Antiferromagnetic Phase Diagram Research Articles

Partially disordered Heisenberg antiferromagnet with short-range stripe correlations

Zero-point quantum fluctuations of a N\'eel order can produce effective interactions between quasi-orphan spins weakly coupled to the lattice. On the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-distorted triangular lattice, this phenomenon leads to a correlated partially disordered phase. In this article, we use matrix product state methods to study a similar model: the $S=1/2$ stuffed square lattice. Tuning the exchange amplitudes we go from a square lattice plus orphan central spins at ${J}^{\ensuremath{'}}/J=0$, to the union jack lattice at ${J}^{\ensuremath{'}}/J=1$, and a square lattice including all spins at $J/{J}^{\ensuremath{'}}=0$. We calculate the complete antiferromagnetic phase diagram, dominated by ferrimagnetic and N\'eel orders, and compare it with existing results. Most importantly, we find a partially disordered phase in the weakly frustrated regime. In this phase, the N\'eel order from the square lattice is unaffected, while the central spins form a collective state with exponentially decaying double-striped correlations. We also study the role of quantum fluctuations by introducing an ordering staggered magnetic field on the square sublattice and find that the central spins order ferromagnetically when fluctuations from the N\'eel order are suppressed.

Magnetic order and phase diagram of magnetic alloy system: MgxNi1–xO alloy

The antiferromagnetic phase diagram of MgxNi1−xO alloy was reexamined theoretically by multicomponent cluster expansion method. It predicts antiferromagnetic state in the alloy with high Mg content, instead of a mixture of antiferromagnetic and paramagnetic states, which was deduced previously from neutron diffraction results. The theoretically found intermediate antiferromagnetic ground states at Mg contents of xMg = 0.25 and 0.75 exhibit very low neutron diffraction intensities, which leads to confusion with paramagnetic state. Our approach here reduced remarkably the computation time in searching the intermediate ground states as well as calculating the magnetic phase diagram.

Chromium analogs of iron-based superconductors

We theoretically investigate the $d^4$ (Cr$^{2+}$) compound BaCr$_2$As$_2$ and show that, despite non-negligible differences in the electronic structure, its many-body physics mirrors that of BaFe$_2$As$_2$, which has instead a $d^6$ (Fe$^{2+}$) configuration. This reflects a symmetry of the electron correlation effects around the half-filled $d^5$ Mott insulating state. The experimentally known metallic antiferromagnetic phase is correctly modeled by dynamical mean-field theory, and for realistic values of the interaction it shows a moderate mass enhancement of order $\sim$2. This value decreases if the ordered moment grows as a result of a stronger interaction. The antiferromagnetic phase diagram for this $d^4$ shows similarities with that calculated for the $d^6$ systems. Correspondingly, in the paramagnetic phase the influence of the half-filled Mott insulator shows up as a crossover from a weakly correlated to an orbitally differentiated "Hund's metal" phase which reflects an analogous phenomenon in $d^6$ iron compounds including a strong enhancement of the compressibility in a zone just inside the frontier between the normal and the Hund's metal. The experimental evidence and our theoretical description place BaCr$_2$As$_2$ at interaction strength slightly below the crossover which implies that negative pressures and/or electron doping (e.g. Cr $\rightarrow$ Mn,Fe or Ba $\rightarrow$ Sc,Y,La) might strongly enhance the compressibility, thereby possibly inducing a pairing instability in this non-superconducting compound.

Antiferromagnetic phase diagram of the cuprate superconductors

Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa$_2$Cu$_3$O$_{6+x}$ compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.

Phase diagram of low-dimensional antiferromagnets with competing order parameters: A Landau-theory approach

We present a detailed analysis of the phase diagram of antiferromagnets with competing exchange-driven and field-induced order parameters. By using the quasi-1D antiferromagnet BaCu_2Si_2O_7 as a test case, we demonstrate that a model based on a Ginzburg-Landau type of approach provides an adequate description of both the magnetization process and of the phase diagram. The developed model not only accounts correctly for the observed spin-reorientation transitions, but it predicts also their unusual angular dependence.

High-TcSuperconductivity and Antiferromagnetism in Multilayered Copper Oxides –A New Paradigm of Superconducting Mechanism–

High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO 2 plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a disorder-free CuO 2 plane with hole carriers. We present our experimental findings such as the existence of the AFM metallic state in doped Mott insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of d -wave SC with a maximum T c just outside a critical carrier density, at which the AFM moment on a CuO 2 plane disappears. These results can be accounted for by the Mott physics based on the t – J model. The superexchange interaction J in among spins plays a vital role as a glue for Cooper pairs or mobile spin-singlet pairs, in contrast to the phonon-mediated attractive interaction among electrons established in the Bardeen–Cooper–Schrieffer (BCS) theory. We remark that the attractive interaction for raising the T c of HTSC up to temperatures as high as 160 K is the large J in (∼0.12 eV), which binds electrons of opposite spins to be on neighboring sites, and that there are no bosonic glues. It is the Coulomb repulsive interaction U (> 6 eV) among Cu-3 d electrons that plays a central role in the physics behind high- T c phenomena. A new paradigm of the SC mechanism opens to strongly correlated electron matter.

