branch in the system. The anisotropy constant,antiferromagnetic intralayer and interlayer coupling have important roles in a balance of the quantum competition.
International Nuclear Information System (INIS)
Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO)2x4D2O and La2-xSrxCuO4. The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2 Heisenberg antiferromagnet Cu(DCOO)24D2O. Along the antiferromagnetic zone boundary a pronounced intensity variation is found for the dominant single-magnon excitations. This variation tracks an already known zone boundary dispersion. Using polarization analysis to separate the components of the excitation spectrum, a continuum of longitudinally polarized multimagnon excitations is discovered at energies above the single-magnon branch. At low energies, the findings are well described by linear spin wave theory. At high energies, linear spin wave theory fails and instead the data are very well accounted for by state-of-the-art Quantum Monte Carlo computations. In the second part of the thesis, the spin excitation spectra of the high temperature superconductors La1.90Sr0.10CuO4 and La1.84Sr0.16Cu characterized. The main discovery is that the excitations are dispersive at both doping levels. The dispersion strongly resembles that seen in other high-Tc superconductors. The presence of dispersive excitations does not require superconductivity to exist. For La1.84Sr0.16CuO4, but not for La1.90Sr0.10CuO4, the onset superconductivity gives rise to a spectral weight shift which displays qualitative and quantitative similarities to the resonance mode observed in other high-Tc superconductors. (au)
Energy Technology Data Exchange (ETDEWEB)
Bech Christensen, N
2005-01-01
Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO){sub 2}x4D{sub 2}O and La{sub 2-x}Sr{sub x}CuO{sub 4}. The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2 Heisenberg antiferromagnet Cu(DCOO){sub 2}4D{sub 2}O. Along the antiferromagnetic zone boundary a pronounced intensity variation is found for the dominant single-magnon excitations. This variation tracks an already known zone boundary dispersion. Using polarization analysis to separate the components of the excitation spectrum, a continuum of longitudinally polarized multimagnon excitations is discovered at energies above the single-magnon branch. At low energies, the findings are well described by linear spin wave theory. At high energies, linear spin wave theory fails and instead the data are very well accounted for by state-of-the-art Quantum Monte Carlo computations. In the second part of the thesis, the spin excitation spectra of the high temperature superconductors La{sub 1.90}Sr{sub 0.10}CuO{sub 4} and La{sub 1.84}Sr{sub 0.16}Cu characterized. The main discovery is that the excitations are dispersive at both doping levels. The dispersion strongly resembles that seen in other high-T{sub c} superconductors. The presence of dispersive excitations does not require superconductivity to exist. For La{sub 1.84}Sr{sub 0.16}CuO{sub 4}, but not for La{sub 1.90}Sr{sub 0.10}CuO{sub 4}, the onset superconductivity gives rise to a spectral weight shift which displays qualitative and quantitative similarities to the resonance mode observed in other high-T{sub c} superconductors. (au)
Spin structures in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
Brok, Erik
In this thesis magnetic structures of antiferromagnetic nanoparticles are studied as a function of particle size and aggregation. In nanoparticles the magnetic structure can be different from that of the corresponding bulk system due to the following reasons: a) a significant surface contribution...... a detailed knowledge of it can be important for applications of antiferromagnetic nanoparticles for example combined with ferromagnetic nanoparticles in nanocomposite devices. In this thesis the magnetic structure, in particular the orientation of the spins in the antiferromagnetic sublattices......, is investigated in systems of magnetic nanoparticles using a variety of experimental techniques. The spin structure in systems with spin canting, due to magnetic atoms in low symmetry surroundings, is studied in a theoretical model that is able to quantitatively explain observations of anomalous temperature...
Spin Structure Analyses of Antiferromagnets
International Nuclear Information System (INIS)
We have synthesized series of powder sample of incommensurate antiferromagnetic multiferroics, (Mn, Co)WO4 and Al doped Ba0.5Sr1.5Zn2Fe12O22, incommensurate antiferromagnetic multiferroics. Their spin structure was studied by using the HRPD. In addition, we have synthesized series of crystalline samples of incommensurate multiferroics, (Mn, Co)WO4 and olivines. Their spin structure was investigated using neutron diffraction under high magnetic field. As a result, we were able to draw the phase diagram of (Mn, Co)WO4 as a function of composition and temperature. We learned the how the spin structure changes with increased ionic substitution. Finally we have drawn the phase diagram of the multicritical olivine Mn2SiS4/Mn2GeS4 as a function of filed and temperature through the spin structure studies
Antiferromagnetic Spin Wave Field-Effect Transistor
Cheng, Ran; Daniels, Matthew W.; Zhu, Jian-Gang; Xiao, Di
2016-04-01
In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate. Theses two modes, distinguished by their opposite polarization and available only in antiferromagnets, give rise to a novel degree of freedom to encode and process information. We show that the spin wave polarization can be manipulated by an electric field induced Dzyaloshinskii-Moriya interaction and magnetic anisotropy. We propose a prototype spin wave field-effect transistor which realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate its application in THz signal modulation. Our findings open up the exciting possibility of digital data processing utilizing antiferromagnetic spin waves and enable the direct projection of optical computing concepts onto the mesoscopic scale.
Diffusive magnonic spin transport in antiferromagnetic insulators
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-02-01
It has been shown recently that a layer of the antiferromagnetic insulator (AFI) NiO can be used to transport spin current between a ferromagnet (FM) and a nonmagnetic metal (NM). In the experiments one uses the microwave-driven ferromagnetic resonance in a FM layer to produce a spin pumped spin current that flows through an AFI layer and reaches a NM layer where it is converted into a charge current by means of the inverse spin Hall effect. Here we present a theory for the spin transport in an AFI that relies on the spin current carried by the diffusion of thermal antiferromagnetic magnons. The theory explains quite well the measured dependence of the voltage in the NM layer on the thickness of the NiO layer.
Transformation of spin current by antiferromagnetic insulators
Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.
2015-01-01
It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current by 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 $\\pi/2$,...
Electric probe for spin transition and fluctuation
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'diaye, Alpha T.; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Tserkovnyak, Yaroslov; Qiu, Z. Q.; Saitoh, Eiji
Spin fluctuation and transition have always been one of central topics of magnetism and condense matter science. To probe them, neutron scatterings have been used as powerful tools. A part of neutrons injected into a sample is scattered by spin fluctuation inside the sample. This process transcribes the spin fluctuation onto scattering intensity, which is commonly represented by dynamical magnetic susceptibility of the sample and is maximized at magnetic phase transitions. Importantly, a neutron carries spin without electric charge, and it thus can bring spin into a sample without being disturbed by electric energy: an advantage of neutrons, although large facilities such as a nuclear reactor is necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop micro probe for spin fluctuation and transition; not only a neutron beam, spin current is also a flux of spin without an electric charge and its transport reflects spin fluctuation in a sample. We demonstrate detection of anti-ferromagnetic transition in ultra-thin CoO films via frequency dependent spin-current transmission measurements.
Small antiferromagnetic spin systems-Sublattice Hamiltonians
International Nuclear Information System (INIS)
A few examples of four-spin Heisenberg systems with dominant antiferromagnetic couplings are considered. All systems can be described by the so-called sublattice Hamiltonian H=SA.SB or its modifications, where SX is the total spin of a sublattice X=A, B. In such a case (eigen)energies are simple functions of the total spin number S, total spins of sublattices SA, SB, and the Hamiltonian parameters (ratios of exchange integrals). Moreover, eigenstates are strictly determined by a coupling scheme assumed and the appropriate Clebsch-Gordan coefficients. In this sense the systems considered are classical ones.
Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets
Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.
2016-05-01
Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.
Terahertz Antiferromagnetic Spin Hall Nano-Oscillator
Cheng, Ran; Xiao, Di; Brataas, Arne
2016-05-01
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calculated numerically as a function of the dc current input for different feedback strengths. Our findings open a route towards terahertz antiferromagnetic spin-torque oscillators.
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.;
2000-01-01
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
High-field spin dynamics of antiferromagnetic quantum spin chains
DEFF Research Database (Denmark)
Enderle, M.; Regnault, L.P.; Broholm, C.; Reich, D.; Zaliznyak, I.; Sieling, M.; Rønnow, H.M.; McMorrow, D.F.
The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...
Shiota, Takayoshi; Mukuda, Hidekazu; Uekubo, Masahiro; Engetsu, Fuko; Yashima, Mitsuharu; Kitaoka, Yoshio; Lai, Kwing To; Usui, Hidetomo; Kuroki, Kazuhiko; Miyasaka, Shigeki; Tajima, Setsuko
2016-05-01
We report on 31P-NMR studies of LaFe(As1‑xPx)(O1‑yFy) over wide compositions for 0 ≤ x ≤ 1 and 0 ≤ y ≤ 0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing Tc. Systematic 31P-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to Tc with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of dxz/yz, whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of dxy and dxz/yz. We remark that the nonmonotonic variation of Tc as a function of x and y in LaFe(As1‑xPx)(O1‑yFy) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.
Thermal Generation of Spin Current in an Antiferromagnet.
Seki, S; Ideue, T; Kubota, M; Kozuka, Y; Takagi, R; Nakamura, M; Kaneko, Y; Kawasaki, M; Tokura, Y
2015-12-31
The longitudinal spin Seebeck effect has been investigated for a uniaxial antiferromagnetic insulator Cr(2)O(3), characterized by a spin-flop transition under magnetic field along the c axis. We have found that a temperature gradient applied normal to the Cr(2)O(3)/Pt interface induces inverse spin Hall voltage of spin-current origin in Pt, whose magnitude turns out to be always proportional to magnetization in Cr(2)O(3). The possible contribution of the anomalous Nernst effect is confirmed to be negligibly small. The above results establish that an antiferromagnetic spin wave can be an effective carrier of spin current. PMID:26765011
Spin waves in antiferromagnetic FeF2
DEFF Research Database (Denmark)
Hutchings, M T; Rainford, B.D.; Guggenheim, H J
1970-01-01
Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin Hamilton......Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin...
International Nuclear Information System (INIS)
Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a open-quotes single lobeclose quotes spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ℎωBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, they are extremely short-ranged, extending only to the nearest neighbors. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3. copyright 1998 The American Physical Society
Spin transfer torque in antiferromagnetic spin valves: From clean to disordered regimes
Saidaoui, Hamed Ben Mohamed
2014-05-28
Current-driven spin torques in metallic spin valves composed of antiferromagnets are theoretically studied using the nonequilibrium Green\\'s function method implemented on a tight-binding model. We focus our attention on G-type and L-type antiferromagnets in both clean and disordered regimes. In such structures, spin torques can either rotate the magnetic order parameter coherently (coherent torque) or compete with the internal antiferromagnetic exchange (exchange torque). We show that, depending on the symmetry of the spin valve, the coherent and exchange torques can either be in the plane, ∝n×(q×n) or out of the plane ∝n×q, where q and n are the directions of the order parameter of the polarizer and the free antiferromagnetic layers, respectively. Although disorder conserves the symmetry of the torques, it strongly reduces the torque magnitude, pointing out the need for momentum conservation to ensure strong spin torque in antiferromagnetic spin valves.
Local Spin Correlations in Heisenberg Antiferromagnets
Weihong, Zheng; Oitmaa, J.
2000-01-01
We use linked cluster series expansion methods to estimate the values of various short distance correlation functions in $S=1/2$ Heisenberg antiferromagnets at T=0, for dimension $d=1,2,3$. The method incorporates the possibility of spontaneous symmetry breaking, which is manifest in $d=2,3$. The results are important in providing a test for approximate theories of the antiferromagnetic ground state.
Electron spin resonance study of NiO antiferromagnetic nanoparticles
International Nuclear Information System (INIS)
The electron spin resonance (ESR) spectra of antiferromagnetic nanoparticle NiO specimens have been investigated as a function of temperature at x-band (microwave) frequencies. Below the nominal Neel temperature, the x-band resonances arising from the bulk antiferromagnets, including NiO particles with diameters greater than 100 A, all vanish due to the emergence of large molecular exchange fields. The ESR resonance signals of 60 A antiferromagnetic nanoparticles, however, persist to the lowest temperatures. These nanoparticle resonance lines shift to lower fields rapidly as the temperature is decreased, while the lineshapes broaden and distort
Spin fluctuations and unconventional pairing on the Lieb lattice
Energy Technology Data Exchange (ETDEWEB)
Wang, Hu, E-mail: wangh_1222070@126.com; Yu, Shun-Li, E-mail: slyu@nju.edu.cn; Li, Jian-Xin, E-mail: jxli@nju.edu.cn
2014-10-03
The spin fluctuations and superconducting pairing symmetries in the dispersive band of Lieb lattice are studied by fluctuation exchange approximation. The antiferromagnetic spin density wave is found to exist on the A sublattice (the lattice sites with four nearest neighbors) at half filling. When slightly doped away from half filling, a balance between the combined effects of the (π,π) and (0.4π,0) spin fluctuations and the gaining of the condensation energy leads to the nearly degenerate d{sub x{sup 2}−y{sup 2}}- and g{sub xy(x{sup 2}−y{sup 2})}-wave pairing states. After further doped, the d{sub xy}-wave state is favored via the intra-sublattice spin fluctuations with a wave vector (π,0). We emphasize that the sublattices' contribution and the renormalization of the spectral function play a crucial role on the spin fluctuations and the pairing symmetry. The effect of the imbalance of the on-site energy at different sublattices is also discussed. - Highlights: • Staggered AFM order only forms on the sites with four nearest neighbors. • AFM spin fluctuation and condensation energy lead to degeneracy of d and g waves. • Spectral renormalization leads to different sublattice dominant d{sub xy} wave.
International Nuclear Information System (INIS)
We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin-exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field H is less than the lower critical field Hc1; (ii) a ferromagnetic phase of atoms in the hyperfine state |F=1, mF=1> when the external magnetic field exceeds the upper critical field Hc2; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region Hc1c2. At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired mF=1 bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.
Spin torque antiferromagnetic nanooscillator in the presence of magnetic noise
Directory of Open Access Journals (Sweden)
H. Gomonay
2012-12-01
Full Text Available Spin-torque effects in antiferromagnetic (AFM materials are of great interest due to the possible applications as high-speed spintronic devices. In the present paper we analyze the statistical properties of the current-driven AFM nanooscillator that result from the white Gaussian noise of magnetic nature. According to the peculiarities of deterministic dynamics, we derive the Langevin and Fokker-Planck equations in the energy representation of two normal modes. We find the stationary distribution function in the subcritical and overcritical regimes and calculate the current dependence of the average energy, energy fluctuation and their ratio (quality factor. The noncritical mode shows the Boltzmann statistics with the current-dependent effective temperature in the whole range of the current values. The effective temperature of the other, i.e., soft, mode critically depends on the current in the subcritical region. Distribution function of the soft mode follows the Gaussian law above the generation threshold. In the overcritical regime, the total average energy and the quality factor grow with the current value. This raises the AFM nanooscillators to the promising candidates for active spintronic components.
Spin waves in the block checkerboard antiferromagnetic phase
Institute of Scientific and Technical Information of China (English)
Lu Feng; Dai Xi
2012-01-01
Motivated by the discovery of a new family of 122 iron-based superconductors,we present the theoretical results on the ground state phase diagram,spin wave,and dynamic structure factor obtained from the extended J1-J2 Heisenberg model.In the reasonable physical parameter region of K2Fe4Ses,we find that the block checkerboard antiferromagnetic order phase is stable.There are two acoustic spin wave branches and six optical spin wave branches in the block checkerboard antiferromagnetic phase,which have analytic expressions at the high-symmetry points.To further compare the experimental data on neutron scattering,we investigate the saddlepoint structure of the magnetic excitation spectrum and the inelastic neutron scattering pattern based on linear spin wave theory.
Quantum phase competition in antiferromagnetic spin-1 ladders
International Nuclear Information System (INIS)
Motivated by recent chemical explorations into organic-radical-based higher-spin ladder systems, we study the ground-state properties of a wide class of antiferromagnetic spin-1 ladders. Numerical analysis featuring the level-spectroscopy technique reveals the rich phase diagram, correcting a preceding nonlinear-sigma-model prediction. A variational analysis well interprets the phase competition with particular emphasis on the re-entrant phase boundary on the way from single to coupled chains. (author)
Entanglement Perturbation Theory for Antiferromagnetic Heisenberg Spin Chains
Wang, Lihua; Chung, Sung Gong
2012-11-01
A recently developed numerical method, entanglement perturbation theory (EPT), is used to study the antiferromagnetic Heisenberg spin chains with z-axis anisotropy λ and magnetic field B. To demonstrate its accuracy, we first apply EPT to the isotropic spin-1/2 antiferromagnetic Heisenberg model, and find that EPT successfully reproduces the exact Bethe ansatz results for the ground state energy, the local magnetization, and the spin correlation functions (Bethe ansatz result is available for the first seven lattice separations). In particular, EPT confirms for the first time the asymptotic behavior of the spin correlation functions predicted by the conformal field theory, which realizes only for lattice separations larger than 1000. Next, turning on the z-axis anisotropy and the magnetic field, the 2- and 4-spin correlation functions are calculated, and the results are compared with those obtained by bosonization and density matrix renormalization group methods. Finally, for the spin-1 antiferromagnetic Heisenberg model, the ground state phase diagram in λ space is determined by Roomany--Wyld renormalization group (RG) finite size scaling. The results are in good agreement with those obtained by the level-spectroscopy method.
Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics
Directory of Open Access Journals (Sweden)
Joseph Sklenar
2016-05-01
Full Text Available We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.
Theory of the spin Seebeck effect in antiferromagnets
Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.
2016-01-01
The spin Seebeck effect (SSE) consists in the generation of a spin current by a temperature gradient applied in a magnetic film. The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film resulting from the conversion of the spin current into charge current by means of the inverse spin Hall effect. The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin-orbit coupling such as platinum. Recently the SSE has been observed in bilayers made of the antiferromagnet Mn F2 and Pt, revealing dependences of the SSE voltage on temperature and field very different from the ones observed in YIG/Pt. Here we present a theory for the SSE in structures with an antiferromagnetic insulator (AFI) in contact with a normal metal (NM) that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the AFI/NM bilayer. The theory explains quite well the measured dependences of the SSE voltage on the sample temperature and on the applied magnetic field in Mn F2/Pt .
Long range anti-ferromagnetic spin model for prebiotic evolution
Energy Technology Data Exchange (ETDEWEB)
Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)
2003-11-28
I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.
Long range anti-ferromagnetic spin model for prebiotic evolution
International Nuclear Information System (INIS)
I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states
Antiferromagnetic phase transition and spin correlations in NiO
DEFF Research Database (Denmark)
Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker
2009-01-01
We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested by...... process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...
International Nuclear Information System (INIS)
By using the modified spin-wave and gauge invariant methods, we show that at zero temperature in the presence of an inhomogeneous magnetic field with magnitude B gives rise to a persistent magnetization current around a mesoscopic antiferromagnetic Heisenberg spin ring with the DM (Dzyaloshinskii–Moriya) interaction. The results show that the persistent magnetization current is vanishing at large Ds/J (Ds is reduced DM interaction and J is nearest exchange coupling) with α>1 (α is a constant describing the energy gap of the spin system). The result also shows that under the homogeneous magnetic field there exists a non-zero spin current in the spin ring. - Highlights: • Persistent spin current is calculated in anti-ferromagnetic ring. • Persistent magnetization current is vanishing at large Ds/J. • Under homogeneous magnetic field there exists a non-zero spin current in the ring
Spinor dynamics in an antiferromagnetic spin-1 thermal Bose gas
Pechkis, Hyewon K; Schwettmann, Arne; Griffin, Paul F; Barnett, Ryan; Tiesinga, Eite; Lett, Paul D
2013-01-01
We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field.
Mechanisms of Spin-Mixing Instabilities in Antiferromagnetic Molecular Wheels
Soncini, Alessandro; Chibotaru, Liviu F.
2007-08-01
The microscopic theory of field-induced spin-mixing instabilities in antiferromagnetic molecular wheels CsFe8 is proposed. The basic features of magnetic torque measurements [O. Waldmann , Phys. Rev. Lett. 96, 027206 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.027206] are well explained by the interplay of three basic ingredients: the spin-mixing vibronic interaction with field-dependent vibronic constants, cooperative elastic interactions, and spin-mixing interactions independent from vibrations. The main contribution to spin mixing comes from second-order zero-field splitting mechanisms. At variance with previous interpretations, we find that the observed anomalies are not associated with a phase transition.
Spin wave acoustics of antiferromagnetic structures as magnetoacoustic metamaterials
Energy Technology Data Exchange (ETDEWEB)
Gulyaev, Yurii V; Tarasenko, Sergei V; Shavrov, Vladimir G
2011-06-30
This is a review of research results on conditions under which spatially restricted low-temperature antiferromagnets and their composites can be considered as a special class of acoustic magnetic metamaterials (magnetoacoustic metamaterials). In these, the dynamic magnetoacoustic interaction produces a number of effects that are acoustic analogs of polariton effects and which are currently intensively studied in nonmagnetic acoustic metamaterials. It is shown that the elastostatic approach to the analysis of the magnetoelastic dynamics of spatially restricted compensated magnetics is an effective tool in the search for new types of resonance acoustic anomalies, part of which are typical of the magnetostatic spin wave physics (elastostatic bulk and surface spin waves, nonuniform spin-spin resonances with their participation, etc.). (reviews of topical problems)
Spin wave acoustics of antiferromagnetic structures as magnetoacoustic metamaterials
International Nuclear Information System (INIS)
This is a review of research results on conditions under which spatially restricted low-temperature antiferromagnets and their composites can be considered as a special class of acoustic magnetic metamaterials (magnetoacoustic metamaterials). In these, the dynamic magnetoacoustic interaction produces a number of effects that are acoustic analogs of polariton effects and which are currently intensively studied in nonmagnetic acoustic metamaterials. It is shown that the elastostatic approach to the analysis of the magnetoelastic dynamics of spatially restricted compensated magnetics is an effective tool in the search for new types of resonance acoustic anomalies, part of which are typical of the magnetostatic spin wave physics (elastostatic bulk and surface spin waves, nonuniform spin-spin resonances with their participation, etc.). (reviews of topical problems)
Bauer, Johannes; Sachdev, Subir(Department of Physics, Harvard University, Cambridge, MA, 02138, USA)
2015-01-01
We study charge ordered solutions for fermions on a square lattice interacting with dynamic antiferromagnetic fluctuations. Our approach is based on real space Eliashberg equations which are solved self-consistently. We first show that the antiferromagnetic fluctuations can induce arc features in the spectral functions, as spectral weight is suppressed at the hot spots; however, no real pseudogap is generated. At low temperature spontaneous charge order with a $d$-form factor can be stabilize...
Gu, Bo; Su, Gang; Gao, Song
2006-04-01
The magnetization process, the susceptibility, and the specific heat of the spin- 1/2 antiferromagnet (AF)-AF-ferromagnet (F) and F-F-AF trimerized quantum Heisenberg chains have been investigated by means of the transfer matrix renormalization group (TMRG) technique as well as the modified spin-wave (MSW) theory. A magnetization plateau at m=1/6 for both trimerized chains is observed at low temperature. The susceptibility and the specific heat show various behaviors for different ferromagnetic and antiferromagnetic interactions and in different magnetic fields. The TMRG results of susceptibility and the specific heat can be nicely fitted by a linear superposition of double two-level systems, where two fitting equations are proposed. Three branch excitations, one gapless excitation and two gapful excitations, for both systems are found within the MSW theory. It is observed that the MSW theory captures the main characteristics of the thermodynamic behaviors at low temperatures. The TMRG results are also compared with the possible experimental data.
Quantum kagome frustrated antiferromagnets: One route to quantum spin liquids
Mendels, Philippe; Bert, Fabrice
2016-03-01
After introducing the field of Highly Frustrated Magnetism through the quest for a quantum spin liquid in dimension higher than one, we focus on the emblematic case of the kagome network. From a theoretical point of view, the simple Heisenberg case for an antiferromagnetic kagome lattice decorated with quantum spins has been a long-standing problem, not solved yet. Experimental realizations have remained scarce for long until the discovery of herbertsmithite ZnCu3(OH)6Cl2 in 2005. This is one of the very few quantum kagome spin liquid candidates that triggered a burst of activity both on theory and experiment sides. We give a survey of theory outcomes on the "kagome" problem, review the experimental properties of that model candidate and shortly discuss them with respect to recent theoretical results. xml:lang="fr"
Spin waves in antiferromagnetically coupled bimetallic oxalates.
Reis, Peter L; Fishman, Randy S
2009-01-01
Bimetallic oxalates are molecule-based magnets with transition-metal ions M(II) and M(')(III) arranged on an open honeycomb lattice. Performing a Holstein-Primakoff expansion, we obtain the spin-wave spectrum of antiferromagnetically coupled bimetallic oxalates as a function of the crystal-field angular momentum L(2) and L(3) on the M(II) and M(')(III) sites. Our results are applied to the Fe(II)Mn(III), Ni(II)Mn(III) and V(II)V(III) bimetallic oxalates, where the spin-wave gap varies from 0 meV for quenched angular momentum to as high as 15 meV. The presence or absence of magnetic compensation appears to have no effect on the spin-wave gap. PMID:21817242
Spin-Flop Transition and a Tilted Canted Spin Structure in a Coupled Antiferromagnet
Shimahara, Hiroshi; Ito, Kazuhiro
2016-04-01
We study a uniaxial coupled Heisenberg antiferromagnet that consists of two subsystems of classical spins with small and large lengths and spin-flop transitions in a magnetic field parallel to the magnetic easy axis. It is proved that the anisotropy of inter-subsystem coupling stabilizes an asymmetric canted antiferromagnetic phase with a tilted direction of antiferromagnetism that is not perpendicular to the magnetic field. In contrast to the conventional first-order spin-flop transition, the spin-flop transition from the Néel phase to such a tilted canted antiferromagnetic (TCAF) phase is of the second order in the absence of simple anisotropic energies in the subsystems. The transition from the TCAF phase to the high-field saturated spin phase is of the second order in the strong coupling limit of the exchange interactions J1 between the small spins, whereas when J1 is finite, it becomes first-order. Therefore, in the former case, the TCAF phase converts the Néel phase continuously into the saturated phase. The transitions to the TCAF phase are accompanied by additional spontaneous symmetry breaking, causing the uniform magnetization to have a nonzero component perpendicular to the magnetic field.
A transverse Ising bilayer film with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-10-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising bilayer film with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory (EFT) with correlations, in order to clarify whether the appearance of a compensation point is possible below the transition temperature in the system. From these investigations, we have found a lot of characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value, such as the reentrant phenomenon free from the disorder-induced frustration and the novel types of magnetization curve with a compensation point.
Kim, Y H; Kaur, N; Atkins, B M; Dalal, N S; Takano, Y
2009-12-11
At a quantum critical point (QCP)--a zero-temperature singularity in which a line of continuous phase transition terminates--quantum fluctuations diverge in space and time, leading to exotic phenomena that can be observed at nonzero temperatures. Using a quantum antiferromagnet, we present calorimetric evidence that nuclear spins frozen in a high-temperature nonequilibrium state by temperature quenching are annealed by quantum fluctuations near the QCP. This phenomenon, with readily detectable heat release from the nuclear spins as they are annealed, serves as an excellent marker of a quantum critical region around the QCP and provides a probe of the dynamics of the divergent quantum fluctuations. PMID:20366226
Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides
Gu, Mingqiang; Rondinelli, James M.
2016-01-01
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. PMID:27126354
A quadrangular transverse Ising nanowire with an antiferromagnetic spin configuration
Kaneyoshi, T.
2015-11-01
The phase diagrams and the temperature dependences of magnetizations in a transverse Ising nanowire with an antiferromagnetic spin configuration are investigated by the use of the effective-field theory with correlations (EFT) and the core-shell concept. Many characteristic and unexpected behaviors are found for them, especially for thermal variation of total magnetization mT. The reentrant phenomenon induced by a transverse field in the core, the appearance of a compensation point, the non-monotonic variation with a compensation point, the reentrant phenomena with a compensation point and the existence of both a broad maximum and a compensation point have been found in the thermal variations of mT.
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Energy Technology Data Exchange (ETDEWEB)
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu, E-mail: taniyama.t.aa@m.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
2015-08-24
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Barkhausen-like antiferromagnetic to ferromagnetic phase transition driven by spin polarized current
Suzuki, Ippei; Naito, Tomoyuki; Itoh, Mitsuru; Taniyama, Tomoyasu
2015-08-01
We provide clear evidence for the effect of a spin polarized current on the antiferromagnetic to ferromagnetic phase transition of an FeRh wire at Co/FeRh wire junctions, where the antiferromagnetic ground state of FeRh is suppressed by injecting a spin polarized current. We find a discrete change in the current-voltage characteristics with increasing current density, which we attribute to the Barkhausen-like motion of antiferromagnetic/ferromagnetic interfaces within the FeRh wire. The effect can be understood via spin transfer, which exerts a torque to the antiferromagnetic moments of FeRh, together with non-equilibrium magnetic effective field at the interface. The conclusion is reinforced by the fact that spin unpolarized current injection from a nonmagnetic Cu electrode has no effects on the antiferromagnetic state of FeRh.
Antiferromagnetically Spin Polarized Oxygen Observed in Magnetoelectric TbMn2O5
Beale, T. A. W.; Wilkins, S. B.; Johnson, R. D.; Bland, S. R.; Joly, Yves; Forrest, T. R.; McMorrow, D. F.; Yakhou, F.; Prabhakaran, D.; Boothroyd, A. T.; Hatton, P. D.
2010-01-01
We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wave vector. Using the fdmnes code we have accurat...
Quantized phonon-enhanced spin fluctuations
Energy Technology Data Exchange (ETDEWEB)
Koo, Je Huan, E-mail: koo@kw.ac.kr
2015-01-15
We investigate the phonon-enhanced spin flipping of f-electrons via s–f exchange interactions, as previously discussed by ourselves [Phys. Rev. B 61, 4289]. The electron–electron interaction U{sub sf} is an order of magnitude stronger than that of Kondo-type bare spin-flipping. Using the similar configuration of Hydrogen, we calculate the quantized energy eigenvalues of this spin fluctuation. We also compare our energy levels with experimental data obtained from inelastic neutron scatterings in which the data below 40 meV may be attributed to phonon modes.
International Nuclear Information System (INIS)
The spin dynamics of an S = 1, two dimensional (2D) square lattice antiferromagnet, La2NiO4 was studied by neutron scattering experiments in wide energy (E N), the spin wave excitations of La2NiO4 are well described by a classical spin wave theory. The nearest-neighbor-exchange coupling constant, the in-plane and the out-of-plane anisotropy constants at 10 K were determined to be 28.7±0.7 meV, 0.10±0.02 meV and 1.26±0.12 meV, respectively. Above TN, the 2D spin fluctuation was observed over 600 K. The critical slowing down behavior of the fluctuation was observed in the enhancement of the low energy component toward TN. On the other hand, the high energy component is hardly affected by the three dimensional magnetic transition and still exists even at TN as observed in La2CuO4. The spin correlation length and the static structure factor at the 2D zone center were measured and compared with theoretical calculations for 2D Heisenberg antiferromagnets. (author)
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.
Mechanisms for spin supersolidity in S=(1/2) spin-dimer antiferromagnets
International Nuclear Information System (INIS)
Using perturbative expansions and the contractor renormalization (CORE) algorithm, we obtain effective hard-core bosonic Hamiltonians describing the low-energy physics of S=1/2 spin-dimer antiferromagnets known to display supersolid phases under an applied magnetic field. The resulting effective models are investigated by means of mean-field analysis and quantum Monte Carlo simulations. A ''leapfrog mechanism,'' through means of which extra singlets delocalize in a checkerboard-solid environment via correlated hoppings, is unveiled that accounts for the supersolid behavior
Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap
Murmann, S.; Deuretzbacher, F.; Zürn, G.; Bjerlin, J.; Reimann, S. M.; Santos, L.; Lompe, T.; Jochim, S.
2015-11-01
We report on the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These chains are stabilized by strong repulsive interactions between the two spin components without the need for an external periodic potential. We independently characterize the spin configuration of the chains by measuring the spin orientation of the outermost particle in the trap and by projecting the spatial wave function of one spin component on single-particle trap levels. Our results are in good agreement with a spin-chain model for fermionized particles and with numerically exact diagonalizations of the full few-fermion system.
Shinaoka, Hiroshi; Tomita, Yusuke; Motome, Yukitoshi
2014-10-01
Motivated by puzzling aspects of spin-glass behavior reported in frustrated magnetic materials, we theoretically investigate effects of magnetoelastic coupling in geometrically frustrated classical spin models. In particular, we consider bond-disordered Heisenberg antiferromagnets on a pyrochlore lattice coupled to local lattice distortions. By integrating out the lattice degree of freedom, we derive an effective spin-only model, the bilinear-biquadratic model with bond disorder. The effective model is analyzed by classical Monte Carlo simulations using an extended loop algorithm. First, we discuss the phase diagrams in detail by showing the comprehensive Monte Carlo data for thermodynamic and magnetic properties. We show that the spin-glass transition temperature Tf is largely enhanced by the spin-lattice coupling b in the weakly disordered regime. By considering the limit of strong spin-lattice coupling, this enhancement is ascribed to the suppression of thermal fluctuations in semidiscrete degenerate manifold formed in the presence of the spin-lattice coupling. We also find that, by increasing the strength of disorder Δ, the system shows a concomitant transition of the nematic order and spin glass at a temperature determined by b, being almost independent of Δ. This is due to the fact that the spin-glass transition is triggered by the spin collinearity developed by the nematic order. Although further-neighbor exchange interactions originating in the cooperative lattice distortions result in spin-lattice order in the weakly disordered regime, the concomitant transition remains robust with Tf almost independent of Δ. We find that the magnetic susceptibility shows hysteresis between the field-cooled and zero-field-cooled data below Tf, and that the nonlinear susceptibility shows a negative divergence at the transition. These features are common to conventional spin-glass systems. Meanwhile, we find that the specific heat exhibits a broad peak at Tf, and that the
A frustrated spin-1 J1-J2 Heisenberg antiferromagnet: An anisotropic planar pyrochlore model
International Nuclear Information System (INIS)
The zero-temperature ground-state (GS) properties and phase diagram of a frustrated spin-1 J1-J2 Heisenberg model on the checkerboard square lattice are studied, using the coupled cluster method. We consider the case where the nearest-neighbour exchange bonds have strength J1 > 0 and the next-nearest-neighbour exchange bonds present (viz., in the checkerboard pattern of the planar pyrochlore) have strength J2 = κJ1 > 0. We find significant differences from both the spin-1/2 and classical versions of the model. We find that the spin-1 model has a first phase transition at κC1 ≈ 1.00 ± 0.01 (as does the classical model at κcl = 1) between two antiferromagnetic phases, viz., a quasiclassical Néel phase (for κ < κC1) and one of the infinitely degenerate family of quasiclassical phases (for k > κC1) that exists in the classical model for κ > κc1, which is now chosen by the order by disorder mechanism as (probably) the 'doubled Néel' (or Néel*) state. By contrast, none of this family survives quantum fluctuations to form a stable GS phase in the spin-1/2 case. We also find evidence for a second quantum critical point at κC2 ≈ 2.0 ± 0.5 in the spin-1 model, such that for κ > κC2 the quasiclassical (Néel*) ordering melts and a nonclassical phase appears, which, on the basis of preliminary evidence, appears unlikely to have crossed-dimer valence-bond crystalline (CDVBC) ordering, as in the spin-1/2 case. Unlike in the spin-1/2 case, where the Néel and CDVBC phases are separated by a phase with plaquette valence-bond crystalline (PVBC) ordering, we find very preliminary evidence for such a PVBC state in the spin-1 model for all κ > κC2.
Nuclear spin-magnon relaxation in two-dimensional Heisenberg antiferromagnets
International Nuclear Information System (INIS)
Experiments are discussed of the dependence on temperature and magnetic field of the longitudinal relaxation time of single crystals of antiferromagnetically ordered insulators, i.e. in the temperature range below the Neel temperature and in fields up to the spin-flop transition. The experiments are done on 19F nuclei in the Heisenberg antiferromagnets K2MnF4 and K2NiF4, the magnetic structure of which is two-dimensional quadratic. (C.F.)
Large inverse spin Hall effect in the antiferromagnetic metal Ir20Mn80
Mendes, J. B. S.; Cunha, R. O.; Alves Santos, O.; Ribeiro, P. R. T.; Machado, F. L. A.; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.
2014-04-01
A spin current is usually detected by converting it into a charge current through the inverse spin Hall effect (ISHE) in thin layers of a nonmagnetic metal with large spin-orbit coupling, such as Pt, Pd, and Ta. Here we demonstrate that Ir20Mn80, a high-temperature antiferromagnetic metal that is commonly employed in spin-valve devices, exhibits a large inverse spin Hall effect, as recently predicted theoretically. We present results of experiments in which the spin currents are generated either by microwave spin pumping or by the spin Seebeck effect in bilayers of singe-crystal yttrium iron garnet (YIG)/Ir20Mn80 and compare them with measurements in YIG/Pt bilayers. The results of both measurements are consistent, showing that Ir20Mn80 has a spin Hall angle similar to Pt, and that it is an efficient spin-current detector.
International Nuclear Information System (INIS)
It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu–N surfaces can be used to store information (Loth et al 2012 Science 335 196). Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of Néel states and show that the Néel states can become stable enough for the information storage when the number of spins reaches one or two dozens of the Fe spins. We also explore promising methods for manipulating the Néel states. These could help realize information storage with such antiferromagnetic spin systems. (paper)
Spin polaron in two-dimensional antiferromagnetics - from local singlet to compound quasi-particle
Barabanov, A F; Belemuk, A M
2002-01-01
The basic theoretical concepts, related to the spin polaron scenario for the charge excitations in the two-dimensional antiferromagnetics, are presented. The distinctive peculiarity of the developed approach consists in consideration of the local polaron as the zero approximation for the quasi-particles. On the following stage this excitation is coated into the antiferromagnetic spin waves and the radius intermediate polaron is formed. The method makes it possible to continuously describe the transition from the zero temperatures to the finite ones and to consider the wide doping range. The above approach explains basic results of the ARPES-experiments in the CuO sub 2 plane
International Nuclear Information System (INIS)
Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
2016-02-08
Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.
Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash
2016-09-14
Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the [Formula: see text] AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant [Formula: see text] average reduction from the Hartree-Fock value. PMID:27406889
Varma, Chandra M.
2016-08-01
The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau–Ginzburg–Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle–particle vertex in the d-wave channel is the same as the irreducible
Thermodynamic functions for a model antiferromagnet with identical coupling between all spins
International Nuclear Information System (INIS)
A model antiferromagnet consisting of N spins S=1/2, all interacting among themselves with equal strength, and with the external magnetic field H, was analysed, both for Ising spins and vector spins. Starting from the Hamiltonian, the partition function, specific heat and magnetic susceptibility vs temperature T have been calculated for both systems, for finite N (with the interspin coupling I < 0) and for N →∞ (with the coupling I/N < 0). For finite N one finds several relations between the features of the energy levels and the calculated plots, related especially to the number of spins being odd or even. The 1/(NT) behavior of the susceptibility at T→0 for odd N has been interpreted as due to the occurrence of a single frustrated spin pushing the whole system to behave like the free spin in the external magnetic field. For N→∞ (thermodynamic limit) the Kac procedure has been extended to include the effect of magnetic field, both for Ising spins and the vector spins. As compared with the ferromagnetic case, the evaluation of the partition function and related functions is in the case of antiferromagnetic coupling (I < 0) relatively straightforward. We have found the specific heat (per one spin) vs T at finite magnetic field to be proportional to the squared field, turning to zero at the absence of the field. The magnetic susceptibility (per one spin) shows a regular behavior of the paramagnetic type at all temperatures. (author)
19F spin-lattice relaxation in the cubic antiferromagnet KNiF3
Engelsberg, M.
1980-06-01
The temperature dependence of the 19F spin-lattice relaxation in the cubic quasi-isotropic antiferromagnet KNiF3 is studied experimentally and theoretically. Quantitative agreement with measured relaxation rates is obtained over a considerable temperature range by assuming a two-magnon relaxation process in the "domain-flopped" state.
Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes
Energy Technology Data Exchange (ETDEWEB)
Yamada, Toyo Kazu, E-mail: toyoyamada@faculty.chiba-u.jp [Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba (Japan); Vazquez de Parga, Amadeo L. [Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia and Dep. Fisica de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain)
2014-11-03
Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.
Soliton Confinement and the Excitation Spectrum of Spin-Peierls Antiferromagnets
Affleck, Ian
1997-01-01
The excitation spectrum of spin-Peierls antiferromagnets is discussed taking into acount phonon dynamics but treating inter-chain elastic couplings in mean field theory. This gives a ladder of soliton -anti-soliton boundstates, with no soliton continuum, until soliton deconfinement takes place at a transition into a non-dimerized phase.
Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; de la Fuente, César; Arnaudas, José Ignacio
2015-01-01
High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths. PMID:26333417
Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4.
Wakimoto, S; Yamada, K; Tranquada, J M; Frost, C D; Birgeneau, R J; Zhang, H
2007-06-15
Magnetic excitations for energies up to approximately 100 meV are studied for overdoped La(2-x)Sr(x)CuO(4) with x=0.25 and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, 20 magnetism is not related to Fermi surface nesting, but rather is associated with a decreasing volume fraction of (probably fluctuating) antiferromagnetic bubbles. PMID:17677985
Anomalous Curie response of an impurity in a quantum critical spin-1/2 Heisenberg antiferromagnet
Höglund, Kaj; Sandvik, Anders
2007-03-01
There is a disagreement concerning the low-temperature (T) magnetic susceptibility χ^zimp˜C/T of a spin-S impurity in a nearly quantum critical antiferromagnetic host. Field-theoretical work [1] predicted an anomalous Curie constant S^2/30 quantum Monte Carlo simulations in order to resolve the controversy. Our main result is for a vacancy in a quantum critical spin-1/2 Heisenberg antiferromagnet on a bilayer lattice. In our susceptibility data for the S=1/2 impurity we observe a Curie constant C=0.262(2). Although the value falls outside the predicted range, it should correspond to an anomalous impurity response, as proposed in Ref. [1]. [1] S. Sachdev, C. Buragohain, and M. Vojta, Science 286, 2479 (1999); M. Vojta, C. Buragohain, and S. Sachdev, Phys. Rev. B 61, 15152 (2000). [2] O. P. Sushkov, Phys. Rev. B 62, 12135 (2000). [3] M. Troyer, Prog. Theor. Phys. Supp. 145, 326 (2002).
LETTER TO THE EDITOR: Parity-broken ground state for the spin-1 pyrochlore antiferromagnet
Yamashita, Yasufumi; Ueda, Kazuo; Sigrist, Manfred
2001-12-01
The ground-state properties of the spin-1 pyrochlore antiferromagnet are studied by applying the VBS-like tetrahedron-unit decomposition to the original spin system. The symmetrization required on every vertex is taken into account by introducing a ferromagnetic coupling. The pairwise effective Hamiltonian between the adjacent tetrahedrons is obtained by considering the next nearest neighbour and the third neighbour exchange interactions. We find that the transverse component of the spin chirality exhibits a long-range order, breaking the parity symmetry of the tetrahedral group, while the chirality itself is not broken.
Khuntia, P.; Bert, F.; Mendels, P.; Koteswararao, B.; Mahajan, A. V.; Baenitz, M.; Chou, F. C.; Baines, C.; Amato, A.; Furukawa, Y.
2016-03-01
PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu2 + ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T ) evolution of the 1 /T1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.
Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y
2016-03-11
PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation. PMID:27015508
Antiferromagnetic order and spin glass behavior in Dy{sub 2}CuIn{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Siouris, I.M., E-mail: jsiou@pme.duth.gr [Democritus University of Thrace (DUTH), Production and Management Engineering Department, Materials Laboratory, 67100 Xanthi (Greece); Kremer, R.K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Hoelzel, M. [Technische Universitaet Muenchen, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching (Germany)
2011-11-15
The magnetic properties of the intermetallic compound Dy{sub 2}CuIn{sub 3} have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T{sub N}=19.5 K and an additional frequency dependent transition at T{sub ds}{approx}9 K. Neutron diffraction studies confirm the ordered transition at 19.5{+-}1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment {mu}=2.63(4){mu}{sub B}/Dy{sup 3+} parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions. - Highlights: > Dy{sub 2}CuIn{sub 3} is characterized by the dominance of antiferromagnetic (AF) interactions. > Geometric frustration and crystal field effects prevent the formation of the full magnetic moment on the Dy ions. > Two magnetic regimes are recognized: an AF state and a mixed AF-glassy state. > The antiferromagnetic structure of the compound has been determined.
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.
Evidence for asymmetric rotation of spins in antiferromagnetic exchange-spring
Wang, Y. Y.; Song, C.; Wang, G. Y.; Zeng, F.; Pan, F.
2014-12-01
We demonstrate an asymmetric rotation of the antiferromagnetic (AFM) spins in the exchange-spring driven by perpendicularly magnetized Co/Pt. The static and dynamic behaviors of the twisted spin structure are directly revealed by a combination of element specific soft-x-ray absorption spectra and magnetoresistance measurements. X-ray magnetic linear dichroism spectra as a function of AFM thickness clarify the features of the whole exchange-spring, while the interfacial uncompensated spins are identified by the x-ray magnetic circular dichroism spectra. Moreover, the observed tunneling anisotropic magnetoresistance (TAMR) in AFM-based junctions based on this asymmetric rotation provides an electrical approach to monitoring the dynamic twist of the AFM spins. These investigations not only provide a deep insight into the spin structure of the exchange coupling layers but would also advance the development of AFM spintronics.
Evidence for asymmetric rotation of spins in antiferromagnetic exchange-spring
International Nuclear Information System (INIS)
We demonstrate an asymmetric rotation of the antiferromagnetic (AFM) spins in the exchange-spring driven by perpendicularly magnetized Co/Pt. The static and dynamic behaviors of the twisted spin structure are directly revealed by a combination of element specific soft-x-ray absorption spectra and magnetoresistance measurements. X-ray magnetic linear dichroism spectra as a function of AFM thickness clarify the features of the whole exchange-spring, while the interfacial uncompensated spins are identified by the x-ray magnetic circular dichroism spectra. Moreover, the observed tunneling anisotropic magnetoresistance (TAMR) in AFM-based junctions based on this asymmetric rotation provides an electrical approach to monitoring the dynamic twist of the AFM spins. These investigations not only provide a deep insight into the spin structure of the exchange coupling layers but would also advance the development of AFM spintronics. (paper)
Spin Fluctuations and Superconductivity around the Magnetic Instability
Moriya, Toru
2002-01-01
We summarize the present status of the theories of spin fluctuations in dealing with the anomalous or non-Fermi liquid behavior and unconventional superconductivity in strongly correlated electron systems around their magnetic instabilities or quantum critical points. Arguments are given to indicate that the spin fluctuation mechanisms is the common origin of superconductivity in heavy electron systems, 2-dimensional organic conductors and high-T_c cuprates.
Effect of next-nearest neighbor hopping on the spin dynamics in antiferromagnets
Morr, Dirk K.
1998-01-01
Recently, inelastic neutron scattering (INS) experiments on the insulating parent compounds of high-T_c materials were analyzed to extract the value of the superexchange constant $J$. Starting point of the analysis was the nearest-neighbor Heisenberg model. Motivated by recent ARPES experiments, we consider the effects of a next-nearest neighbor hopping, $t'$ in the strong coupling limit of the spin-density wave formalism, where it leads to an antiferromagnetic exchange $J'>0$ between next-ne...
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 frustration effects in an odd-member antiferromagnetic ring and the magnetic Mobius strip
Energy Technology Data Exchange (ETDEWEB)
Cador, Olivier [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Gatteschi, Dante [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy); Sessoli, Roberta [Laboratory of Molecular Magnetism, Department of Chemistry and UdR INSTM, Universita degli Studi di Firenze, Via Lastruccia n. 3, 50019 Sesto Fiorentino (Italy)]. E-mail: roberta.sessoli@unifi.it; Barra, Anne-Laure [Laboratoire des Champs Magnetiques Intenses-CNRS, F-38042 Grenoble Cede 9 (France); Timco, Grigore A. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Winpenny, Richard E.P. [Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)
2005-04-15
The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=32 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Mobius strip. The 'knot' of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site.
Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations
Energy Technology Data Exchange (ETDEWEB)
Kwon, K.D.; Refson, K.; Bone, S.; Qiao, R.; Yang, W.; Liu, Z.; Sposito, G.
2010-11-01
Mackinawite is a naturally occurring layer-type FeS mineral important in biogeochemical cycles and, more recently, in the development of microbial fuel cells. Conflicting results have been published as to the magnetic properties of this mineral, with Moessbauer spectroscopy indicating no magnetic ordering down to 4.2 K but density functional theory (DFT) predicting an antiferromagnetic ground state, similar to the Fe-based high-temperature superconductors with which it is isostructural and for which it is known that magnetism is suppressed by strong itinerant spin fluctuations. We investigated this latter possibility for mackinawite using photoemission spectroscopy, near-edge x-ray absorption fine structure spectroscopy, and DFT computations. Our Fe 3{sub s} core-level photoemission spectrum of mackinawite showed a clear exchange-energy splitting (2.9 eV) consistent with a 1 {micro}{sub B} magnetic moment on the Fe ions, while the Fe L-edge x-ray absorption spectrum indicated rather delocalized Fe 3{sub d} electrons in mackinawite similar to those in Fe metal. Our DFT computations demonstrated that the ground state of mackinawite is single-stripe antiferromagnetic, with an Fe magnetic moment (2.7 {micro}{sub B}) that is significantly larger than the experimental estimate and has a strong dependence on the S height and lattice parameters. All of these trends signal the existence of strong itinerant spin fluctuations. If spin fluctuations prove to be mediators of electron pairing, we conjecture that mackinawite may be one of the simplest Fe-based superconductors.
Coherent spin control by electromagnetic vacuum fluctuations
Jing WANG; Liu, Ren-Bao; Zhu, B. -F.; Sham, L. J.; Steel, D. G.
2009-01-01
In coherent control, electromagnetic vacuum fluctuations usually cause coherence loss through irreversible spontaneous emission. However, since the dissipation via emission is essentially due to correlation of the fluctuations, when emission ends in a superposition of multiple final states, correlation between different pathways may build up if the "which-way" information is not fully resolved (i.e., the emission spectrum is broader than the transition energy range). Such correlation can be e...
Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe.
Wang, Qisi; Shen, Yao; Pan, Bingying; Hao, Yiqing; Ma, Mingwei; Zhou, Fang; Steffens, P; Schmalzl, K; Forrest, T R; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Bourges, P; Sidis, Y; Cao, Huibo; Zhao, Jun
2016-02-01
In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. Here, we study FeSe (ref. )-which exhibits a nematic (orthorhombic) phase transition at Ts = 90 K without antiferromagnetic ordering-by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on cooling through Ts. A sharp spin resonance develops in the superconducting state, whose energy (∼4 meV) is consistent with an electron-boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Our results support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations. PMID:26641018
International Nuclear Information System (INIS)
The paper critically overviews the recent developments of the theory of spatially dispersive spin fluctuations (SF) in itinerant electron magnetism with particular emphasis on spin-fluctuation coupling or spin anharmonicity. It is argued that the conventional self-consistent renormalized (SCR) theory of spin fluctuations is usually used aside of the range of its applicability actually defined by the constraint of weak spin anharmonicity based on the random phase approximation (RPA) arguments. An essential step in understanding SF in itinerant magnets beyond RPA-like arguments was made recently within the soft-mode theory of SF accounting for strong spin anharmonicity caused by zero-point SF. In the present paper we generalize it to apply for a wider range of temperatures and regimes of SF and show it to lead to qualitatively new results caused by zero-point effects. - Highlights: • We review the spin-fluctuation theory of itinerant electron magnets with account of zero-point effects. • We generalize the existing theory to account for different regimes of spin fluctuations. • We show that zero-point spin fluctuations play a crucial role in both low- and high-temperature properties of metallic magnets. • We argue that a new scheme of calculation of ground state properties of magnets is needed including zero-point effects
Energy Technology Data Exchange (ETDEWEB)
Solontsov, A., E-mail: asolontsov@mail.ru [Center for Fundamental and Applied Research, N.L. Dukhov Research Institute for Automatics, 22 Suschevskaya Street, Moscow 127055 (Russian Federation); State Center for Condensed Matter Physics, 6/3 Street M. Zakharova, Moscow 115569 (Russian Federation)
2015-06-01
The paper critically overviews the recent developments of the theory of spatially dispersive spin fluctuations (SF) in itinerant electron magnetism with particular emphasis on spin-fluctuation coupling or spin anharmonicity. It is argued that the conventional self-consistent renormalized (SCR) theory of spin fluctuations is usually used aside of the range of its applicability actually defined by the constraint of weak spin anharmonicity based on the random phase approximation (RPA) arguments. An essential step in understanding SF in itinerant magnets beyond RPA-like arguments was made recently within the soft-mode theory of SF accounting for strong spin anharmonicity caused by zero-point SF. In the present paper we generalize it to apply for a wider range of temperatures and regimes of SF and show it to lead to qualitatively new results caused by zero-point effects. - Highlights: • We review the spin-fluctuation theory of itinerant electron magnets with account of zero-point effects. • We generalize the existing theory to account for different regimes of spin fluctuations. • We show that zero-point spin fluctuations play a crucial role in both low- and high-temperature properties of metallic magnets. • We argue that a new scheme of calculation of ground state properties of magnets is needed including zero-point effects.
Directory of Open Access Journals (Sweden)
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.
Ground state and zero temperature phase diagrams of the XXZ antiferromagnetic spin- {1}/{2} chain
Zhou, P.
1990-05-01
An expression of the XXZ model is given from which the Ising, isotropic XY and Heisenberg models may be more properly obtained by varying only one anisotropy parameter. The ground state and spin configuration of the antiferromagnetic quasi-classical s = {1}/{2}XXZ chain in a magnetic field of arbitrary direction are studied. The phase diagrams with a longitudinal ( h⊥ = 0) and a transverse field ( h‖ = 0) are presented. Because we take into account an effect of anisotropy in the Zeeman interaction, the phase diagrams are quite different from those given by Kurmann, et al. [Physica A 112 (1982) 235]. A ferromagnetic-antiferromagnetic first order phase transition is indicated for the Ising case with h⊥=0.
Competing orders in spin-1 and spin-3/2 XXZ kagome antiferromagnets: A series expansion study
Oitmaa, J.; Singh, R. R. P.
2016-01-01
We study the competition between √{3 }×√{3 } (RT3) and q =0 (Q0) magnetic orders in spin-1 and spin-3/2 kagome-lattice XXZ antiferromagnets with varying XY anisotropy parameter Δ , using series expansion methods. The Hamiltonian is split into two parts: an H0 which favors the classical order in the desired pattern and an H1, which is treated in perturbation theory by a series expansion. We find that the ground state energy series for the RT3 and Q0 phases are identical up to sixth order in the expansion, but ultimately a selection occurs, which depends on spin and the anisotropy Δ . Results for ground state energy and the magnetization are presented. These results are compared with recent spin-wave theory and coupled-cluster calculations. The series results for the phase diagram are close to the predictions of spin-wave theory. For the spin-1 model at the Heisenberg point (Δ =1 ), our results are consistent with a vanishing order parameter, that is, an absence of a magnetically ordered phase. We also develop series expansions for the ground state energy of the spin-1 Heisenberg model in the trimerized phase. We find that the ground state energy in this phase is lower than those of magnetically ordered ones, supporting the existence of a spontaneously trimerized phase in this model.
Spin wave dynamics in Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes
Mi, Bin-Zhou
2016-09-01
The spin wave dynamics, including the magnetization, spin wave dispersion relation, and energy level splitting, of Heisenberg ferromagnetic/antiferromagnetic single-walled nanotubes are systematically calculated by use of the double-time Green's function method within the random phase approximation. The role of temperature, diameter of the tube, and wave vector on spin wave energy spectrum and energy level splitting are carefully analyzed. There are two categories of spin wave modes, which are quantized and degenerate, and the total number of independent magnon branches is dependent on diameter of the tube, caused by the physical symmetry of nanotubes. Moreover, the number of flat spin wave modes increases with diameter of the tube rising. The spin wave energy and the energy level splitting decrease with temperature rising, and become zero as temperature reaches the critical point. At any temperature, the energy level splitting varies with wave vector, and for a larger wave vector it is smaller. When pb=π, the boundary of first Brillouin zone, spin wave energies are degenerate, and the energy level splittings are zero.
International Nuclear Information System (INIS)
Full text: In some low-dimensional quantum antiferromagnets a transition can occur between a Neel ordered ground state, characterised by gapless excitations and long range correlations, and a disordered ground state with a gap and short range correlations. The disordered phase is characterised by strong singlet formation on pairs of neighbouring spins. We have used a new analytic many body approach together with numerical series and exact diagonalisation methods to study such transitions in 1. a bilayer Heisenberg system 2. a spin analogue of the Kondo lattice model at half filling. A Letter on this work has been published. The analytic method is based on a 'bond operator' representation for spins which is used to transform the problem to an interacting Bose gas with a hardcore repulsion which is treated exactly. The results are in excellent agreement with numerical estimates, and represent a significant improvement on previous calculations
Geometric phase of a central spin coupled to an antiferromagnetic environment
Yuan, Xiao-Zhong; Zhu, Ka-Di
2010-01-01
Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated.
Structural and magnetic field effects on spin fluctuations in Sr3Ru2O7
Mukherjee, Shantanu; Lee, Wei-Cheng
2016-08-01
We investigate the evolution of magnetic excitations in Sr3Ru2O7 in the paramagnetic metallic phase using a three-band tight-binding model. The effect of Mn or Ti dopant ions on the Sr3Ru2O7 band structure has been included by taking into account the dopant-induced suppression of the oxygen octahedral rotation in the tight-binding band structure. We find that the low-energy spin fluctuations are dominated by three wave vectors around q ⃗=( (0 ,0 ) ,(π /2 ,π /2 ) ) and (π ,0 ) , which compete with each other. As the octahedral rotation is suppressed with increasing doping, the three wave vectors evolve differently. In particular, the undoped compound has dominant wave vectors at q ⃗=( (0 ,0 ) ,(π /2 ,π /2 ) ) , but doping Sr3Ru2O7 leads to a significant enhancement in the spin susceptibility at the q ⃗=(π ,0 ) wave vector, bringing the system closer to a magnetic instability. All the features calculated from our model are in agreement with neutron scattering experiments. We have also studied the effect of a c -axis Zeeman field on the low-energy spin fluctuations. We find that an increasing magnetic field suppresses the antiferromagnetic (AFM) fluctuations and leads to stronger competition between the AFM and ferromagnetic spin fluctuations. The magnetic field dependence observed in our calculations therefore supports the scenario that the observed nematic phase in the metamagnetic region in Sr3Ru2O7 is intimately related to the presence of a competing ferromagnetic instability.
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.
Unconventional superconductivity from local spin fluctuations in the Kondo lattice.
Bodensiek, Oliver; Žitko, Rok; Vojta, Matthias; Jarrell, Mark; Pruschke, Thomas
2013-04-01
The explanation of heavy-fermion superconductivity is a long-standing challenge to theory. It is commonly thought to be connected to nonlocal fluctuations of either spin or charge degrees of freedom and therefore of unconventional type. Here we present results for the Kondo-lattice model, a paradigmatic model to describe heavy-fermion compounds, obtained from dynamical mean-field theory which captures local correlation effects only. Unexpectedly, we find robust s-wave superconductivity in the heavy-fermion state. We argue that this novel type of pairing is tightly connected to the formation of heavy quasiparticle bands and the presence of strong local spin fluctuations. PMID:25167017
Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling
Del Cima, O M; da Silva, S L L
2015-01-01
The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.
Spin-Peierls States of Quantum Antiferromagnets on the CaV4O9 Lattice
International Nuclear Information System (INIS)
We discuss the quantum paramagnetic phases of Heisenberg antiferromagnets on the 1/5-depleted square lattice found in CaV4O9. The possible phases of the quantum dimer model on this lattice are obtained by a mapping to a quantum-mechanical height model. In addition to the open-quote open-quote decoupled close-quote close-quote phases found earlier, we find a possible intermediate spin-Peierls phase with spontaneously broken lattice symmetry. Experimental signatures of the different quantum paramagnetic phases are discussed. copyright 1996 The American Physical Society
Double-layer antiferromagnetic quantum spin-1/2 Heisenberg model: study of the ground state
International Nuclear Information System (INIS)
The crossover from two-dimensional to three-dimensional behavior in the quasi-two-dimensional quantum Heisenberg antiferromagnetic model in the presence of a magnetic field, at T=0 (ground state), is studied by using effective-field theory. In the model a nearest neighbour spin pair interacts with strength J in the xy-plane and with λJ (0=c is obtained as a function of parameter λ, where we have different values of the classical case (Ising model) Hc/J=4+2λ
Pu, Zhengguo; Zhang, Jun; Yi, Su; Wang, Dajun; Zhang, Wenxian
2016-05-01
We theoretically investigate four types of dynamical instability, in particular the periodic and oscillatory type IO, in an antiferromagnetic spin-1 Bose-Einstein condensate in a nonzero magnetic field, by employing the coupled-mode theory and numerical method. This is in sharp contrast to the dynamical stability of the same system in zero field. Remarkably, a pattern transition from a periodic dynamical instability IO to a uniform one IIIO occurs at a critical magnetic field. All four types of dynamical instability and the pattern transition are ready to be detected in 23Na condensates within the availability of the current experimental techniques.
On the second-neighbour correlator in 1D XXX quantum antiferromagnetic spin chain
International Nuclear Information System (INIS)
We have calculated the energy per site for the ground state of the antiferromagnetic quantum spin chain with variable range exchange h(j-k) ∝ sinh2 a sinh-2 a(j-k) in the framework of the asymptotic Bethe ansatz. By expanding it in powers of e-2a, we have confirmed the value of the second-neighbour correlator for the model with nearest-neighbour exchange obtained earlier in the atomic limit of the Hubbard chain. (author). Letter-to-the-editor
A spin-valve-like magnetoresistance of an antiferromagnet-based tunnel junction
Czech Academy of Sciences Publication Activity Database
Park, B.G.; Wunderlich, Joerg; Martí, X.; Holý, V.; Kurosaki, Y.; Yamada, M.; Yamamoto, H.; Nishide, A.; Hayakawa, J.; Takahashi, H.; Shick, Alexander; Jungwirth, Tomáš
2011-01-01
Roč. 10, č. 5 (2011), s. 347-351. ISSN 1476-1122 R&D Projects: GA AV ČR KAN400100652; GA MŠk LC510; GA MŠk(CZ) 7E08087 EU Projects: European Commission(XE) 214499 - NAMASTE; European Commission(XE) 215368 - SemiSpinNet Grant ostatní: AVČR(CZ) Premium Academiae; 7 FP ERC Advanced Grant 0MSPIN(XE) 268066 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10100520 Keywords : spintronic s * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 32.841, year: 2011
Yu, Rong; Roscilde, Tommaso; Haas, Stephan
2006-01-01
Site dilution of spin-gapped antiferromagnets leads to localized free moments, which can order antiferromagnetically in two and higher dimensions. Here we show how a weak magnetic field drives this order-by-disorder state into a novel disordered-free-moment phase, characterized by the formation of local singlets between neighboring moments and by localized moments aligned antiparallel to the field. This disordered phase is characterized by the absence of a gap, as it is the case in a Bose gla...
Directory of Open Access Journals (Sweden)
G. C. Fouokeng
2014-01-01
Full Text Available We analyze the influence of a two-state autocorrelated noise on the decoherence and on the tunneling Landau-Zener (LZ transitions during a two-level crossing of a central electron spin (CES coupled to a one dimensional anisotropic-antiferomagnetic spin, driven by a time-dependent global external magnetic field. The energy splitting of the coupled spin system is found through an approach that computes the noise-averaged frequency. At low magnetic field intensity, the decoherence (or entangled state of a coupled spin system is dominated by the noise intensity. The effects of the magnetic field pulse and the spin gap antiferromagnetic material used suggest to us that they may be used as tools for the direct observation of the tunneling splitting through the LZ transitions in the sudden limit. We found that the dynamical frequencies display basin-like behavior decay with time, with the birth of entanglement, while the LZ transition probability shows Gaussian shape.
Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system
Fukami, Shunsuke; Zhang, Chaoliang; Duttagupta, Samik; Kurenkov, Aleksandr; Ohno, Hideo
2016-05-01
Spin-orbit torque (SOT)-induced magnetization switching shows promise for realizing ultrafast and reliable spintronics devices. Bipolar switching of the perpendicular magnetization by the SOT is achieved under an in-plane magnetic field collinear with an applied current. Typical structures studied so far comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in the NM is responsible for the switching. Here we show that an antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large enough to switch the magnetization of the FM. In this material system, thanks to the exchange bias of the AFM, we observe the switching in the absence of an applied field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with a perpendicular easy axis. Furthermore, tailoring the stack achieves a memristor-like behaviour where a portion of the reversed magnetization can be controlled in an analogue manner. The AFM/FM system is thus a promising building block for SOT devices as well as providing an attractive pathway towards neuromorphic computing.
Li, Zixiang; Yao, Hong; Wang, Fa; Lee, Dung-Hai
Superconductivity is an emergent phenomena in the sense that the energy scale at which Cooper pairs form is generically much lower than the bare energy scale, namely the electron kinetic energy bandwidth. Addressing the mechanism of Cooper pairing amounts to finding out the effective interaction (or the renormalized interaction) that operates at the low energies. Finding such interaction from the bare microscopic Hamiltonian has not been possible for strong correlated superconductors such as the copper-oxide high temperature superconductor. In fact even one is given the effective interaction, determining its implied electronic instabilities without making any approximation has been a formidable task. Here, we perform sign-free quantum Monte-Carlo simulations to study the antiferromagnetic, superconducting, and the charge density wave instabilities which are ubiquitous in both electron and hole doped cuprates. Our result suggests only after including both the nematic and antiferromagnetic fluctuation, are the observed properties associated with these instabilities reproduced by the theory.
Spin fluctuations and magnetic order in Nb1-xZrxFe2
International Nuclear Information System (INIS)
Zero and longitudinal field μSR have been used to study the evolution of spin correlations and magnetic order resulting from 10at% substitution of Zr for Nb in the weak itinerant antiferromagnet NbFe2. Rapidly fluctuating atomic fields (λ=0.02μs-1) are found to persist almost unchanged to low temperatures. These coexist with a narrow distribution of static fields (σ=0.2μs-1) which evolves from a gaussian to lorentzian form between 90K and the Curie temperature of 43K. It is suggested that these effects may be a consequence of topologically frustrated exchange between Fe sites in the C14 structure. (orig.)
Directory of Open Access Journals (Sweden)
R. L. Wang
2012-09-01
Full Text Available Effect of thermal cycle on the interfacial antiferromagnetic (AFM spin configuration and exchange bias in Ni50Mn36Sb14 alloy has been investigated. The results indicate thermal cycle can induce further martensitic transition from part of arrested FM phase to AFM phase, leading to the reconstruction of interfacial antiferromagnetic spin configuration. The shape of hysteresis loops at 5 K after cooling back can be tuned from a single-shifted loop to a nearly symmetric double-shifted loop gradually accompanied with exchange bias field increasing to peak value and then decreasing. The evolutions can be illustrated intuitively by a simple AFM bidomain model.
Theory of spin-fluctuation induced superconductivity in iron-based superconductors
Energy Technology Data Exchange (ETDEWEB)
Zhang, Junhua [Iowa State Univ., Ames, IA (United States)
2011-01-01
In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum
Theory of spin-fluctuation induced superconductivity in iron-based superconductors
International Nuclear Information System (INIS)
In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum
Spin-Jahn-Teller effect in the antiferromagnetic molecular wheel CsFe8
International Nuclear Information System (INIS)
Antiferromagnetic molecular wheels are ring-like arrangements of exchange-coupled magnetic metal ions. As a function of a magnetic field, the Zeeman splitting leads to a series of level-crossings (LCs) at characteristic fields, where the ground state changes from total spin S=0 to S=1, S=2, and so on. Previous magnetic torque and 1H-NMR measurements on CsFe8 single crystals demonstrated phase transitions at the LCs at low temperatures. They were explained by a field-induced spin-Jahn-Teller effect (JTE) due to a magneto-elastic coupling between the spins in the wheel and the lattice. Some models for this process were developed, but a full microscopic understanding is lacking. New high-field torque data were recorded, which provide a comprehensive picture of the angular as well as temperature dependence of the phase transition. A strong angle dependence of the critical fields and temperatures with two qualitatively different regimes was observed, which allows us to distinguish the relative contributions of zero-field splitting and Dzyaloshinsky-Moriya interactions to the spin-JTE.
Spin-Jahn-Teller effect in the antiferromagnetic molecular wheel CsFe{sub 8}
Energy Technology Data Exchange (ETDEWEB)
Lotze, Johannes; Waldmann, Oliver [Physikalisches Institut, Universitaet Freiburg (Germany); Chamayou, Anne-Christine; Janiak, Christoph [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg (Germany); Ako, Ayuk M.; Powell, Annie K. [Institut fuer Anorganische Chemie, Universitaet Karlsruhe (Germany); Sheikin, Ilya [Grenoble High Magnetic Field Laboratory, CNRS, Grenoble (France)
2010-07-01
Antiferromagnetic molecular wheels are ring-like arrangements of exchange-coupled magnetic metal ions. As a function of a magnetic field, the Zeeman splitting leads to a series of level-crossings (LCs) at characteristic fields, where the ground state changes from total spin S=0 to S=1, S=2, and so on. Previous magnetic torque and {sup 1}H-NMR measurements on CsFe{sub 8} single crystals demonstrated phase transitions at the LCs at low temperatures. They were explained by a field-induced spin-Jahn-Teller effect (JTE) due to a magneto-elastic coupling between the spins in the wheel and the lattice. Some models for this process were developed, but a full microscopic understanding is lacking. New high-field torque data were recorded, which provide a comprehensive picture of the angular as well as temperature dependence of the phase transition. A strong angle dependence of the critical fields and temperatures with two qualitatively different regimes was observed, which allows us to distinguish the relative contributions of zero-field splitting and Dzyaloshinsky-Moriya interactions to the spin-JTE.
Arima T.; Iwai S.; Itoh H; Yamada K; Ishikawa T; Yamada S; Sasaki T.
2013-01-01
Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.
Temperature dependence of fluctuation time scales in spin glasses
DEFF Research Database (Denmark)
Kenning, Gregory G.; Bowen, J.; Sibani, Paolo;
2010-01-01
Using a series of fast cooling protocols we have probed aging effects in the spin glass state as a function of temperature. Analyzing the logarithmic decay found at very long time scales within a simple phenomenological barrier model, leads to the extraction of the fluctuation time scale of the s......-aging behavior in scaling aged TRM decay curves, as recently discussed theoretically~\\cite{Sibani09}.......Using a series of fast cooling protocols we have probed aging effects in the spin glass state as a function of temperature. Analyzing the logarithmic decay found at very long time scales within a simple phenomenological barrier model, leads to the extraction of the fluctuation time scale of the...... system at a particular temperature. This is the smallest dynamical time-scale, defining a lower-cut off in a hierarchical description of the dynamics. We find that this fluctuation time scale, which is approximately equal to atomic spin fluctuation time scales near the transition temperature, follows a...
Energy Technology Data Exchange (ETDEWEB)
Drichko, Natalia; Hackl, Rudi; Schlueter, John A.
2015-10-15
Using Raman scattering, the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (T-c = 11.8 K) and the related antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl are studied. Raman scattering provides unique spectroscopic information about magnetic degrees of freedom that has been otherwise unavailable on such organic conductors. Below T = 200 K a broad band at about 500 cm(-1) develops in both compounds. We identify this band with two-magnon excitation. The position and the temperature dependence of the spectral weight are similar in the antiferromagnet and in the metallic Fermi liquid. We conclude that antiferromagnetic correlations are similarly present in the magnetic insulator and the Fermi-liquid state of the superconductor.
Antiferromagnetic spin and twin domain walls govern hysteretic expressions of exchange anisotropy
Armstrong, Jason N.; Sullivan, Matthew R.; Chopra, Harsh Deep
2009-09-01
The present study shows that antiferromagnetic spin and twin domain walls govern the hysteretic expressions of exchange anisotropy at low and high fields, respectively, using annealed NiO single crystals and Co. In the presence of twin walls, spin walls are shown to be a geometrical necessity in the antiferromagnetic NiO. A threshold field (˜10000Oe) exists below which twin walls are frozen, and rotational hysteresis is dominated by losses due to spin walls. Above the threshold field, twin walls become mobile, resulting in a sharp increase in rotational hysteresis. Remarkably, rotational hysteresis associated with spin walls is similar to that of an ordinary ferromagnet—as the field strength increases, rotational hysteresis tends toward zero. However, unlike an ordinary ferromagnet where rotational hysteresis becomes zero above its saturation field, rotational hysteresis in antiferromagnet drops but then sharply increases once the threshold field for twin wall motion is exceeded. In crystals without spin walls, low-field rotational hysteresis is zero or negligible. Domain imaging of twin walls in antiferromagnet and Weiss walls in ferromagnet reveals a one-to-one spatial correlation even though twin walls are considered to have no net dipoles. This surprising result is explained by the fact that crystallographic interfaces in real crystals are not atomically sharp or ideal, and the defective interface invariably results in net moment across the finite width of the twin wall. The field dependence of domain walls in Co film exchange coupled to NiO shows global similarities to previously reported behavior of Co films deposited on nanocrystalline NiO [H. D. Chopra, D. X. Yang, P. J. Chen, H. J. Brown, L. J. Swartzendruber, and W. F. Egelhoff, Jr., Phys. Rev. B 61, 15312 (2000)]. In both cases, domain wall motion is not the dominant mode of magnetization reversal (wall motion is entirely absent in the present study while wall motion was only occasionally observed in
CIP spin torque effect in the spin valve pinned with an oxide antiferromagnetic layer
International Nuclear Information System (INIS)
Spin valve Ni0.85Co0.15O/Co85Fe15/Cu/Co85Fe15 was manufactured by a RF magnetron sputtering system. M(H) and R(H) characteristics of the spin valve were measured in CIP configuration at room temperature has a magnetoresistance ratio of about 8% and a high exchange bias at room temperature. The current density and angle between the applied magnetic field and injection current were changed in an aim to observe their effects on MR and exchange bias of the spin valve. The current density and angle strongly affect MR and exchange bias. Both MR and exchange bias clearly decrease in dependence of the current density and direction of the magnetic field. It is supposed to be related with a current-induced spin torque in device.
Soliton Lattice State of Spin-1/2 Antiferromagnetic Chain in an External Magnetic Field
Institute of Scientific and Technical Information of China (English)
WANG Zhi-Guo; ZHANG Yu-Mei; GAO Yang
2002-01-01
One-dimensional spin-1-2 anisotropic Heisenberg antiferromagnet in a longitudinal external magnetic field is studied using bosonization method and Gaussian wave functional techniques which take account of the spatial structure.The magnetization and the energy of the ground state which depend on the external magnetic field are calculated.For the case of anisotropic parameter △＞△0,increasing of the external magnetic field above the threshold value leads to the appearance of the soliton lattice state in the ground state,until to an another critical field where the ground state changes to the canted state phase.Therefore,with increasing external magnetic field,the ground state experiences four different phases successively,namely,antiferromagnetic Ising,soliton lattice state canted state,and magnetization saturated phases.When △＜△0,the soliton lattice state phase does not appear,with increasing external field,the paramagnetic phase smoothly evolves into the canted state phase,finally reaches magnetization saturated phase.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
DEFF Research Database (Denmark)
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 pea...
Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves
Energy Technology Data Exchange (ETDEWEB)
Gubbiotti, G., E-mail: gubbiotti@fisica.unipg.it; Tacchi, S. [Istituto Officina dei Materiali del CNR (IOM-CNR), Unità di Perugia, I-06123 Perugia (Italy); Del Bianco, L. [Department of Physics and Astronomy, University of Bologna, I-40127 Bologna (Italy); Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Bonfiglioli, E.; Giovannini, L.; Spizzo, F.; Zivieri, R. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Tamisari, M. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia (Italy)
2015-05-07
Brillouin light scattering (BLS) was exploited to study the spin wave properties of spin-valve (SV) type samples basically consisting of two 5 nm-thick NiFe layers (separated by a Cu spacer of 5 nm), differently biased through the interface exchange coupling with an antiferromagnetic IrMn layer. Three samples were investigated: a reference SV sample, without IrMn (reference); one sample with an IrMn underlayer (10 nm thick) coupled to the bottom NiFe film; one sample with IrMn underlayer and overlayer of different thickness (10 nm and 6 nm), coupled to the bottom and top NiFe film, respectively. The exchange coupling with the IrMn, causing the insurgence of the exchange bias effect, allowed the relative orientation of the NiFe magnetization vectors to be controlled by an external magnetic field, as assessed through hysteresis loop measurements by magneto-optic magnetometry. Thus, BLS spectra were acquired by sweeping the magnetic field so as to encompass both the parallel and antiparallel alignment of the NiFe layers. The BLS results, well reproduced by the presented theoretical model, clearly revealed the combined effects on the spin dynamic properties of the dipolar interaction between the two NiFe films and of the interface IrMn/NiFe exchange coupling.
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.
Frustration in a transverse Ising nanoisland with an antiferromagnetic spin configuration
Energy Technology Data Exchange (ETDEWEB)
Kaneyoshi, T., E-mail: kaneyosi@is.nagoya-u.ac.Jp
2015-09-01
The phase diagrams, saturation magnetizations and temperature dependences of magnetizations in a transverse Ising nanoisland with an antiferromagnetic spin configuration are studied by the uses of the effective-field theory with correlations (EFT) and the mean-field approximation (MFA), in order to clarify whether the MFA can be successfully applied to the theoretical discussions of naonoislands. From these investigations, we have found a lot of unexpected characteristic phenomena in these properties, when the value of an interlayer coupling takes a large value. We have also found that the applications of the MFA to the magnetic properties are extremely restricted for nanoislands, when the value of an interlayer coupling takes a large value, in contrast to a number of bulk studies.
Wu, R.; Yun, C.; Ding, S. L.; Wen, X.; Liu, S. Q.; Wang, C. S.; Han, J. Z.; Du, H. L.; Yang, J. B.
2016-08-01
The motion of antiferromagnetic interfacial spins is investigated through the temperature evolution of training effect in a Co/CoO film with in-plane biaxial anisotropy. Significant differences in the training effect and its temperature dependence are observed in the magnetic easy axis and hard axis (HA) and ascribed to the different motion modes of antiferromagnetic interfacial spins, the collective spin cluster rotation (CSR) and the single spin reversal (SSR), caused by different magnetization reversal modes of ferromagnetic layer. These motion modes of antiferromagnetic spins are successfully separated using a combination of an exponential function and a classic n-1/2 function. A larger CSR to SSR ratio and a shorter lifetime of CSR found in the HA indicates that the domain rotation in the ferromagnetic layer tends to activate and accelerate a CSR mode in the antiferromagnetic spins.
Spin dynamics of the 2D spin ½ quantum antiferromagnet copper deuteroformate tetradeuterate (CFTD)
DEFF Research Database (Denmark)
Rønnow, H.M.; McMorrow, D.F.; Coldea, R.; Harrison, A.; Youngson, I.D.; Perring, T.G.; Aeppli, G.; Syljuåsen, O.; Lefmann, K.; Rischel, C.
2001-01-01
energy is observed, which is attributed to a wave vector dependent quantum renormalization. At higher temperatures, spin-wavelike excitations persist, but are found to broaden and soften. By combining our data with numerical calculations, and with existing theoretical work, a consistent description of...
DEFF Research Database (Denmark)
Kawasaki, Yu; Gavilano, Jorge L.; Keller, Lukas; Schefer, Juerg; Christensen, Niels Bech; Amato, Alex; Ohno, Takashi; Kishimoto, Yutaka; He, Zhangzhen; Ueda, Yutaka; Itoh, Mitsuru
2011-01-01
,0,1), independent of external magnetic fields for fields below a critical value H-c(T). The ordered moments of 2.18 mu(B) per Co ion are aligned along the crystallographic c axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged...
Sun, Kai; Lawler, Michael J.; Kim, Eun-Ah
2009-01-01
We study the interplay between charge and spin ordering in electronic liquid crystalline states with a particular emphasis on fluctuating spin stripe phenomena observed in recent neutron scattering experiments\\cite{Hinkov2008, Haug2009}. Based on a phenomenological model, we propose that charge nematic ordering is indeed behind the formation of temperature dependent incommensurate inelastic peaks near wavevector $(\\pi,\\pi)$ in the dynamic structure factor of YBa$_2$Cu$_3$O$_{6+y}$. We strengt...
Spin polarized STM imaging of the Fe3O4 (0 0 1) surface using antiferromagnetic tips
Jordan, K.; Mariotto, G.; Ceballos, S. F.; Murphy, S.; Shvets, I. V.
2005-04-01
Spin polarized STM is used to image the charge ordered Fe3O4 (0 0 1) surface, using antiferromagnetic MnNi probes. Such a surface is characterized by the presence of Fe- Fe and Fe- Fe dimers. These dimers have different spin configurations, which are resolved using a MnNi probe. The surface is also imaged with paramagnetic W tips, which do not distinguish between the dimers, providing further evidence for a spin polarized contribution to the tunnel current with MnNi tips.
Heavy-fermion, kondo, spin glass-like, and antiferromagnetic behavior in (Ce,Gd)Al/sub 3/
International Nuclear Information System (INIS)
We have found that Ce/sub 1-x/Gd/sub x/Al3 with x = 0.23 is a heavy-fermion system which undergoes a spin glass transition. The amplitude of the peak in the susceptibility that characterizes the spin glass transition passes through a sharp maximum at x = 0.5. For x = 0.635 and 0.77 the system undergoes a spin glass-like transition at 1000K and an antiferromagnetic transition at 200K
Spin excitations in the odd homonuclear antiferromagnetic molecular nanomagnet Fe{sub 9}
Energy Technology Data Exchange (ETDEWEB)
Konstantinidis, Nikolaos P.; Nehrkorn, Joscha; Stuiber, Stefan; Waldmann, Oliver [Physikalisches Institut, Universitaet Freiburg, 79104 Freiburg (Germany)
2011-07-01
The homonuclear ring Fe{sub 9} has an odd number of antiferromagnetically coupled Fe{sup I}II spin-5/2 centers, therefore frustration plays an important role in determining its magnetic properties. Molecular wheels of odd size have been known to possess a doubly-degenerate lowest level in each total spin S sector in the absence of magnetic anisotropy. We have performed inelastic neutron scattering measurements which produced very sharp peaks that located the transitions between the energy levels very accurately. Our magnetic susceptibility data also provided an estimate for the strength of the exchange interactions, while torque magnetometry reveals the presence of weak magnetic anisotropy. Different Hamiltonians are used to find the appropriate model for the magnetic properties of Fe{sub 9}, with the energy levels characterized by the symmetry of the Hamiltonian. Exchange interactions that respect the spatial symmetry of the molecule coupled with a uniform single-site anisotropy term can not reproduce the splitting of the lowest energy levels. Especially the lowest lying S=3/2 doublet is unexpectedly robust against perturbations. This particular nature of the theoretically generated low-energy spectrum will be discussed.
Makhfudz, Imam; Pujol, Pierre
We propose a mechanism for the protection against spin gapped states in doped antiferromagnets. It requires the presence of a Chern-Simons term that can be generated by a coupling between spin and an insulator.We first demonstrate that in the presence of this term the vortex loop excitations of the spin sector behave as anyons with fractional statistics. To generate such a term, the fermions should have a massive Dirac spectrum coupled to the emergent spin field of the spin sector. The Dirac spectrum can be realized by a planar spin configuration arising as the lowest-energy configuration of a square lattice antiferromagnet Hamiltonian involving a Dzyaloshinskii- Moriya interaction. The mass is provided by a combination of dimerization and staggered chemical potential.We finally showthat for realistic parameters, anyonic vortex loop condensationwill likely never occur and thus the spin gapped state is prevented.We also propose real magnetic materials for an experimental verification of our theory. Reference: Imam Makhfudz and Pierre Pujol,Phys.Rev. B 92, 144507 (2015).
DEFF Research Database (Denmark)
Jin, Zuanming; Mics, Zoltán; Ma, Guohong;
2013-01-01
We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet yttrium orthoferrite, YFeO3, associated with a quasiferromagnetic (quasi-FM) spin resonance at a frequency of 0.3 THz, using a single-incident THz pulse. The spin resonance is excited impulsively by the ma...
DEFF Research Database (Denmark)
Kenzelmann, M.; Cowley, R.A.; Buyers, W.J.L.; Coldea, R.; Enderle, M.; McMorrow, D.F.
2002-01-01
We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar o...... the experiment is not consistent with the random phase approximation for coupled quantum chains. At T=200 K, the structure factor and second energy moment of the excitation spectrum are in excellent agreement with the high-temperature series expansion.......We have mapped from the quantum to the classical limit the spin excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain system CsNiCl3 in its paramagnetic phase from T=5 to 200 K. Neutron scattering shows that the excitations are resonant and dispersive up to at least T=70 Ksimilar or...... agreement with quantum Monte Carlo calculations for the spin-1 chain. xi is also consistent with the single mode approximation, suggesting that the excitations are short-lived single particle excitations. Below T=12 K where three-dimensional spin correlations are important, xi is shorter than predicted and...
Spin flop relaxation in the quasi-1d Heisenberg antiferromagnet CsMnBr 3 · 2H 2O
Chirwa, M.; Top, J.; Flokstra, J.
1983-12-01
The relaxation phenomena associated with the antiferromagnetic to spin-flop phase transition in the quasi one dimensional Heisenberg antiferromagnet CsMnBr 3 · 2H 2O have been determined in the temperature range 1.6-4.2 K using an automatic frequency-sweeping SQUID susceptometer. Below Tλ = 2.17 K the relaxation rate τ -1 displays an exponential temperature dependence given by τ-1 = ω0 exp(- E/ kT) where ω0 = 2.48 × 10 4 s -1 and E/ k = 3.62 K, the activation energy of the relaxation process. Above Tλ broadened absorption curves and flattened Argand diagrams are observed. The ratio K1/ K2 (=0.22 ± 0.02) of the orthorhombic anisotropy constants and a weak power-law temperature dependence of the critical spin-flop field Hcr were determined.
Energy Technology Data Exchange (ETDEWEB)
Ma, Q. L., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp [WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, 980-8577 Sendai (Japan); Iihama, S. [Department of Applied Physics, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Zhang, X. M. [Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)
2015-11-30
The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation.
International Nuclear Information System (INIS)
The laser-induced spin dynamics of FeCo in perpendicularly magnetized L10-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation
Disorder effects in the S=1 antiferromagnetic spin ladder CaV2O4
Guitarra, S. R.; Caneiro, A.; Niebieskikwiat, D.
2015-10-01
We study the physical properties of the antiferromagnetic spin ladder CaV2O4 (CVO) and the Y-doped related compound Ca0.9Y0.1V2O4. In the latter, X-ray diffraction demonstrates the segregation of a small amount of a vanadium-perovskite impurity phase, leading to the formation of V vacancies within the main CVO-type structure. The 1D character of this calcium-vanadite enhances the influence of the vacancies on the electric and magnetic properties of Ca0.9Y0.1V2O4. Electrical transport is characterized by a variable-range hopping mechanism determined by the charging energy of nm-sized segments of V chains delimited by V vacancies, i.e. a Coulomb gap is formed at the Fermi level. These vacancies also locally affect the magnetic correlations, breaking the long-range AFM order observed in CaV2O4 and producing exchange bias when the Y-doped sample is cooled with an applied magnetic field.
International Nuclear Information System (INIS)
For one-dimensional quantum spin chain systems recent experimental and theoretical studies indicate unexpectedly large, in some cases diverging spin and heat transport coefficients. Local probes, like e.g. muon spin relaxation (μSR) can indirectly characterize the spin transport properties of low dimensional systems via the magnetic field dependence of the spin lattice relaxation rate λ(B). For diffusive spin transport λ∝B-0.5 is expected. For the ground state of the isotropic spin-1/2 antiferromagnetic Heisenberg chain the eigenstates of the Heisenberg Hamiltonian dominate the spin transport, which is then ballistic. Using the Mueller ansatz λ∝B-1 is expected in this case. For SrCuO2 we find λ∝B-0.9(3). This result is temperature independent for 5 K≤T ≤300 K. Within conformal field theory and using the Mueller ansatz we conclude ballistic spin transport in SrCuO2.
Energy Technology Data Exchange (ETDEWEB)
Guo, Y. M.; Ruan, M. Y.; Cheng, J. J.; Sun, Y. C. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Ouyang, Z. W., E-mail: zwouyang@mail.hust.edu.cn; Xia, Z. C. [Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Rao, G. H. [School of Materials Science and Engineering, Guilin University of Electronic Technology, Guilin 541004 (China)
2015-06-14
High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < T{sub N} = 55 K) of spin-chain multiferroic Gd{sub 2}BaNiO{sub 5}. The spin reorientation at T{sub SR} = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.
Institute of Scientific and Technical Information of China (English)
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.
International Nuclear Information System (INIS)
High-spin-polarization materials are desired for the realization of high-performance spintronic devices. We combine recent experimental and theoretical findings to theoretically design several high-spin-polarization materials in binary D03-type Heusler alloys: gapless (zero-gap) half-metallic ferrimagnets of V3Si and V3Ge, half-metallic antiferromagnets of Mn3Al and Mn3Ga, half-metallic ferrimagnets of Mn3Si and Mn3Ge, and a spin gapless semiconductor of Cr3Al. The high spin polarization, zero net magnetic moment, zero energy gap, and slight disorder compared to the ternary and quaternary Heusler alloys make these binary materials promising candidates for spintronic applications. All results are obtained by the electronic structure calculations from first-principles
Inverse spin Hall effect of antiferromagnetic MnIr in exchange biased NiFe/MnIr films
International Nuclear Information System (INIS)
Antiferromagnetic Mn3Ir, which is widely employed in exchange-biased applications, has attracted much attention recently due to its predicted and subsequently observed large spin Hall effect, therefore increasing its potential for spintronic devices in place of conventional paramagnetic 5d spin Hall metals. (Pt, Ta and W) Via the electrical detection of ferromagnetic resonance, we study a series of exchange biased NiFe/MnIr films for various MnIr thicknesses. In these systems, spin-pumped spin currents from NiFe are converted into dc voltages within MnIr via the inverse spin Hall effect (ISHE), which mixes with spin rectification voltages generated from NiFe. Through angular measurements, we separate these different voltage contributions to qualitatively detect non-zero ISHE in MnIr, which coexists with a non-zero unidirectional anisotropy. We find significant extrinsic damping contributions which prevent the accurate quantification of spin pumping-induced ISHE in MnIr films. The results show that spin currents may propagate and dissipate in MnIr films through ISHE in the presence of exchange bias. (paper)
Mott physics and spin fluctuations: A functional viewpoint
Ayral, Thomas; Parcollet, Olivier
2016-06-01
We present a formalism for strongly correlated systems with fermions coupled to bosonic modes. We construct the three-particle irreducible functional K by successive Legendre transformations of the free energy of the system. We derive a closed set of equations for the fermionic and bosonic self-energies for a given K . We then introduce a local approximation for K , which extends the idea of dynamical mean-field theory (DMFT) approaches from two- to three-particle irreducibility. This approximation entails the locality of the three-leg electron-boson vertex Λ (i ω ,i Ω ) , which is self-consistently computed using a quantum impurity model with dynamical charge and spin interactions. This local vertex is used to construct frequency- and momentum-dependent electronic self-energies and polarizations. By construction, the method interpolates between the spin-fluctuation or G W approximations at weak coupling and the atomic limit at strong coupling. We apply it to the Hubbard model on two-dimensional square and triangular lattices. We complement the results of [T. Ayral and O. Parcollet, Phys. Rev. B 92, 115109 (2015), 10.1103/PhysRevB.92.115109] by (i) showing that, at half-filling, as DMFT, the method describes the Fermi-liquid metallic state and the Mott insulator, separated by a first-order interaction-driven Mott transition at low temperatures, (ii) investigating the influence of frustration, and (iii) discussing the influence of the bosonic decoupling channel.
Institute of Scientific and Technical Information of China (English)
Jiang Xue-Fan; Liu Xian-Feng; Wu Yin-Zhong; Han Jiu-Rong
2012-01-01
The magnetic and electronic properties of the geometrically frustrated triangular antiferromagnet CuCrO2 are investigated by first principles through density functional theory calculations within the generalized gradient approximations (GGA)+U scheme.The spin exchange interactions up to the third nearest neighbours in the ab plane as well as the coupling between adjacent layers are calculated to examine the magnetism and spin frustration.It is found that CuCrO2 has a natural two-dimensional characteristic of the magnetic interaction.Using Monte-Carlo simulation,we obtain the Néel temperature to be 29.9 K,which accords well with the experimental value of 24 K.Based on noncollinear magnetic structure calculations,we verify that the incommensurate spiral-spin structure with (110) spiral plane is believable for the magnetic ground state,which is consistent with the experimental observations.Due to intra-layer geometric spin frustration,parallel helical-spin chains arise along the a,b,or a + b directions,each with a screw-rotation angle of about 120°.Our calculations of the density of states show that the spin frustration plays an important role in the change of d-p hybridization,while the spin-orbit coupling has a very limited influence on the electronic structure.
Directory of Open Access Journals (Sweden)
Arima T.
2013-03-01
Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.
International Nuclear Information System (INIS)
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 (Δ) and magnetic field (H), where Δ=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 ms=(mA−mB)/2 and total m=(mA+mB)/2 magnetizations are numerically calculated, where in the limit of ms→0 the critical line TN(H,Δ) is obtained. The phase diagram in the T−H plane is discussed as a function of the parameter Δ for all values of H∈[0,Hc(Δ)], where Hc(Δ) correspond the critical field (TN=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=Hc(Δ)≥Hc(Δ=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of Δ∈[0,1]. This reentrant behavior increases with increase of the anisotropy parameter Δ. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: ► In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. ► Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. ► We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.
Palii, Andrei V; Reu, Oleg S; Ostrovsky, Sergei M; Klokishner, Sophia I; Tsukerblat, Boris S; Sun, Zhong-Ming; Mao, Jiang-Gao; Prosvirin, Andrey V; Zhao, Han-Hua; Dunbar, Kim R
2008-11-01
In this article we report for the first time experimental details concerning the synthesis and full characterization (including the single-crystal X-ray structure) of the spin-canted zigzag-chain compound [Co(H2L)(H2O)]infinity [L = 4-Me-C6H4-CH2N(CPO3H2)2], which contains antiferromagnetically coupled, highly magnetically anisotropic Co(II) ions with unquenched orbital angular momenta, and we also propose a new model to explain the single-chain magnet behavior of this compound. The model takes into account (1) the tetragonal crystal field and the spin-orbit interaction acting on each Co(II) ion, (2) the antiferromagnetic Heisenberg exchange between neighboring Co(II) ions, and (3) the tilting of the tetragonal axes of the neighboring Co units in the zigzag structure. We show that the tilting of the anisotropy axes gives rise to spin canting and consequently to a nonvanishing magnetization for the compound. In the case of a strong tetragonal field that stabilizes the orbital doublet of Co(II), the effective pseudo-spin-1/2 Hamiltonian describing the interaction between the Co ions in their ground Kramers doublet states is shown to be of the Ising type. An analytical expression for the static magnetic susceptibility of the infinite spin-canted chain is obtained. The model provides an excellent fit to the experimental data on both the static and dynamic magnetic properties of the chain. PMID:18839950
Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality
Wölfle, Peter; Abrahams, Elihu
2016-02-01
We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.
Mi, Bin-Zhou
2016-07-01
The thermodynamic properties of the frustrated arbitrary spin-S J1-J2 Heisenberg antiferromagnet on the body-centered-cubic lattice for Néel phase are systematically calculated by use of the double-time Green's function method within the random phase approximation (RPA). The role of spin quantum number and frustration strength on sublattice magnetization, Néel temperature, internal energy, and free energy are carefully analyzed. The curve of zero-temperature sublattice magnetization / S versus frustration strength J2/J1 values are almost flat at the larger spin quantum number S=10. With the increase of normalized temperature T/TN, the larger the spin quantum number S, the faster the / S drops, and the smaller influence of J2/J1 on the / S versus T/TN curve. Under the RPA approach, the Néel temperature TN /Sp and the internal energy E/Sp at the Néel point are independent of spin quantum number S. The numerical results show that the internal energy E/Sp at the Néel point seems independent of the frustration strength J2/J1. This indicates that thermodynamic quantities have universal characteristics for large spin quantum number.
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
Sandratskii, Leonid M.; Buczek, Paweł
2011-01-01
The study of the spin excitations in antiferromagnetic (AFM) and ferromagnetic (FM) phases of FeRh is reported. We demonstrate that although the Fe atomic moments are well defined there is a number of important phenomena absent in the Heisenberg description: Landau damping of spin waves, large Rh moments induced by the AFM magnons, the formation of the optical magnons terminated by Stoner excitations. We relate the properties of the spin-wave damping to the features of the Stoner continuum an...
Spin fluctuations and unconventional superconducting pairing in iron-based superconductors
Institute of Scientific and Technical Information of China (English)
Yu Shun-Li; Li Jian-Xin
2013-01-01
In this article,we review the recent theoretical works on the spin fluctuations and superconductivity in iron-based superconductors.Using the fluctuation exchange approximation and multi-orbital tight-binding models,we study the characteristics of the spin fluctuations and the symmetries of the superconducting gaps for different iron-based superconductors.We explore the systems with both electron-like and hole-like Fermi surfaces (FS) and the systems with only the electronlike FS.We argue that the spin-fluctuation theories are successful in explaining at least the essential part of the problems,indicating that the spin fluctuation is the common origin of superconductivity in iron-based superconductors.
Energy Technology Data Exchange (ETDEWEB)
Adelnia, Fatemeh [Dipartimento di Fisica, Università degli Studi di Milano and INSTM, I-20133 Milano (Italy); Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia (Italy); Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano [Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma (Italy); Ghirri, Alberto; Candini, Andrea [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Cervetti, Christian [Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Evangelisti, Marco [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain); Affronte, Marco [CNR Institute Nanosciences S3, I- 41125 Modena (Italy); Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy); Sheikin, Ilya [Grenoble High Magnetic Field Laboratory, CNRS-LNCMI, 25, B.P. 166, 38042 Grenoble Cedex 9 (France); Winpenny, Richard; Timco, Grigore [The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester (United Kingdom); Borsa, Ferdinando [Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia (Italy); and others
2015-12-28
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr{sub 8}Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ{sub 0}H{sub c1} = 2.15 T is found to be an almost true LC while the second LC at μ{sub 0}H{sub c2} = 6.95 T has an anti-crossing gap of Δ{sub 12} = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ{sub 0}H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10{sup 10} rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
International Nuclear Information System (INIS)
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering
Adelnia, Fatemeh; Chiesa, Alessandro; Bordignon, Sara; Carretta, Stefano; Ghirri, Alberto; Candini, Andrea; Cervetti, Christian; Evangelisti, Marco; Affronte, Marco; Sheikin, Ilya; Winpenny, Richard; Timco, Grigore; Borsa, Ferdinando; Lascialfari, Alessandro
2015-12-01
A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr8Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ0Hc1 = 2.15 T is found to be an almost true LC while the second LC at μ0Hc2 = 6.95 T has an anti-crossing gap of Δ12 = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ0H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ˜ 1010 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.
Hanle effect in (In,Ga)As quantum dots: Role of nuclear spin fluctuations
Kuznetsova, M. S.; Flisinski, K.; Gerlovin, I. Ya.; Ignatiev, I. V.; Kavokin, K. V.; Verbin, S. Yu.; Yakovlev, D. R.; Reuter, D; Wieck, A. D.; Bayer, M.
2013-01-01
The role of nuclear spin fluctuations in the dynamic polarization of nuclear spins by electrons is investigated in (In,Ga)As quantum dots. The photoluminescence polarization under circularly polarized optical pumping in transverse magnetic fields (Hanle effect) is studied. A weak additional magnetic field parallel to the optical axis is used to control the efficiency of nuclear spin cooling and the sign of nuclear spin temperature. The shape of the Hanle curve is drastically modified with cha...
Li, Yuesheng; Liao, Haijun; Zhang, Zhen; Li, Shiyan; Jin, Feng; Ling, Langsheng; Zhang, Lei; Zou, Youming; Pi, Li; Yang, Zhaorong; Wang, Junfeng; Wu, Zhonghua; Zhang, Qingming
2015-11-01
Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ -4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.
Superconductivity and Antiferromagnetism in Quasi-one-dimensional Organic Conductors
Dupuis, N.; Bourbonnais, C.; Nickel, J. C.
2005-01-01
We review the current understanding of superconductivity in the quasi-one-dimensional organic conductors of the Bechgaard and Fabre salt families. We discuss the interplay between superconductivity, antiferromagnetism, and charge-density-wave fluctuations. The connection to recent experimental observations supporting unconventional pairing and the possibility of a triplet-spin order parameter for the superconducting phase is also presented.
Quantum Monte Carlo simulation of antiferromagnetic spin ladder (C5H12N)2CuBr4
Freitas, Augusto S.
2016-07-01
In this paper I present a Quantum Monte Carlo (QMC) study of the magnetic properties of an antiferromagnetic spin ladder (C5H12N)2CuBr4. This compound is the prototype of the Heisenberg model for a two leg spin ladder in the presence of an external magnetic field. The susceptibility phase diagram has a rounded peak in the vicinity of T=7.4 K, obeys Troyer's law for low temperatures, and Curie's law for high temperatures. I also study the susceptibility diagram in low temperatures and I found the spin gap Δ=9.26 K, in good concordance with the experimental value, 9.5 K. In high field, I present a diagram of magnetization as a function of temperature. In the vicinity of a critical field, Hci, the magnetization scales with T1/2 and this result was found also in the QMC simulation. In all the results, there is a very good concordance with the experimental data. I also show in this paper that the spin gap is null and the susceptibility is proportional to T for low temperatures when relatively high values of the ladders' coupling is taken in account.
Energy Technology Data Exchange (ETDEWEB)
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.
Ordered Phase in the Fermionized Heisenberg Antiferromagnet
Azakov, S.; Dilaver, M.; Oztas, A. M.
1999-01-01
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using saddle point approximation in path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into acc...
International Nuclear Information System (INIS)
The spin correlations ωrz, r=1,2,3, and the probability pN of finding a system in the Neel state for the antiferromagnetic ring Fe6III (the so-called 'small ferric wheel') are calculated. States with magnetization M=0 and total spin 0≤S≤15, labeled by two (out of four) one-dimensional irreducible representations (irreps) of the point symmetry group D6, are taken into account. This choice follows from importance of these irreps in analyzing low-lying states in each S multiplet. Taking into account the Clebsch-Gordan coefficients for coupling total spins of sublattices (SA=SB=(15/2)) the global Neel probability pN* can be determined. Dependences of these quantities on state energy (per bond and in the units of exchange integral J) and the total spin S are analyzed. Providing we have determined pN(S), etc., for other antiferromagnetic rings (Fe10, for instance) we could try to approximate results for the largest synthesized ferric wheel Fe18. Since thermodynamic properties of Fe6 have been investigated recently, in the present considerations they are not discussed, but only used to verify obtained values of eigenenergies. Numerical results are calculated with high precision using two main tools: (i) thorough analysis of symmetry properties including methods of algebraic combinatorics and (ii) multiple precision arithmetic library GMP. The system considered yields more than 45 000 basic states (the so-called Ising configurations), but application of the method proposed reduces this problem to 20-dimensional eigenproblem for the ground state (S=0). The largest eigenproblem has to be solved for S=4; its dimension is 60. These two facts (high precision and small resultant eigenproblems) confirm the efficiency and usefulness of such an approach, so it is briefly discussed here
Phenomenological lattice model for dynamic spin and charge fluctuations in the cuprates
Vojta, Matthias; Sachdev, Subir
2004-01-01
Motivated by recent neutron scattering experiments on the cuprate superconductors, we present a phenomenological framework describing the dynamics of collective spin excitations coupled to charge/bond order fluctuations. Our quantum lattice model contains two order parameter fields, and can capture spin excitations both in broken-symmetry states with static lattice modulations, as well as in homogeneous states where the charge/bond order is fluctuating. We present results for different types ...
Effects of quantum zero-point spin fluctuations on the ground state of plutonium
Ratnikov, P. V.; Solontsov, A.
2013-01-01
The magnetic stability of {\\delta}-plutonium is analyzed taking into account zero-point spin fluctuations. Within the generalized theory of spin fluctuations described within a simple phenomenological model neglecting its spatial dispersion we show that zero-point local magnetic moments are giant (at.Pu) and suppress the magnetic order predicted by ab initio calculations resulting in the observed paramagnetic state of {\\delta}-plutonium.
International Nuclear Information System (INIS)
Nuclear resonance investigations on the 23Na and the 139La nuclei in filled skutterudites MFe4Sb12 (M=Na, La) are reported. In contrast to NaFe4Sb12 for the La compound the effective magnetic moment is remarkably lower and the Curie-Weiss temperature is negative which indicates antiferromagnetic correlations. The spin-lattice relaxation rates 1/T1 exhibit a qualitatively different temperature behavior which provides clear evidence for dissimilar types of itinerant magnetism in the two compounds. For NaFe4Sb12 1/T1 vs. T indicates itinerant ferromagnetism with ordering at Tc=85K, whereas for the La0.9Fe4Sb12 weak itinerant antiferromagnetism with no ordering is found. 1/T1 is analyzed in terms of Moriya's self-consistent renormalization theory (SCR) for itinerant magnetic materials
Suppression of spin fluctuations in TiBe2 by high magnetic fields
International Nuclear Information System (INIS)
Measurement of the low-temperature specific heat of a well-characterized 15.6-mg sample of TiBe2 was performed in magnetic fields of 0, 6.5, 11.4, 14.2, and 17.0 T. The results indicate a striking depression of the spin-fluctuation-caused upturn with increasing field in the lower-temperature specific heat and very little change at higher temperatures where the spin fluctuations are less predominant. A field for full suppression of the spin fluctuations is extrapolated to be above about 25 T. The field at which the onset of spin-fluctuation depression occurs is 5.2 +- 0.3 T, suggesting that the previously observed anomalies in the susceptibility and differential susceptibility of TiBe2 at 5.5 T are connected to the onset of the depression of spin fluctuations. Furthermore, this onset of spin-fluctuation depression at 5.2 +- 0.3 T coupled with the extrapolation to full suppression above 25 T serves to unify the interpretations of previous data on TiBe2 by Wohlfarth, by Acker et al., and by van Deursen et al. which were previously thought to be in contradiction
Melnikov, N. B.; Reser, B. I.; Paradezhenko, G. V.
2016-08-01
To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.
Sandratskii, Leonid M.; Buczek, Paweł
2012-01-01
The study of the spin excitations in antiferromagnetic (AFM) and ferromagnetic (FM) phases of FeRh is reported. We demonstrate that, although the Fe atomic moments are well defined, there is a number of important phenomena absent in the Heisenberg description: Landau damping of spin waves, large Rh moments induced by the AFM magnons, and the formation of the optical magnons terminated by Stoner excitations. We relate the properties of the spin-wave damping to the features of the Stoner continuum and compare the chirality of the spin excitations in AFM, FM, and paramagnetic systems.
Sadeghi, Azam; Alaei, Mojtaba; Shahbazi, Farhad; Gingras, Michel J. P.
2015-04-01
FeF3, with its half-filled Fe3 +3 d orbital, hence zero orbital angular momentum and S =5 /2 , is often put forward as a prototypical highly frustrated classical Heisenberg pyrochlore antiferromagnet. By employing ab initio density functional theory, we obtain an effective spin Hamiltonian for this material. This Hamiltonian contains nearest-neighbor antiferromagnetic Heisenberg, biquadratic, and Dzyaloshinskii-Moriya interactions as dominant terms and we use Monte Carlo simulations to investigate the nonzero temperature properties of this minimal model. We find that upon decreasing temperature, the system passes through a Coulomb phase, composed of short-range correlated coplanar states, before transforming into an "all-in/all-out" (AIAO) state via a very weakly first-order transition at a critical temperature Tc≈22 K, in good agreement with the experimental value for a reasonable set of Coulomb interaction U and Hund's coupling JH describing the material. Despite the transition being first order, the AIAO order parameter evolves below Tc with a power-law behavior characterized by a pseudo "critical exponent" β ≈0.18 in accord with experiment. We comment on the origin of this unusual β value.
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.
DEFF Research Database (Denmark)
Clarke, S.J.; Harrison, A.; Mason, T.E.; Visser, D.
1999-01-01
Copper(II) formate tetrahydrate (CFTH) is a model square S = 1/2 Heisenberg antiferromagnet with T-N = 16.54 +/- 0.05 K. The dispersion of spin-waves in the magnetic layers of a fully deuterated sample of this material has been mapped at 4.3 K by inelastic neutron scattering from the zone centre at...
International Nuclear Information System (INIS)
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem−3O3m+3 Aurivillius compounds with m=4–8 were studied using X-ray diffraction, 57Fe Mössbauer spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2 K while in the compound with m=5 the antiferromagnetic type transition was observed at 11 K. In the case of compounds with m=6–8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350 K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5–8. - Highlights: • Aurivillius compounds prepared by solid-state sintering. • Coexistence of antiferromagnetic and paramagnetic phases seen by Mössbauer spectra. • Hyperfine interactions parameters of compounds determined. • Antiferromagnetic spin glass-like ordering observed down to 10 K
Spin fluctuations in iron based superconductors probed by NMR relaxation rate
Energy Technology Data Exchange (ETDEWEB)
Graefe, Uwe; Kuehne, Tim; Wurmehl, Sabine; Buechner, Bernd; Grafe, Hans-Joachim [IFW Dresden, Institute for Solid State Research, PF 270116, 01171 Dresden (Germany); Hammerath, Franziska [IFW Dresden, Institute for Solid State Research, PF 270116, 01171 Dresden (Germany); Department of Physics ' ' A. Volta' ' , University of Pavia-CNISM, I-27100 Pavia (Italy); Lang, Guillaume [3LPEM-UPR5, CNRS, ESPCI Paris Tech, 10 Rue Vauquelin, 75005 Paris (France)
2013-07-01
We present {sup 75}As nuclear magnetic resonance (NMR) results in F doped LaOFeAs iron pnictides. In the underdoped superconducting samples, pronounced spin fluctuations lead to a peak in the NMR spin lattice relaxation rate, (T{sub 1}T){sup -1}. The peak shows a typical field dependence that indicates a critical slowing of spin fluctuations: it is reduced in height and shifted to higher temperatures. In contrast, a similar peak in the underdoped magnetic samples at the ordering temperature of the spin density wave does not show such a field dependence. Furthermore, the peak is absent in optimally and overdoped samples, suggesting the absence of strong spin fluctuations. Our results indicate a glassy magnetic ordering in the underdoped samples that is in contrast to the often reported Curie Weiss like increase of spin fluctuations towards T{sub c}. Additional measurements of the linewidth and the spin spin relaxation rate are in agreement with such a glassy magnetic ordering that is most likely competing with superconductivity. Our results will be compared to Co doped BaFe{sub 2}As{sub 2}, where a similar peak in (T{sub 1}T){sup -1} has been observed.
Spin fluctuations in iron based superconductors probed by NMR relaxation rate
International Nuclear Information System (INIS)
We present 75As nuclear magnetic resonance (NMR) results in F doped LaOFeAs iron pnictides. In the underdoped superconducting samples, pronounced spin fluctuations lead to a peak in the NMR spin lattice relaxation rate, (T1T)-1. The peak shows a typical field dependence that indicates a critical slowing of spin fluctuations: it is reduced in height and shifted to higher temperatures. In contrast, a similar peak in the underdoped magnetic samples at the ordering temperature of the spin density wave does not show such a field dependence. Furthermore, the peak is absent in optimally and overdoped samples, suggesting the absence of strong spin fluctuations. Our results indicate a glassy magnetic ordering in the underdoped samples that is in contrast to the often reported Curie Weiss like increase of spin fluctuations towards Tc. Additional measurements of the linewidth and the spin spin relaxation rate are in agreement with such a glassy magnetic ordering that is most likely competing with superconductivity. Our results will be compared to Co doped BaFe2As2, where a similar peak in (T1T)-1 has been observed.
Spin-glass, antiferromagnetism and Kondo behavior in Ce2Au1-CoSi3 alloys
Indian Academy of Sciences (India)
Subham Majumdar; E V Sampathkumaran; St Berger; M Della Mea; H Michor; E Bauer; M Brando; J Hemberger; A Loidl
2002-05-01
Recently, the solid solution Ce2Au1-CoSi3 has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce2AuSi3, ac susceptibility () and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce2AuSi3 lies at the left-hand side of the maximum in Doniach’s magnetic phase diagram. The ac data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.
Exact ground and excited states of an antiferromagnetic quantum spin model
International Nuclear Information System (INIS)
A quasi-one-dimensional spin model which consists of a chain of octahedra of spins has been suggested for which a certain parameter regime of the Hamiltonian, the ground state, can be written down exactly. The ground state is highly degenerate and can be other than a singlet. Also, several excited states can be constructed exactly. The ground state is a local RVB state for which resonance is confined to rings of spins. Some exact numerical results for an octahedron of spins have also been reported. (author). 16 refs, 2 figs, 1 tab
Disorder effects in the S=1 antiferromagnetic spin ladder CaV{sub 2}O{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Guitarra, S.R. [Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Quito (Ecuador); Caneiro, A. [Instituto Balseiro - Centro Atómico Bariloche, 8400 Bariloche (Argentina); Niebieskikwiat, D., E-mail: dniebieskikwiat@usfq.edu.ec [Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Quito (Ecuador)
2015-10-15
We study the physical properties of the antiferromagnetic spin ladder CaV{sub 2}O{sub 4} (CVO) and the Y-doped related compound Ca{sub 0.9}Y{sub 0.1}V{sub 2}O{sub 4}. In the latter, X-ray diffraction demonstrates the segregation of a small amount of a vanadium–perovskite impurity phase, leading to the formation of V vacancies within the main CVO-type structure. The 1D character of this calcium–vanadite enhances the influence of the vacancies on the electric and magnetic properties of Ca{sub 0.9}Y{sub 0.1}V{sub 2}O{sub 4}. Electrical transport is characterized by a variable-range hopping mechanism determined by the charging energy of nm-sized segments of V chains delimited by V vacancies, i.e. a Coulomb gap is formed at the Fermi level. These vacancies also locally affect the magnetic correlations, breaking the long-range AFM order observed in CaV{sub 2}O{sub 4} and producing exchange bias when the Y-doped sample is cooled with an applied magnetic field. - Highlights: • We study disorder effects in the quasi-1D antiferromagnetic spin ladder CaV{sub 2}O{sub 4}. • V vacancies in CaV{sub 2}O{sub 4} lead to variable-range hopping electrical transport. • The charging energy of nm-sized V chains determine the transport mechanism exponents. • V vacancies break the long-range AFM order of CaV{sub 2}O{sub 4}. • Local magnetic correlations in the vicinity of the defects produce exchange bias.
Mukai, Y; Yamamoto, T; Kageyama, H; Tanaka, K
2016-01-01
We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (~40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics.
Néel Temperature of Antiferromagnets for Phase Transitions Driven by Spin-wave Interactions
Ayuela, Andrés; Klein, Douglas J.; March, Norman H.
2013-01-01
In a recent article,1 a wide variety of phase transitions, with transition (t) temperature Tt , were shown to be usefully characterized by the form kBTt Echar exp1/ λ where λ measured the strength of the quasiparticle interactions driving the phase transition. The present article is concerned primarily with antiferromagnets (AFs) having Néel temperature TN. It is first argued that the characteristic energy Echar can be usefully represented by kBθ, where θ is the Curie-Weiss ...
Spintronics of antiferromagnetic systems
International Nuclear Information System (INIS)
Spintronics of antiferromagnetics is a new field that has developed in a fascinating research topic in physics of magnetism. Antiferromagnetics, like ferromagnetic materials experience the influence of spin-polarized current, even though they show no macroscopic magnetization. The mechanism of this phenomenon is related to spin-dependent interaction between free and localized electrons-sd-exchange. Due to the peculiarities of antiferromagnetic materials (complicated magnetic structure, essential role of the exchange interactions, lack of macroscopic magnetization) spintronics of antiferromagnets appeals to new theoretical and experimental approaches. The purpose of this review is to systemize and summarize the recent progress in this field. We start with a short introduction into the structure and dynamics of antiferromagnets and proceed with discussion of different microscopic and phenomenological theories for description of current-induced phenomena in ferro-/antiferromagnetic heterostructures. We also consider the problems of the reverse influence of antiferromagnetic ordering on current, and effectiveness of the fully antiferromagnetic spin valve. In addition, we shortly review and interpret the available experimental results.
Spin exchange and superconductivity in a $t-J'-V$ model for two-dimensional quarter-filled systems
Greco, Andres; Merino, Jaime; Foussats, Adriana; McKenzie, Ross H.
2004-01-01
The effect of antiferromagnetic spin fluctuations on two-dimensional quarter-filled systems is studied theoretically. An effective $t-J'-V$ model on a square lattice which accounts for checkerboard charge fluctuations and next-nearest-neighbors antiferromagnetic spin fluctuations is considered. From calculations based on large-N theory on this model it is found that the exchange interaction, $J'$, increases the attraction between electrons in the d$_{xy}$ channel only, so that both charge and...
Evolution from antiferromagnetic order to spin-glass state in Fe1.05−xCuxTe system
International Nuclear Information System (INIS)
Well understanding about the physical properties of FeTe compound, as a parent of superconducting Fe(Te, Se) system, is very important for exploring superconducting mechanism in the Fe-based superconductors. Here, based on the transport and magnetization measurements, we report the Cu doping effects on the physical properties of Fe1.05Te compound. We found that in the undoped sample, an antiferromagnetic (AFM) transition accompanying a semiconductor–metal transition occurs at 70 K. With the increase of Cu content x, the AFM transition temperature decreases monotonously at first. When x⩾0.05, both the metallic behavior and long-range AFM ordering disappear. Meanwhile, a spin-glass state emerges at low temperatures. The evolution of the transport and the magnetic properties with the Cu content x is summarized and a phase diagram is proposed. Our results indicate that a local spin picture may be more appropriate than an itinerant model for the Fe1.05Te compound.
Soh, J. H.; Tucker, G. S.; Pratt, D. K.; Abernathy, D. L.; Stone, M. B.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.
2013-11-01
The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.
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.
Zero-Temperature Fluctuations in Short-Range Spin Glasses
Arguin, L.-P.; Newman, C. M.; Stein, D. L.; Wehr, J.
2016-06-01
We consider the energy difference restricted to a finite volume for certain pairs of incongruent ground states (if they exist) in the d-dimensional Edwards-Anderson Ising spin glass at zero temperature. We prove that the variance of this quantity with respect to the couplings grows proportionally to the volume in any d ≥ 2. An essential aspect of our result is the use of the excitation metastate. As an illustration of potential applications, we use this result to restrict the possible structure of spin glass ground states in two dimensions.
Quantum narrowing effect in a spin-Peierls system with quantum lattice fluctuation
International Nuclear Information System (INIS)
We investigate a one-dimensional S=1/2 antiferromagnetic Heisenberg model coupled to quantum lattice vibration using a quantum Monte Carlo method. We study the ground-state lattice fluctuation where the system shows a characteristic structure factor. We also study the mass dependence of magnetic properties such as the magnetic susceptibility and the magnetic excitation spectrum. For heavy mass, the system shows the same behavior as the case of classical lattice vibration. On the other hand, for light mass, magnetic properties coincide with those of the static uniform chain. We investigate the physical mechanism of this behavior and propose the picture of quantum narrowing. (author)
Hu, Lin; Wu, Xiaojun; Yang, Jinlong
2016-07-14
To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ∼3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm(2) V(-1) s(-1) in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is larger than those of pure metals, such as Fe, Co, and Ni. These advantages render 2D Mn2C sheet with great potential applications in nanometer-scale antiferromagnetic spintronics. PMID:27304676
Reggiani, N.; Guzzo, M. M.; Colonia, J. H.; de Holanda, P. C.
1998-01-01
Taking into account the stringent limits from helioseismology observations on possible matter density fluctuations described by magnetohydrodynamics theory, we find the corresponding time variations of solar neutrino survival probability due to the resonant spin-flavor precession phenomenon with amplitude of order O(10%). We discuss the physics potential of high statistics real time experiments, like as Superkamiokande, to observe the effects of such magnetohydrodynamics fluctuations on their...
Self-energy of spin-fluctuation-mediated superconductors: Inconsistency against ARPES for cuprates
Energy Technology Data Exchange (ETDEWEB)
Hong, Seung Hwan; Bok, Jin Mo [Department of Physics and Institute for Basic Science Research, SungKyunKwan University, Suwon 440-746 (Korea, Republic of); Choi, Han-Yong, E-mail: hychoi@skku.ac.kr [Department of Physics and Institute for Basic Science Research, SungKyunKwan University, Suwon 440-746 (Korea, Republic of); Asia Pacific Center for Theoretical Physics, Pohang 790-784 (Korea, Republic of)
2013-10-15
Highlights: • The angle and frequency dependence of the self-energy can be deduced from ARPES analysis. • It can also be calculated from the Eliashberg equation using the spin fluctuation spectrum from inelastic neutron scatterings. • Comparison between the self-energies from the APRES and INS are not consistent. • The spin fluctuations may not be responsible for the quasiparticle dynamics in the cuprate superconductors. -- Abstract: We perform a consistency check of the spin-fluctuation-mediated d-wave pairing against the angle resolved photoemission spectroscopy (ARPES) for the cuprate superconductors. Using the inelastic neutron scattering (INS) spin susceptibility spectrum reported by Vignolle et al. in the Eliashberg equation, we calculate the self-energy of the quasi-particles for the optimally doped La{sub 2−x}Sr{sub x}CuO{sub 4}. The self-energy can also be deduced by analyzing the ARPES intensity. The angle and frequency dependence of the calculated diagonal self-energy from the spin fluctuations does not seem to be consistent with that deduced from ARPES.
International Nuclear Information System (INIS)
We have studied the dynamics of Tb spins in the intermetallic compound TbNiAl in the paramagnetic (pm) and ordered antiferromagnetic (afm) phases by means of neutron time-of-flight and spin-echo spectroscopy. It is a remarkable and very unusual characteristic of TbNiAl that its afm phase (below TN=47 K) contains regular long-range ordered spins as well as frustrated spins. The latter are identified by a strongly reduced moment measured by neutron diffraction. The new quasielastic measurements show that the frustrated moments relax on a time scale of 0.01 ns to 0.1 ns. Their autocorrelation function I(q,t) is q independent and exponential in time. While in the pm phase the spin relaxation is complete, i.e., I(q,t) goes to zero in the time range of the measurement, in the afm phase I(q,t) stays above zero
Magnetic excitations in one-dimensional spin-orbital models
Herzog, A; Oles, A.M.; Horsch, P.; Sirker, J.
2011-01-01
We study the dynamics and thermodynamics of one-dimensional spin-orbital models relevant for transition metal oxides. We show that collective spin, orbital, and combined spin-orbital excitations with infinite lifetime can exist, if the ground state of both sectors is ferromagnetic. Our main focus is the case of effectively ferromagnetic (antiferromagnetic) exchange for the spin (orbital) sector, respectively, and we investigate the renormalization of spin excitations via spin-orbital fluctuat...
Yannouleas, Constantine; Brandt, Benedikt B.; Landman, Uzi
2016-07-01
Advances with trapped ultracold atoms intensified interest in simulating complex physical phenomena, including quantum magnetism and transitions from itinerant to non-itinerant behavior. Here we show formation of antiferromagnetic ground states of few ultracold fermionic atoms in single and double well (DW) traps, through microscopic Hamiltonian exact diagonalization for two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells, and (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D, nature. The spectra and spin-resolved conditional probabilities reveal for both cases, under strong repulsion, atomic spatial localization at extemporaneously created sites, forming quantum molecular magnetic structures with non-itinerant character. These findings usher future theoretical and experimental explorations into the highly correlated behavior of ultracold strongly repelling fermionic atoms in higher dimensions, beyond the fermionization physics that is strictly applicable only in the 1D case. The results for four atoms are well described with finite Heisenberg spin-chain and cluster models. The numerical simulations of three fermionic atoms in symmetric DWs reveal the emergent appearance of coupled resonating 2D Heisenberg clusters, whose emulation requires the use of a t–J-like model, akin to that used in investigations of high T c superconductivity. The highly entangled states discovered in the microscopic and model calculations of controllably detuned, asymmetric, DWs suggest three-cold-atom DW quantum computing qubits.
Energy Technology Data Exchange (ETDEWEB)
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.
International Nuclear Information System (INIS)
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
Random antiferromagnetic quantum spin chains: Exact results from scaling of rare regions
Igloi, F.; Juhasz, R.; Rieger, H.
1999-01-01
We study XY and dimerized XX spin-1/2 chains with random exchange couplings by analytical and numerical methods and scaling considerations. We extend previous investigations to dynamical properties, to surface quantities and operator profiles, and give a detailed analysis of the Griffiths phase. We present a phenomenological scaling theory of average quantities based on the scaling properties of rare regions, in which the distribution of the couplings follows a surviving random walk character...
Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core
Berthod, C.
2015-12-01
In copper- and iron-based unconventional superconductors, the Bogoliubov quasiparticles interact with a spin resonance at momentum (π ,π ) . This interaction is revealed by specific signatures in the quasiparticle spectroscopies, like kinks in photoemission and dips in tunneling. We study these signatures, as they appear inside and around a vortex core in the local density of states (LDOS), a property accessible experimentally by scanning tunneling spectroscopy. Our model retains the whole nonlocal structure of the self-energy in space and time and is therefore not amenable to a Hamiltonian treatment using Bogoliubov-de Gennes equations. The interaction with the spin resonance does not suppress the zero-bias peak at the vortex center, although it reduces its spectral weight; neither does it smear out the vortex LDOS, but rather it adds structure to it. Some of the signatures we find may have been already measured in FeSe, but remained unnoticed. We compare the LDOS as a function of both energy and position with and without coupling to the spin resonance and observe, in particular, that the quasiparticle interference patterns around the vortex are strongly damped by the coupling. We study in detail the transfer of spectral weight induced both locally and globally by the interaction and also by the formation of the vortex. Finally, we introduce a new way of imaging the quasiparticles in real space, which combines locality and momentum-space sensitivity. This approach allows one to access quasiparticle properties that are not contained in the LDOS.
Magnetic fluctuations in heavy-fermion metals
DEFF Research Database (Denmark)
Mason, T.E.; Petersen, T.; Aeppli, G.; Buyers, W.J.L.; Bucher, E.; Garrett, J.D.; Clausen, K.N.; Menovsky, A.A.
Elastic and inelastic neutron scattering have been used to study the antiferromagnetic ordering and magnetic excitations of the U heavy-fermion superconductors UPd2Al3 and URu2Si2 above and below T-N. While both materials exhibit the coexistence of superconductivity and antiferromagnetic order, the...... nature of the antiferromagnetic order and magnetic fluctuations is qualitatively quite different. UPd2Al3 resembles a rare earth magnetic system with coupling of the 4f electrons to the conduction electrons manifested in a broadening of otherwise conventional spin wave excitations. This is in marked...
Unusual spin dynamics in the doped antiferromagnetic phase of YBa2(Cu0.98Zn0.02)3O6.39
International Nuclear Information System (INIS)
Inelastic neutron scattering experiments have been carried out on a YBa2(Cu0.98Zn0.02)3O6.39 single crystal to investigate the spin-excitation spectrum in the hole-doped antiferromagnetic state. New excitations are found at low energy as a consequence of electron-hole interactions, whereas standard magnons are recovered at sufficiently high energy. (orig.)
Kim, MinJae; Kim, Beom Hyun; Choi, Hong Chul; B. I. Min
2009-01-01
KO2 exhibits concomitant antiferromagnetic (AFM) and structural transitions, both of which originate from the open-shell 2p electrons of O$_{2}^{-}$ molecules. The structural transition is accompanied by the coherent tilting of O$_{2}^{-}$ molecular axes. The interplay among the spin-orbital-lattice degrees of freedom in KO2 is investigated by employing the first-principles electronic structure theory and the kinetic-exchange interaction scheme. We have shown that the insulating nature of the...
International Nuclear Information System (INIS)
The exactly integrable isotropic Heisenberg chain of N spins s is studied, and numerical solutions to the Bethe ansatz equations corresponding to the antiferromagnetic vacuum (for sN ≤ 128) and the simplest excitations have been obtained. For s = 1, a complete set of states for N = 6 is given, and the vacuum solution for finite N is estimated analytically. The deviations from the string picture at large N are discussed
Spinon, soliton, and breather in the spin-1/2 antiferromagnetic chain compound KCuGaF6
Umegaki, Izumi; Tanaka, Hidekazu; Kurita, Nobuyuki; Ono, Toshio; Laver, Mark; Niedermayer, Christof; Rüegg, Christian; Ohira-Kawamura, Seiko; Nakajima, Kenji; Kakurai, Kazuhisa
2015-11-01
Elementary excitations of the S =1/2 one-dimensional antiferromagnet KCuGaF6 were investigated by inelastic neutron scattering in zero and finite magnetic fields perpendicular to the (1 ,1 ,0 ) plane combined with specific heat measurements. KCuGaF6 exhibits no long-range magnetic ordering down to 50 mK despite the large exchange interaction J /kB=103 K. At zero magnetic field, well-defined spinon excitations were observed. The energy of the des Cloizeaux and Pearson [J. des Cloizeaux and J. J. Pearson, Phys. Rev. 128, 2131 (1962), 10.1103/PhysRev.128.2131] mode of the spinon excitations is somewhat larger than that calculated with the above exchange constant. This discrepancy is mostly ascribed to the effective X Y anisotropy arising from the large Dzyaloshinsky-Moriya [T. Moriya, Phys. Rev. 120, 91 (1960), 10.1103/PhysRev.120.91] interaction with an alternating D vector. KCuGaF6 in a magnetic field is represented by the quantum sine-Gordon model, for which low-energy elementary excitations are composed of solitons and antisolitons and their bound states called breathers. Unlike the theoretical prediction, it was found that the energy of a soliton is smaller than that of the first breather, although the energy of the first breather coincides with that observed in a previous electron spin resonance measurement.
Spin fluctuations and dx2-y2 pairing in the cuprate superconductors: a progress report
International Nuclear Information System (INIS)
I present an overview of recent progress using a nearly antiferromagnetic Fermi liquid description of normal state behavior on three key issues for high temperature superconductivity in the cuprate superconductors: the physical characteristics and physical origin of the anomalous spin and charge behavior in the normal state; the mechanism for high temperature superconductivity, and the superconducting pairing state. I select four topics for detailed discussion: characterizing pseudogap and pseudoscaling behavior in the normal state; calculating magnetotransport in YBa2Cu3O7, demonstrating the relationship between the effective pairing potential for superconductivity and dx2-y2 pairing; and recent evidence for dx2-y2 pairing from NMR experiments on the Knight shift and the spin-echo decay time in YBa2Cu4O8. (orig.)
The fishnet as anti-ferromagnetic phase of world sheet Ising spins
International Nuclear Information System (INIS)
We identify the strong coupling fishnet diagram with a certain Ising spin configuration in the light cone world sheet description of planar TrPHI3 field theory. Then, using a mean field formalism, we take the remaining planar diagrams into account in an average way. Since the fishnet spin configuration is regular but non-uniform, we introduce two mean fields phi,phi' where the fishnet diagram is the case phi=1, phi'=0. For general values of these fields, the system is then approximated as a light-cone quantized string with a field dependent effective string tension Teff(phi,phi'). We also calculate the world sheet energy density E(phi,phi'), and find the field values that minimize it in the presence of a transverse space infra-red cutoff ε>0. The criterion for string formation is that the tension in this minimum energy state remains non-zero as ε→0. In the most simple-minded implementation of the mean field method, which neglects all short range correlations of the Ising spins, we find, in this limit, that the tension vanishes for weak and moderate coupling, but for very large coupling does indeed stay non-zero. However, a more elaborate treatment, taking temporal correlations into account (but still neglecting spatial correlations), removes this 'phase transition' and the string tension of the minimum energy state vanishes for all values of the coupling when ε→0. Our mean field analysis thus suggests that the 'fishnet phase' of TrPHI3 theory is unstable, and there is no string formation for any value of the coupling. This is probably a reasonable outcome given the instability of the underlying theory. It is encouraging for our method, that an approach designed for a string description can predict, where appropriate, the absence of string formation within an intuitive and simple approximation
Parente, Walter E. F.; Pacobahyba, J. T. M.; Araújo, Ijanílio G.; Neto, Minos A.; Ricardo de Sousa, J.
2015-11-01
We will study phase diagram the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii-Moriya interaction (D) and a uniform longitudinal (H) magnetic field, where we have observed an anomaly at low temperatures. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagram in the H - D plane on a simple cubic lattice (z=6). We analyzed the cases: anisotropic Heisenberg - case I: (Δ = 1), anisotropic Heisenberg - case II: (Δ = 0.5) and anisotropic Heisenberg - case III: (Δ = 0), where only second order phase transitions are observed.
Spin fluctuations and superconductivity in Mo.sub.3./sub.Sb.sub.7./sub..
Czech Academy of Sciences Publication Activity Database
Candolfi, C.; Lenoir, B.; Dauscher, A.; Bellouard, C.; Hejtmánek, Jiří; Šantavá, Eva; Tobola, J.
2007-01-01
Roč. 99, č. 3 (2007), 037006/1-037006/4. ISSN 0031-9007 Institutional research plan: CEZ:AV0Z10100521 Keywords : spin fluctuation s * paramagnons * superconductivity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.944, year: 2007
Doping dependence of spin fluctuations and electron correlations in iron pnictides
Czech Academy of Sciences Publication Activity Database
Ikeda, H.; Arita, R.; Kuneš, Jan
2010-01-01
Roč. 82, č. 2 (2010), 024508/1-024508/6. ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : iron pnicitdes * dynamic spin susceptibility * fluctuation- exchange approximation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010 http://prb.aps.org/abstract/PRB/v82/i2/e024508
Neutron scattering studies of three one-dimensional antiferromagnets
Kenzelmann, M
2001-01-01
observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...
Quantum lattice fluctuations in the ground state of an XY spin-Peierls chain
International Nuclear Information System (INIS)
An analytical approach, based on the unitary transformation method, has been developed to study the effect of quantum lattice fluctuations on the ground state of an XY spin-Peierls chain, which is equivalent to the spinless Su-Schrieffer-Heeger model in half-filling after the Jordan-Wigner transformation. We show that when the spin-phonon coupling constant α2/4K decreases or the phonon frequency ωπ increases the lattice dimerization and the gap in the fermion spectrum decrease gradually. At some critical value (α2/4K)c or ωπc, the system becomes gapless and the lattice dimerization disappears. This can be attributed to the fact that the ground state fails to develop the spin-Peierls long-range order because of the quantum lattice fluctuations. (author). 14 refs, 5 figs
Unusual Charge Transport and Spin Response of Doped Bilayer Triangular Antiferromagnets
Institute of Scientific and Technical Information of China (English)
LIANG Ying; MA Tian-Xing; FENG Shi-Ping
2003-01-01
Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.
International Nuclear Information System (INIS)
Highlights: • Magnetic glassy state of Pr117Co54.5Sn115.2 freezes at ∼11 K. • Glassy state coexists with short range antiferromagnetic order. • Antiferromagnetic clusters developed at ∼11 K. • Negative temperature coefficient semiconductor-like resistivity from 2 to 300 K. - Abstract: The magnetic properties of Pr117Co54.5Sn115.2 – a member of a family of materials with a giant unit cell – have been investigated by dc magnetization, ac magnetic susceptibility, specific heat, and electrical resistivity measurements. A magnetic glassy state at freezing temperature of ∼11 K was determined from the magnetic susceptibility and specific heat data. The glassy state in Pr117Co54.5Sn115.2 is not the conventional spin glass with randomly oriented magnetic moments, but it is related to clusters of atoms that exist in the complex crystal lattice of the material. Furthermore, the glassy state coexists with short range antiferromagnetic order, leading to the development of antiferromagnetic clusters. A weak anomaly in the specific heat data centered around 11 K supports the formation of magnetic cluster glass state in Pr117Co54.5Sn115.2. Semiconductor-like resistivity with a negative temperature coefficient from 2 to 300 K is also observed in Pr117Co54.5Sn115.2
Spin fluctuation in YBaFe4O7+δ with geometrically frustrated pyrochlore lattice of Fe spins
International Nuclear Information System (INIS)
Magnetic excitation spectra were measured by inelastic neutron scattering on a powder sample of YBaFe4O7+δ having a geometrically frustrated pyrochlore lattice of Fe spins. The observed scattering intensity map constructed in the energy ω–wave vector Q space has a streaklike magnetic contribution extending to a rather high-ω region at the Q position of Qp ∼ 1.25 Å-1, where the width κ and position Qp of the streak are found to be insensitive to both the temperature T and ω. These results indicate the existence of the short-time spin correlation of Fe hexagons in the pyrochlore lattice, and can be understood by considering the spin fluctuation arising from the purely frustrating nature of three-dimensional classical insulating systems. (author)
Antiferromagnets at Low Temperatures
International Nuclear Information System (INIS)
The low-temperature properties of the Heisenberg antiferromagnet in 2+1 space-time dimensions are analyzed within the framework of effective Lagrangians. It is shown that the magnon-magnon interaction is very weak and repulsive, manifesting itself through a term proportional to five powers of the temperature in the pressure. The structure of the low-temperature series for antiferromagnets in 2+1 dimensions is compared with the structure of the analogous series for antiferromagnets in 3+1 dimensions. The model-independent and systematic effective field theory approach clearly proves to be superior to conventional condensed matter methods such as spin-wave theory.
Energy Technology Data Exchange (ETDEWEB)
Gupta, Sachin, E-mail: gsachin55@gmail.com, E-mail: suresh@phy.iitb.ac.in; Suresh, K. G., E-mail: gsachin55@gmail.com, E-mail: suresh@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Das, A. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Nigam, A. K. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India); Hoser, A. [Helmholtz-Zentrum Berlin, Hahn-Meitner Platz 1, 14-109 Berlin (Germany)
2015-06-01
Polycrystalline NdCuSi is found to show co-existence of antiferromagnetic (AFM) and ferromagnetic (FM) phases at low temperatures, as revealed by neutron diffraction data. The coexistence is attributed to the competing exchange interactions and crystal field effect. The compound shows a large, low-field magnetoresistance (MR) of ∼ − 32% at 20 kOe below T{sub N} (3.1 K), which becomes ∼ − 36% at 50 kOe. The MR value at 50 kOe is found to be the highest among the RTX compounds. Magnetocaloric effect (MCE) is also found to show a large value of ∼11 J/kg K close to T{sub N}. Resistivity data show the presence of spin fluctuations, which get suppressed by the applied field. Large MR and MCE in this compound arise due to the coexistence of the two phases. The field dependencies of MR and MCE show quadratic behavior, confirming the presence of spin fluctuations.
Hu, Lin; Wu, Xiaojun; Yang, Jinlong
2016-06-01
To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ~3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm2 V-1 s-1 in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is larger than those of pure metals, such as Fe, Co, and Ni. These advantages render 2D Mn2C sheet with great potential applications in nanometer-scale antiferromagnetic spintronics.To realize antiferromagnetic spintronics in the nanoscale, it is highly desirable to identify new nanometer-scale antiferromagnetic metals with both high Néel temperature and large spin-orbit coupling. In this work, on the basis of first-principles calculation and particle swarm optimization (PSO) global structure search, we demonstrate that a two-dimensional Mn2C monolayer is an antiferromagnetic metal with a Mn magnetic moment of ~3μB. Mn2C monolayer has an anti-site structure of MoS2 sheet with carbon atoms hexagonally coordinated by neighboring Mn atoms. Remarkably, the in-plane carrier mobility of 2D Mn2C is highly anisotropic, amounting to about 47 000 cm2 V-1 s-1 in the a' direction, which is much higher than that of MoS2 monolayer. The Néel temperature of Mn2C monolayer is high up to 720 K. Due to strong spin-orbit coupling in plane, the magnetic anisotropy energy of Mn2C monolayer is
Large spin fluctuations and moment-volume coupling in Fe in an fcc environment
International Nuclear Information System (INIS)
Complete text of publication follows. Polarized paramagnetic neutron diffraction experiments show that the persisting ferromagnetic correlations above the Curie temperature and the associated magnetic moment of fcc Fe1-xNix alloys with x > 0.30 weaken with increasing temperature reflecting a temperature dependence of the band splitting. In alloys with x ≤ 0.30 the magnetic moment becomes more temperature insensitive and, as the pure Fe concentration is reached, it begins to increase with increasing temperature [1]. The observed property is attributed to a combination of effects arising from spin fluctuations pertinent to itinerant system and to moment-volume fluctuations arising from low-spin to high-spin transitions in systems incorporating a high concentration of fcc-Fe. The experiments are extended to broader fcc stability temperature ranges by using and Fe0.77Ni0.13Mn0.07C0.03 alloy and further and more clear evidence for the temperature driven low-spin to high-spin transitions is shown. (author) [1] M. Acet, E.F. Wassermann, K. Andersen, A. Murani and O. Schaerpf, Europhys. Lett., 40 (1997) 93
Quantum order by disorder in frustrated diamond lattice antiferromagnets
Bernier, Jean-Sebastien; Lawler, Michael J.; Kim, Yong Baek
2008-01-01
We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the N\\'eel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between $(k,k,0)$-spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc$_2$S$...
Pal, A.; Akintola, K.; Potma, M.; Ishikado, M.; Eisaki, H.; Hardy, W.N.; Bonn, D. A.; Liang, R; Sonier, J. E.
2016-01-01
We report low temperature muon spin relaxation (muSR) measurements of the high-transition-temperature (Tc) cuprate superconductors Bi{2+x}Sr{2-x}CaCu2O{8+\\delta} and YBa2Cu3O6.57, aimed at detecting the mysterious intra-unit cell (IUC) magnetic order that has been observed by spin polarized neutron scattering in the pseudogap phase of four different cuprate families. A lack of confirmation by local magnetic probe methods has raised the possibility that the magnetic order fluctuates slowly eno...
Simulation of Statistical Fluctuations in the Spin Precession Measurements at RHIC
International Nuclear Information System (INIS)
Measurements of the driven spin coherent precession Sx(t)=Sx^{(0)} - Sx^{(1)} sin(?t+?0) were initiated in RHIC Run13. The expected value of the precession amplitude Sx^{(1)} ~ 2 x 10-4 is about the statistical error in a single measurement and data fit gives a biased estimate of the Sx^{(1)}. For a proper statistical interpretation of the results of the several measurements, statistical fluctuations were studied using Monte-Carlo simulation. Preliminary results of the spin precession measurements in RHIC Run13 are presented.
Glass-like recovery of antiferromagnetic spin ordering in a photo-excited manganite Pr0.7Ca0.3MnO3
Energy Technology Data Exchange (ETDEWEB)
Zhou, S.Y.; Langner, M.C.; Zhu, Y.; Chuang, Y.-D.; Rini, M.; Glover, T.E.; Hertlein, M.P.; Gonzalez, A.G. Cruz; Tahir, N.; Tomioka, Y.; Tokura, Y.; Hussain, Z.; Schoenlein, R.W.
2014-01-16
Electronic orderings of charges, orbitals and spins are observed in many strongly correlated electron materials, and revealing their dynamics is a critical step toward understanding the underlying physics of important emergent phenomena. Here we use time-resolved resonant soft x-ray scattering spectroscopy to probe the dynamics of antiferromagnetic spin ordering in the manganite Pr0:7Ca0:3MnO3 following ultrafast photo-exitation. Our studies reveal a glass-like recovery of the spin ordering and a crossover in the dimensionality of the restoring interaction from quasi-1D at low pump fluence to 3D at high pump fluence. This behavior arises from the metastable state created by photo-excitation, a state characterized by spin disordered metallic droplets within the larger charge- and spin-ordered insulating domains. Comparison with time-resolved resistivity measurements suggests that the collapse of spin ordering is correlated with the insulator-to-metal transition, but the recovery of the insulating phase does not depend on the re-establishment of the spin ordering.
International Nuclear Information System (INIS)
UPt3 is a heavy-fermion superconductor with indications of coexisting long-range ferromagnetic spin fluctuations. Measurements of its specific heat at pressures of 0, 3.8, and 8.9 kbar between 0.35 and 20 K show that the spin-fluctuation terms are extremely sensitive to pressure: the linear term decreases by --25% at 8.9 kbar; the T3 and T3 lnT terms decrease by factors of the order of 4. Comparison with the pressure dependence of the critical temperature suggests that the superconductivity is of a form that is enhanced by spin fluctuations
Jartych, E.; Pikula, T.; Mazurek, M.; Lisinska-Czekaj, A.; Czekaj, D.; Gaska, K.; Przewoznik, J.; Kapusta, C.; Surowiec, Z.
2013-09-01
The structure, hyperfine interactions and magnetic properties of the series of multiferroic Bim+1Ti3Fem-3O3m+3 Aurivillius compounds with m=4-8 were studied using X-ray diffraction, 57Fe Mössbauer spectroscopy and vibrating sample magnetometry. Samples were prepared by the conventional solid-state sintering method. Bulk magnetic measurements showed that for m=4 the compound is paramagnetic down to 2 K while in the compound with m=5 the antiferromagnetic type transition was observed at 11 K. In the case of compounds with m=6-8 much more complex magnetic behavior was found. For these compounds a gradual spin freezing and antiferromagnetic spin glass-like ordering were observed on decreasing temperature. The temperature of spin glass freezing was determined as 260, 280 and 350 K for m=6, 7 and 8, respectively. Room-temperature Mössbauer spectra of all the compounds studied confirm their paramagnetic state. However, liquid nitrogen and liquid helium temperature measurements reveal magnetic ordering with a residual paramagnetic phase contribution for the compounds with m=5-8.
NMR evidence for spin fluctuations in underdoped LaO1-xFxFeAs
International Nuclear Information System (INIS)
We present 75As Nuclear Magnetic Resonance (NMR) measurements on the iron-based superconductor LaO1-xFxFeAs with 0 ≤ x ≤ 0.1, covering a broad range of the phase diagram from magnetically-ordered to optimally-doped superconducting samples. For underdoped samples (x=0.05,x=0.075) the 75As NMR spin-lattice relaxation rate (T1T)-1 shows a Curie-Weiss-like increase at intermediate temperatures, indicating the slowing down of spin fluctuations. However, a simple Curie-Weiss fit fails to describe (T1T)-1(T) above 250 K and the occurrence of a peak in (T1T)-1 slightly above Tc. Instead, the data can be well described by considering a BPP-model for fluctuating magnetic fields in combination with a doping-independent linear temperature dependence at high temperature. At optimal doping (x=0.1) spin fluctuations are suppressed and only the linear contribution to (T1T)-1 is left. This stands in contrast to other pnictides, such as Ba(Fe1-xCoxAs)2 and Ba(FeAs1-xPx)2. Our analysis is consistent with charge carrier localization in underdoped LaO1-xFxFeAs as seen by means of resistivity measurements.
International Nuclear Information System (INIS)
The temperature variation of the sublattice magnetization of the quadratic double-layer antiferromagnet K3Mn2F7 has been determined by measuring the NMR frequency of the 19F nuclei adjacent to the Mn sites in the double-layer. The data have been analyzed in terms of a two-dimensional four-sublattice spin-wave theory with inclusion of temperature-dependent and temperature-independent renormalization as formulated by Oguchi, as well as temperature variation of the k = 0 energy gap, and with exact integration over the Brillouin zone
Antiferromagnetic crystalline topological insulators
LIU, CHAO-XING
2013-01-01
The gapless surface Dirac cone of time reversal invariant topological insulators is protected by time reversal symmetry due to the Kramers' theorem. Spin degree of freedom is usually required since Kramers' theorem only guarantees double degeneracy for spinful fermions, but not for spinless fermions. In this paper, we present an antiferromagnetic spinless model, which breaks time reversal symmetry. Similar to time reversal invariant topological insulators, this model possesses a topologically...
International Nuclear Information System (INIS)
In this paper, we do a complete classification of valence-bond crystals (VBCs) on the kagomé lattice based on general arguments of symmetry only and thus identify many new VBCs for different unit cell sizes. For the spin-1/2 Heisenberg antiferromagnet, we study the relative energetics of competing gapless spin liquids (SLs) and VBC phases within the class of Gutzwiller-projected fermionic wave functions using variational Monte Carlo techniques, hence implementing exactly the constraint of one fermion per site. By using a state-of-the-art optimization method, we conclusively show that the U(1) Dirac SL is remarkably stable towards dimerizing into all 6-, 12- and 36-site unit cell VBCs. This stability is also preserved on addition of a next-nearest-neighbor super-exchange coupling of both antiferromagnetic and ferromagnetic (FM) type. However, we find that a 36-site unit cell VBC is stabilized on addition of a very small next-nearest-neighbor FM super-exchange coupling, i.e. |J2| ≈ 0.045, and this VBC is the same in terms of space-group symmetry as that obtained in an effective quantum dimer model study. It breaks reflection symmetry, has a nontrivial flux pattern and is a strong dimerization of the uniform RVB SL. (paper)
International Nuclear Information System (INIS)
By employing neutron spin echo (NSE) and small-angle neutron scattering (SANS), we first determined the nano-scale q-behaviors of the frozen concentration fluctuations in a swollen poly (N-isopropyl acrylamide) (NIPA) gel. For a NIPA gel, we observed a crossover from collective diffusion to Zimm single chain dynamics as scattering vector q increases, which is well established for a semidilute polymer solution. We further observed significant retardation of decay of NSE for a NIPA gel at low q, which is attributed to the elastic scattering from the frozen concentration fluctuations. After a careful analysis of two decay curves of a NIPA gel and solution, it turned out that the elastic scattering, occupying about 40% of the total intensity at q=0, decreases obeying q-4 at high q. (author)
Electronic Structure, Magnetism and Spin-Fluctuations in Fe-As Based Superconductors
Energy Technology Data Exchange (ETDEWEB)
Singh, David J [ORNL; Du, Mao-Hua [ORNL; Zhang, Lijun [ORNL; Subedi, Alaska P [ORNL; An, Jiming [ORNL
2009-01-01
The physical properties of the layered iron superconductors and related phases are discussed starting from first principles calculations. The electronic structure is described as that of metallic Fe{sup 2+} square lattice sheets with substantial direct Fe-Fe hopping and interactions with the neighboring anionic pnictogens or chalcogens. The materials have a semi-metallic band structure, and in particular the Fermi surface consists of small cylindrical electron sections centered at the zone corner, and compensating hole sections at the zone boundary. The density of states N(E{sub F}) is high placing the materials near itinerant magnetism in general, and furthermore the small Fermi surface sections are well nested leading to a tendency towards a spin density wave. Comparison of experimental and density functional results imply the presence of exceptionally strong spin fluctuations in these materials. Superconductivity is discussed within this context.
Yamakawa, Youichi; Kontani, Hiroshi
2015-06-26
We present a microscopic derivation of the nematic charge-density wave (CDW) formation in cuprate superconductors based on the three-orbital d-p Hubbard model by introducing the vertex correction (VC) into the charge susceptibility. The CDW instability at q=(Δ(FS),0), (0,Δ(FS)) appears when the spin fluctuations are strong, due to the strong charge-spin interference represented by the VC. Here, Δ(FS) is the wave number between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is expressed as the "intra-unit-cell orbital order" accompanied by the charge transfer between the neighboring atomic orbitals, which is actually observed by the scanning tunneling microscope measurements. We predict that the cuprate CDW and the nematic orbital order in Fe-based superconductors are closely related spin-fluctuation-driven phenomena. PMID:26197139
Electric voltage generation by antiferromagnetic dynamics
Yamane, Yuta; Ieda, Jun'ichi; Sinova, Jairo
2016-05-01
We theoretically demonstrate dc and ac electric voltage generation due to spin motive forces originating from domain wall motion and magnetic resonance, respectively, in two-sublattice antiferromagnets. Our theory accounts for the canting between the sublattice magnetizations, the nonadiabatic electron spin dynamics, and the Rashba spin-orbit coupling, with the intersublattice electron dynamics treated as a perturbation. This work suggests a way to observe and explore the dynamics of antiferromagnetic textures by electrical means, an important aspect in the emerging field of antiferromagnetic spintronics, where both manipulation and detection of antiferromagnets are needed.
Dos Santos Lima, Leonardo
We study the two-dimensional Heisenberg antiferromagnetic model with ion single anisotropy in the square lattice in the presence of nonmagnetic impurities at T = 0 using the SU(3) Schwinger boson theory. In particular, we discuss the influence of site disorder on the quantum phase transition of this model at Dc that separates the Néel phase, D Dc . We find that the long-range order in D CNPq, FAPEMIG, CAPES.
Ti3CrCu4: A possible 2-D ferromagnetic spin fluctuating system
Dhar, S. K.; Provino, A.; Manfrinetti, P.; Kulkarni, R.; Goyal, Neeraj; Paudyal, D.
2016-05-01
Ti3CrCu4 is a new ternary compound which crystallizes in the tetragonal Ti3Pd5 structure type. The Cr atoms form square nets in the a-b plane (a = 3.124 Å) which are separated by an unusually large distance c = 11.228 Å along the tetragonal axis, thus forming a -2-D Cr-sublattice. The paramagnetic susceptibility is characterized by a low effective moment, μeff = 1.1 μB, a low paramagnetic Curie temperature θP (below 7 K) and a temperature independent χ0 = 6.7 x 10-4 emu/mol. The magnetization at 1.8 K increases rapidly with field nearly saturating to 0.2 μB/f.u. The zero field heat capacity C/T shows an upturn below 7 K (˜190 mJ/mol K2 at ˜0.1K) which is suppressed in applied magnetic fields and interpreted as suggesting the presence of spin fluctuations. The resistivity at low temperatures shows non-Fermi liquid behavior. Overall, the experimental data thus reveal an unusual magnetic state in Ti3CrCu4, which likely has its origin in the layered nature of the Cr sub-lattice and ferromagnetic spin fluctuations. Density functional theoretical calculations reveal a sharp Cr density of states peak just above the Fermi level, indicating the propensity of Ti3CrCu4 to become magnetic.
International Nuclear Information System (INIS)
Avoiding the loss of coherence of quantum mechanical states is an important prerequisite for quantum information processing. Dynamical decoupling (DD) is one of the most effective experimental methods for maintaining coherence, especially when one can access only the qubit system and not its environment (bath). It involves the application of pulses to the system whose net effect is a reversal of the system-environment interaction. In any real system, however, the environment is not static, and therefore the reversal of the system-environment interaction becomes imperfect if the spacing between refocusing pulses becomes comparable to or longer than the correlation time of the environment. The efficiency of the refocusing improves therefore if the spacing between the pulses is reduced. Here, we quantify the efficiency of different DD sequences in preserving different quantum states. We use 13C nuclear spins as qubits and an environment of 1H nuclear spins as the environment, which couples to the qubit via magnetic dipole-dipole couplings. Strong dipole-dipole couplings between the proton spins result in a rapidly fluctuating environment with a correlation time of the order of 100 μs. Our experimental results show that short delays between the pulses yield better performance if they are compared with the bath correlation time. However, as the pulse spacing becomes shorter than the bath correlation time, an optimum is reached. For even shorter delays, the pulse imperfections dominate over the decoherence losses and cause the quantum state to decay.
Modeling Spin Fluctuations and Magnetic Excitations from Time-Dependent Density Functional Theory
Gorni, Tommaso; Timrov, Iurii; Dal Corso, Andrea; Baroni, Stefano
Harnessing spin fluctuations and magnetic excitations in materials is key in many fields of technology, spanning from memory devices to information transfer and processing, to name but a few. A proper understanding of the interplay between collective and single-particle spin excitations is still lacking, and it is expected that first-principle simulations based on TDDFT may shed light on this interplay, as well as on the role of important effects such as relativistic ones and related magnetic anisotropies. All the numerical approaches proposed so far to tackle this problem are based on the computationally demanding solution of the Sternheimer equations for the response orbitals or the even more demanding solution of coupled Dyson equations for the spin and charge susceptibilities. The Liouville-Lanczos approach to TDDFT has already proven to be a valuable alternative, the most striking of its features being the avoidance of sums over unoccupied single-particle states and the frequency-independence of the main numerical bottleneck. In this work we present an extension of this methodology to magnetic systems and its implementation in the Quantum ESPRESSO distribution, together with a few preliminary results on the magnon dispersions in bulk Fe.
Spinon dynamics in quantum integrable antiferromagnets
Vlijm, R.; Caux, J.-S.
2016-05-01
The excitations of the Heisenberg antiferromagnetic spin chain in zero field are known as spinons. As pairwise-created fractionalized excitations, spinons are important in the understanding of inelastic neutron scattering experiments in (quasi-)one-dimensional materials. In the present paper, we consider the real space-time dynamics of spinons originating from a local spin flip on the antiferromagnetic ground state of the (an)isotropic Heisenberg spin-1/2 model and the Babujan-Takhtajan spin-1 model. By utilizing algebraic Bethe ansatz methods at finite system size to compute the expectation value of the local magnetization and spin-spin correlations, spinons are visualized as propagating domain walls in the antiferromagnetic spin ordering with anisotropy dependent behavior. The spin-spin correlation after the spin flip displays a light cone, satisfying the Lieb-Robinson bound for the propagation of correlations at the spinon velocity.
Pan, Bingying; Wang, Yang; Zhang, Lijuan; Li, Shiyan
2014-04-01
Single crystals of a metal organic complex (C5H12N)CuBr3 (C5H12N = piperidinium, pipH for short) have been synthesized, and the structure was determined by single-crystal X-ray diffraction. (pipH)CuBr3 crystallizes in the monoclinic group C2/c. Edging-sharing CuBr5 units link to form zigzag chains along the c axis, and the neighboring Cu(II) ions with spin-1/2 are bridged by bibromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fisher formula for the antiferromagnetic spin-1/2 chain, giving the intrachain magnetic coupling constant J ≈ -17 K. At zero field, (pipH)CuBr3 shows three-dimensional (3D) order below TN = 1.68 K. Calculated by the mean-field theory, the interchain coupling constant J' = -0.91 K is obtained and the ordered magnetic moment m0 is about 0.23 μB. This value of m0 makes (pipH)CuBr3 a rare compound suitable to study the 1D-3D dimensional cross-over problem in magnetism, since both 3D order and one-dimensional (1D) quantum fluctuations are prominent. In addition, specific heat measurements reveal two successive magnetic transitions with lowering temperature when external field μ0H ≥ 3 T is applied along the a' axis. The μ0H-T phase diagram of (pipH)CuBr3 is roughly constructed. PMID:24617285
Schwinger-boson studies of the single hole motion in a 2d quantum antiferromagnet
International Nuclear Information System (INIS)
Within the Schwinger-boson approach for the t-J model, the single hole problem in a two-dimensional quantum antiferromagnet is studied by using the quantum Bogoliubov-de Gennes formalism which treats the distortion of the spin background and quantum spin fluctuations on an equal footing. Several self-trapped localized hole states are found in the distorted spin-background as in the case of an anisotropic Heisenberg model. These localized hole states survive at finite temperatures when the antiferromagnetic order becomes short-ranged. The energy separation between the two lowest states is reduced by considering the spin-background distortion, but it remains finite. (author). 17 refs, 5 figs, 1 tab
Han, K S; Mean, B J; Lee, K H; Seo, S W; Lee, M H; Lee, W C
2000-01-01
We have prepared Zn- and Ni-substituted YBa sub 2 Cu sub 3 O sub 7 (YBa sub 2 Cu sub 3 sub - sub x M sub x O sub 7 , M=Zn or Ni, x=0.00 approx 0.09) and performed sup 6 sup 3 sup , sup 6 sup 5 Cu nuclear quadrupole resonance (NQR) measurements for the plane site at 300 and 100 K. Substitutional effects on the relaxation rates are markedly different. Both the spin-lattice and the spin-spin relaxation rates decrease for Zn-doped YBCO. However, those increase for Ni-doped YBCO. This contrast in local electronic dynamics provides clear microscopic evidence that Zn forms no local moment while Ni develops a local moment. Consequently, the antiferromagnetic spin fluctuation is suppressed by Zn doping whereas it is preserved by Ni doping. This is also confirmed by the ratio of the sup 6 sup 3 sup , sup 6 sup 5 Cu spin-lattice relaxation rates for the plane coppers.
Duan, T. F.; Ren, W. J.; Liu, W.; Zhang, Z. D.
2016-08-01
The magnetic structure of MnSn2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field (H) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H-T phase diagram has been established.
The Magnetism of Li doped La$_{2}$CuO$_4$: the antiferromagnetic spin-shard state
Sushkov, O. P.; Neto, A. H. Castro
2005-01-01
We study the dynamics of a single hole in Li and Sr doped La$_{2}$CuO$_4$ and its extension to a finite hole concentration. We compare the physics of La$_{2-x}$Sr$_x$CuO$_4$ and La$_{2}$Cu$_{1-x}$Li$_x$O$_4$ and explain why these systems are remarkably different. We demonstrate that holes in La$_{2}$Cu$_{1-x}$Li$_x$O$_4$ are always localized and that there is a critical concentration, $x_c\\approx 0.03$, above which the holes break the global antiferromagnetic state into an array of weakly cou...
Low-energy spin fluctuations in the non-Fermi-liquid compound YbRh2Si2
Directory of Open Access Journals (Sweden)
O. Stockert et al
2007-01-01
Full Text Available We report on inelastic neutron scattering experiments on YbRh2Si2 powder to study the low-energy spin dynamics at temperatures between T=0.8 and 22 K. The low-energy magnetic response is quasielastic. However, it exhibits an unusual form not modelled by a simple relaxation rate yielding a Lorentzian lineshape, but can satisfactorily be described by a phenomenological model involving a distribution of relaxation rates. The lower bound of the relaxation rates varies roughly linear with temperature indicating a pronounced slowing down of the critical modes above the antiferromagnetic ordering temperature TNapprox70 mK.
Observation of the orbital quantum dynamics in the spin-1/2 hexagonal antiferromagnet B a3CuS b2O9
Han, Yibo; Hagiwara, Masayuki; Nakano, Takehito; Nozue, Yasuo; Kimura, Kenta; Halim, Mario; Nakatsuji, Satoru
2015-11-01
We have studied orbital dynamics in the spin liquid candidate B a3CuS b2O9 using multifrequency electron-spin resonance. We prepared two high-quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the g factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of ˜100 ps below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.
DEFF Research Database (Denmark)
Christensen, Niels Bech
seen in other high-T_csuperconductors. The presence of dispersive excitations does not require superconductivity to exist. For La_1_._8_4Sr_0_._1_6CuO_4, but not for La_1_._9_0Sr_0_._1_0CuO_4, the onset of superconductivity gives rise to a spectral weight shift which displaysqualitative and...
Low-energy paramagnetic spin fluctuations in the weak itinerant ferromagnet MnSi
Ishikawa, Y.; Noda, Y.; Fincher, C.; Shirane, G.
1982-01-01
Low-energy paramagnetic excitations in the weak itinerant ferromagnet (WIF) MnSi have been studied by neutron scattering. The observed spectrum has a Lorentzian form (ΓΓ2+ω2) and is clearly separated from excitations in the Stoner continuum. The generalized susceptibility, χ(q), has been obtained by integrating the scattering intensity over energy. It is found that χ(q) depends upon the wave vector q as χ(q)-1=κ2(T)+q2 for qWIF. The linewidth Γ is found to be proportional to qχ(q) as predicted by the MK theory, in contrast with the q2χ(q) relation expected in a Heisenberg system. These results provide the first direct experimental evidence for the existence of MK spin fluctuations in a WIF above Tc.
Localized spin fluctuations in 4d and 5d transition metals with iron impurities
International Nuclear Information System (INIS)
The superconducting transition temperatures of TcMn, TcFe, and TcCo alloys have been measured. The rapid depression of the transition temperature of Tc by Fe impurities can be understood in terms of Roessler and Kiwi's theory for localized spin fluctuations in superconducting alloys. The magnetic character of Fe impurities in Tc, Ru, and Ir hosts has also been studied by Moessbauer experiments in the temperature region of 1.4 - 290 K and in external fields up to 50 kOe. Saturation hyperfine fields in 50 kOe are -7.3 +- 1 kOe for TcFe, -1 +- 1 kOe for RuFe, and -9.3 +- 1 kOe for IrFe, being much smaller than those of usual Kondo alloys. A qualitative explanation of these small hyperfine fields is attempted by a stochastic model based on the LSF concept. (author)
Strong coupling critique of spin fluctuation driven charge order in underdoped cuprates
Mishra, Vivek; Norman, M. R.
2015-08-01
Charge order has emerged as a generic feature of doped cuprates, leading to important questions about its origin and its relation to superconductivity. Recent experiments on two classes of hole doped cuprates indicate a novel d -wave symmetry for the order. These were motivated by earlier spin fluctuation theoretical studies based on an expansion about hot spots in the Brillouin zone that indicated such an order would be competitive with d -wave superconductivity. Here, we reexamine this problem by solving strong coupling equations in the full Brillouin zone for experimentally relevant parameters. We find that bond-oriented order, as seen experimentally, is strongly suppressed. We also include coupling to B1 g phonons and do not see any qualitative change. Our results argue against an itinerant model for the charge order, implying instead that such order is likely due to Coulombic phase separation of the doped holes.
Pressure dependence of critical temperature of bulk FeSe from spin fluctuation theory
Hirschfeld, Peter; Kreisel, Andreas; Wang, Yan; Tomic, Milan; Jeschke, Harald; Jacko, Anthony; Valenti, Roser; Maier, Thomas; Scalapino, Douglas
2013-03-01
The critical temperature of the 8K superconductor FeSe is extremely sensitive to pressure, rising to a maximum of 40K at about 10GPa. We test the ability of the current generation of fluctuation exchange pairing theories to account for this effect, by downfolding the density functional theory electronic structure for each pressure to a tight binding model. The Fermi surface found in such a procedure is then used with fixed Hubbard parameters to determine the pairing strength using the random phase approximation for the spin singlet pairing vertex. We find that the evolution of the Fermi surface captured by such an approach is alone not sufficient to explain the observed pressure dependence, and discuss alternative approaches. PJH, YW, AK were supported by DOE DE-FG02-05ER46236, the financial support of MT, HJ, and RV from the DFG Schwerpunktprogramm 1458 is kindly acknowledged.
Spin wave excitations in AFe1.5Se2 (A = K, Tl): analytical study
International Nuclear Information System (INIS)
By generalizing the equation of motion method, we can analytically solve the spin wave excitations for the intercalated ternary iron-selenide AFe1.5Se2 (A = K, Tl) in a complex 4 × 2 collinear antiferromagnetic order. It is found that there are one acoustic branch (gapless Goldstone mode) and two gapful optical branches of spin wave excitations with each in double degeneracy. By examining the non-imaginary excitation frequency condition, we can determine the corresponding phase boundary. The exchange couplings between Fe moments in AFe1.5Se2 are derived based on the first-principles total energy calculations. The Fe spin is found to be S= 3/2 through computing the antiferromagnetic quantum fluctuation. It is also found that a very small spin-orientation anisotropy can remarkably suppress the antiferromagnetic quantum fluctuation. The spin dynamical structure factors are calculated and discussed in association with neutron inelastic scattering experiment.
Energy Technology Data Exchange (ETDEWEB)
Miyashita, Satoshi [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Yonemitsu, Kenji, E-mail: satoshi@ims.ac.j [Institute for Molecular Science, Okazaki 444-8585 (Japan)
2009-02-01
Effects of spin fluctuations, charge fluctuations and lattice distortions on charge orders in theta-(BEDT-TTF){sub 2}RbZn(SCN){sub 4} and alpha-(BEDT-TTF){sub 2}I{sub 3} are investigated theoretically in a two-dimensional extended Peierls-Hubbard model. By using exact diagonalization, we have calculated hole-density distributions and transfer modulations with transfer integrals based on the corresponding high-temperature structures as a function of electron-phonon couplings. The results clearly show the origin of their lattice-effect differences, namely, the lattice effect on theta-(BEDT-TTF){sub 2}RbZn(SCN){sub 4} is much larger than that on alpha-(BEDT-TTF){sub 2}I{sub 3}. This finding is systematically explained by the strong-coupling perturbation theory. It is found that spin fluctuations induce lattice distortions in theta-(BEDT-TTF){sub 2}RbZn(SCN){sub 4}, but their effects are partially cancelled by charge fluctuations in alpha-(BEDT-TTF){sub 2}I{sub 3}.
21 cm signal from cosmic dawn: Imprints of spin temperature fluctuations and peculiar velocities
Ghara, Raghunath; Datta, Kanan K
2014-01-01
Observations of fluctuations in the 21 cm brightness temperature $\\delta T_b$ from reionization promise to provide information on the physical processes during that epoch. We present a formalism for generating the distribution of $\\delta T_b$ using dark matter $N$-body simulations and an one-dimensional radiative transfer code. The spectral energy distribution of the radiation sources is assumed to consist of a stellar-like and a mini-quasar like component. Our analysis is able to take into account the fluctuations in the spin temperature $T_S$ of neutral hydrogen arising from inhomogeneous X-ray heating and Ly$\\alpha$ coupling during cosmic dawn. We find that the power spectrum at large scales ($k \\sim 0.1$ Mpc$^{-1}$), when plotted as a function of redshift, shows three peaks. The middle peak has the largest amplitude and occurs when $\\sim 10\\%$ of the gas (by volume) is heated above the CMB temperature, irrespective of the X-ray source properties. The power spectrum when plotted against $k$ shows a "bump"-...
Huang, Yi-Zhen; Xi, Bin; Chen, Xi; Li, Wei; Wang, Zheng-Chuan; Su, Gang
2016-06-01
The quantum phase transition, scaling behaviors, and thermodynamics in the spin-1/2 quantum Heisenberg model with antiferromagnetic coupling J >0 in the armchair direction and ferromagnetic interaction J'ratio Q2 and spin stiffness ρ in two directions for various coupling ratios α =J'/J under different lattice sizes, we found that a quantum phase transition from the dimerized phase to the stripe phase occurs at the quantum critical point αc=-0.93 . Through the finite-size scaling analysis on Q2, ρx, and ρy, we determined the critical exponent related to the correlation length ν to be 0.7212(8), implying that this transition falls into a classical Heisenberg O(3) universality. A zero magnetization plateau is observed in the dimerized phase, whose width decreases with increasing α . A phase diagram in the coupling ratio α -magnetic field h plane is obtained, where four phases, including dimerized, stripe, canted stripe, and polarized, are identified. It is also unveiled that the temperature dependence of the specific heat C (T ) for different α 's intersects precisely at one point, similar to that of liquid 3He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q2, ρ , and C (T ) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.
Spin-current probe for phase transition in an insulator.
Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z Q; Saitoh, Eiji
2016-01-01
Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices. PMID:27573443
International Nuclear Information System (INIS)
Measurements of the proton spin-lattice relaxation rate (1/T1) at a pressure of 1 bar in a single crystal of (TMTSF)2PF6 (TMTSF is tetramethyltetraselenafulvalene) are reported for the magnetic field in the range 0.25-1.48 T aligned along the b'- and c*-axes over the temperature range 2-30 K. The methyl group rotation contribution to 1/T1 is subtracted to obtain the spin density wave (SDW) contribution. Through measurements of 1/T1 below and above the spin flop transition it is determined that phason fluctuations of the SDW are responsible for most of the relaxation. Depinning the SDW's by an electric field leaves 1/T1 nearly unchanged, which indicates that the SDW and its fluctuation rate near 108 rad/s persist when the SDW is sliding. Analysis of the peak in 1/T1 near 3 K on the applied magnetic field suggests that it represents a slowing of thermally activated fluctuations with an activation energy Δ/kB = 18.3 ± 4.0 K, which is close to the single particle gap for this material. The contribution of critical fluctuations to 1/T1 is consistent with the transition being weakly first order. Unlike the relaxation in the ordered phase, the contribution of the critical fluctuations is isotropic and has little, if any dependence on magnetic field. (orig.)
Mailhot, A.; Plumer, M. L.; Caillé, A.
1993-01-01
The results of a detailed histogram Monte-Carlo study of critical-fluctuation effects on the magnetic-field temperature phase diagram associated with the hexagonal Heisenberg antiferromagnet with weak axial anisotropy are reported. The multiphase point where three lines of continuous transitions merge at the spin-flop boundary exhibits a structure consistent with scaling theory but without the usual umbilicus as found in the case of a bicritical point.
Identical spin fluctuations in Cu- and Co-doped BaFe2As2 independent of electron doping
Grafe, H.-J.; Gräfe, U.; Dioguardi, A. P.; Curro, N. J.; Aswartham, S.; Wurmehl, S.; Büchner, B.
2014-09-01
We present As75 nuclear magnetic resonance measurements on single crystals of BaFe2As2, BaFe1.8Co0.2As2, and BaFe1.82Cu0.18As2. While only Co doping induces bulk superconductivity on a broad doping range, the spin fluctuations probed by the nuclear spin-lattice relaxation rate (T1T )-1 are identical for both dopings down to Tc. Below this temperature, (T1T)-1 of the Cu-doped sample continues to rise, proving that (a) there is a quantum critical point below the superconducting dome, and (b) adding electrons does not affect the spin fluctuations. Consequently, we analyze the Knight shift data in terms of a two-component scenario, with one hyperfine coupling to an itinerant degree of freedom and the other to Fe moments.
Thermoinduced magnetization in nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
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....
The robustness of the quantum spin Hall effect to the thickness fluctuation in HgTe quantum wells
Institute of Scientific and Technical Information of China (English)
Guo Huai-Ming; Zhang Xiang-Lin; Feng Shi-Ping
2012-01-01
The quantum spin Hall effect (QSHE) was first realized in HgTe quantum wells (QWs),which remain the only known two-dimensional topological insulator so far.In this paper,we have systematically studied the effect of the thickness fluctuation of HgTe QWs on the QSHE.We start with the case of constant mass with random distributions,and reveal that the disordered system can be well described by a virtual uniform QW with an effective mass when the number of components is small.When the number is infinite and corresponds to the real fluctuation,we find that the QSHE is not only robust,but also can be generated by relatively strong fluctuation.Our results imply that the thickness fluctuation does not cause backscattering,and the QSHE is robust to it.
Hydration-induced anisotropic spin fluctuations in NaxCoO2 · 1.3H2O superconductor
Matano, K.; Lin, C. T.; Zheng, Guo-qing
2008-12-01
We report 59Co NMR studies in single crystals of the cobalt oxide superconductor Na0.42CoO2·1.3H2O (Tc=4.25 K) and its parent compound Na0.42CoO2. We find that both the magnitude and the temperature (T) dependence of the Knight shifts are identical in the two compounds above Tc. The spin-lattice relaxation rate (1/T1) is also identical above T0~60 K for both compounds. Below T0, the unhydrated sample is found to be a non-correlated metal that well conforms to the Fermi liquid theory, while spin fluctuations develop in the superconductor. These results indicate that water intercalation does not change the density of states at the Fermi level or the carrier density but its primary role is to bring about spin fluctuations. Our result shows that, in the hydrated superconducting compound, the electron correlation is anisotropic. Namely, the spin fluctuation around the finite wave vector is much stronger along the a-axis direction than that along the c-axis direction.
Becca, Federico; Iqbal, Yasir; Poilblanc, Didier
2012-02-01
Within the class of Gutzwiller projected fermionic wave functions, by using quantum variational Monte Carlo simulations, we investigated the energetics of all possible Z2 spin liquids that can potentially occur as ground states of the nearest-neighbor S=1/2 quantum Heisenberg model on the Kagome lattice [1]. We conclusively show that all gapped and gapless Z2 spin liquids are higher in energy compared to the U(1) gapless states in whose neighborhoods they lie. In particular, the most promising gapped Z2 spin liquid (the so-called Z2[0,π]β state), conjectured to describe the ground state [2], is always higher in energy compared to the U(1) Dirac spin liquid. We also extended the U(1) Dirac state and the uniform RVB spin liquid to include next-nearest-neighbor hopping terms, and studied its local and global stability towards various valence bond crystal patterns. We found that a non-trivial 36-site VBC is stabilized upon addition of a small ferromagnetic exchange coupling [3]. [4pt] [1] Y. Iqbal, F. Becca, and D. Poilblanc, Phys. Rev. B 84, 020407(R) (2011)[0pt] [2] Y.-M. Lu, Y. Ran, and P.A. Lee. Phys. Rev. B 83, 224413 (2011)[0pt] [3] Y. Iqbal, F. Becca, and D. Poilblanc, Phys. Rev. B 83, 100404(R) (2011)
International Nuclear Information System (INIS)
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase
Akmaldinov, Kamil; Ducruet, Clarisse; Alvarez-Herault, Jeremy; Baltz, Vincent
2015-03-01
For thermally-assisted magnetic random access memories (TA-MRAM), lowering bit-cells dispersions of exchange bias is necessary. In this study, we prove that spin-glass-like phases (SG) spread over the ferromagnetic/antiferromagnetic (F/AF) storage layer are the main cause of such distributions once the film is nanofabricated into a device. In particular, we show that the less the SG, the lower the bit-cell dispersion. More precisely, the amount of SG was varied from sample to sample by sputtering various AFs: IrMn, FeMn and their alloys. Blocking temperature distributions were measured to quantify the amount of SG at the wafer level. The wafers were then patterned to obtain 1kb devices and all the cells were tested electrically. Finally, the resulting loop shift cumulative distribution functions accounting for the bit-cell dispersions were correlated to the initial amount of SG. In addition to bridging the gap between fundamental SG and a technological application, we also demonstrated that blocking temperature distributions are a versatile method to qualify TA-MRAM production batches before processing. Univ. Grenoble-Alpes/CNRS/INAC-CEA, 38000 Grenoble, France.
Energy Technology Data Exchange (ETDEWEB)
Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Li, Wei [Department of Physics, Beihang University, Beijing 100191 (China); You, Wen-Long [School of Physical Science and Technology, Soochow University, Suzhou, Jiangsu 215006 (China); Su, Gang [Theoretical Condensed Matter Physics and Computational Materials Physics Laboratory, College of Physical Sciences, University of Chinese Academy of Sciences, P.O. Box 4588, Beijing 100049 (China); Tian, Guang-Shan [School of Physics, Peking University, Beijing 100871 (China)
2015-03-01
The ground-state properties of the spin-1/2 Ferromagnetic–Ferromagnetic–Antiferromagnetic (F–F–AF) trimerized chain are investigated by the infinite time-evolving block decimation (iTEBD) method. A ground-state phase diagram including three different phases, i.e., a fully polarized phase, a 1/3 plateau phase, and a non-plateau phase, is obtained. All the quantum phase transitions (QPTs) can be described well by the model independent bipartite entanglement. QPTs between the non-plateau phase and the other two phases belong to the second-order category. Doubly degenerate entanglement spectrum and nontrivial string order are observed in the 1/3 plateau phase, which can be used to distinguish it from the other phases. By the scaling behavior of the bipartite entanglement, the central charge of the critical non-plateau phase is determined to be c≃ 1. - Highlights: • A rich ground-state phase diagram is obtained. • QPTs can be well described by singular behavior of entanglement. • The 1/3 magnetization plateau is characterized by entanglement plateau. • Doubly degenerate entanglement spectrum is observed in the 1/3 plateau phase. • Nontrivial string order is observed in the 1/3 plateau phase.
Ito, Kazuhiro; Shimahara, Hiroshi
2016-02-01
We examine the mean field theory of a uniaxial coupled Heisenberg antiferromagnet with two subsystems, one of which consists of strongly interacting small spins and the other consists of weakly interacting large spins. We reanalyze the experimental data of specific heat and magnetic susceptibility obtained by previous authors for the organic compound λ-(BETS)2FeCl4 at low temperatures, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. The model parameters for this compound are evaluated, where the applicability of the theory is checked. As a result, it is found that J1 ≫ J12 ≫ J2, where J1, J2, and J12 denote the exchange coupling constant between π spins, that between 3d spins, and that between π and 3d spins, respectively. At the low-temperature limit, both sublattice magnetizations of the 3d and π spins are saturated, and the present model is reduced to the Schottky model, which successfully explains experimental observations in previous studies. As temperature increases, fluctuations of 3d spins increase, while π spins remain almost saturated. Near the critical temperature, both spins fluctuate significantly, and thus the mean field approximation breaks down. It is revealed that the magnetic anisotropy, which may be crucial to the antiferromagnetic long-range order, originates from J12 rather than from J2 and that the angle between the magnetic easy-axis and the crystal c-axis is approximately 26-27° in the present effective model.
Nearly critical spin and charge fluctuations in KFe2As2 observed by high-pressure NMR
Wang, P. S.; Zhou, P.; Dai, J.; Zhang, J.; Ding, X. X.; Lin, H.; Wen, H. H.; Normand, B.; Yu, R.; Yu, Weiqiang
2016-02-01
We report a high-pressure 75As NMR study on the heavily hole-doped iron pnictide superconductor KFe2As2 (Tc≈3.8 K). The low-energy spin fluctuations are found to decrease with applied pressure up to 2 GPa, but then to increase again, changing in lockstep with the pressure-induced evolution of Tc. Their diverging nature suggests close proximity to a magnetic quantum critical point at a negative pressure of P ≃-0.6 GPa. Above 2.2 GPa, the 75As satellite spectra split below 40 K, indicating a breaking of As site symmetry and an incipient charge order. These pressure-controlled phenomena demonstrate the presence of nearly critical fluctuations in both spin and charge, providing essential input for the origin of superconductivity.
Wang, Ze
2012-01-01
Denoising is critical to improving the quality and stability of cerebral blood flow (CBF) quantification in arterial spin labeled (ASL) perfusion MRI due to the intrinsic low signal-to-noise-ratio (SNR) of ASL data. Previous studies have been focused on reducing the spatial or temporal noise using standard filtering techniques, and less attention has been paid to two global nuisance effects, the residual motion artifacts and the global signal fluctuations. Since both nuisances affect the whol...
Spin valves based on Mn{sub 75}Ir{sub 25} antiferromagnet with controllable functional parameters
Energy Technology Data Exchange (ETDEWEB)
Milyaev, M. A., E-mail: milyaev@imp.uran.ru; Naumova, L. I.; Kamenskii, I. Yu.; Ustinov, V. V. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2015-12-15
Using the example of spin valves of the Ta(50 Å)/Ni{sub 80}Fe{sub 20}(30 Å)/Co{sub 90}Fe{sub 10}(15 Å)/Cu(28 Å)/Co{sub 90}Fe{sub 10}(20 Å)/Mn{sub 75}Ir{sub 25}(50 Å)/Ta(20 Å) composition, factors controlling the hysteresis properties are studied for the case of macro- and microscopic sizes of an experimental sample. It is shown that a linear change in the magnetoresistance with small hysteresis while retaining the giant magnetoresistance effect at a level of 8% can be obtained in a micro-object (meander) using thermomagnetic treatment.
Triangular Ising antiferromagnets with quenched nonmagnetic impurities.
Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying
2010-05-01
In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185
Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points
Energy Technology Data Exchange (ETDEWEB)
Fischer, I.A.
2006-07-01
studied how the interplay of precession and damping affects various thermodynamic and transport quantities. We found that the susceptibility {chi}={delta}M/{delta}B is the thermodynamic quantity which shows the most significant change upon approaching the quantum critical point and which gives experimental access to the (dangerously irrelevant) spin-spin interactions. Finally, we studied the quantum critical behaviour of two-dimensional antiferromagnetic metals. Going beyond an order parameter theory, we included the electronic quasiparticles as well as the fluctuating magnetization in a functional Renormalization Group calculation. Preliminary results indicate a divergence in the fRG-equations already at a finite distance from the quantum critical point. this is incompatible with the Hertz-Millis picture. (orig.)
Exchange and spin Jahn-Teller distortions for triangular cluster of spin-1/2
International Nuclear Information System (INIS)
We study the effects of magnetoelastic coupling on the degenerate ground state of the spin-1/2 antiferromagnetic Heisenberg model for a regular triangular spin cluster. Static displacement of spins spontaneously lifts the degeneracy of the ground state through the distance dependence of exchange coupling, i.e., a spin John-Teller mechanism takes place. On the other hand, dynamical displacement does not lift the degeneracy, although the cluster distorts spontaneously. The energy decrease obtained by dynamical theory is twice that obtained by static theory because of quantum fluctuation. (author)
Quantum Phase Transitions of Antiferromagnets and the Cuprate Superconductors
Sachdev, Subir
I begin with a proposed global phase diagram of the cuprate superconductors as a function of carrier concentration, magnetic field, and temperature, and highlight its connection to numerous recent experiments. The phase diagram is then used as a point of departure for a pedagogical review of various quantum phases and phase transitions of insulators, superconductors, and metals. The bond operator method is used to describe the transition of dimerized antiferromagnetic insulators between magnetically ordered states and spin-gap states. The Schwinger boson method is applied to frustrated square lattice antiferromagnets: phase diagrams containing collinear and spirally ordered magnetic states, Z_2 spin liquids, and valence bond solids are presented, and described by an effective gauge theory of spinons. Insights from these theories of insulators are then applied to a variety of symmetry breaking transitions in d-wave superconductors. The latter systems also contain fermionic quasiparticles with a massless Dirac spectrum, and their influence on the order parameter fluctuations and quantum criticality is carefully discussed. I conclude with an introduction to strong coupling problems associated with symmetry breaking transitions in two-dimensional metals, where the order parameter fluctuations couple to a gapless line of fermionic excitations along the Fermi surface.
International Nuclear Information System (INIS)
The antiferromagnetic insulator La1.5Ca0.5CoO4 has been investigated by Co L2,3-edge and O K-edge X-ray absorption spectroscopy (XAS) measurements and Co L2,3-edge resonant soft X-ray magnetic scattering (RXMS) measurement to determine the Co electronic structures associated with magnetic ordering. Co L2,3-edge linear-dichroic XAS shows that Co2+ takes a high-spin (HS) state and Co3+ takes a low-spin (LS) state. Using Co L2,3-edge RXMS, we directly determined that an antiferromagnetic order is formed with a HS state of Co2+ ions. Moreover, the spin and orbital angular momenta of the Co2+ HS state are quantitatively estimated to be 1.1 ± 0.1 and 1.0 ± 0.1, respectively, and to align parallel in the ab plane by utilizing the cluster model calculation. The large orbital angular momentum of the Co2+ HS state originates from the small D4h-symmetry crystal field splitting of t2g levels, which is comparable with the spin-orbit coupling constant of the Co 3d orbital. (author)
International Nuclear Information System (INIS)
The effect of magnetic field on non-propagating spin fluctuations in weak itinerant-electron ferromagnet Ni75Al25 has been, for the first time, quantified through the field dependence of spin fluctuation contribution to the electrical resistivity and magnetoresistivity over a wide range of temperatures. For a given field value, non-stoichiometry reduces the magnitude of the negative magnetoresistivity at all temperatures more so for temperatures close to the Curie temperature. (author)
Calvo, Rafael; Sartoris, Rosana P.; Calvo, Hernán L.; Chagas, Edson F.; Rapp, Raul E.
2016-05-01
We study the spin chain behavior, a transition to 3D magnetic order and the magnitudes of the exchange interactions for the metal-amino acid complex Cu(D,L-alanine)2•H2O, a model compound to investigate exchange couplings supported by chemical paths characteristic of biomolecules. Thermal and magnetic data were obtained as a function of temperature (T) and magnetic field (B0). The magnetic contribution to the specific heat, measured between 0.48 and 30 K, displays above 1.8 K a 1D spin-chain behavior that can be fitted with an intrachain antiferromagnetic (AFM) exchange coupling constant 2J0=(-2.12±0.08) cm-1 (defined as ℋex(i,i+1) = -2J0SiṡSi+1), between neighbor coppers at 4.49 Å along chains connected by non-covalent and H-bonds. We also observe a narrow specific heat peak at 0.89 K indicating a phase transition to a 3D magnetically ordered phase. Magnetization curves at fixed T = 2, 4 and 7 K with B0 between 0 and 9 T, and at T between 2 and 300 K with several fixed values of B0 were globally fitted by an intrachain AFM exchange coupling constant 2J0=(-2.27±0.02) cm-1 and g = 2.091±0.005. Interchain interactions J1 between coppers in neighbor chains connected through long chemical paths with total length of 9.51 Å cannot be estimated from magnetization curves. However, observation of the phase transition in the specific heat data allows estimating the range 0.1≤|2J1|≤0.4 cm-1, covering the predictions of various approximations. We analyze the magnitudes of 2J0 and 2J1 in terms of the structure of the corresponding chemical paths. The main contribution in supporting the intrachain interaction is assigned to H-bonds while the interchain interactions are supported by paths containing H-bonds and carboxylate bridges, with the role of the H-bonds being predominant. We compare the obtained intrachain coupling with studies of compounds showing similar behavior and discuss the validity of the approximations allowing to calculate the interchain
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1984-01-01
The correlation theory is applied to a Heisenberg antiferromagnet in a magnetic field. Special cases covered are the ferromagnet and an anisotropic Heisenberg model. The theory includes selfconsistently correlation effects in static and dynamic properties. It is a generalization of the random......-phase approximation and is applicable to the quantum spin case for any dimension and temperature. The static susceptibilities and the excitation spectrum are calculated. Besides the spin-wave excitations a central peak is found which can be understood as coming from local longitudinal fluctuations. The results of the...... theory are exemplified by numerical calculations for the onedimensional S=1 quantum antiferromagnetic chain. Qualitative agreement is found with computer simulations on a classical chain....
Chekhovich, E. A.; Hopkinson, M.; Skolnick, M. S.; Tartakovskii, A. I.
2015-01-01
Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we rep...
Chekhovich, E. A.; Hopkinson, M.; Skolnick, M. S.; Tartakovskii, A. I.
2015-01-01
Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we rep...
Spin-chain system as a tunable simulator of frustrated planar magnetism
Klanjsek, M.; Horvatic, M.; Berthier, C.; Mayaffre, H.; Canevet, E.; Grenier, B.; Lejay, P.; Orignac, E.
2012-01-01
At low temperatures, weakly coupled spin chains develop a magnetic order that reflects the character of gapless spin fluctuations along the chains. Using nuclear magnetic resonance, we identify and characterize two ordered states in the gapless region of the antiferromagnetic, Ising-like spin-chain system BaCo2V2O8, both arising from the incommensurate fluctuations along the chains. They correspond to the columnar and ferromagnetic ordered states of the frustrated J1-J2 spin model on a square...
Quantum lattice fluctuations in a frustrated Heisenberg spin-Peierls chain
Weisse, A.; Wellein, G.; Fehske, H.
1999-01-01
As a simple model for spin-Peierls systems we study a frustrated Heisenberg chain coupled to optical phonons. In view of the anorganic spin-Peierls compound CuGeO3 we consider two different mechanisms of spin-phonon coupling. Combining variational concepts in the adiabatic regime and perturbation theory in the anti-adiabatic regime we derive effective spin Hamiltonians which cover the dynamical effect of phonons in an approximate way. Ground-state phase diagrams of these models are determined...
McHale, P.; Monthoux, P.
2002-01-01
In the simplest model of magnetic pairing, the transition temperature to the superconducting state depends on the dynamical susceptibility $\\chi({\\bf q},\\omega)$. We discuss how $T_c$ is affected by different momentum and frequency parts of $\\chi({\\bf q},\\omega)$ for nearly antiferromagnetic and nearly ferromagnetic metals in two dimensions. While in the case of phonon-mediated superconductivity any addition of spectral weight to $\\alpha^2F(\\omega)$ at $\\omega >0$ leads to an increase in $T_c...
International Nuclear Information System (INIS)
We have applied the self-consistent renormalized (SCR) spin fluctuation theory to calculate several physical quantities measured for Ce1-xLaxRu2Si2 (x = 0, 0.05 and 0.075), namely the specific heat, resistivity, thermal expansion, spin-lattice relaxation and inelastic neutron scattering. A quantitative agreement between experiments and the theory has been obtained in all cases, indicating that the spin fluctuations dominate the thermal and dynamical properties near the magnetic instability in this system. Comparisons are also made with the recent renormalization group approach to the quantum critical point in itinerant systems. (author)
Quantum lattice fluctuations in a frustrated Heisenberg spin-Peierls chain
Weiße, A.; Wellein, G.; Fehske, H.
1999-09-01
As a simple model for spin-Peierls systems we study a frustrated Heisenberg chain coupled to optical phonons. In view of the anorganic spin-Peierls compound CuGeO3 we consider two different mechanisms of spin-phonon coupling. Combining variational concepts in the adiabatic regime and perturbation theory in the antiadiabatic regime we derive effective spin Hamiltonians which cover the dynamical effect of phonons in an approximate way. Ground-state phase diagrams of these models are determined, and the effect of frustration is discussed. Comparing the properties of the ground state and low-lying excitations with exact diagonalization data for the full quantum spin-phonon models, good agreement is found especially in the antiadiabatic regime.
Spin wave collapse and incommensurate fluctuations in URu_{2}Si_{2}
DEFF Research Database (Denmark)
Buyers, W.J.L.; Tun, Z.; Petersen, T.;
1994-01-01
To test if the T(N) = 17.7 K transition in URu2Si2 is driven by a divergence of a magnetic order parameter we performed high-resolution neutron scattering. At the ordering wave vector the spin-wave energy collapsed. and the susceptibility diverged as T(N) was approached. This confirms that the or...... order parameter is the magnetic dipole, as shown by recent symmetry arguments and polarized neutron experiments [1]. We also observe incommensurate fluctuations, suggesting that competing temperature-dependent interactions may influence this weak-moment transition.......To test if the T(N) = 17.7 K transition in URu2Si2 is driven by a divergence of a magnetic order parameter we performed high-resolution neutron scattering. At the ordering wave vector the spin-wave energy collapsed. and the susceptibility diverged as T(N) was approached. This confirms that the...
Anomalous Nernst-effect and spin fluctuations in LaFeAsO1-xFx
International Nuclear Information System (INIS)
We present Nernst-effect investigations on LaFeAsO1-xFx. In the parent compound the formation of a SDW state leads to a huge enhancement of the Nernst coefficient at TN. Despite the absence of SDW order at underdoped superconducting doping levels, a similar anomalous behavior is also observed (with smaller magnitude), which is suggestive of a spin-fluctuation enhanced Nernst-effect. Interestingly, at optimal doping level the Nernst coefficient is only weakly temperature dependent and appears more conventional.
Constructing a magnetic handle for antiferromagnetic manganites
Glavic, Artur; Dixit, Hemant; Cooper, Valentino R.; Aczel, Adam A.
2016-04-01
An intrinsic property of antiferromagnetic materials is the compensation of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets SrMnO3 and NdMnO3. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to A -type antiferromagnetism in thick NdMnO3 layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the SrMnO3 layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro- to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices.
Tran, Minh-Tien; Kim, Ki-Seok
2010-01-01
We reveal that local interactions in graphene allow novel spin liquids between the semi-metal and antiferromagnetic Mott insulating phases, identified with algebraic spin liquid and Z$_{2}$ spin liquid, respectively. We argue that the algebraic spin liquid can be regarded as the two dimensional realization of one dimensional spin dynamics, where antiferromagnetic correlations show exactly the same power-law dependence as valence bond correlations. Nature of the Z$_{2}$ spin liquid turns out t...
Effects of impurities and vortices on the low-energy spin excitations in high-T_{c} materials
DEFF Research Database (Denmark)
Andersen, Brian Møller; Graser, S.; Schmid, M.; Kampf, A. F.; Hirschfeld, P.J.
2011-01-01
We review a theoretical scenario for the origin of the spin-glass phase of underdoped cuprate materials. In particular it is shown how disorder in a correlated d-wave superconductor generates a magnetic phase by inducing local droplets of antiferromagnetic order which eventually merge and form a ...... disorder and/or applied magnetic fields lead to a slowing down of the dynamical spin fluctuations in agreement with neutron scattering and muon spin rotation (mSR) experiments....
Order and disorder in two geometrically frustrated antiferromagnets
International Nuclear Information System (INIS)
A great deal of attention has been given in recent years to the search for spin systems, both theoretical and experimental, with disordered ground states. The origin of magnetic ordering is fairly well understood and most systems do display some form of long range order. Notable exceptions are systems with so-called spin liquid states. These states exhibit novel magnetic properties which can not be fully explained by current theories. To study magnetic systems with spin liquid ground states, we look for models in which we expect fluctuations to destroy long range order. Geometrically frustrated systems, in which lattice geometry enhances fluctuations and inhibits the formation of long range order, have attracted a tremendous amount of attention from both experimentalists and theorists. In this thesis, we study two geometrically frustrated magnetic systems. Classical magnetism and geometrical frustration are introduced in Chapter 1, while geometrical frustration in quantum mechanical spin systems is reviewed in Chapter 3. Our first study, detailed in Chapter 2, deals with how dipolar interactions affect the ground state ordering in a classical Heisenberg antiferromagnet on the pyrochlore lattice, a network of corner sharing tetrahedra. Antiferromagnetic exchange alone is known not to induce ordering in this system. We analyze low temperature order resulting from the combined interactions, both by using a mean-field approach and by examining the energy cost of fluctuations about an ordered state. We discuss behavior as a function of the ratio of the dipolar and exchange interaction strengths and find two types of ordered phase. Below a certain value of this ratio, we find that the system orders in a four-sublattice Neel state. For interaction strengths above this critical ratio, the system orders with an incommensurate wavevector. We relate our results to the recent experimental work and reproduce and extend the theoretical calculations on the pyrochlore compound, Gd
Edge states in Open Antiferromagnetic Heisenberg Chains
Qin, Shaojin; Ng, Tai-Kai; Su, Zhao-Bin
1995-01-01
In this letter we report our results in investigating edge effects of open antiferromagnetic Heisenberg spin chains with spin magnitudes $S=1/2, 1,3/2,2$ using the density-matrix renormalization group (DMRG) method initiated by White. For integer spin chains, we find that edge states with spin magnitude $S_{edge}=S/2$ exist, in agreement with Valence-Bond-Solid model picture. For half-integer spin chains, we find that no edge states exist for $S=1/2$ spin chain, but edge state exists in $S=3/...
Ground-state selection from anharmonic zero-point energy in the pyrochlore antiferromagnet
Hizi, Uzi; Henley, Christopher L.
2004-03-01
In the pyrochlore lattice Heisenberg antiferromagnet, for large spin length S, the massive classical ground state degeneracy is partly lifted by the zero-point energy of quantum fluctuations at harmonic order in spin waves. [1] In a system of O(L^3) spins, there remained O(exp(const L)) collinear states, exactly degenerate to that order. We have extended the calculation to quartic order, assuming a Gaussian variational wavefunction (equivalent to Hartree-Fock approximation). Preliminary quartic calculations do break the harmonic-order degeneracy of two periodic ground states. We estimate the scaling with S of the mean-square spin fluctuations (which diverge at harmonic order). The results differ from analogous ones for the kagome Heisenberg antiferromagnet [2], where the harmonic-order ground states are coplanar. Our aim is to represent the quartic energy differences by an effective Ising Hamiltonian in the spirit of [1]. [1] C. L. Henley, APS March Meeting 2001, abstract W24.010. [2] A. Chubukov, PRL 69, 832 (1992); C. L. Henley and E. P. Chan, J. Mag. Mag. Mater. 140-144, 1693 (1995).
Energy Technology Data Exchange (ETDEWEB)
Phuc, Nguyen Thanh; Kawaguchi, Yuki [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Ueda, Masahito [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); ERATO Macroscopic Quantum Control Project, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
2011-10-15
We investigate the effects of thermal and quantum fluctuations on the phase diagram of a spin-1 {sup 87}Rb Bose-Einstein condensate (BEC) under the quadratic Zeeman effect. Due to the large ratio of spin-independent to spin-dependent interactions of {sup 87}Rb atoms, the effect of noncondensed atoms on the condensate is much more significant than that in scalar BECs. We find that the condensate and spontaneous magnetization emerge at different temperatures when the ground state is in the broken-axisymmetry phase. In this phase, a magnetized condensate induces spin coherence of noncondensed atoms in different magnetic sublevels, resulting in temperature-dependent magnetization of the noncondensate. We also examine the effect of quantum fluctuations on the order parameter at absolute zero and find that the ground-state phase diagram is significantly altered by quantum depletion.
Ferromagnetic response of a ``high-temperature'' quantum antiferromagnet
Wang, Xin
2014-03-01
We study the antiferromagnetic phase of the ionic Hubbard model at finite temperature using dynamical mean-field theory. We find that the ionic potential plays a dual role in determining the antiferromagnetic order. A small ionic potential (compared to the Hubbard repulsion) increases the super-exchange coupling, thereby implying an increase of the Neel temperature of the system, which should facilitate observation of antiferromagnetic ordering experimentally. On the other hand, for large ionic potential, the antiferromagnetic ordering is killed and the system becomes a charge density wave with electron occupancies alternating between 0 and 2. This novel way of degrading antiferromagnetism leads to spin polarization of the low energy single particle density of states. The dynamic response of the system thus mimics ferromagnetic behavior, although the system is still an antiferromagnet in terms of the static spin order. Work done in collaboration with Rajdeep Sensarma and Sankar Das Sarma, and supported by NSF-JQI-PFC, AFOSR MURI, and ARO MURI.
Weiß, Philipp S.; Narozhny, Boris N.; Schmalian, Jörg; Wölfle, Peter
2016-01-01
We study the temperature-dependent quantum correction to conductivity due to the interplay of spin density fluctuations and weak disorder for a two-dimensional metal near an antiferromagnetic (AFM) quantum critical point. AFM spin density fluctuations carry large momenta around the ordering vector Q and, at lowest order of the spin-fermion coupling, only scatter electrons between "hot spots" of the Fermi surface which are connected by Q . Earlier, it was seen that the quantum interference between AFM spin density fluctuations and soft diffusive modes of the disordered metal is suppressed, a consequence of the large-momentum scattering. The suppression of this interference results in a nonsingular temperature dependence of the corresponding interaction correction to conductivity. However, at higher order of the spin-fermion coupling, electrons on the entire Fermi surface can be scattered successively by two spin density fluctuations and, in total, suffer a small momentum transfer. This higher-order process can be described by composite modes which carry small momenta. We show that the interference between formally subleading composite modes and diffusive modes generates singular interaction corrections which ultimately dominate over the nonsingular first-order correction at low temperatures. We derive an effective low-energy theory from the spin-fermion model which includes the above-mentioned higher-order process implicitly and show that for weak spin-fermion coupling the small-momentum transfer is mediated by a composite propagator. Employing the conventional diagrammatic approach to impurity scattering, we find the correction δ σ ∝+ln2T for temperatures above an exponentially small crossover scale.
Dynamics of random spin systems
International Nuclear Information System (INIS)
We present inelastic neutron scattering experiments on three prototypical random magnets. For the dilute, insulating antiferromagnet Rb2Co/sub c/Mg/sub 1-c/F4, the randomness has purely geometrical consequences, and the anomalous dynamical behavior which we observe for c close to the magnetic percolation threshold is due to the fractal nature of percolating networks. Comparison of inelastic and quasielastic scattering data demonstrate the dynamical nature of the spin glass transition in amorphous, metallic MnSi. Finally, we show the coexistence of spin waves and static spin fluctuations near the crossover from ferromagnetic to spin glass behaviors in amorphous (Fe/sub x/Mn/sub 1-x/)75P16B6Al3
Energy Technology Data Exchange (ETDEWEB)
Amari, S., E-mail: siham_amari@yahoo.fr [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria); Mecabih, S.; Abbar, B.; Bouhafs, B. [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria)
2012-09-15
In this work, we aim to examine the spin-polarized electronic band structures, the local densities of states as well as the magnetism of Zn{sub 1-x}TM{sub x}Se (TM=Cr, Fe, Co and Ni) diluted magnetic semiconductors in the ferromagnetic (FM) and antiferromagnetic (AFM) phases, and with 25% of TM. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation (GGA) form. We treated the ferromagnetic and antiferromagnetic phases and we found that all compounds are stable in the ferromagnetic structure. Structural properties are computed after total energy minimization. Our results show that the cohesive energies of Zn{sub 0.75}TM{sub 0.25}Se are greater than that of zinc blende ZnSe. We discuss the electronic structures, total and partial densities of states, local moments and the p-d exchange splitting. Furthermore, we found that p-d hybridization reduces the local magnetic moment of TM and produces small local magnetic moments on the nonmagnetic Zn and Se sites. We found also that in the AFM phase the TM local magnetic moments are smaller than in the FM phase; this is due to the greater interaction of the TM d-up and d-down orbitals. - Highlights: Black-Right-Pointing-Pointer The calculation of the exchange constants of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer Prediction of the spin-exchange splitting of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer The study of ZnTMSe diluted magnetic semiconductors in the FM and AFM phases.
Fluctuation of the nuclear spin axis in deep-inelastic reactions
International Nuclear Information System (INIS)
In a high resolution γ-spectroscopic study of 96.5-MeV 16O + 48Ti deep-inelastic reactions the authors have found selective population of yrast states in the decay of the heavy fragment. In coincidence with a ΔE-E heavy ion telescope at THETAsup(lab) = 350 γ-spectra were recorded with a Ge(Li) detector placed in the reaction plane at 450, 900 and 1800 and out-of-plane in the direction of the scattering normal. From the intensities and the anisotropies of the discrete yrast transitions the authors obtain detailed information about the spin transfer in the primary reaction and the fragment spin alignment. (orig./AH)
Heisenberg antiferromagnet on the Husimi lattice
Liao, H. J.; Xie, Z. Y.; Chen, J.; Han, X. J.; Xie, H. D.; Normand, B.; Xiang, T.
2016-02-01
We perform a systematic study of the antiferromagnetic Heisenberg model on the Husimi lattice using numerical tensor-network methods based on projected entangled simplex states. The nature of the ground state varies strongly with the spin quantum number S . For S =1/2 , it is an algebraic (gapless) quantum spin liquid. For S =1 , it is a gapped, nonmagnetic state with spontaneous breaking of triangle symmetry (a trimerized simplex-solid state). For S =2 , it is a simplex-solid state with a spin gap and no symmetry breaking; both integer-spin simplex-solid states are characterized by specific degeneracies in the entanglement spectrum. For S =3/2 , and indeed for all spin values S ≥5/2 , the ground states have 120∘ antiferromagnetic order. In a finite magnetic field, we find that, irrespective of the value of S , there is always a plateau in the magnetization at m =1/3 .
Investigation of the critical relaxation in MnF$_{2}$ by muon spin rotation
De Renzi, R; Cox, S F J; Guidi, G; Tedeschi, R A
1982-01-01
The magnetic relaxation in MnF/sub 2/ has been studied by means of Muon Spin Rotation. An increase was found close to T/sub N/ in the damping of the precession signal from positive muons implanted in a single-crystal sample. This is attributed to the critical slowing down of the antiferromagnetic spin fluctuations. An orientation-dependent shift in the signal frequency was also detected. The location of the muon in the lattice is tentatively determined.
The low-temperature phase of the Heisenberg antiferromagnet in a fermionic representation
International Nuclear Information System (INIS)
Thermal properties of the ordered phase of the spin 1/2 isotropic Heisenberg Antiferromagnet on a d-dimensional hypercubical lattice are studied within the fermionic representation when the constraint of a single occupancy condition is taken into account by the method suggested by Popov and Fedotov. Using a saddle point approximation in the path integral approach we discuss not only the leading order but also the fluctuations around the saddle point at one-loop level. The influence of taking into account the single occupancy condition is discussed at all steps. (author)
Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate.
Seo, Sang Won; Kang, Seji; Kwon, Woo Jin; Shin, Yong-il
2015-07-01
We report on the observation of half-quantum vortices (HQVs) in the easy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate. Using in situ magnetization-sensitive imaging, we observe that pairs of HQVs with opposite core magnetization are generated when singly charged quantum vortices are injected into the condensate. The dynamics of HQV pair formation is characterized by measuring the temporal evolutions of the pair separation distance and the core magnetization, which reveals the short-range nature of the repulsive interactions between the HQVs. We find that spin fluctuations arising from thermal population of transverse magnon excitations do not significantly affect the HQV pair formation dynamics. Our results demonstrate the instability of a singly charged vortex in the antiferromagnetic spinor condensate. PMID:26182102
NMR study of spin fluctuations and superconductivity in LaFeAsO1-xHx
Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Yoichi; Kontani, Hiroshi
2013-03-01
We have performed NMR measurements in LaFeAsO1-xHx, an isomorphic compound of LaFeAsO1-xFx. LaFeAsO1-xHx is most recently known for having double superconducting (SC) domes on H doping. LaFeAsO1-xHx is an electron- doped system, and protons act as H-1 as well as F-1. The first SC dome is very similar between F and H doping, suggesting that H doping supplies the same amount of electrons as F doping. Interestingly, an excess amount of H up to x=0.5 can be replaced with O2-. In the H-overdoped regime (x > 0 . 2), LaFeAsO1-xHx undergoes the second superconducting state. We measured the relaxation rate of LaFeAsO1-xHx for x=0.2 and 0.4, and fond an anomalous electronic state; spin fluctuations measured from 1 /T1 T is enhanced with increasing the doping level from x = 0 . 2 to 0.4. The enhancement of spin fluctuations with increasing carrier doping is a new phenomenon that has not observed in LaFeAsO1-xFx in which the upper limit of the doping level is at most x = 0 . 2 . We will discuss the phenomenon in relation to superconductivity. Grant (KAKENHI 23340101) from the Ministry of Education, Sports and Science, Japan
Cao, Chongde; Wildes, Andrew; Li, Haifeng; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modula...
Exchange bias in diluted-antiferromagnet/antiferromagnet bilayers
International Nuclear Information System (INIS)
The hysteresis-loop properties of a diluted-antiferromagnetic (DAF) layer exchange coupling to an antiferromagnetic (AF) layer are investigated by means of numerical simulations. Remarkable loop shift and coercivity enhancement are observed in such DAF/AF bilayers, while they are absent in the uncoupled DAF single layer. The influences of pinned domains, dilution, cooling field and DAF layer thickness on the loop shift are investigated systematically. The result unambiguously confirms an exchange bias (EB) effect in the DAF/AF bilayers. It also reveals that the EB effect originates from the pinned AF domains within the DAF layer. In contrast to conventional EB systems, frozen uncompensated spins are not found at the interface of the AF pinning layer. (paper)
Critical Casimir force and its fluctuations in lattice spin models: exact and Monte Carlo results.
Dantchev, Daniel; Krech, Michael
2004-04-01
We present general arguments and construct a stress tensor operator for finite lattice spin models. The average value of this operator gives the Casimir force of the system close to the bulk critical temperature T(c). We verify our arguments via exact results for the force in the two-dimensional Ising model, d -dimensional Gaussian, and mean spherical model with 2 = k(b) T(c) (d-1)Delta/ (L/a)(d), where L is the distance between the plates and Delta is the (universal) Casimir amplitude. PMID:15169081
International Nuclear Information System (INIS)
We review the main properties of spin waves condensation to a coherent quantum state, named homogeneously precessing domain (HPD). We describe the long range coherent transport of magnetization by spin supercurrent in antiferromagnetic superfluid He3. This quantum phenomenon was discovered 20 years ago. Since then, many magnetic extensions of superconductivity and superfluidity have been observed: spin Josephson phenomena, spin-current vortices, spin phase slippage, long distance magnetization transport by spin supercurrents, etc. Several new supercurrent phenomena have been discovered, like magnetically excited coherent quantum states, NMR in the molecular Landau field, spin-current turbulence, formation of stable non-topological solitons, etc
Observation of magnetic fragmentation in spin ice
Petit, S.; Lhotel, E.; Canals, B.; Ciomaga Hatnean, M.; Ollivier, J.; Mutka, H.; Ressouche, E.; Wildes, A. R.; Lees, M. R.; Balakrishnan, G.
2016-08-01
Fractionalized excitations that emerge from a many-body system have revealed rich physics and concepts, from composite fermions in two-dimensional electron systems, revealed through the fractional quantum Hall effect, to spinons in antiferromagnetic chains and, more recently, fractionalization of Dirac electrons in graphene and magnetic monopoles in spin ice. Even more surprising is the fragmentation of the degrees of freedom themselves, leading to coexisting and a priori independent ground states. This puzzling phenomenon was recently put forward in the context of spin ice, in which the magnetic moment field can fragment, resulting in a dual ground state consisting of a fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic monopole crystal. Here we show, by means of neutron scattering measurements, that such fragmentation occurs in the spin ice candidate Nd2Zr2O7. We observe the spectacular coexistence of an antiferromagnetic order induced by the monopole crystallization and a fluctuating state with ferromagnetic correlations. Experimentally, this fragmentation manifests itself through the superposition of magnetic Bragg peaks, characteristic of the ordered phase, and a pinch point pattern, characteristic of the Coulomb phase. These results highlight the relevance of the fragmentation concept to describe the physics of systems that are simultaneously ordered and fluctuating.
International Nuclear Information System (INIS)
The geometrically frustrated antiferromagnet Gd2Ti2O7 is an easy-planer anisotropic system in which single ion anisotropy mainly arises due to the considerable admixture of higher Russel-Saunders terms of Gd3+ ion to its ground term 8S. The g-value of the ground CF doublet becomes anisotropic, g parallel = 1.99, g perpendicular = 7.97, instead of the free-ion isotropic value 2. The ground multiplet 8S7/2 splits into 4 doublets with total splitting ∼16 K, thus exhibiting its characteristic specific heat feature below 5 K. (author)
Lattice distortion in disordered antiferromagnetic XY models
Institute of Scientific and Technical Information of China (English)
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.
Spin fluctuation effects on the conductance through a single Pd atom contact
Energy Technology Data Exchange (ETDEWEB)
Romero, M A; Goldberg, E C [Instituto de Desarrollo Tecnologico para la Industria Quimica (INTEC), Universidad Nacional del Litoral, Consejo Nacional de Investigaciones CientIficas y Tecnicas (CONICET), Gueemes 3450 CC 91, 3000 Santa Fe (Argentina); Gomez-Carrillo, S C; Bolcatto, P G [Departamento de Fisica, Facultad de IngenierIa Quimica, Universidad Nacional de Litoral, Santiago del Estero 2829, 3000 Santa Fe (Argentina)
2009-05-27
A controversy about the conductance through single atoms still exists. There are many experiments where values lower than the quantum unity G{sub 0} = 2e{sup 2}/h have been found associated to Kondo regimes with high Kondo temperatures. Specifically in the Pd single atom contact, conductance values close to G{sub 0}/2 at room temperature have been reported. In this work we propose a theoretical analysis of a break junction of Pd where the charge fluctuation in the single atom contact is limited to the most probable one: d{sup 10}{r_reversible}d{sup 9}. The projected density of states and the characteristics of the electron transport are calculated by using a realistic description of the interacting system. A Kondo regime is found where the conductance values and their dependence on temperature are in good agreement with the experimental trends observed in the conduction of single molecule transistors based on transition metal coordination complexes.
Tricritical behavior of the frustrated XY antiferromagnet
Plumer, M. L.; Mailhot, A.; Caillé, A.
1994-01-01
Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding th...
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
Anisotropic inplane spin correlation in the parent and Co-doped BaFe2As2: A neutron scattering study
International Nuclear Information System (INIS)
Highlights: • Doping dependence study of inplane spin correlation in the normal states. • Anisotropy is larger for the higher doping level. • Temperature dependence of spin correlation in the parent compound is unusual. - Abstract: Antiferromagnetic spin fluctuations were investigated in the normal states of the parent (x = 0), under-doped (x = 0.04) and optimally-doped (x = 0.06) Ba(Fe1-xCox)2As2 single crystals using inelastic neutron scattering technique. For all the doping levels, quasi-two-dimensional antiferromagnetic fluctuations were observed as a broad peak localized at Q=(1/2,1/2,l). At lower energies, the peak shows an apparent anisotropy in the hk0 plane; longitudinal peak widths are considerably smaller than transverse widths. The anisotropy is larger for the higher doping level. These results are consistent with the random phase approximation (RPA) calculations taking account of the orbital character of the electronic bands, confirming that the anisotropic nature of the spin fluctuations in the normal states is mostly dominated by the nesting of Fermi surfaces. On the other hand, the quasi-two-dimensional spin correlations grow much rapidly for decreasing temperature in the x = 0 parent compound, compared to that expected for nearly antiferromagnetic metals. This may be another sign of the unconventional nature of the antiferromagnetic transition in BaFe2As2
Antiferromagnetism and d-wave superconductivity in the Hubbard model
International Nuclear Information System (INIS)
The two-dimensional Hubbard model is a promising effective model for the electronic degrees of freedom in the copper-oxide planes of high temperature superconductors. We present a functional renormalization group approach to this model with focus on antiferromagnetism and d-wave superconductivity. In order to make the relevant degrees of freedom more explicitly accessible on all length scales, we introduce composite bosonic fields mediating the interaction between the fermions. Spontaneous symmetry breaking is reflected in a non-vanishing expectation value of a bosonic field. The emergence of a coupling in the d-wave pairing channel triggered by spin wave fluctuations is demonstrated. Furthermore, the highest temperature at which the interaction strength for the electrons diverges in the renormalization flow is calculated for both antiferromagnetism and d-wave superconductivity over a wide range of doping. This ''pseudo-critical'' temperature signals the onset of local ordering. Moreover, the temperature dependence of d-wave superconducting order is studied within a simplified model characterized by a single coupling in the d-wave pairing channel. The phase transition within this model is found to be of the Kosterlitz-Thouless type. (orig.)
Antiferromagnetism and d-wave superconductivity in the Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Krahl, H.C.
2007-07-25
The two-dimensional Hubbard model is a promising effective model for the electronic degrees of freedom in the copper-oxide planes of high temperature superconductors. We present a functional renormalization group approach to this model with focus on antiferromagnetism and d-wave superconductivity. In order to make the relevant degrees of freedom more explicitly accessible on all length scales, we introduce composite bosonic fields mediating the interaction between the fermions. Spontaneous symmetry breaking is reflected in a non-vanishing expectation value of a bosonic field. The emergence of a coupling in the d-wave pairing channel triggered by spin wave fluctuations is demonstrated. Furthermore, the highest temperature at which the interaction strength for the electrons diverges in the renormalization flow is calculated for both antiferromagnetism and d-wave superconductivity over a wide range of doping. This ''pseudo-critical'' temperature signals the onset of local ordering. Moreover, the temperature dependence of d-wave superconducting order is studied within a simplified model characterized by a single coupling in the d-wave pairing channel. The phase transition within this model is found to be of the Kosterlitz-Thouless type. (orig.)
Wang, Ze
2012-12-01
Denoising is critical to improving the quality and stability of cerebral blood flow (CBF) quantification in arterial spin labeled (ASL) perfusion magnetic resonance imaging (MRI) due to the intrinsic low signal-to-noise-ratio (SNR) of ASL data. Previous studies have been focused on reducing the spatial or temporal noise using standard filtering techniques, and less attention has been paid to two global nuisance effects, the residual motion artifacts and the global signal fluctuations. Since both nuisances affect the whole brain, removing them in advance should enhance the CBF quantification quality for ASL MRI. The purpose of this paper was to assess this potential benefit. Three methods were proposed to suppress each or both of the two global nuisances. Their performances for CBF quantification were validated using ASL data acquired from 13 subjects. Evaluation results showed that covarying out both global nuisances significantly improved temporal SNR and test-retest stability of CBF measurement. Although the concept of removing both nuisances is not technically novel per se, this paper clearly showed the benefits for ASL CBF quantification. Dissemination of the proposed methods in a free ASL data processing toolbox should be of interest to a broad range of ASL users. PMID:22789842
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. PMID:27518832
Energy Technology Data Exchange (ETDEWEB)
Zhu, Jian-xin [Los Alamos National Laboratory; Dai, Jianhui [ZHEJIANG UNIV; Si, Qimiao [RICE UNIV
2009-01-01
Some of the high {Tc} iron pnictides contain rare-earth elements, raising the question of how the existence and tunability of a d-electron antiferromagnetic order influences the heavy fermion behavior of the f-moments. With CeOFeP and CeOFeAs in mind as prototypes, we derive an extended Anderson lattice model appropriate for these quaternary systems. We show that the Kondo screening of the f-moments are efficiently suppressed by the d-electron ordering. We also argue that, inside the d-electron ordered state (as in CeOFeAs), the f-moments provide a rare realization of a quantum frustrated magnet with competing J{sub 1}-J{sub 2}-J{sub 3} interactions in an effective square lattice. Implications ofr the heavy fermion physics in broader contexts are also discussed.
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
International Nuclear Information System (INIS)
domain wall formation, antiferromagnetically induced density shifts, and we show the relevant role of spin-imbalance for antiferromagnetic states. Since the first step for understanding the physics of the examined models was the application of a mean field approximation, we analyze the effect of including the second order terms of the weak coupling perturbation expansion for the repulsive model. We show that our results survive the influence of quantum fluctuations and show that the renormalization factors for order parameters and critical temperatures lead to a weaker influence of the fluctuations on the results in finite sized systems than on the results in the thermodynamical limit. Furthermore, in the context of second order theory we address the question whether results obtained in the dynamical mean field theory (DMFT), which is meanwhile a frequently used method for describing trapped systems, survive the effect of the non-local Feynman diagrams neglected in DMFT. (
Magnetic Properties of Quantum Ferrimagnetic Spin Chains
Yamamoto, Shoji
1998-01-01
Magnetic susceptibilities of spin-$(S,s)$ ferrimagnetic Heisenberg chains are numerically investigated. It is argued how the ferromagnetic and antiferromagnetic features of quantum ferrimagnets are exhibited as functions of $(S,s)$. Spin-$(S,s)$ ferrimagnetic chains behave like combinations of spin-$(S-s)$ ferromagnetic and spin-$(2s)$ antiferromagnetic chains provided $S=2s$.
Golovenchits, E I
2001-01-01
One studied spin dynamics and dynamics of lattice in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu) crystals within 20-250 GHz frequency range and within 50350 K temperature interval. One detected abrupt variation of absorption coefficient within wide range of frequencies above 120 GHz at 20, 80 and 150 K temperatures in R sub 2 CuO sub 4 (R = Pr, Sm, and Eu), respectively. Absorption jumpings result from structural phase transitions. Wide ranges of spin-wave excitations were observed in all examined crystals in high-temperature phase. Close to temperatures of phase transitions within wide range of frequencies including frequencies corresponding to ranges of spin-wave excitations one observed lines of a absorption caused by lattice dynamics
International Nuclear Information System (INIS)
By employing neutron spin echo and small-angle neutron scattering, we determined the structure factor of the frozen concentration fluctuations on nano-length scales in a swollen poly(N-isopropyl acrylamide) gel. The frozen contribution, showing a plateau at the low scattering wavenumber q (-1) and a rapid decrease close to q-4 at high q (>0.02 A-1), is intimately related to the abnormal butterfly scattering pattern appearing at low q under deformation. (orig.)
International Nuclear Information System (INIS)
It has been shown that the spin-density wave instability does not coexist with s-like anisotropic superconductivity in the molecular field approach to the nearly half-filled two-dimensional Hubbard model. The phase diagram of the interplay of normal state, spin density wave, d-wave and extended s-wave superconducting orderings has been constructed. The possibility of the first order transition from the normal state and the superconducting state to the SDW-phase has been discussed. (author). 14 refs, 2 figs
Indian Academy of Sciences (India)
K K Choudhary; N Gupta; N Kaurav; S Katiyal; S K Ghosh
2014-08-01
The anomalous temperature-dependent electrical resistivity ρ() of La0.875Sr0.125MnO3 manganite nanoparticles (particle size 18 nm) is theoretically analysed. ρ() exhibits semiconducting phase in lowtemperature regime (20 < < 53 K), shows a minima near 53 K and increases with at high temperatures (53 < < 170 K). The resistivity in metallic phase ( > 53 K) is theoretically analysed by considering the strong spin-fluctuation effect, which is modelled using Drude–Lorentz type function. In addition to the spin fluctuation-induced contribution, the electron–phonon and electron–electron $ ρe–e() = 2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons ( ρac) as well as high-frequency optical phonons ( ρop) were estimated using Bloch–Gruneisen (BG) model of resistivity. It is observed that the resistivity contribution due to electron–electron interaction shows typical quadratic temperature dependence. Spin fluctuation-induced resistivity is dominant over electron–electron and electron–phonon contributions in overall temperature range in the manganite nanoparticles. Resistivity in the semiconducting phase is discussed with small polaron conduction (SPC) model. SPC model consistently retraces the low-temperature resistivity behaviour ( < 53 K). Finally, the theoretically calculated resistivity compared with experimental data is found to be consistent in wide range of temperature.
Antiferromagnetic noise correlations in optical lattices
DEFF Research Database (Denmark)
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...
Christianson, A. D.
2012-02-01
The origin of superconductivity in the Fe-based superconductors, like that in other unconventional superconductors, remains shrouded in mystery. How the pairing bosons emerge either due to or in spite of the strong magnetic interactions found in the Fe-based superconductors is one of the most thoroughly investigated questions in the field. A prominent example of the interplay of superconductivity and magnetism is the dramatic shift of spectral weight from the low energy spin excitations to an energy which is related to the superconducting gap resulting in a peak in the spin excitation spectrum localized in both momentum and energy which occurs at the onset of superconductivity. The appearance of the new peak in the spin excitation spectrum below the superconducting transition temperature is referred to as s spin resonance and is most commonly interpreted as indicating a sign change of the superconducting order parameter on different portions of the Fermi surface and thus is consistent with an extended s-wave or s± pairing symmetry in many Fe-based superconductors. We will review the observations and implications of the spin resonance across the Fe-based superconductors. In particular we will examine the relationship between the resonance energy and the superconducting transition temperature as a function of chemical doping and pressure. While the spin resonance provides important information about pairing symmetry, there does not appear to be sufficient spectral to explain the pairing strength. Thus the remainder of the spin excitation spectrum must be examined to determine if spin fluctuations are ultimately responsible for pairing in the Fe-based materials. Consequently, we will discuss in detail the way in which the spin excitations evolve from the nonsuperconducting compounds to their superconducting relatives as a function of chemical doping.
Directory of Open Access Journals (Sweden)
Hiroshi Akiba
2012-07-01
Full Text Available Quasi-two-dimensional organic conductor λ-BETS2FeCl4 (BETS = bis(ethylenedithiotetraselenafulvalene transforms from a paramagnetic metal (PM to an antiferromagnetic insulator (AFI at a transition temperature, TMI, of 8.3 K under zero magnetic field. To understand the mechanism of this PM-AFI phase transition, we studied the thermodynamic properties of λ-BETS2FeCl4. We observed, below TMI, a six-level Schottky hump in its specific heat and a broad shoulder in its magnetic susceptibility. Just below the transition temperature TMI, about 80% of 3d spin degree of freedom is sustained. These temperature dependences clarify that π and 3d spins do not cooperatively form the AF order at TMI. In λ-BETS2FexGa1−xCl4 system, the increasing Fe 3d spin density enhances the internal magnetic field caused by π spin antiferromagnetic (AF ordering, although the 3d spin itself maintains large entropy against the AF ordering. It was confirmed that the Fe 3d spin provided favorable conditions for this mysterious PM-AFI phase transition in the π electron system. We propose that this phase transition originates from the magnetic anisotropy introduced by the π-d interaction, which suppressed the low dimensional fluctuation in the π spin system.
Unconventional resistivity at the border of metallic antiferromagnetism in NiS2
Niklowitz, P. G.; Alireza, P. L.; Steiner, M. J.; Lonzarich, G. G.; Braithwaite, D.; Knebel, G.; Flouquet, J.; Wilson, J. A.
2008-03-01
We report low-temperature and high-pressure measurements of the electrical resistivity ρ(T) of the antiferromagnetic compound NiS2 in its high-pressure metallic state. The form of ρ(T,p) suggests the presence of a quantum phase transition at a critical pressure pc=76±5kbar . Near pc , the temperature variation of ρ(T) is similar to that observed in NiS2-xSex near the critical composition x=1 , where metallic antiferromagnetism is suppressed at ambient pressure. In both cases, ρ(T) varies approximately as T1.5 over a wide range below 100K . This lets us assume that the high-pressure metallic phase of stoichiometric NiS2 also develops itinerant antiferromagnetism, which becomes suppressed at pc . However, on closer analysis, the resistivity exponent in NiS2 exhibits an undulating variation with temperature not seen in NiSSe (x=1) . This difference in behavior may be due to the effects of spin-fluctuation scattering of charge carriers on cold and hot spots of the Fermi surface in the presence of quenched disorder, which is higher in NiSSe than in stoichiometric NiS2 .
On the ground state of antiferromagnets at zero temperature
Mayer, I.; Angelov, S. A.
1984-02-01
The wave function describing a perfect antiferromagnetic ordering of spins at 0 K (the singlet projection of the Néel function) was proved to be not an eigenfunction of the exchange Hamiltonian: the long-range order is reduced as to permit a higher correlation between the nearest-neighbour spins.
Spins in the vortices of a high-temperature superconductor
DEFF Research Database (Denmark)
Lake, B.; Aeppli, G.; Clausen, K.N.; McMorrow, D.F.; Lefmann, K.; Hussey, N.E.; Mangkorntong, N.; Nohara, M.; Takagi, H.; Mason, T.E.; Schröder, A.
2001-01-01
Neutron scattering is used to characterize the magnetism of the vortices for the optimally doped high-temperature superconductor La2-xSrxCuO4 (x = 0.163) in an applied magnetic field. As temperature is reduced, Low-frequency spin fluctuations first disappear with the loss of vortex mobility, but...... then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic...
Antiferromagnetic coupling across silicon regulated by tunneling currents
Gareev, Rashid; Schmid, Maximilian; Vancea, Johann; Back, Christian; Schreiber, Reinert; Buergler, Daniel; Stromberg, Frank; Wende, Heiko
2012-02-01
We present the room temperature enhancement of antiferromagnetic coupling in epitaxial Fe(3 nm)/Si(2.4 nm)/Fe(3 nm) structures by voltage-driven spin-polarized tunneling currents. Using the ballistic electron magnetic microscopy we established that the saturation field for the collector current corresponding to parallel alignment of magnetizations rises up with the tunneling current, thus demonstrating stabilization of the antiparallel alignment and increase of antiferromagnetic coupling. We connect the enhancement of antiferromagnetic coupling with local dynamic spin torques mediated by spin-polarized tunneling electrons. Finally, in the antiparallel state the spin-polarized majority (minority) electrons exert dynamic torques in the bottom (upper) iron layer and, thus, additionally stabilize magnetization alignment.
Brant, Jacilynn A; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A
2014-12-01
Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN ≈ 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors km = [1/2, 1/2, 1/2] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mössbauer spectroscopy confirmed the presence of Fe(2+) and Sn(4+) as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy. PMID:25397682
Quantum order by disorder in frustrated diamond lattice antiferromagnets.
Bernier, Jean-Sébastien; Lawler, Michael J; Kim, Yong Baek
2008-07-25
We present a quantum theory of frustrated diamond lattice antiferromagnets. Considering quantum fluctuations as the predominant mechanism relieving spin frustration, we find a rich phase diagram comprising of six phases with coplanar spiral ordering in addition to the Néel phase. By computing the specific heat of these ordered phases, we obtain a remarkable agreement between (k, k, 0) spiral ordering and the experimental specific heat data for the diamond lattice spinel compounds MnSc2S4, Co3O4, and CoRh2O4, i.e., specific heat data is a strong evidence for (k, k, 0) spiral ordering in all of these materials. This prediction can be tested in future neutron scattering experiments on Co3O4 and CoRh2O4, and is consistent with existing neutron scattering data on MnSc2S4. Based on this agreement, we infer a monotonically increasing relationship between frustration and the strength of quantum fluctuations. PMID:18764361
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.
Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets
Kadomtseva, A.M.; Zvezdin, A. K.; Popov, Yu. F.; Pyatakov, A. P.; Vorob'ev, G. P.
2004-01-01
The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to the diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear m...
Phase separation of holes in antiferromagnets
International Nuclear Information System (INIS)
It is shown that dilute holes in an antiferromagnet are unstable against phase separation into a hole-rich phase and a no-hole phase. When the spin exchange interaction J exceeds a critical value Jc, one phase consists of all holes, the other all electrons. The argument is presented in detail for the t--J model but evidence of phase separation in other models is mentioned. 11 refs
Pan, B. Y.; Wang, Y.; Zhang, L J; Li, S. Y.
2013-01-01
Single crystals of a metal organic complex \\ce{(C5H12N)CuBr3} (\\ce{C5H12N} = piperidinium, pipH for short) have been synthesized and the structure was determined by single-crystal X-ray diffraction. \\ce{(pipH)CuBr3} crystallizes in the monoclinic group $C$2/$c$. Edging-sharing \\ce{CuBr5} units link to form zigzag chains along the $c$ axis and the neighboring Cu(II) ions with spin-1/2 are bridged by bi-bromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fi...
Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn{sub 0.5}Fe{sub 0.5}O{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Nhalil, Hariharan, E-mail: hariharan@physics.iisc.ernet.in, E-mail: hariharan.nhalil@gmail.com; Sanathkumar, R.; Elizabeth, Suja [Department of Physics, Indian Institute of Science, Bangalore 560012 (India); Nair, Harikrishnan S. [Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006 (South Africa); Strydom, André M. [Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, P.O. Box 524, Auckland Park 2006 (South Africa); Max Planck Institute for Chemical Physics of Solids (MPICPfS), Nöthnitzerstraße 40, 01187 Dresden (Germany)
2015-05-07
Orthorhombic single crystals of TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} are found to exhibit spin-reorientation, magnetization reversal, and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b, and c. A broad magnetic transition is visible at T{sub N}{sup Fe/Mn}=286 K due to paramagnetic to A{sub x}G{sub y}C{sub z} ordering. A sharp transition is observed at T{sub SR}{sup Fe/Mn}=28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to G{sub x}A{sub y}F{sub z} configuration. The negative magnetization observed below T{sub SR}{sup Fe/Mn} along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2 K. TbMn{sub 0.5}Fe{sub 0.5}O{sub 3} could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.
Lv, Yi-Fei; Xiang, Jian-Yong; Wen, Fu-Sheng; Lv, Wei-Ming; Hu, Wen-Tao; Liu, Zhong-Yuan
2015-03-01
Single phase of Fe3+-doped α-Ga2-xFexO3 (α-GFxO, x = 0.1, 0.2, 0.3, 0.4) is synthesized by treating the β-Ga2-xFexO3 (β-GFxO) precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe3+ content. Calorimetric measurements show that the temperature of the phase transition from α-GFxO to β-GFxO increases, while the associated enthalpy change decreases upon increasing Fe3+ content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3+ content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe3+ ions is antiferromagnetic. Remnant magnetization is observed in the Fe3+-doped α-GFxO and is attributed to the spin glass in the magnetic sublattice. At high Fe3+ doping level (x = 0.4), two evident peaks are observed in the image part of the AC susceptibility . The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α-GF0.4O is suggested to be the behavior of two spin glasses. Project supported by the National Basic Research Program of China (Grant No. 2010CB731605), the National Science Fund for Distinguished Young Scholars of China (Grant No. 51025103), the National Natural Science Foundation of China (Grant Nos. 51172198 and 51102206), the Natural Science Foundation of Hebei Province, China (Grant No. E2014203144), the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province, China (Grant No. YQ2014009), and the Research Program of the College Science & Technology of Hebei Province, China (Grant No. QN2014047).
International Nuclear Information System (INIS)
The magnetic anisotropy and the spin fluctuations of the paramagnetic molecule [Fe(OMe)(dpm)2]2 are analyzed by means of Moessbauer spectroscopy in the temperature range [7.6-33] K. Spectra in the presence of a 5 T magnetic field directed along the γ rays were collected, by using a sample of pseudo-single crystal prepared by oriented grains. From the fits of the spectra, the hyperfine parameters are determined. Fits give also the value and direction of the magnetic anisotropy, referred to the electric field gradient (EFG) principal axes. The latter, together with the EFG components, were evaluated by means of ROHF ab initio calculations. Lastly, the rate of the spin transitions in function of T is discussed
Classical and quantum anisotropic Heisenberg antiferromagnets
Directory of Open Access Journals (Sweden)
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.
Control of antiferromagnetic domain distribution via polarization-dependent optical annealing.
Higuchi, Takuya; Kuwata-Gonokami, Makoto
2016-01-01
The absence of net magnetization inside antiferromagnetic domains has made the control of their spatial distribution quite challenging. Here we experimentally demonstrate an optical method for controlling antiferromagnetic domain distributions in MnF2. Reduced crystalline symmetry can couple an order parameter with non-conjugate external stimuli. In the case of MnF2, time-reversal symmetry is macroscopically broken reflecting the different orientations of the two magnetic sublattices. Thus, it exhibits different absorption coefficients between two orthogonal linear polarizations below its antiferromagnetic transition temperature under an external magnetic field. Illumination with linearly polarized laser light under this condition selectively destructs the formation of a particular antiferromagnetic order via heating. As a result, the other antiferromagnetic order is favoured inside the laser spot, achieving spatially localized selection of an antiferromagnetic order. Applications to control of interface states at antiferromagnetic domain boundaries, exchange bias and control of spin currents are expected. PMID:26911337
Bond-Dilution-Induced Quantum Phase Transitions in Heisenberg Antiferromagnets
Yasuda, Chitoshi; Todo, Synge; Takayama, Hajime
2006-01-01
Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of the quantum Monte Carlo simulation. It is found that, when the ground state of the non-diluted system is a non-magnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid gap in the original spin gap, and under a further stronger bond dilution an antiferromagnetic long-...
Nanoparticles of antiferromagnetic materials
DEFF Research Database (Denmark)
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...
Neutron Scattering Studies of the Anti-ferromagnetic Phase of Cd1-xMnxTe
DEFF Research Database (Denmark)
Giebultowicz, T.; Minor, W.; Buras, B.; Lebech, Bente; Galazka, R. R.
1982-01-01
Studies of the magnetic properties of crystals of the mixed semiconductors Cd1-xMnxTe indicate that: (i) for x ≤ 0.17 the crystals are paramagnetic at all temperatures, (ii) for 0.17
Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model
International Nuclear Information System (INIS)
Results of a renormalization group study for the 2-dimensional Hubbard model close to half-filling at finite temperature are presented. Bosonic degrees of freedom corresponding to antiferromagnetic and d-wave superconducting order are introduced, and flow equations for the corresponding coupling constants are deduced from an exact flow equation for the effective average action. The influence of bosonic fluctuations on the onset of local antiferromagnetic order is discussed. At low enough temperatures and close to half-filling the discrete symmetry of the lattice is broken and incommensurate antiferromagnetic fluctuations dominate. The phase diagram is shown for the parameter regime close to half-filling in the presence of vanishing as well as non-vanishing next-to-nearest-neighbor hopping t'. Finally, the potential emergence of d-wave superconducting order at larger distances from half-filling is discussed.
Cumulant approach to weakly doped antiferromagnets
International Nuclear Information System (INIS)
We present an approach to static and dynamical properties of holes and spins in weakly doped antiferromagnets in two dimensions. The calculations are based on a recently introduced cumulant approach to ground endash state properties of correlated electronic systems. The present method allows us to evaluate hole and spin-wave dispersion relations by considering hole or spin excitations of the ground state. Usually, these dispersions are found from time-dependent correlation functions. To demonstrate the ability of the approach we first derive the dispersion relation for the lowest single hole excitation at half-filling. However, the main purpose of this paper is to focus on the mutual influence of mobile holes and spin waves in the weakly doped system. It is shown that low-energy spin excitations strongly admix to the ground state. The coupling of spin waves and holes leads to a strong suppression of the staggered magnetization which cannot be explained by a simple rigid-band picture for the hole quasiparticles. Also the experimentally observed doping dependence of the spin-wave excitation energies can be understood within our formalism. copyright 1996 The American Physical Society
International Nuclear Information System (INIS)
The relevance of higher multipoles of giant isovector modes in the charge distribution of deep inelastic fragments is discussed and found to depend strongly on mass asymmetry. The sources of angular momentum fluctuations are investigated. Quantal effects are considered as well as effects arising from non-equilibrium and equilibrium statistical fluctuations. A model based upon equilibrium statistical mechanics is considered in detail, and used to predict both 2nd moments of the angular momentum distributions and the angular momentum misalignment. Analytical expressions are derived to calculate the angular distributions of sequentially emitted particles, fission fragments, as well as gamma rays in terms of the angular momentum misalignment. Recent data on the angular distributions of sequential alphas, fission and gamma rays are analyzed in terms of the model. 29 figures, 1 table
Energy Technology Data Exchange (ETDEWEB)
Moretto, L.G.
1980-08-01
The relevance of higher multipoles of giant isovector modes in the charge distribution of deep inelastic fragments is discussed and found to depend strongly on mass asymmetry. The sources of angular momentum fluctuations are investigated. Quantal effects are considered as well as effects arising from non-equilibrium and equilibrium statistical fluctuations. A model based upon equilibrium statistical mechanics is considered in detail, and used to predict both 2nd moments of the angular momentum distributions and the angular momentum misalignment. Analytical expressions are derived to calculate the angular distributions of sequentially emitted particles, fission fragments, as well as gamma rays in terms of the angular momentum misalignment. Recent data on the angular distributions of sequential alphas, fission and gamma rays are analyzed in terms of the model. 29 figures, 1 table.
International Nuclear Information System (INIS)
We report observation and resonance Raman studies of spin-pair excitations in YBa2Cu3O6+x (0.372Cu4O8 superconductors. These excitations at energy ∼3J (2700±150 cm-1), similar to two-magnon excitations in insulators, are evidence that antiferromagnetic fluctuations with spatial extent of at least three lattice constants are not overdamped in the underdoped superconductors. With optimal hole dopings, where Tc>80 K, the two-magnon peak can no longer be seen above the flat Raman continuum. Photoluminescence and the origin of the broad-spectrum Raman continuum are also discussed
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
Energy Technology Data Exchange (ETDEWEB)
Gottwald, Tobias
2010-08-27
domain wall formation, antiferromagnetically induced density shifts, and we show the relevant role of spin-imbalance for antiferromagnetic states. Since the first step for understanding the physics of the examined models was the application of a mean field approximation, we analyze the effect of including the second order terms of the weak coupling perturbation expansion for the repulsive model. We show that our results survive the influence of quantum fluctuations and show that the renormalization factors for order parameters and critical temperatures lead to a weaker influence of the fluctuations on the results in finite sized systems than on the results in the thermodynamical limit. Furthermore, in the context of second order theory we address the question whether results obtained in the dynamical mean field theory (DMFT), which is meanwhile a frequently used method for describing trapped systems, survive the effect of the non-local Feynman diagrams neglected in DMFT. (orig.)
Observation of Antiferromagnetic Resonance in an Organic Superconductor
DEFF Research Database (Denmark)
Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.
1982-01-01
Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...
Ferro- and antiferro-magnetism in (Np, Pu)BC
Czech Academy of Sciences Publication Activity Database
Klimczuk, T.; Shick, Alexander; Kozub, Agnieszka L.; Griveau, J.C.; Colineau, E.; Falmbigl, M.; Wastin, F.; Rogl, P.
2015-01-01
Roč. 3, č. 4 (2015), "041803-1"-"041803-9". ISSN 2166-532X R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : ferromagetism * antiferromagnetism * magnetic anisotropy * strong electron correlations * spin-orbit coupling Subject RIV: BM - Solid Matter Physics ; Magnetism
An antiferromagnetic transverse Ising nanoisland; unconventional surface effects
Kaneyoshi, T.
2015-12-01
The phase diagrams and temperature dependences of magnetizations in a transverse Ising nanosisland with an antiferromagnetic spin configuration are studied by the use of the effective-field theory with correlations (EFT). Some novel features, such as the re-entrant phenomena with two compensation points being free from disorder induced frustration, are obtained for the magnetic properties in the system.
Drone-fermions in the two-dimensional antiferromagnet
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Coupling the valley degree of freedom to antiferromagnetic order
Li, Xiao; Cao, Ting; Niu, Qian; Shi, Junren; Feng, Ji
2013-01-01
Conventional electronics are based invariably on the intrinsic degrees of freedom of an electron, namely, its charge and spin. The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley as a new electronic degree of freedom has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by ...
Prospect for antiferromagnetic spintronics
Czech Academy of Sciences Publication Activity Database
Martí, Xavier; Fina, I.; Jungwirth, Tomáš
2015-01-01
Roč. 51, č. 4 (2015), s. 2900104. ISSN 0018-9464 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G Grant ostatní: ERC Advanced Grant 0MSPIN(XE) 268066 Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014
Chiral magnetism and spontaneous spin Hall effect of interacting Bose superfluids.
Li, Xiaopeng; Natu, Stefan S; Paramekanti, Arun; Das Sarma, S
2014-01-01
Recent experiments on ultracold atoms in optical lattices have synthesized a variety of tunable bands with degenerate double-well structures in momentum space. Such degeneracies in the single-particle spectrum strongly enhance quantum fluctuations, and often lead to exotic many-body ground states. Here we consider weakly interacting spinor Bose gases in such bands, and discover a universal quantum 'order by disorder' phenomenon which selects a novel superfluid with chiral spin order displaying remarkable properties such as spontaneous spin Hall effect and momentum space antiferromagnetism. For bosons in the excited Dirac band of a hexagonal lattice, such a state supports staggered spin loop currents in real space. We show that Bloch oscillations provide a powerful dynamical route to quantum state preparation of such a chiral spin superfluid. Our predictions can be readily tested in spin-resolved time-of-flight experiments. PMID:25300774
Characterization of the Dilute Ising Antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
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
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.
Antiferromagnetic topological insulators in cold atomic gases
Essin, Andrew M.; Gurarie, Victor
2011-01-01
We propose a spin-dependent optical lattice potential that realizes a three-dimensional antiferromagnetic topological insulator in a gas of cold, two-state fermions such as alkaline earths, as well as a model that describes the tight-binding limit of this potential. We discuss the physically observable responses of the gas that can verify the presence of this phase. We also point out how this model can be used to obtain two-dimensional flat bands with nonzero Chern number.
The electronic structure of antiferromagnetic chromium
DEFF Research Database (Denmark)
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...... the calculated ground state properties into agreement with experiment. The magnetisation is studied as function of volume in several models, and it is shown that a Stoner picture provides an extremely accurate description of the full calculation provided the sp-d hybridisation is taken into account. It is found...
Quantum spin liquids: a large-S route
Tchernyshyov, Oleg
2003-01-01
This paper explores the large-S route to quantum disorder in the Heisenberg antiferromagnet on the pyrochlore lattice and its homologues in lower dimensions. It is shown that zero-point fluctuations of spins shape up a valence-bond solid at low temperatures for one two-dimensional lattice and a liquid with very short-range valence-bond correlations for another. A one-dimensional model demonstrates potential significance of quantum interference effects (as in Haldane's gap): the quantum meltin...
Quantum fluctuations stabilize skyrmion textures
Roldán-Molina, A.; Santander, M. J.; Núñez, A.S.; Fernández Rossier, Joaquín
2015-01-01
We study the quantum spin waves associated to skyrmion textures. We show that the zero-point energy associated to the quantum spin fluctuations of a noncollinear spin texture produce Casimir-like magnetic fields. We study the effect of these Casimir fields on the topologically protected noncollinear spin textures known as skyrmions. In a Heisenberg model with Dzyalonshinkii-Moriya interactions, chosen so the classical ground state displays skyrmion textures, we calculate the spin-wave spectru...
Spin liquid state in the disordered triangular lattice Sc2Ga2CuO7 revealed by NMR
Khuntia, P.; Kumar, R.; Mahajan, A. V.; Baenitz, M.; Furukawa, Y.
2016-04-01
We present microscopic magnetic properties of a two-dimensional triangular lattice Sc2Ga2CuO7 , consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J /kB≈35 K between Cu2 + (S =1 /2 ) spins in the triangular biplane is obtained from the analysis of intrinsic magnetic susceptibility data. The intrinsic magnetic susceptibility, extracted from 71Ga NMR shift data, displays the presence of AFM short range spin correlations and remains finite down to 50 mK, suggesting a nonsinglet ground state. The nuclear spin-lattice relaxation rate (1 /T1 ) reveals a slowing down of Cu2 + spin fluctuations with decreasing T down to 100 mK. Magnetic specific heat (Cm) and 1 /T1 exhibit power law behavior at low temperatures, implying the gapless nature of the spin excitation spectrum. The absence of long range magnetic ordering down to ˜J /700 , nonzero spin susceptibility at low T , and the power law behavior of Cm and 1 /T1 suggest a gapless quantum spin liquid (QSL) state. Our results demonstrate that persistent spin dynamics induced by frustration maintain a quantum-disordered state at T →0 in this triangular lattice antiferromagnet. This suggests that the low energy modes are dominated by spinon excitations in the QSL state due to randomness engendered by disorder and frustration.
Holes in a two-dimensional quantum antiferromagnet
International Nuclear Information System (INIS)
A brief review is presented on the studies of the hole motion in a two-dimensional quantum antiferromagnetic. An extended introduction is given to cover the background of the problem. The quantum Bogoliubov-de Gennes formalism which treats the local distortion of the spin configuration and the quantum renormalization process on an equal footing, is outlined. The latest development on the central issue, whether a hole can freely propagate on an antiferromagnetic background, is overviewed. (author). 108 refs, 11 figs, 1 tab
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.
Dynamic rotor mode in antiferromagnetic nanoparticles
DEFF Research Database (Denmark)
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....... However, the signal from inelastic neutron scattering remains above that temperature, indicating a magnetic system in constant motion. In addition, the precession frequency of the inelastic magnetic signal shows an increase above 100 K. Numerical Langevin simulations of spin dynamics reproduce all...... measured neutron data and reveal that thermally activated spin canting gives rise to an unusual type of coherent magnetic precession mode. This "rotor" mode can be seen as a high-temperature version of superparamagnetism and is driven by exchange interactions between the two magnetic sublattices. The...
Ising antiferromagnet on the Archimedean lattices
Yu, Unjong
2015-06-01
Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.
Quantum Phase Transitions in Antiferromagnets and Superfluids
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet
Arsenijević, Stevan; Ok, Jong Mok; Robinson, Peter; Ghannadzadeh, Saman; Katsnelson, Mikhail I.; Kim, Jun Sung; Hussey, Nigel E.
2016-02-01
We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zero-field thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T >70 K . We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4 d correlated electrons of the Pd ions with the short-range spin correlations of the Cr3 + spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality.
Antiferromagnetic proximity effect in epitaxial CoO/NiO/MgO(001) systems.
Li, Q; Liang, J H; Luo, Y M; Ding, Z; Gu, T; Hu, Z; Hua, C Y; Lin, H-J; Pi, T W; Kang, S P; Won, C; Wu, Y Z
2016-01-01
Magnetic proximity effect between two magnetic layers is an important focus of research for discovering new physical properties of magnetic systems. Antiferromagnets (AFMs) are fundamental systems with magnetic ordering and promising candidate materials in the emerging field of antiferromagnetic spintronics. However, the magnetic proximity effect between antiferromagnetic bilayers is rarely studied because detecting the spin orientation of AFMs is challenging. Using X-ray linear dichroism and magneto-optical Kerr effect measurements, we investigated antiferromagnetic proximity effects in epitaxial CoO/NiO/MgO(001) systems. We found the antiferromagnetic spin of the NiO underwent a spin reorientation transition from in-plane to out-of-plane with increasing NiO thickness, with the existence of vertical exchange spring spin alignment in thick NiO. More interestingly, the Néel temperature of the CoO layer was greatly enhanced by the adjacent NiO layer, with the extent of the enhancement closely dependent on the spin orientation of NiO layer. This phenomenon was attributed to different exchange coupling strengths at the AFM/AFM interface depending on the relative spin directions. Our results indicate a new route for modifying the spin configuration and ordering temperature of AFMs through the magnetic proximity effect near room temperature, which should further benefit the design of AFM spintronic devices. PMID:26932164
Antiferromagnetic proximity effect in epitaxial CoO/NiO/MgO(001) systems
Li, Q.; Liang, J. H.; Luo, Y. M.; Ding, Z.; Gu, T.; Hu, Z.; Hua, C. Y.; Lin, H.-J.; Pi, T. W.; Kang, S. P.; Won, C.; Wu, Y. Z.
2016-03-01
Magnetic proximity effect between two magnetic layers is an important focus of research for discovering new physical properties of magnetic systems. Antiferromagnets (AFMs) are fundamental systems with magnetic ordering and promising candidate materials in the emerging field of antiferromagnetic spintronics. However, the magnetic proximity effect between antiferromagnetic bilayers is rarely studied because detecting the spin orientation of AFMs is challenging. Using X-ray linear dichroism and magneto-optical Kerr effect measurements, we investigated antiferromagnetic proximity effects in epitaxial CoO/NiO/MgO(001) systems. We found the antiferromagnetic spin of the NiO underwent a spin reorientation transition from in-plane to out-of-plane with increasing NiO thickness, with the existence of vertical exchange spring spin alignment in thick NiO. More interestingly, the Néel temperature of the CoO layer was greatly enhanced by the adjacent NiO layer, with the extent of the enhancement closely dependent on the spin orientation of NiO layer. This phenomenon was attributed to different exchange coupling strengths at the AFM/AFM interface depending on the relative spin directions. Our results indicate a new route for modifying the spin configuration and ordering temperature of AFMs through the magnetic proximity effect near room temperature, which should further benefit the design of AFM spintronic devices.
Spin dynamics in the metallic state of YBa2(Cu0.98Zn0.02)3O6+x
International Nuclear Information System (INIS)
Inelastic neutron scattering measurements have been carried out on a YBa2(Cu0.98Zn0.02)3O6+x single crystal in both underdoped (x 0.7) and overdoped (x = 0.97) regimes. In the zinc substituted system, spin dynamics is drastically changed in respect to the pure compound: (i) the resonance peak almost vanishes, (ii) the spin gap is filled, (iii) new antiferromagnetic excitations are found at low energy. These new magnetic fluctuations, which persist in the normal state, account for a local enhancement of AF correlations around nonmagnetic impurities. Besides, it is worth emphasizing that features, not directly related to superconductivity, i.e., the contribution to the spin dynamics apart from the resonance peak and the spin pseudo-gap observed in the underdoped regime above Tc, coexist with the new low energy magnetic fluctuations
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.
2016-02-01
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 106 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.
Hybrid Spin Noise Spectroscopy and the Spin Hall Effect
Slipko, V. A.; Sinitsyn, N. A.; Pershin, Y. V.
2013-01-01
Here we suggest a novel hybrid spin noise spectroscopy technique, which is sensitive to the spin Hall effect. It is shown that, while the standard spin-spin correlation function is not sensitive to the spin Hall effect, spin-transverse voltage and transverse voltage-voltage correlation functions provide the missing sensitivity being linear and quadratic in the spin Hall coefficient, respectively. The correlation between transverse voltage and spin fluctuations appears as a result of spin-char...
Quantum critical behavior in a two-layer antiferromagnet
International Nuclear Information System (INIS)
We analyze quantum Monte Carlo data in the vicinity of the quantum transition between a Neel state and a quantum paramagnet in a two-layer, square-lattice spin-1/2 Heisenberg antiferromagnet. The real-space correlation function and the universal amplitude ratio of the structure factor and the dynamic susceptibility show clear evidence of quantum critical behavior at low temperatures. The numerical results are in good quantitative agreement with 1/N calculations for the O(N) nonlinear σ model. A discrepancy, reported earlier, between the critical properties of the antiferromagnet and the σ model is resolved. We also discuss the values of prefactors of the dynamic susceptibility and the structure factor in a single-layer antiferromagnet at low T
Spin fluctuations and covalence in neutron Bragg scattering from YBa2Cu3O6 and La2CuO4
International Nuclear Information System (INIS)
A puzzle is pointed out concerning the low-temperature behavlor of La2CuO4 and YBa2Cu3O6, the insulating ''parents'' of the high-Tc superconductors, and indicate a possible solution. The measured ordered magnetic moment is about 0.64 μB per Cu, in agreement with the value calculated on the basis of the Heisenberg Hamiltonian. But this calculation is within a nearly purely ionic or localized picture of the Cu d hole, the reduction from 1.1 μB (g∼2.2) being entirely due to spin fluctuations. Thus the almost perfect agreement leaves no room for the moment reduction due to covalence or 3d-2p hybridization, expected to be large in these oxides. A possible explanation might lie in the fact that an ostensibly symmetry-based argument relating the calculated moment (in the symmetry-unbroken state) to that measured is not valid, as has recently been shown
Babadi, Mehrtash; Demler, Eugene; Knap, Michael
2015-10-01
We study theoretically the far-from-equilibrium relaxation dynamics of spin spiral states in the three-dimensional isotropic Heisenberg model. The investigated problem serves as an archetype for understanding quantum dynamics of isolated many-body systems in the vicinity of a spontaneously broken continuous symmetry. We present a field-theoretical formalism that systematically improves on the mean field for describing the real-time quantum dynamics of generic spin-1 /2 systems. This is achieved by mapping spins to Majorana fermions followed by a 1 /N expansion of the resulting two-particle-irreducible effective action. Our analysis reveals rich fluctuation-induced relaxation dynamics in the unitary evolution of spin spiral states. In particular, we find the sudden appearance of long-lived prethermalized plateaus with diverging lifetimes as the spiral winding is tuned toward the thermodynamically stable ferro- or antiferromagnetic phases. The emerging prethermalized states are characterized by different bosonic modes being thermally populated at different effective temperatures and by a hierarchical relaxation process reminiscent of glassy systems. Spin-spin correlators found by solving the nonequilibrium Bethe-Salpeter equation provide further insight into the dynamic formation of correlations, the fate of unstable collective modes, and the emergence of fluctuation-dissipation relations. Our predictions can be verified experimentally using recent realizations of spin spiral states with ultracold atoms in a quantum gas microscope [S. Hild et al., Phys. Rev. Lett. 113, 147205 (2014), 10.1103/PhysRevLett.113.147205].
Resonating Valence Bond states for low dimensional S=1 antiferromagnets
Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai
2014-03-01
We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.
Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy
Selke, Walter
2013-01-01
The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, and competing planar single-ion anisotropy in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. The biconical (supersolid) phase, bordering the antiferromagnetic and spin-flop phases, is found to become thermally unstable well below the onset of the disordered, paramagnetic phase, leading to interesting multicritical points.
Magnetic structure of Cu in antiferromagnetic REBa sub 2 Cu sub 3 O sub y
Energy Technology Data Exchange (ETDEWEB)
Luetgemeier, H.; Brand, R.A.; Sauer, C.; Rupp, B.; Meuffels, P.M.; Zinn, W. (Inst. fuer Festkoerperforschung, KFA Juelich (Germany, F.R.))
1989-12-01
The NQR spectra of Cu and the Moessbauer effect spectra of Fe in oxygen deficient antiferromagnetic 123 compounds have been investigated. A transition from the high temperature anti-ferromagnetic spin structure of the magnetic moments at the Cu(2) sites with the stacking sequence + - + - to another one at low temperature (+ + - -) is induced by a small amount (about 1%) of magnetic impurities at the Cu(1) sites. The Cu(1) ions themselves carry no magnetic moments. (orig.).
Magnetic structure of Cu in antiferromagnetic reba2Cu3Oy
International Nuclear Information System (INIS)
This paper reports an investigation of the NQR spectra of Cu and the Mossbauer effect spectra of Fe in oxygen deficient antiferromagnetic 123 compounds. A transition from the high temperature antiferromagnetic spin structure of the magnetic moments at the Cu(2) sites with the stacking sequence + - + - to another one at low temperature (+ + - -) is induced by a small amount (about 1%) of magnetic impurities at the Cu(1) sites. The Cu(1) ions themselves carry no magnetic moments
Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films
International Nuclear Information System (INIS)
This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs
Singular field response and singular screening of vacancies in antiferromagnets.
Wollny, Alexander; Andrade, Eric C; Vojta, Matthias
2012-10-26
For isolated vacancies in ordered local-moment antiferromagnets we show that the magnetic-field linear-response limit is generically singular: The magnetic moment associated with a vacancy in zero field is different from that in a finite field h in the limit h→0(+). The origin is a universal and singular screening cloud, which moreover leads to perfect screening as h→0(+) for magnets which display spin-flop bulk states in the weak-field limit. PMID:23215218
Antiferromagnetic Exchange Interactions from Hybrid Density Functional Theory
Martin, Richard L.; Illas, Francesc
1997-08-01
A hybrid theory which combines the full nonlocal ``exact'' exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO4, KNiF3, and K2NiF4. The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO4.
Antiferromagnetic exchange interactions from hybrid density functional theory
Martin, Richard L.; Illas i Riera, Francesc
1997-01-01
A hybrid theory which combines the full nonlocal ¿exact¿ exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO4, KNiF3, and K2NiF4. The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO4.
Antiferromagnetic Exchange Interactions from Hybrid Density Functional Theory
International Nuclear Information System (INIS)
A hybrid theory which combines the full nonlocal open-quotes exactclose quotes exchange interaction with the local spin-density approximation of density-functional theory is shown to lead to marked improvement in the description of antiferromagnetically coupled systems. Semiquantitative agreement with experiment is found for the magnitude of the coupling constant in La2CuO 4 , KNiF3 , and K2NiF 4 . The magnitude of the unpaired spin population on the metal site is in excellent agreement with experiment for La2CuO 4 . copyright 1997 The American Physical Society
Angle-dependent loop shifts in antiferromagnetic nanoparticles
Mao, Zhongquan; Zhan, Xiaozhi; Chen, Xi
2016-08-01
Experimentally hysteresis loop shifts have been widely observed in antiferromagnetic (AF) nanoparticles. Here numerical investigations show that this effect is dependent on the angle between the easy axis of the AF spins and the applied magnetic field in uncompensated nanoparticles. In contrast, the loop shifts disappear in compensated nanoparticles. The results suggest that the uncompensated spins and field directions are essential ingredients to generate loop shifts in AF nanoparticle systems. The present study hints at a possible way to optimize the magnetic performance of AF nanostructures.
Search for quantum spin ice in Tb2Ti2O7 at milli-Kelvin temperatures
International Nuclear Information System (INIS)
Spin ice attracts great interest as a state in which emergent fractionalized excitations and magnetic-field induced topological forms of order may occur. However, little is known about the importance of quantum fluctuations for the spin ice state. We report a search for so-called quantum spin ice, i.e., a spin ice state driven by quantum fluctuations. Using a vibrating coil magnetometer as combined with a dilution refrigerator, we performed comprehensive magnetization measurements in high-quality single crystals of Tb2Ti2O7. As an isostructural sibling of the conventional spin ice systems Ho2Ti2O7 and Dy2Ti2O7 strong quantum fluctuations are believed to suppress long-range magnetic order in Tb2Ti2O7 despite strong antiferromagnetic interactions. We find that Tb2Ti2O7 clearly remains paramagnetic down to the lowest temperatures studied without the magnetic field dependence predicted theoretically for quantum spin ice.
Conductance of ferro- and antiferro-magnetic single-atom contacts: A first-principles study
International Nuclear Information System (INIS)
We present a first-principles study on the spin dependent conductance of five single-atom magnetic junctions consisting of a magnetic tip and an adatom adsorbed on a magnetic surface, i.e., the Co-Co/Co(001) and Ni-X/Ni(001) (X = Fe, Co, Ni, Cu) junctions. When their spin configuration changes from ferromagnetism to anti-ferromagnetism, the spin-up conductance increases while the spin-down one decreases. For the junctions with a magnetic adatom, there is nearly no spin valve effect as the decreased spin-down conductance counteracts the increased spin-up one. For the junction with a nonmagnetic adatom (Ni-Cu/Ni(001)), a spin valve effect is obtained with a variation of 22% in the total conductance. In addition, the change in spin configuration enhances the spin filter effect for the Ni-Fe/Ni(001) junction but suppresses it for the other junctions
Dynamical current-induced ferromagnetic and antiferromagnetic resonances
Guimarães, F. S. M.; Lounis, S.; Costa, A. T.; Muniz, R. B.
2015-12-01
We demonstrate that ferromagnetic and antiferromagnetic excitations can be triggered by the dynamical spin accumulations induced by the bulk and surface contributions of the spin Hall effect. Due to the spin-orbit interaction, a time-dependent spin density is generated by an oscillatory electric field applied parallel to the atomic planes of Fe/W(110) multilayers. For symmetric trilayers of Fe/W/Fe in which the Fe layers are ferromagnetically coupled, we demonstrate that only the collective out-of-phase precession mode is excited, while the uniform (in-phase) mode remains silent. When they are antiferromagnetically coupled, the oscillatory electric field sets the Fe magnetizations into elliptical precession motions with opposite angular velocities. The manipulation of different collective spin-wave dynamical modes through the engineering of the multilayers and their thicknesses may be used to develop ultrafast spintronics devices. Our work provides a general framework that probes the realistic responses of materials in the time or frequency domain.
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. PMID:27232041
Magnetic fluctuations in heavy fermion systems
International Nuclear Information System (INIS)
Magnetic order and fluctuations in the heavy Fermion systems UPt3, U2Zn17 and URu2Si2 have been studied by neutron scattering. Single crystalline samples and triple-axis neutron-scattering techniques with energy transfers between 0 and 40 meV and energy resolutions between 0.1 meV and 4 meV have been employed. UPt3 develops an antiferromagnetically ordered moment of (0.02±0.005) μB below TN = 5 K which doubles the unit cell in the basal plane and coexists with superconductivity below Tc = 0.5 K. The magnetic fluctuations are relaxational, and enhanced at the antiferromagnetic zone center in a low-energy regime. The characteristic zone-center relaxation energy is 0.3 meV. The temperature- and field-dependence of the antiferromagnetic order in the superconducting phase suggest a close relation between these two properties in UPt3. U2Zn17 has a broad spectrum of magnetic fluctuations, even below TN = 9.7 K, of which the transverse part below 10 meV is strongly enhanced at the antiferromagnetic zone center. The system has an anomalously extended critical region and the antiferromagnetic phase transition seems to be driven by the temperature-dependence of an effective RKKY interaction, as anticipated theoretically. URu2Si2, a strongly anisotropic heavy Fermion system, has a high-energy regime of antiferromagnetically-correlated overdamped magnetic fluctuations. Below TN = 17.5 K weak antiferromagnetic order, μ = (0.04±0.01)μB, with finite correlations along the tetragonal c axis, develops along with a low-energy regime of strongly dispersive singlet-singlet excitations. Below Tc = 1 K antiferromagnetism coexists with superconductivity. A phenomenological model describing the exchange-enhanced overdamped magnetic fluctuations of heavy Fermion systems is proposed. Our experimental results are compared to the anomalous bulk properties of heavy Fermion systems, and to magnetic fluctuations in other metallic magnets. (orig.)
Magnetic Energy Fluctuations: Observations by Light Scattering
Lyons, K. B.; Fleury, P. A.
1982-01-01
The first observations of magnetic energy fluctuations by light scattering are reported. The spectra observed in antiferromagnetic KNiF3 are strongly polarized, mildly q dependent, but strongly temperature dependent near TN=248.5 K. The observed line shapes exhibit two characteristic frequencies, one less than 0.6 GHz and the other between 5 and 15 GHz, depending on temperature.
Coherent spin mixing dynamics in thermal $^{87}$Rb spin-1 and spin-2 gases
He, Xiaodong; Li, Xiaoke; Wang, Fudong; Xu, Zhifang; Wang, Dajun
2015-01-01
We study the non-equilibrium coherent spin mixing dynamics in ferromagnetic spin-1 and antiferromagnetic spin-2 thermal gases of ultracold $^{87}$Rb atoms. Long lasting spin population oscillations with magnetic field dependent resonances are observed in both cases. Our observations are well reproduced by Boltzmann equations of the Wigner distribution function. Compared to the equation of motion of spinor Bose-Einstein condensates, the only difference here is a factor of two increase in the spin-dependent interaction, which is confirmed directly in the spin-2 case by measuring the relation between the oscillation amplitude and the sample's density.
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.
Field-controlled spin current in frustrated spin chains
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A.K. Kolezhuk
2009-01-01
Full Text Available We study states with spontaneous spin current, emerging in frustrated antiferromagnetic spin-S chains subject to a strong external magnetic field. As a numerical tool, we use a non-Abelian symmetry realization of the density matrix renormalization group. The field dependence of the order parameter and the critical exponents are presented for zigzag chains with S=1/2, 1, 3/2, and 2.
Correlations in the Ising antiferromagnet on the anisotropic kagome lattice
International Nuclear Information System (INIS)
We study the correlation function of middle spins, i.e. of spins on intermediate sites between two adjacent parallel lattice axes, of the spatially anisotropic Ising antiferromagnet on the kagome lattice. It is given rigorously by a Toeplitz determinant. The large-distance behaviour of this correlation function is obtained by analytic methods. For shorter distances we evaluate the Toeplitz determinant numerically. The correlation function is found to vanish exactly on a line Jd(T) in the T − J (temperature versus coupling constant) phase diagram. This disorder line divides the phase diagram into two regions. For J d(T) the correlations display the features of an unfrustrated two-dimensional Ising magnet, whereas for J > Jd(T) the correlations between the middle spins are seen to be strongly influenced by the short-range antiferromagnetic order that prevails among the spins of the adjacent lattice axes. While for J d(T) there is a region with ferrimagnetic long-range order, the model remains disordered for J > Jd(T) down to T = 0
DEFF Research Database (Denmark)
Winkelmann, M.; Graf, H.A.; Andersen, N.H.
1994-01-01
the Cu-O chains of the MgCu2O3 structure give rise to a predominantly one-dimensional (1D) magnetic behavior. This is revealed by the quantitative interpretation of the susceptibility measurements. Below T(N), the 3D magnetic structure, derived from neutron-diffraction experiments, can be described...... is similar to the one producing an infinitely degenerate state in antiferromagnetic fcc lattices. Doping experiments with Li clearly demonstrate the importance of spin fluctuations and fluctuations of the local exchange fields for lifting the degeneracy in such a system. A remarkably small amount of Li...... (about 2 mole % Li) is sufficient to disturb the magnetic lattice in such a way that the almost collinear spin arrangement changes into an arrangement where the spins of one sublattice are strongly canted with respect to the spins of the other sublattice....
Kamra, A.; Witek, F.P.; Meyer, S.; Huebl, H.; Geprägs, S.; Gross, R.; Bauer, G. E. W.; Goennenwein, S. T. B.
2014-01-01
We measure the low-frequency thermal fluctuations of pure spin current in a Platinum film deposited on yttrium iron garnet via the inverse spin Hall effect (ISHE)-mediated voltage noise as a function of the angle $\\alpha$ between the magnetization and the transport direction. The results are consistent with the fluctuation dissipation theorem in terms of the recently discovered spin Hall magnetoresistance (SMR). We present a microscopic description of the $\\alpha$ dependence of the voltage no...
Antiferromagnetic resonance in the cubic perovskite KNiF3
Yamaguchi, H.; Katsumata, K.; Hagiwara, M.; Tokunaga, M.; Liu, H. L.; Zibold, A.; Tanner, D. B.; Wang, Y. J.
1999-03-01
Low-temperature high-magnetic-field far-infrared spectroscopy and electron-spin-resonance measurements have been performed on single crystals of the cubic perovskite KNiF3. We found the absorption at 48.7+/-0.3 cm-1 observed by Richards [P. L. Richards, J. Appl. Phys. 34, 1237 (1963)] that was attributed to antiferromagnetic resonance (AFMR) is not magnetic in origin. Instead, a different absorption is well fit by a theory of AFMR with uniaxial anisotropy. Analysis yields an anisotropy energy of 8.7×10-3 cm-1. The ratio between the anisotropy field and the exchange field is 2.4×10-5. Thus, KNiF3 is an excellent example of a Heisenberg antiferromagnet.
Fermi surface and antiferromagnetism of FeRh
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Nakada, K. [Department of Quantum Matter, ADSM, Hiroshima University, Higashi Hiroshima 739-8530 (Japan)]. E-mail: nakada@hiroshima-u.ac.jp; Yamada, H. [Faculty of Science, Shinshu University, Matsumoto 390-8621 (Japan)
2007-03-15
In order to examine the stabilization of antiferromagnetic state with the observed spin ordering wave vector Q in an ordered alloy FeRh with a CsCl-type structure, the nesting effect of the Fermi surfaces is discussed by using the electronic structures calculated by the FLAPW method. Although the nesting of Fermi surfaces cannot be seen so clearly, it is found that there exists rather wide region in the Brillouin zone where the energy at the crossing point between the energies E(k) and E(k+Q) of electron and hole is within a few mRy above or below the Fermi level. This fact is shown to stabilize the antiferromagnetic state in FeRh, together with the fact that a hole surface exists on other place in the Brillouin zone.
DEFF Research Database (Denmark)
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 supersede...
Energy Technology Data Exchange (ETDEWEB)
Deng, Xiao-Yan [Graduate School, Tianjin Polytechnic University, Tianjin 300387 (China); Dou, Jun-Ya [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China); Liu, Guang-Hua, E-mail: liuguanghua@tjpu.edu.cn [Department of Physics, Tianjin Polytechnic University, Tianjin 300387 (China)
2015-10-15
The magnetization process of a spin-1/2 J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Heisenberg chain is investigated by the infinite time-evolving block decimation (iTEBD) method. A magnetization phase diagram including three different phases, i.e., a fully polarized (FP) phase, a 1/2 plateau phase, and a spin-fluid (SF) phase, is obtained. All the quantum phase transitions (QPTs) are determined to belong to the second-order category, and the central charge in the critical SF phase equals 1. In addition, a 1/2 plateau phase also exists in the classical J{sub 1}–J{sub 1}–J{sub 2}–J{sub 2} tetrameric Ising chain. The F–F–AF–AF (or AF–AF–F–F) type longitudinal correlation is found to be important and necessary for the appearance of the 1/2 plateau state in both quantum and classical cases. - Highlights: • 1/2 magnetization plateau can be realized in both quantum and classical cases. • 1/2 plateau is characterized by constant magnetization, entanglement and correlation. • Central charge of the spin-fluid phase is determined to be 1. • F–F–AF–AF correlation is important for the appearance of the 1/2 plateau.
Avoided antiferromagnetic order and QCP in CeCoIn5
International Nuclear Information System (INIS)
We measured the specific heat and resistivity of heavy fermion CeCoIn5 between the superconducting critical field Hc2=4.95 and 9T, with the field in the [001] direction, and at temperatures down to 50mK. These results show that this compound has a quantum critical point (QCP) with the magnetic field as the tuning parameter. For a field of 5T just above Hc2 the temperature dependence of both specific heat Cp(T) and resistivity ρ(T) show non-Fermi liquid (NFL) behavior down to the lowest temperatures with Cp(T)∝-log(T) and ρ(T)-ρ(T=0)∝T. For fields above 8T the data exhibit a crossover from a NFL to a Fermi liquid behavior. Specific heat and resistivity data show behavior predicted by spin-fluctuation theory, suggesting that the NFL behavior is due to incipient antiferromagnetism (AFM) in CeCoIn5 with the quantum critical point in the vicinity of Hc2. For fields below Hc2 the AFM phase separated by a QCP from the paramagnetic ground state is not observed, as the system becomes first superconducting
Uranium nitride. A cubic antiferromagnet with anisotropic critical behaviour
International Nuclear Information System (INIS)
Highly anisotropic critical scattering associated with the transition at Tsub(N)=49.5K to the type-I antiferromagnetic structure has been observed in uranium nitride. The transverse susceptibility is found to be unobservably small. The longitudinal susceptibility diverges at Tsub(N) and its anisotropy shows that the spins within the (001) ferromagnetic sheets of the [001] domain are much more highly correlated than they are with the spins lying in adjacent (001) sheets. The correlation range within the sheets is much greater than that expected for a Heisenberg system with the same Tsub(N). The rod-like scattering extended along the spin and domain direction is reminiscent of two-dimensional behaviour. The results are inconsistent with a simple localized model and may reflect the itinerant nature of the 5f electrons. (author)
Nuclear spin relaxation in high-Tc superconductors
International Nuclear Information System (INIS)
The project was to investigate the electronic states of thallium-containing high-Tc superconductors applying the NMR techniques, the main goal being to find answers to the following questions not yet resolved: 1) What is the valence of the Tl ions in these materials? 2) What anisotropy is there at the various lattice sites? 3) Can metal-type behaviour signs be found? 4) How strong are antiferromagnetic correlations? 5) How does the structure of the flux line lattice look like in the superconducting state? The experiments revealed precise information on both the valence and the anisotropy of interactions, from which the symmetry of the Tl positions could be derived. It was possible to directly observe in the NMR experiment the exchange of Ca and Tl atoms, and from the resulting defect line together with the corresponding knight shift and spin-lattice relaxation, metal-type behaviour was concluded to occur in the superconductors. A comparative analysis of the spin-lattice relaxation at various lattice sites allowed to establish a correlation between antiferromagnetic fluctuations and metal-type charge carriers, and to describe the influence on the critical temperature. (orig./MM)
Magnetic correlations in the 2D S=5/2 honeycomb antiferromagnet MnPS3
DEFF Research Database (Denmark)
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...
International Nuclear Information System (INIS)
Highlights: • In a layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity. • The long-range antiferromagnetism quickly disappear with doping away from the Van Hove singularity. • For pnictides the antiferromagnetism exists as a result of the nesting condition. • Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist. -- Abstract: We consider the Hubbard model in terms of the perturbative diagrammatic approach (UNF⩽1) where the interaction between two electrons with antiparallel spins in the lowest order of perturbation is described by the short-range repulsive contact (on-site) interaction (U>0). We argue that in layered 2D cuprates the long-range order antiferromagnetism is driven mainly by the Van Hove singularity, whereas in the case of pnictides the antiferromagnetism exists as a result of the nesting condition. We show that when the interaction is quite strong (UNF≈1) in the case of the Van Hove singularity the electron system undergoes the antiferromagnetic phase transition with the log-range order parameter and large insulating gap. The long-range antiferromagnetism quickly disappear, as shown, with the doping away from the Van Hove singularity, but the antiferromagnetic short-range correlation persists (UNF < 1) due to Coulomb repulsive interaction which is the mechanism for superconductivity in cuprates. We argue that in the case of pnictides the antiferromagnetism appears when the nesting conditions for the Fermi surface are met. Since the doping steadily changes the nesting conditions, the antiferromagnetism and superconductivity may coexist as has been observed in pnictides. We show that the proximity of the antiferromagnetism and superconductivity implies the repulsive interaction between electrons, which turns into attractive between quasiparticles as shown by the authors in the article published on the same issue as this one and
Merodio, P.; Kalitsov, A.; Chshiev, M.; Velev, J.
2016-06-01
Based on model calculations, we predict a magnetoelectric tunneling electroresistance effect in multiferroic tunnel junctions consisting of ferromagnetic electrodes and magnetoelectric antiferromagnetic barriers. Switching of the antiferromagnetic order parameter in the barrier in applied electric field by means of the magnetoelectric coupling leads to a substantial change of the resistance of the junction. The effect is explained in terms of the switching of the orientations of local magnetizations at the barrier interfaces affecting the spin-dependent interface transmission probabilities. Magnetoelectric multiferroic materials with finite ferroelectric polarization exhibit an enhanced resistive change due to polarization-induced spin-dependent screening. These results suggest that devices with active barriers based on single-phase magnetoelectric antiferromagnets represent an alternative nonvolatile memory concept.
Quantum oscillations in antiferromagnetic CaFe2As2 on the brink of superconductivity
International Nuclear Information System (INIS)
We report quantum oscillation measurements on CaFe2As2 under strong magnetic fields-recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05% of the paramagnetic Brillouin zone volume-consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkaline earth AFe2As2 antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area Fα and the effective mass mα* of the primary observed pocket on the antiferromagnetic/structural transition temperature Ts are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase. (fast track communication)
Molecular orbital study on antiferromagnetic coupling mechanism in a silver (I) complex
Institute of Scientific and Technical Information of China (English)
ZHANG Guiqin; HUANG Jiangen; HUANG Yuanhe; FANG Decai; ZHANG Deqing
2005-01-01
The mechanism of antiferromagnetic coupling in an Ag (I) complex of nitronyl nitroxide is investigated by means of the broken-symmetry approach within the density functional method (DFT-BS). The magneto-structural correlation and the single-occupied molecular orbital (SOMO) analysis reveal the existence of the antiferromagnetic coupling pathway along nitronyl nitroxide units via Ag (I) ion, and that the Ag (I) ion plays an important bridge role. The spin population analysis also shows the existence of spin delocalization along the ONCNO-Ag-ONCNO chain. It is found that the non-typical covalent bonds with major ionic character between Ag (I) ions and oxygen atoms of nitronyl nitroxide units can be used to mediate the spin-spin interaction of nitronyl nitroxides.
A variational coupled-cluster study of magnon-density-wave excitations in quantum antiferromagnets
Xian, Y.
2006-01-01
We extend recently proposed variational coupled-cluster method to describe excitation states of quantum antiferromagnetic bipartite lattices. We reproduce the spin-wave excitations (i.e., magnons with spin $\\pm 1$). In addition, we obtain a new, spin-zero excitation (magnon-density waves) which has been missing in all existing spin-wave theories. Within our approximation, this magnon-density-wave excitation has a nonzero energy gap in a cubic lattice and is gapless in a square lattice, simila...
Fluctuation theorem in spintronics
International Nuclear Information System (INIS)
Microscopic reversibility is a key in deriving the Onsager relation. It even leads a new exact relationship that would be valid far from equilibrium, called fluctuation theorem (FT). The FT provides a precise statement for the second law of thermodynamics; and remarkably, reproduces the linear response theory. We consider the FT in the spin-dependent transport and derive universal relations among nonlinear spin and charge transport coefficients. We apply the relations to a quantum dot embedded in a two-terminal Aharonov-Bohm interferometer and check that the relations are satisfied.
Spin-liquid behavior and weak static magnetism in pyrochlore Pr2Ir2O7
Energy Technology Data Exchange (ETDEWEB)
Heffner, R H [Los Alamos National Laboratory; Maclaughlin, D E [NON LANL; Nakatsuji, S [NON LANL; Machida, Y [NON LANL
2008-01-01
Muon spin relaxation experiments have been performed in powder samples of the pyrochlore iridate Pr{sub 2}Ir{sub 2}O{sub 7} for temperatures in the range 0.02-250 K. Two-component muon spin relaxation functions are observed up to {approx}> 150 K, indicating static magnetism with a freezing temperature T{sub f} of this value or higher. The static muon spin relaxation rate {Delta}. suggests weak-moment freezing ({approx} 10{sup -1} {micro}{sub B} at T = 0), probably due to Ir{sup 4+} spin ordering as in isostructural Y{sub 2}Ir{sub 2}O{sub 7}. The temperature dependence of {Delta} is highly unusual, decreasing smoothly by orders of magnitude but remaining nonzero for T < T{sub f}. The smoothness of {Delta}(T) suggests that Pr{sup 3+} moments do not order down to 0.025 K. The dynamic relaxation rate {Lambda} increases markedly below {approx}20 K, indicating a shift of spin fluctuation noise power to low frequencies in the spin-liquid state. At low temperatures {Lambda} is strong and temperature-independent, indicative of numerous low-lying spin excitations as is common in frustrated antiferromagnets.
Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature.
Nakatsuji, Satoru; Kiyohara, Naoki; Higo, Tomoya
2015-11-12
In ferromagnetic conductors, an electric current may induce a transverse voltage drop in zero applied magnetic field: this anomalous Hall effect is observed to be proportional to magnetization, and thus is not usually seen in antiferromagnets in zero field. Recent developments in theory and experiment have provided a framework for understanding the anomalous Hall effect using Berry-phase concepts, and this perspective has led to predictions that, under certain conditions, a large anomalous Hall effect may appear in spin liquids and antiferromagnets without net spin magnetization. Although such a spontaneous Hall effect has now been observed in a spin liquid state, a zero-field anomalous Hall effect has hitherto not been reported for antiferromagnets. Here we report empirical evidence for a large anomalous Hall effect in an antiferromagnet that has vanishingly small magnetization. In particular, we find that Mn3Sn, an antiferromagnet that has a non-collinear 120-degree spin order, exhibits a large anomalous Hall conductivity of around 20 per ohm per centimetre at room temperature and more than 100 per ohm per centimetre at low temperatures, reaching the same order of magnitude as in ferromagnetic metals. Notably, the chiral antiferromagnetic state has a very weak and soft ferromagnetic moment of about 0.002 Bohr magnetons per Mn atom (refs 10, 12), allowing us to switch the sign of the Hall effect with a small magnetic field of around a few hundred oersted. This soft response of the large anomalous Hall effect could be useful for various applications including spintronics--for example, to develop a memory device that produces almost no perturbing stray fields. PMID:26524519
Construction and study of exact ground states for a class of quantum antiferromagnets
International Nuclear Information System (INIS)
Techniques of quantum probability are used to construct the exact ground states for a class of quantum spin systems in one dimension. This class in particular contains the antiferromagnetic models introduced by various authors under the name of VBS-models. The construction permits a detailed study of these ground states. (A.C.A.S.)
't Hooft-Polyakov monopoles in an antiferromagnetic Bose-Einstein condensate
Stoof, H.T.C.; Vliegen, E.; Al Khawaja, U.
2001-01-01
We show that an antiferromagnetic spin-1 Bose-Einstein condensate, which can for instance be created with 23-Na atoms in an optical trap, has not only singular line-like vortex excitations, but also allows for singular point-like topological excitations, i.e., 't Hooft-Polyakov monopoles. We discuss the static and dynamic properties of these monopoles.
The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet
Cherepanov, V B; Podivilov, E V
2001-01-01
The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance
Electrical switching of an antiferromagnet
Czech Academy of Sciences Publication Activity Database
Wadley, P.; Howells, B.; Železný, J.; Andrews, C.; Hills, V.; Campion, R. P.; Novák, Vít; Olejník, Kamil; Maccherozzi, F.; Dhesi, S.S.; Martin, S.Y.; Wagner, T.; Wunderlich, Joerg; Freimuth, F.; Mokrousov, Y.; Kuneš, Jan; Chauhan, J.S.; Grzybowski, M.J.; Rushforth, A.W.; Edmonds, K. W.; Gallagher, B. L.; Jungwirth, Tomáš
2016-01-01
Roč. 351, č. 6273 (2016), 587-590. ISSN 0036-8075 R&D Projects: GA MŠk(CZ) LM2011026; GA ČR GB14-37427G EU Projects: European Commission(XE) 268066 - 0MSPIN Institutional support: RVO:68378271 Keywords : spintronics * antiferromagnets * current induced switching Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 33.611, year: 2014
Bond-centered, bond-ordered stripes in doped antiferromagnets
Wrobel, P.; Maciag, A; Eder, R.
2004-01-01
Motivated by recent inelastic neutron scattering experiments on cuprates, we discuss the formation of bond order in the stripe phase. We suggest that the spin Peierls order emerges in hole-rich domain walls (DWs) formed between hole-poor regions in which long-range antiferromagnetic (AF) correlations exist. On the example of a single stripe we analyze the stability of such structures. The motion of a hole inside the DW which takes the form of a bond ordered ladder is in principle unrestricted...
Room-temperature antiferromagnetism in CuMnAs
Czech Academy of Sciences Publication Activity Database
Máca, František; Mašek, Jan; Stelmakhovych, O.; Martí, X.; Reichlová, Helena; Uhlířová, K.; Beran, Přemysl; Wadley, P.; Novák, Vít; Jungwirth, Tomáš
2012-01-01
Roč. 324, č. 8 (2012), s. 1606-1612. ISSN 0304-8853 R&D Projects: GA MŠk LC510 EU Projects: European Commission(XE) 215368 - SemiSpinNet; European Commission(XE) 268066 - 0MSPIN Grant ostatní: AVČR(CZ) Praemium Academiae Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10100521; CEZ:AV0Z10480505 Keywords : antiferromagnetic semiconductors * spintronics * molecular beam epitaxy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.826, year: 2012
Non-Hermitian Quantum Annealing in the Antiferromagnetic Ising Chain
Nesterov, Alexander I; Zepeda, Juan C Beas; Bishop, Alan R
2013-01-01
A non-Hermitian quantum optimization algorithm is created and used to find the ground state of an antiferromagnetic Ising chain. We demonstrate analytically and numerically (for up to N=1024 spins) that our approach leads to a significant reduction of the annealing time that is proportional to $\\ln N$, which is much less than the time (proportional to $N^2$) required for the quantum annealing based on the corresponding Hermitian algorithm. We propose to use this approach to achieve similar speed-up for NP-complete problems by using classical computers in combination with quantum algorithms.
Pressure effects on antiferromagnetism in UNiAl
International Nuclear Information System (INIS)
The temperature dependencies of the electrical resistivity ρ for current along and perpendicular to the c axis were measured on single crystalline UNiAl under various hydrostatic pressures. The ρ(T) curves at ambient pressure exhibit a Cr anomaly around the Neel temperature TN. Application of pressure causes a reduction of TN value. Linear extrapolation of low-pressure TN vs p data yields an estimate of a critical pressure for antiferromagnetism pc≅10 GPa. Measurements above 1 GPa, however, reveal a collapse of the antiferromagnetic (AF) ordering already below 3 GPa, although AF correlations seem to affect resistivity behavior ρ(T) in pressures up to 8 GPa. A sudden change of the ρ(T) curve character for i(perpendicular sign)c and TN indicates a pressure-induced change of magnetic ordering or fluctuations within the basal plane. The results are discussed in terms of the instability of the itinerant 5f-electron antiferromagnetism in UNiAl. (c) 2000 American Institute of Physics
Magnetic ordering in spin-orbit Mott insulator Ba2IrO4 probed by μSR
International Nuclear Information System (INIS)
Magnetic properties in the novel spin-orbit Mott insulator Ba2IrO4 were studied using muon spin rotation (μSR) technique. Zero-field μSR experiments revealed that Ba2IrO4 shows an antiferromagnetic transition at TN ∼ 240 K without any spontaneous magnetization. The most stable μ+ site was determined by the electrostatic (Madelung) potential calculation. The effective magnetic moment of the iridium ions (|μ|) in the antiferromagnetic ordered state was calculated using a dipolar-field model, with an internal field obtained by μSR experiments. The magnetic moment is significantly reduced (|μ| ∼ 0.34 μB) due to a low-dimensional quantum spin fluctuation with a large intra-plane correlation. The magnetic ground state of the spin-orbit Mott insulator Ba2IrO4 is quite similar to those in parent materials of high-TC cuprate superconductors such as La2CuO4.
Magnetic Nanostructures Spin Dynamics and Spin Transport
Farle, Michael
2013-01-01
Nanomagnetism and spintronics is a rapidly expanding and increasingly important field of research with many applications already on the market and many more to be expected in the near future. This field started in the mid-1980s with the discovery of the GMR effect, recently awarded with the Nobel prize to Albert Fert and Peter Grünberg. The present volume covers the most important and most timely aspects of magnetic heterostructures, including spin torque effects, spin injection, spin transport, spin fluctuations, proximity effects, and electrical control of spin valves. The chapters are written by internationally recognized experts in their respective fields and provide an overview of the latest status.
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.
Colossal magnetodielectric effect and spin flop in magnetoelectric Co4Nb2O9 crystal
Yin, L. H.; Zou, Y. M.; Yang, J.; Dai, J. M.; Song, W. H.; Zhu, X. B.; Sun, Y. P.
2016-07-01
We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co4Nb2O9 crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature TN. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ˜138% around TN. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co4Nb2O9. These results suggest that linear ME materials with large ME coupling might be potentially used to realize large MD effect for future application.
Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR
International Nuclear Information System (INIS)
In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs), For this we have selected two different classes of SMMs: a ferrimagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/Tl) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the tunneling rate vs T and H for the first time. For AFM rings, we have shown that 1/Tl probes the thermal fluctuations of the magnetization in the intermediate temperature range. We find that the fluctuations are dominated by a single characteristic frequency which has a power law T-dependence indicative of fluctuations due to electron-acoustic phonon interactions
Quantum channels in random spin chains
International Nuclear Information System (INIS)
We study the entanglement between pairs of qubits in a random antiferromagnetic spin-1/2 chain at zero temperature. We show that some very distant pairs of qubits are highly entangled, being almost pure Bell states. Furthermore, the probability to obtain such spin pairs is proportional to the chain disorder strength and inversely proportional to the square of their separation
Conversion from transparent antiferromagnet KNiF3 to transparent ferrimagnets
Manaka, H.; Watanabe, Y.; Kikunaga, K.; Yamamoto, T.; Terada, N.; Obara, K.
2008-01-01
We succeeded in performing a magnetic conversion from transparent antiferromagnet KNiF3 to transparent ferrimagnets, with a spontaneous ferromagnetic moment by a percolation method. Considering Coulomb repulsion, the origin of the spontaneous ferromagnetic moment is explained by an inhomogeneous antiferromagnetic spin arrangement, even if nonmagnetic ions are dispersed homogenously over KNiF3. The ferromagnetic transition temperature was obtained to be 24-26K. The transmittance at 600-1000nm was excellent. This compound shows an alternative that can be used for an optical isolator that uses commercial semiconductor lasers, and can widely be used in next generation optical information networks.
Field-induced lattice staircase in a frustrated antiferromagnet CuFeO2
International Nuclear Information System (INIS)
The results of synchrotron x-ray diffraction and magnetization measurements on a triangular lattice antiferromagnet CuFeO2 subjected to a pulsed high magnetic field are reported. We find the lattice constant, b, contracts stepwise with increasing magnetic field in coincidence with the multistep magnetization changes. These changes in the lattice constant scale with the magnetization changes. We argue that the competition among the ferromagnetic direct and antiferromagnetic superexchange interactions is a main source for this phenomenon. With the changes of the magnetic structure under an applied magnetic field, the number of up spins increases and the lattice contracts to gain the former exchange energy
Real-space renormalization-group studies of low-dimensional quantum antiferromagnets
International Nuclear Information System (INIS)
We study the ground state of one- and two-dimensional (square-lattice) spin-1/2 quantum antiferromagnets using a numerical real-space renormalization-group (RG) approach. In our RG approach we consider blocks of various sizes but with an odd number of sites; we retain only the doublet ground state and we integrate out the higher-energy states by means of second-order quasidegenerate perturbation theory. That is, we assume that the role of the excited states of a block, in the RG iteration process, is to renormalize the effective coupling parameters between blocks. We compute the ground-state energy of a spin-1/2 linear chain for various block sizes and find close agreement with the Bethe-ansatz exact solution. In the case of the spin-1/2 square-lattice quantum antiferromagnet, the obtained ground-state energy is in reasonable agreement with the available numerical estimates
Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet
Directory of Open Access Journals (Sweden)
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.
Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho.
Rettig, L; Dornes, C; Thielemann-Kühn, N; Pontius, N; Zabel, H; Schlagel, D L; Lograsso, T A; Chollet, M; Robert, A; Sikorski, M; Song, S; Glownia, J M; Schüßler-Langeheine, C; Johnson, S L; Staub, U
2016-06-24
Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho L_{3} absorption edge, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation. Tuning the x-ray energy to the electric dipole (E1, 2p→5d) or quadrupole (E2, 2p→4f) transition allows us to selectively and independently study the spin dynamics of the itinerant 5d and localized 4f electronic subsystems via the suppression of the magnetic (2 1 3-τ) satellite peak. We find demagnetization time scales very similar to ferromagnetic 4f systems, suggesting that the loss of magnetic order occurs via a similar spin-flip process in both cases. The simultaneous demagnetization of both subsystems demonstrates strong intra-atomic 4f-5d exchange coupling. In addition, an ultrafast lattice contraction due to the release of magneto-striction leads to a transient shift of the magnetic satellite peak. PMID:27391747
Electrical control of antiferromagnetic metal up to 15 nm
Zhang, PengXiang; Yin, GuFan; Wang, YuYan; Cui, Bin; Pan, Feng; Song, Cheng
2016-08-01
Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in [Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction, the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.
Percolation and spin glass transition
International Nuclear Information System (INIS)
The behaviour of clusters of curved and normal plaquette particles in a bond random, +-J, Ising model is studied in finite square and triangular lattices. Computer results for the concentration of antiferromagnetic bonds when percolating clusters first appears are found to be close to those reported for the occurrence and disappearance of spin glass phases in these systems. (author)
Frustrated diamond-chain quantum XXZ Heisenberg antiferromagnet in a magnetic field
International Nuclear Information System (INIS)
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
Indications of c-axis Charge Transport in Hole Doped Triangular Antiferromagnets
Institute of Scientific and Technical Information of China (English)
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.
Energy Technology Data Exchange (ETDEWEB)
Cao, Xiaobin
2011-01-15
The quasi-one-dimensional systems exhibit some unusual phenomenon, such as the Peierls instability, the pseudogap phenomena and the absence of a Fermi-Dirac distribution function line shape in the photoemission spectroscopy. Ever since the discovery of materials with highly anisotropic properties, it has been recognized that fluctuations play an important role above the three-dimensional phase transition. This regime where the precursor fluctuations are presented can be described by the so called fluctuating gap model (FGM) which was derived from the Froehlich Hamiltonian to study the low energy physics of the one-dimensional electron-phonon system. Not only is the FGM of great interest in the context of quasi-one-dimensional materials, liquid metal and spin waves above T{sub c} in ferromagnets, but also in the semiclassical approximation of superconductivity, it is possible to replace the original three-dimensional problem by a directional average over effectively one-dimensional problem which in the weak coupling limit is described by the FGM. In this work, we investigate the FGM in a wide temperature range with different statistics of the order parameter fluctuations. We derive a formally exact solution to this problem and calculate the density of states, the spectral function and the optical conductivity. In our calculation, we show that a Dyson singularity appears in the low energy density of states for Gaussian fluctuations in the commensurate case. In the incommensurate case, there is no such kind of singularity, and the zero frequency density of states varies differently as a function of the correlation lengths for different statistics of the order parameter fluctuations. Using the density of states we calculated with non-Gaussian order parameter fluctuations, we are able to calculate the static spin susceptibility which agrees with the experimental data very well. In the calculation of the spectral functions, we show that as the correlation increases, the
International Nuclear Information System (INIS)
The quasi-one-dimensional systems exhibit some unusual phenomenon, such as the Peierls instability, the pseudogap phenomena and the absence of a Fermi-Dirac distribution function line shape in the photoemission spectroscopy. Ever since the discovery of materials with highly anisotropic properties, it has been recognized that fluctuations play an important role above the three-dimensional phase transition. This regime where the precursor fluctuations are presented can be described by the so called fluctuating gap model (FGM) which was derived from the Froehlich Hamiltonian to study the low energy physics of the one-dimensional electron-phonon system. Not only is the FGM of great interest in the context of quasi-one-dimensional materials, liquid metal and spin waves above Tc in ferromagnets, but also in the semiclassical approximation of superconductivity, it is possible to replace the original three-dimensional problem by a directional average over effectively one-dimensional problem which in the weak coupling limit is described by the FGM. In this work, we investigate the FGM in a wide temperature range with different statistics of the order parameter fluctuations. We derive a formally exact solution to this problem and calculate the density of states, the spectral function and the optical conductivity. In our calculation, we show that a Dyson singularity appears in the low energy density of states for Gaussian fluctuations in the commensurate case. In the incommensurate case, there is no such kind of singularity, and the zero frequency density of states varies differently as a function of the correlation lengths for different statistics of the order parameter fluctuations. Using the density of states we calculated with non-Gaussian order parameter fluctuations, we are able to calculate the static spin susceptibility which agrees with the experimental data very well. In the calculation of the spectral functions, we show that as the correlation increases, the quasi
Barker, Joseph; Tretiakov, Oleg A.
2016-04-01
Skyrmions are topologically protected entities in magnetic materials which have the potential to be used in spintronics for information storage and processing. However, Skyrmions in ferromagnets have some intrinsic difficulties which must be overcome to use them for spintronic applications, such as the inability to move straight along current. We show that Skyrmions can also be stabilized and manipulated in antiferromagnetic materials. An antiferromagnetic Skyrmion is a compound topological object with a similar but of opposite sign spin texture on each sublattice, which, e.g., results in a complete cancellation of the Magnus force. We find that the composite nature of antiferromagnetic Skyrmions gives rise to different dynamical behavior due to both an applied current and temperature effects.
Incommensurate spin ordering and fluctuations in underdoped La{sub 2-x}Ba{sub x}CuO{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Dunsiger, Sarah [Physics Department E21, Technical University of Munich, Garching (Germany); Zhao, Yang; Gaulin, Bruce; Dabkowska, Hanna [Department of Physics and Astronomy, McMaster University, Hamilton, ON (Canada); Yamani, Zahra; Buyers, William [Canadian Neutron Beam Centre, NRC, Chalk River Laboratories, Chalk River, ON (Canada); Qiu, Yiming; Copley, John [National Institute of Standards and Technology, Gaithersburg, Maryland (United States); Sidis, Yvan; Bourges, Philippe [Laboratoire Leon Brillouin, CEA-Saclay, Gif-sur-Yvette (France)
2008-07-01
The diverse magnetic properties of the La{sub 2-x}(Sr,Ba){sub x}CuO{sub 4} transition metal oxides may be tuned in a controllable way by doping with mobile holes. In one interpretation, the holes are believed to organise into correlated static or dynamic stripes. We report the first observation of static incommensurate spin ordering in underdoped La{sub 2-x}Ba{sub x}CuO{sub 4} (x=0.025, 0.05, 0.08) using neutron diffraction. Elastic collinear incommensurate peaks are observed below the superconducting transition (T{sub C}{proportional_to}27 K) in La{sub 2-x}Ba{sub x}CuO{sub 4} (x=0.08). In marked contrast, diagonal satellite peaks have been observed at low temperature in positions rotated by 45 {sup circle} within the (HK0) plane for La{sub 2-x}Ba{sub x}CuO{sub 4} (x{proportional_to}0.025, 0.05). Our neutron scattering results are compared with analogous studies on La{sub 2-x}Sr{sub x}CuO{sub 4} which indicate that such a rotation of the spin structure may be a generic feature of the underdoped La-214 cuprates.
Magnetic fluctuations induced insulator-to-metal transition in Ca(IrxRu1-x) O3
Singh, Deepak; Gunasekera, Jagath; Dahal, Ashutosh; Harriger, Leland; Heitmann, Thomas
2015-03-01
The Fermi liquid theory dictates the metal-insulator transition in a continuous fashion via the divergence of the quasiparticle mass m*. However, the metallic phase near the Mott insulator in the metal-insulator phase diagram based on the Hubbard model is dominated by the fluctuations of spin, charge and orbital correlations; often termed as the anomalous metallic phase. In this presentation, experimental results manifesting the magnetic fluctuations induced insulator-to-metal transition in Ca(IrxRu1-x) O3 will be discussed in the framework of the Hubbard model. For x = 1, the compound CaIrO3 is a Mott insulator with antiferromagnetic order below T ~ 110 K. A gradual substitution of Ir by Ru results in the onset of anomalous metallic behavior as a function of the tuning parameter x. At x = 0, the compound CaRuO3 is a non-Fermi liquid metal with no apparent magnetic order. While the orthorhombic structural integrity is maintained throughout the group, strong magnetic fluctuations is detected below x = 0.8. The role of magnetic fluctuations in the metallic transition is further confirmed by first principle theoretical calculation.
Kamra, A.; Witek, F.P.; Meyer, S.; Huebl, H.; Geprägs, S.; Gross, R.; Bauer, G.E.W.; Goennenwein, S.T.B.
2014-01-01
We measure the low-frequency thermal fluctuations of pure spin current in a platinum film deposited on yttrium iron garnet via the inverse spin Hall effect (ISHE)-mediated voltage noise as a function of the angle α between the magnetization and the transport direction. The results are consistent wit
Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe
Kriegner, D.; Výborný, K.; Olejník, K.; Reichlová, H.; Novák, V.; Marti, X.; Gazquez, J.; Saidl, V.; Němec, P.; Volobuev, V. V.; Springholz, G.; Holý, V.; Jungwirth, T.
2016-06-01
Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II-VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Néel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets.
Nonequilibrium spin noise spectroscopy
Li, Fuxiang; Pershin, Yuriy V.; Slipko, Valeriy A.; Sinitsyn, Nikolai A.
2013-01-01
Spin Noise Spectroscopy (SNS) is an experimental approach to obtain correlators of mesoscopic spin fluctuations in time by purely optical means. We explore the information that this technique can provide when it is applied to a weakly non-equilibrium regime when an electric current is driven through a sample by an electric field. We find that the noise power spectrum of conducting electrons experiences a shift, which is proportional to the strength of the spin-orbit coupling for electrons mov...
Magnetic interactions and spin configuration in FeRh and Fe/FeRh systems
Energy Technology Data Exchange (ETDEWEB)
Kuncser, V. E-mail: kuncser@alpha2.infim.ro; Keune, W.; Sahoo, B.; Duman, E.; Acet, M.; Radu, F.; Valeanu, M.; Crisan, O.; Filoti, G
2004-05-01
The magnetic interactions and the Fe spin structure have been studied in Fe(6 nm)/FeRh systems by magnetometry, magneto-optic Kerr effect and conversion electron Moessbauer spectroscopy. A spin-flop coupling mechanism, with the interfacial spins of the ferromagnetic phase perpendicular to the spins of the antiferromagnetic phase was experimentally proved.
On the peculiar properties of triangular-chain EuCr{sub 3}(BO{sub 3}){sub 4} antiferromagnet
Energy Technology Data Exchange (ETDEWEB)
Gondek, Ł., E-mail: lgondek@agh.edu.pl [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); Szytuła, A. [M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków (Poland); Przewoźnik, J.; Żukrowski, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków (Poland); Prokhorov, A.; Chernush, L.; Zubov, E. [A.A. Galkin Donetsk Physico-Technical Institute, NANU, 83114 Donetsk, R. Luxembourg str. 72 (Ukraine); Dyakonov, V. [A.A. Galkin Donetsk Physico-Technical Institute, NANU, 83114 Donetsk, R. Luxembourg str. 72 (Ukraine); Institute of Physics, PAS, 02-668 Warsaw, Al. Lotników 32/46 (Poland); Duraj, R. [Institute of Physics Technical University of Cracow, Podchorazych 1, 30-084 Krakow (Poland); Tyvanchuk, Yu. [Analytical Chemistry Department, Ivan Franko National University of Lviv, Kyryla and Mephodiya 6, 79005 Lviv (Ukraine)
2014-02-15
In this paper we report studies on EuCr{sub 3}(BO{sub 3}){sub 4} compound, that is a member of newly discovered family of huntite-related specimens for non-linear optics. For the first time, the uncommon temperature dependence of the EuCr{sub 3}(BO{sub 3}){sub 4} lattice parameters is reported. Additionally, the magnetism of this compound is extremely interesting. Namely, a possible interplay in between potentially magnetic rare-earth ions and 3d metal stacked within quasi-1D chain that can lead to a great variety of magnetic behaviour. Indeed, in our studies we have found 3D-long range ordering with metamagnetic behaviour, while at higher temperature the magnetic chains become uncoupled. - Graphical abstract: Torsion-like vibrations are the key to understand negative thermal expansion along the a-axis. Display Omitted - Highlights: • EuCr{sub 3}(BO{sub 3}){sub 4} is a peculiar triangular-chain antiferromagnet. • Rare earth sublattice is non-magnetic with Eu{sup 3+} configuration. • Cr{sup 3+} magnetic moments show 1-D behaviour along with spin fluctuations. • Torsion vibrations of Cr triangular tubes lead to anomalous expansion of unit cell.
Czech Academy of Sciences Publication Activity Database
Shick, Alexander; Khmelevskyi, S.; Mryasov, O. N.; Wunderlich, J.; Jungwirth, Tomáš
2010-01-01
Roč. 81, č. 21 (2010), 212409/1-212409/4. ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100912; GA ČR GA202/07/0456; GA AV ČR KAN400100652; GA ČR GEFON/06/E002 Grant ostatní: EU FP7(XE) #215368; EU FP7 NAMASTE(XE) No.214499 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10100521 Keywords : magnetic anisotropy * tunneling anisotropic magneto -resistance * exchange bias Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010 http://link.aps.org/doi/10.1103/PhysRevB.81.212409
A nonmagnetic impurity in a 2D quantum critical antiferromagnet
Troyer, Matthias
2003-03-01
We compute the properties of a mobile hole and a static impurity injected into a two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point. A static S=1/2 impurity doped into a quantum-disordered spin gap system induces a local moment with spin S=1/2 and a corresponding Curie-like impurity susceptibility, while the same impurity in a Néel ordered state only gives a finite impurity susceptibility. For the quantum critical system however an interesting field-theoretical prediction has been made that there the impurity spin susceptibility still has a Curie-like divergence, but with a universal effective spin that is neither an integer nor a half-odd integer [1]. In large-scale quantum Monte Carlo (QMC) simulations using the loop algorithm we calculate the impurity susceptibility and find that, unfortunately, this effect is not observable since the renormalization of the effective spin away from S=1/2 is minimal. Other predictions of the field theory, such as a new critical exponent η' describing the time-dependent impurity spin correlations can however be confirmed [2]. Next we compute the spectral function of a hole injected into a 2D antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point [3]. We show that, near van Hove singularities, the problem maps onto that of a static vacancy. This allows the calculation of the spectral function in a QMC simulation without encountering the negative sign problem. We find a vanishing quasiparticle residue at the critical point, a new exponent η_h0.080.04 describing the frequency dependence of the spectral function G_h(ω)(ɛ_0-ω)-1+ηh and discuss possible relevance to photoemission spectra of cuprate superconductors near the antinodal points. ^1 S. Sachdev, C. Buragohain and M. Vojta, Science 286, 2479 (1999). ^2 M. Troyer, in Prog. Theor. Phys. Suppl. 145 (2002); M. Körner and M. Troyer, ibid. ^3 S. Sachdev, M. Troyer, and M. Vojta, Phys. Rev
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.
Phase transition and critical behavior of spin-orbital coupled spinel ZnV2O4
Li, Wang; Rong-juan, Wang; Yuan-yuan, Zhu; Zhi-hong, Lu; Rui, Xiong; Yong, Liu; Jing, Shi
2016-01-01
We present the temperature-dependent susceptibility and specific heat measurement of spinel ZnV2O4. The structural transition with orbital ordering and the antiferromagnetic transition with spin ordering were observed at 50 K and 37 K, respectively. By analysis of the hysteresis behavior between the specific heat curves obtained in warming and cooling processes, the structural transition was confirmed to be the first-order transition, while the antiferromagnetic transition was found to be of the second-order type. At the structural transition, the latent heat and entropy change were calculated from the excess specific heat, and the derivative of pressure with respect to temperature was obtained using the Clausius-Clapayron equation. At the magnetic transition, the width of the critical fluctuation region was obtained to be about 0.5 K by comparing with Gaussian fluctuations. In the critical region, the critical behavior was analyzed by using renormalization-group theory. The critical amplitude ratio A+/A- = 1.46, which deviates from the 3D Heisenburg model; while the critical exponent α is -0.011, which is close to the 3D XY model. We proposed that these abnormal critical behaviors can be attributed to strong spin-orbital coupling accompanied with the antiferromagnetic transition. Moreover, in the low temperature range (2-5 K), the Fermi energy, the density of states near the Fermi surface, and the low limit of Debye temperature were estimated to be 2.42 eV, 2.48 eV-1, and 240 K, respectively. Project supported by the National Basic Research Program of China (Grant No. 2012CB821404), the National Natural Science Foundation of China (Grant Nos. 51172166 and 61106005), the National Science Fund for Talent Training in Basic Science, China (Grant No. J1210061), and the Doctoral Fund of Ministry of Education of China (Grant No. 20110141110007).
Institute of Scientific and Technical Information of China (English)
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.
Quantum oscillations in antiferromagnetic CaFe{sub 2}As{sub 2} on the brink of superconductivity
Energy Technology Data Exchange (ETDEWEB)
Harrison, N; McDonald, R D; Mielke, C H; Bauer, E D; Ronning, F; Thompson, J D [Los Alamos National Laboratory, MS-E536, Los Alamos, NM 87545 (United States)
2009-08-12
We report quantum oscillation measurements on CaFe{sub 2}As{sub 2} under strong magnetic fields-recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05% of the paramagnetic Brillouin zone volume-consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkaline earth AFe{sub 2}As{sub 2} antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area F{sub {alpha}} and the effective mass m{sub {alpha}}* of the primary observed pocket on the antiferromagnetic/structural transition temperature T{sub s} are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase. (fast track communication)
Kambe, S.; Hattori, T.; Sakai, H.; Tokunaga, Y.; Walstedt, R. E.
2016-05-01
We report, as an example, a complete analysis of nuclear spin-lattice relaxation time (T1) data for the strongly correlated antiferromagnet UPtGa5, which has a typical HoCoGa5 (115) structure. Using a high-quality single-crystal sample, the T dependence of T1 at 195Pt and at two crystallographically inequivalent 69Ga sites has been measured for H ∥a and c axes. Using previously obtained hyperfine coupling tensors from static Knight shift results, the anisotropic spin fluctuation energy and q ⃗ dependence of the dynamic susceptibility have been determined completely, forming a clear contrast to the cases of superconducting CeRhIn5,CeCoIn5, and CeIrIn5, which are considered to be very near to a quantum critical point. We also note that a similar hyperfine coupling scheme to that of CeRhIn5 has been found for UPtGa5.
Universality in antiferromagnetic strange metals
Maier, Stefan A.; Strack, Philipp
2016-04-01
We propose a theory of metals at the spin-density-wave quantum-critical point in spatial dimension d =2 . We provide a first estimate of the full set of critical exponents (dynamical exponent z =2.13 , correlation length ν =1.02 , spin susceptibility γ =0.96 , electronic non-Fermi liquid ητf=0.53 , spin-wave Landau damping ητb=1.06 ), which determine the universal power laws in thermodynamics and response functions in the quantum-critical regime relevant for experiments in heavy-fermion systems and iron pnictides. We present approximate numerical and analytical solutions of Polchinski-Wetterich-type flow equations with soft frequency regulators for an effective action of electrons coupled to spin-wave bosons. Performing the renormalization group in frequency instead of momentum space allows to track changes of the Fermi-surface shape and to capture Landau damping during the flow. The technique is easily generalizable from models retaining only patches of the Fermi surface to full, compact Fermi surfaces.
The magnetic properties of CsCrCl3, an antiferromagnetic chain compound with single-ion anisotropy
International Nuclear Information System (INIS)
The magnetic structure and excitations of the linear chain hexagonal perovskite salt CsCrCl3 have been studied by susceptibility, powder and single crystal neutron diffraction and coherent inelastic neutron scattering. Below the Neel temperature, Tsub(N) = 16 K, the spins lie in the basal plane with antiferromagnetic ordering along the c-axis chains. At 4.5 K there is strong dispersion of the spin-wave energy along c but no measurable dispersion perpendicular to c. (orig.)
Synthetic antiferromagnetic nanoparticles with tunable susceptibilities
Hu, Wei; Wilson, Robert J.; Earhart, Christopher M.; Koh, Ai Leen; Sinclair, Robert; Wang, Shan X.
2009-01-01
High-moment monodisperse disk-shaped Co–Fe magnetic nanoparticles, stable in aqueous solution, were physically fabricated by using nanoimprinted templates and vacuum deposition techniques. These multilayer synthetic antiferromagnetic nanoparticles exhibit nearly zero magnetic remanence and coercivity, and susceptibilities which can be tuned by exploiting interlayer magnetic interactions. In addition, a low cost method of scaling up the production of sub-100 nm synthetic antiferromagnetic nano...
Electron-phonon interaction and antiferromagnetic correlations
Sangiovanni, G.; Gunnarsson, O.; Koch, E.; Castellani, C.; M. Capone
2006-01-01
We study effects of the Coulomb repulsion on the electron-phonon interaction (EPI) in a model of cuprates at zero and finite doping. We find that antiferromagnetic correlations strongly enhance EPI effects on the electron Green's function with respect to the paramagnetic correlated system, but the net effect of the Coulomb interaction is a moderate suppression of the EPI. Doping leads to additional suppression, due to reduced antiferromagnetic correlations. In contrast, the Coulomb interactio...
International Nuclear Information System (INIS)
Fluctuation phenomena are the ''tip of the iceberg'' revealing the existence, behind even the most quiescent appearing macroscopic states, of an underlying world of agitated, ever-changing microscopic processes. While the presence of these fluctuations can be ignored in some cases, e.g. if one is satisfied with purely thermostatic description of systems in equilibrium, they are central to the understanding of other phenomena, e.g. the nucleation of a new phase following the quenching of a system into the co-existence region. This volume contains a collection of review articles, written by experts in the field, on the subject of fluctuation phenomena. Some of the articles are of a very general nature discussing the modern mathematical formulation of the problems involved, while other articles deal with specific topics such as kinetics of phase transitions and conductivity in solids. The juxtaposition of the variety of physical situations in which fluctuation phenomena play an important role is novel and should give the reader an insight into this subject
Antiferromagnetic fractons in percolating magnets
International Nuclear Information System (INIS)
We report the observations of the dynamical structure factors S(q,ω) for antiffero-magnetic fractons in diluted three-dimensional (3d) and two-dimensional (2d) Heisenberg systems, RbMn0.4Mg0.6F3 and Rb2Mn0.598Mg0.402F4, with a magnetic concentration close to the percolation concentration, which were obtained by means of high-resolution (ΔE=17.5 μeV) inelastic neutron scattering experiments. The peak intensity A(q) and the dispersion relation E(q) show the clear scaling laws following to A(q) ∝ q-y with y=2.9±0.1 and E(q) ∝ qz with z=2.5±0.1 for the 3d system, and y=2.9±0.2 and z=1.8±0.2 for the 2d system. The validity of the single-length-scaling postulate (SLSP) for S(q,ω) are demonstrated, for the first time. In addition, we show that the spectral dimension of antiferromagnetic fractons is unity independent of the embedding Euclidean dimension of the systems. These values are consistent with the theoretical predictions. (author)
Neto, Minos A.; de Sousa, J. Ricardo; Padilha, Igor T.; Rodriguez Salmon, Octavio D.; Roberto Viana, J.; Dinóla Neto, F.
2016-06-01
We study the three-dimensional antiferromagnetic Ising model in both uniform longitudinal (H) and transverse (Ω) magnetic fields by using the effective-field theory (EFT) with finite cluster N = 1 spin (EFT-1). We analyzed the behavior of the magnetic susceptibility to investigate the reentrant phenomena that we have seen in the same phase diagram previously obtained in other papers. Our results shows the presence of two divergences in the susceptibility that indicates the existence of a reentrant behavior.
One- and two-magnon Raman scattering in the canted antiferromagnet NiF{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Meloche, E. [Department of Physics and Astronomy, University of Western Ont., London, Ont., N6A 3K7 (Canada); Cottam, M.G. [Department of Physics and Astronomy, University of Western Ont., London, Ont., N6A 3K7 (Canada)]. E-mail: cottam@uwo.ca; Gnezdilov, V.P. [Institute for Microstructural Sciences, National Research Council, Ottawa, Ont., K1A 0R6 (Canada); Lockwood, D.J. [Institute for Microstructural Sciences, National Research Council, Ottawa, Ont., K1A 0R6 (Canada)
2007-03-15
The magnons in the canted rutile-structure antiferromagnet NiF{sub 2} have been studied by Raman scattering. Results are presented for the polarization dependences of the one-magnon spectum over a wide range of temperatures below T {sub N} and the two-magnon spectrums at low temperatures. A theoretical analysis of the data, including the important role of the spin canting for the one-magnon properties, is shown to provide good agreement with the measurements.
Raman scattering in a two-layer antiferromagnet
Morr, Dirk K.; Chubukov, Andrey V.; Kampf, Arno P.; Blumberg, G.
1996-08-01
Two-magnon Raman scattering is a useful tool to verify recent suggestions concerning the value of the interplanar exchange constant in antiferromagnetic two-layer systems, such as YBa2Cu3O6+x. We present a theory for Raman scattering in a two-layer antiferromagnet. We study the spectra for the electronic and magnetic excitations across the charge transfer gap within the one-band Hubbard model and derive the matrix elements for the Raman scattering cross section in a diagrammatic formalism. We analyze the effect of the interlayer exchange coupling J2 for the Raman spectra in A1g and B1g scattering geometries both in the nonresonant regime (when the Loudon-Fleury model is valid) and at resonance. We show that within the Loudon-Fleury approximation, a nonzero J2 gives rise to a finite signal in A1g scattering geometry. Both in this approximation and at resonance the intensity in the A1g channel has a peak at small transferred frequency equal to twice the gap in the spin-wave spectrum. We compare our results with experiments in YBa2Cu3O6.1 and Sr2CuO2Cl2 compounds and argue that the large value of J2 suggested in a number of recent studies is incompatible with Raman experiments in A1g geometry.
Cluster study of the neutron-scattering form factor for antiferromagnetic KNiF3 and NiO
Chang, Hyunju; Harrison, J. F.; Kaplan, T. A.; Mahanti, S. D.
1994-06-01
Motivated by difficulties in understanding the magnetism of the insulating parent of high-Tc supeconductors, we have studied the less covalent, and thus simpler, antiferromagnetic (AF) insulators NiO and KNiF3. We also consider the apparently covalent material La2NiO4, which is closely related to the high-Tc superconductor parent La2CuO4. Despite many studies of KNiF3 and NiO via cluster calculations, we found that a satisfactory ab initio cluster theory of the neutron form factor is lacking. We have carried out such a calculation in the unrestricted Hartree-Fock (UHF) approximation, taking the basic cluster as (NiF6)4- and (NiO6)10- for KNiF3 and NiO, respectively, treating the remaining lattice in the point-charge model. We show that correlation effects and Pauli repulsion corrections to the point charges are negligible in these cases. After correcting for the zero-point spin fluctuations, the UHF form factor agrees well with experiment in KNiF3, where the absolute value of the form factor is known for small scattering vectors q. The UHF calculations agree satisfactorily with the relative form factor data for NiO, which cover a large range of ||q|| (the absolute experimental values are not available); the agreement in shape includes the variations with q due to asphericity of the spin density. We also found that the UHF results on La2NiO4, obtained by using similar methods, disagree sharply with experiment.
Ground state properties of a spin chain within Heisenberg model with a single lacking spin site
MEBROUKI, M.
2011-01-01
The ground state and first excited state energies of an antiferromagnetic spin-1/2 chain with and without a single lacking spin site are computed using exact diagonalization method, within the Heisenberg model. In order to keep both parts of a spin chain with a lacking site connected, next nearest neighbors interactions are then introduced. Also, the Density Matrix Renormalization Group (DMRG) method is used, to investigate ground state energies of large system sizes; which permits us to inq...
Spin nematic state for a spin S=3/2 isotropic non-Heisenberg magnet
Fridman, Yu. A.; Kosmachev, O. A.; Ivanov, B. A.
2009-01-01
$S=3/2$ system with general isotropic nearest-neighbor exchange within a mean-field approximation possesses a magnetically ordered ferromagnetic state and antiferromagnetic state, and two different spin nematic states, with zero spin expectation values. Both spin nematic phases display complicated symmetry break, including standard rotational break described by the vector-director $\\vec {u}$ and specific symmetry break with respect to the time reversal. The break of time reversal is determine...
Spin and valley transports in junctions of Dirac fermions
Yokoyama, Takehito
2014-01-01
We study spin and valley transports in junctions composed of silicene and topological crystalline insulators. We consider normal/magnetic/normal Dirac metal junctions where a gate electrode is attached to the magnetic region. In normal/antiferromagnetic/normal silicene junction, we show that the current through this junction is valley and spin polarized due to the coupling between valley and spin degrees of freedom, and the valley and spin polarizations can be tuned by local application of a ...
Spontaneous Pattern Formation in an Antiferromagnetic Quantum Gas
International Nuclear Information System (INIS)
In this Letter we report on the spontaneous formation of surprisingly regular periodic magnetic patterns in an antiferromagnetic Bose-Einstein condensate (BEC). The structures evolve within a quasi-one-dimensional BEC of 87Rb atoms on length scales of a millimeter with typical periodicities of 20...30 μm, given by the spin healing length. We observe two sets of characteristic patterns which can be controlled by an external magnetic field. We identify these patterns as linearly unstable modes within a mean-field approach and calculate their mode structure as well as time and energy scales, which we find to be in good agreement with observations. These investigations open new prospects for controlled studies of symmetry breaking and complex quantum magnetism in bulk BEC.
Monte Carlo study of four-spinon dynamic structure function in antiferromagnetic Heisenberg model
International Nuclear Information System (INIS)
Using Monte Carlo integration methods, we describe the behavior of the exact four-s pinon dynamic structure function S4 in the antiferromagnetic spin 1/2 Heisenberg quantum spin chain as a function of the neutron energy ω and momentum transfer k. We also determine the fourspinon continuum, the extent of the region in the (k, ω) plane outside which S4 is identically zero. In each case, the behavior of S4 is shown to be consistent with the four-spinon continuum and compared to the one of the exact two-spinon dynamic structure function S2. Overall shape similarity is noted. (author)
Color confinement from fluctuating topology
Kharzeev, Dmitri E
2015-01-01
QCD possesses a compact gauge group, and this implies a non-trivial topological structure of the vacuum. In this contribution to the Gribov-85 Memorial volume, we first discuss the origin of Gribov copies and their interpretation in terms of fluctuating topology in the QCD vacuum. We then describe the recent work with E. Levin that links the confinement of gluons and color screening to the fluctuating topology, and discuss implications for spin physics, high energy scattering, and the physics of quark-gluon plasma.
Quantum fluctuations stabilize skyrmion textures
Roldán-Molina, A.; Santander, M. J.; Nunez, A. S.; Fernández-Rossier, J.
2015-12-01
We study the quantum spin waves associated to skyrmion textures. We show that the zero-point energy associated to the quantum spin fluctuations of a noncollinear spin texture produce Casimir-like magnetic fields. We study the effect of these Casimir fields on the topologically protected noncollinear spin textures known as skyrmions. In a Heisenberg model with Dzyalonshinkii-Moriya interactions, chosen so the classical ground state displays skyrmion textures, we calculate the spin-wave spectrum, using the Holstein-Primakoff approximation, and the associated zero-point energy, to the lowest order in the spin-wave expansion. Our calculations are done both for the single-skyrmion case, for which we obtain a discrete set of skyrmion bound states, as well as for the skyrmion crystal, for which the resulting spectrum gives the spin-wave bands. In both cases, our calculations show that the Casimir magnetic field contributes up to 10% of the total Zeeman energy necessary to delete the skyrmion texture with an applied field.
International Nuclear Information System (INIS)
We analyze the logarithmic corrections due to ferromagnetic impurity ending bonds of open spin 1/2 antiferromagnetic chains, using the density matrix renormalization group technique. A universal finite size scaling ∼ 1/L log L for impurity contributions in the quasi-degenerate ground state energy is demonstrated for a zigzag spin 1/2 chain at the critical next nearest neighbor coupling and the standard Heisenberg spin 1/2 chain, in the long chain limit. Using an exact solution for the latter case it is argued that one can extract the impurity contributions to the entropy and specific heat from the scaling analysis. It is also shown that a pure spin 3/2 open Heisenberg chain belongs to the same universality class. (author)
Random SU(2)-symmetric spin-S chains
Quito, V. L.; Hoyos, José A.; Miranda, E.
2016-08-01
We study the low-energy physics of a broad class of time-reversal invariant and SU(2)-symmetric one-dimensional spin-S systems in the presence of quenched disorder via a strong-disorder renormalization-group technique. We show that, in general, there is an antiferromagnetic phase with an emergent SU (2 S +1 ) symmetry. The ground state of this phase is a random singlet state in which the singlets are formed by pairs of spins. For integer spins, there is an additional antiferromagnetic phase which does not exhibit any emergent symmetry (except for S =1 ). The corresponding ground state is a random singlet one but the singlets are formed mostly by trios of spins. In each case the corresponding low-energy dynamics is activated, i.e., with a formally infinite dynamical exponent, and related to distinct infinite-randomness fixed points. The phase diagram has two other phases with ferromagnetic tendencies: a disordered ferromagnetic phase and a large spin phase in which the effective disorder is asymptotically finite. In the latter case, the dynamical scaling is governed by a conventional power law with a finite dynamical exponent.
Superconductivity, antiferromagnetism and ferromagnetism in periodic table of D.I. Mendeleev
International Nuclear Information System (INIS)
Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4th period. Elements with superconductivity, by which d-shells start to fill up, are at the beginning of each period; then follow antiferromagnetics and ferromagnetics (in 4th period and lanthanides), or elements without any of the three listed order types (5th period and 6th period), in which the d (f)-shells continue to fill up almost exceedingly; then again appear superconductors by filling the p-shell up to the number is equal to 4. We calculated the radii of the external d (f)- and p-orbitals and the nearest to them orbitals with the Slater method. These trends were explained by distinction of degree of division of the external d (f)- or p-orbitals of the neighboring atoms in the crystal. Largest division occurs in ferromagnetics. In antiferromagnetics it is smaller than in ferromagnetics. It is demonstrated that in the superconducting crystals the external dor p-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals. Furthermore the external d- or p-shells of some elements in the 5th and 6th periods approach the deeper shells of neighboring atoms. Hence the electron in this shell is situated in neighboring atoms in a different electric field from its own. This fact is open to speculation that the separation of spin and charge in electron, disposed on the external d- or p-orbitals, is quite possible. The charges without spin become bosons. Spins that have the magnetic moments are ordered antiparallel in pairs. Magnetic field transfers this pair in a parallel state and a magnetic flux component along of magnetic field from the pair is equal to one fluxon (the quant of the magnetic flux).
International Nuclear Information System (INIS)
We consider the spin-1/2 antiferromagnetic Heisenberg model on the two-dimensional square-kagome lattice with almost dispersionless lowest magnon band. For a general exchange coupling geometry we elaborate low-energy effective Hamiltonians which emerge at high magnetic fields. The effective model to describe the low-energy degrees of freedom of the initial frustrated quantum spin model is the (unfrustrated) square-lattice spin-1/2 XXZ model in a z-aligned magnetic field. For the effective model we perform quantum Monte Carlo simulations to discuss the low-temperature properties of the square-kagome quantum Heisenberg antiferromagnet at high magnetic fields. We pay special attention to a magnetic-field driven Berezinskii-Kosterlitz-Thouless phase transition which occurs at low temperatures
Spin-Wave Dispersion and Sublattice Magnetization in NiCl_2
DEFF Research Database (Denmark)
Lindgård, Per-Anker; Birgeneau, R. J.; Als-Nielsen, Jens Aage;
1975-01-01
NiCl2 is a Heisenberg planar antiferromagnet composed of hexagonal ferromagnetic Ni2+ sheets with effective XY symmetry weakly coupled antiferromagnetically to adjacent Ni2+ sheets. The near two-dimensionality dimples a directionally-dependent spin-wave renormalization together with an unusual...
Dissipative Dynamics of Quantum Fluctuations
Benatti, F; Floreanini, R
2015-01-01
One way to look for complex behaviours in many-body quantum systems is to let the number $N$ of degrees of freedom become large and focus upon collective observables. Mean-field quantities scaling as $1/N$ tend to commute, whence complexity at the quantum level can only be inherited from complexity at the classical level. Instead, fluctuations of microscopic observables scale as $1/\\sqrt{N}$ and exhibit collective Bosonic features, typical of a mesoscopic regime half-way between the quantum one at the microscopic level and the classical one at the level of macroscopic averages. Here, we consider the mesoscopic behaviour emerging from an infinite quantum spin chain undergoing a microscopic dissipative, irreversible dynamics and from global states without long-range correlations and invariant under lattice translations and dynamics. We show that, from the fluctuations of one site spin observables whose linear span is mapped into itself by the dynamics, there emerge bosonic operators obeying a mesoscopic dissipa...
Jamming Behavior of Domain Walls in an Antiferromagnetic Film
Sinha, Sunil
2014-03-01
Over the last few years, attempts have been made to unify many aspects of the freezing behavior of glasses, granular materials, gels, supercooled liquids, etc. into a general conceptual framework of what is called jamming behavior. This occurs when particles reach packing densities high enough that their motions become highly restricted. A general phase diagram has been proposed onto which various materials systems, e.g glasses or granular materials, can be mapped. We will discuss some recent applications of resonant and non-resonant soft X-ray Grazing Incidence Scattering to mesoscopic science, for example the study of magnetic domain wall fluctuations in thin films. For these studies, we use resonant magnetic x-ray scattering with a coherent photon beam and the technique of X-ray Photon Correlation Spectroscopy. find that at the ordering temperature the domains of an antiferromagnetic system, namely Dysprosium metal, behave very much also like a jammed system and their associated fluctuations exhibit behavior which exhibit some of the universal characteristics of jammed systems, such as non-exponential relaxation and Vogel-Fulcher type freezing. Work supported by Basic Energy Sciences, U.S. Dept. of Energy under Grant Number: DE-SC0003678.
Block-Spin Approach to Electron Correlations
Monthoux, P.
1997-01-01
We consider an expansion of the ground state wavefunction of quantum lattice many-body systems in a basis whose states are tensor products of block-spin wavefunctions. We demonstrate by applying the method to the antiferromagnetic spin-1/2 chain that by selecting the most important many-body states the technique affords a severe truncation of the Hilbert space while maintaining high accuracy.
Interconnections between magnetic state and transport currents in antiferromagnetic Sr2IrO4
Tsoi, Maxim
Interconnections between magnetic state and transport currents in ferromagnetic (F) heterostructures are the basis for spintronic applications, e.g. tunneling magnetoresistance and spin-transfer torque phenomena provide a means to read and write information in magnetic memory devices like STTRAM. Similar interconnections were proposed to occur in systems where F-components are replaced with antiferromagnets (AFM). We demonstrated experimentally the existence of such interconnections in antiferromagnetic Mott insulator Sr2IrO4: first, we found a very large anisotropic magnetoresistance (AMR) which can be used to monitor (read) the magnetic state of AFM; second, we demonstrated the feasibility of reversible resistive switching driven by high-density currents/high electric fields which can be used for writing in AFM memory applications. These results support the feasibility of AFM spintronics where antiferromagnets are used in place of ferromagnets. 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.
Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy
Bruun, G.; Andersen, Brian; Sørensen, Anders; Demler, Eugene A.
2009-01-01
Spin noise spectroscopy with a single laser beam is demonstrated theoretically to provide a direct probe of the spatial correlations of cold fermionic gases. We show how the generic many-body phenomena of anti-bunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.
Relaxation rates of electronic and nuclear magnons in antiferromagnetic materials
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The mechanisms that contribute for the spin-wave relaxation rate in antiferromagnetic materials that belong to two different families, one with cubic simmetry and the other one with uniaxial simmetry are discussed. The typical representatives of these two classes are RbMnF3 and MnF2, respectively. We have done an unified theory to explain the nuclear and electronic spin-wave relaxation rates in RbMnF3 which is based on a mechanism that arises from the crystalline inhomogeneities. The theory was good for both cases, where three-magnon confluence processes without momentum conservation (due to inhomogeneities) were able to explain the general features of the relaxation rates. We have also performed measurements of the AFMR linewidth of MnF2 doped with different concentrations of cobalt and taken care of minimizing the radiation damping. The experimental data were explained by non-momentum conserving magnon-phonon processes. Our results lead to believe that non-momentum conserving processes are the most suitable to explain relaxation rates in materials where one can not define a translational simmetry in the lattice. (author)
Spin-Orbit Coupling and Spin Textures in Optical Superlattices
Li, Junru; Shteynas, Boris; Burchesky, Sean; Top, Furkan Cagri; Su, Edward; Lee, Jeongwon; Jamison, Alan O; Ketterle, Wolfgang
2016-01-01
We proposed and demonstrated a new approach for realizing spin orbit coupling with ultracold atoms. We use orbital levels in a double well potential as pseudospin states. Two-photon Raman transitions between left and right wells induce spin-orbit coupling. This scheme does not require near resonant light, features adjustable interactions by shaping the double well potential, and does not depend on special properties of the atoms. A pseudospinor Bose-Einstein condensate spontaneously acquires an antiferromagnetic pseudospin texture which breaks the lattice symmetry similar to a supersolid.
Lamrani, A. Fakhim; Ouchri, M.; Benyoussef, A.; Belaiche, M.; Loulidi, M.
2013-11-01
Electronic structure calculations based on density functional theory within the generalized gradient approximation for double perovskite Sr2FeMoO6 and Sr2OsMoO6 have been performed using the accurate full potential augmented spherical wave method. By substituting Fe atoms by Os in the double perovskite structure oxides we have shown that it is possible to realize half-metallic antiferromagnets with 100% spin polarization of the conduction electrons crossing the Fermi level, without showing a net magnetization. To support our results, GGA+U electronic structure calculations have been performed showing that the half-metallic antiferromagnetic state still persists. We conclude that the origin of the antiferromagnetism in Sr2OsMoO6 may be attributed to both superexchange and generalized double exchange mechanisms via the B(3d,5d)-O(2p)-B'(4d) coupling.
Sarkar, Sujit; Hu, C. D.
2008-01-01
We study the quantum spin pumping of an antiferromagnetic spin-1/2 chain with competing exchange interactions. We show that spatially periodic potential modulated in space and time acts as a quantum spin pump. In our model system, an applied electric field causes a spin gap to its critical ground state by introducing bond-alternation exchange interactions. We study quantum spin pumping at different quantized magnetization states and also explain physically the presence and absence of quantum ...
Antiferromagnets Structure in Adsorbed O2 Monolayers
DEFF Research Database (Denmark)
Nielsen, Mourits; McTague, J. P.
1977-01-01
Neutron diffraction from monolayers of O2 adsorbed on graphite shows structural arrangements similar to the dense planes of bulk O2. At monolayer completion and above, a magnetic superlattice reflection shows well-developed antiferromagnetic order for T ⩽ 10 K. The submonolayer phase also shows...
Magnetic Properties of Nanoparticles of Antiferromagnetic Materials
DEFF Research Database (Denmark)
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 fo...
Antiferromagnetic resonance in GdVO4
International Nuclear Information System (INIS)
Microwave spectroscopy is used to study gadolinium orthovanadate in the antiferromagnetic phase, from 2.2 to 1.4 K. AFMR data at 9.4 and 34.8 GHz are analyzed and the temperature dependence for the anisotropy constant is obtained. (author)
Experimental Realization of a Quantum Spin Pump
DEFF Research Database (Denmark)
Watson, Susan; Potok, R.; M. Marcus, C.;
2003-01-01
We demonstrate the operation of a quantum spin pump based on cyclic radio-frequency excitation of a GaAs quantum dot, including the ability to pump pure spin without pumping charge. The device takes advantage of bidirectional mesoscopic fluctuations of pumped current, made spin-dependent by the...... application of an in-plane Zeeman field. Spin currents are measured by placing the pump in a focusing geometry with a spin-selective collector....
Nuclear Spin Noise and STM Noise Spectroscopy
Balatsky, A. V.; Fransson, J.; Mozyrsky, D.; Manassen, Yishay
2006-01-01
We consider fluctuations of the electronic spin due to coupling to nuclear spin. Noise spectroscopy of an electronic spin can be revealed in the Scanning Tunnelling Microscope (STM). We argue that the noise spectroscopy of electronic spin can reveal the nuclear spin dynamics due to hyperfine coupling. Tunnelling current develops satellites of the main lines at Larmor frequency and at zero frequency due to hyperfine coupling. We also address the role of the rf field that is at or near the reso...
Magnetic field-induced spatial spin reorientation in dysprosium orthoferrite
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It has been revealed that a magnetic field H parallel b applied dysprosium orthoferrite induces at low temperature T ≤ 5.5 K spatial spin reorientation Γ1 → Γ1234 → Γ4. The transition from the antiferromagnetic state Γ1 to the state Γ1234 with spatial orientation of ferro- and antiferromagnetic vectors is a second-order phase transition and that from the state Γ1234 to the weak ferromagnetic one Γ4 is a first-order transition
Theory of long-wavelength spin waves in exchange biased bilayers
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Long-wavelength spin waves are examined in an exchange biased ferromagnet/antiferromagnet bilayer. The frequencies of the excitations are calculated as a function of external field strength and orientation. It is suggested that the angular dependence of the frequencies can lead to linewidth enhancements, in agreement with recent experimental results. It is also shown that the study of the spin wave frequencies can yield the strengths of the antiferromagnet anisotropy and interlayer coupling. [copyright] 2001 American Institute of Physics