Antiferromagnetism, superconductivity, and pseudogap in three-layered high-Tccuprates Ba2Ca2Cu3O6(F,O)2probed by Cu-NMR

We report on the phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in three-layered Ba_2Ca_2Cu_3O_6(F,O)_2 by means of Cu-NMR measurements. It is demonstrated that AFM and SC uniformly coexist in three-layered compounds as well as in four- and five-layered ones. The critical hole density p_c for the long range AFM order is determined as p_c ~ 0.075, which is larger than p_c ~ 0.02 and 0.055 in single- and bi-layered compounds, and smaller than p_c ~ 0.08-0.09 and 0.10-0.11 in four- and five-layered compounds, respectively. This variation of p_c is attributed to the magnetic interlayer coupling which becomes stronger as the stacking number of CuO_2 layers increases; that is, the uniform coexistence of AFM and SC is a universal phenomenon in underdoped regions when a magnetic interlayer coupling is strong enough to stabilize an AFM ordering. In addition, we highlight an unusual pseudogap behavior in three-layered compounds -- the gap behavior in low-energy magnetic excitations collapses in an underdoped region where the ground state is the AFM-SC mixed phase.

13C NMR investigation of low-temperature states in one-dimensional organic cation radical salt, (TMTTF)2SbF6, under high pressures

13C nuclear magnetic resonance (NMR) measurements under the application of hydrostatic pressure were carried out on the one-dimensional organic conductor, (TMTTF)2SbF6, to investigate the competed antiferromagnetic and spin-singlet ground states. The charge-ordering (CO) transition temperature, TCO, (155 K at ambient pressure), decreased to 100 K under a pressure of 5 kbar, and was suppressed above 8 kbar. Under pressures between 5 kbar and 14 kbar, the low-pressure side antiferromagnetic state (AF-I) was suppressed. At the same time, a spin-gap phase was stabilized. Above 17 kbar, another antiferromagnetic phase appeared below approximately 15 ~ 20 K. A possible reentrant antiferromagnetic phase diagram is discussed from a microscopic point-of-view.

Quenched-vacancy induced spin-glass order

The ferromagnetic phase of an Ising model in d=3 , with any amount of quenched antiferromagnetic bond randomness, is shown to undergo a transition to a spin-glass phase under sufficient quenched bond dilution. This result, demonstrated here with the numerically exact global renormalization-group solution of a d=3 hierarchical lattice, is expected to hold true generally, for the cubic lattice and for quenched site dilution. Conversely, in the ferromagnetic-spin-glass-antiferromagnetic phase diagram, the spin-glass phase expands under quenched dilution at the expense of the ferromagnetic and antiferromagnetic phases. In the ferromagnetic-spin-glass phase transition induced by quenched dilution, reentrance as a function of temperature is seen, as previously found in the ferromagnetic-spin-glass transition induced by increasing the antiferromagnetic bond concentration.

Unconventional superconductivity and antiferromagnetic quantum phase transition in [formula omitted]: 115In-NQR study under pressure

We report on the pressure ( P)-induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with T c ∼ 2.1 K at P = 2.05 GPa and the AFM quantum phase transition (QPT) occurs near P = 2.1 GPa . These results reveal the existence of the tetracritical point in the P– T phase diagram of AFM and SC in CeRnIn 5 . We also found the gapless nature in the uniformly coexisting phase of AFM and SC, indicating an intimate relationship between AFM and SC.

Quantum phase diagram of antiferromagnetism and superconductivity with a tetracritical point inCeRhIn5in zero magnetic field

We report on a pressure-temperature phase diagram of antiferromagnetism (AFM) and superconductivity (SC) in $\mathrm{Ce}\mathrm{Rh}{\mathrm{In}}_{5}$ studied by the nuclear-quadrupole-resonance measurements under pressure. It is demonstrated that an AFM phase transition takes place inside the superconducting state. This result reveals that a tetracritical point exists in the phase diagram of AFM and SC at zero magnetic field. The finding of unconventional SC characteristics in the uniformly coexisting phase of AFM and SC suggests that both phases may be mediated by the same magnetic interaction.

Magnetic phase diagrams for models of synthetic antiferromagnets

Phenomenological macrospin models have been studied to elucidate the field-driven reorientation transitions in antiferromagnetically coupled magnetic thin-film elements with uniaxial anisotropy. For planar bilayer systems, there are four topologically different phase diagrams depending on the ratio of anisotropy to exchange energy. Only for weak anisotropies, the usual phase diagram of antiferromagnets with a spin flop is realized. Analytic and numeric results are presented for a model of a synthetic antiferromagnet composed of four layers, where two ferromagnetically coupled bilayers are coupled antiferromagnetically. Applied fields may stabilize collinear ferrimagnetic and canted phases in these four-layer systems for certain ranges of the ratio between ferromagnetic exchange and antiferromagnetic exchange.

Antiferromagnetic quantum phase transition in superconducting phase in CeRhIn5

We report on the pressure (P)-induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their boarder at zero magnetic field. The nuclear quadrupole resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with Tc∼2.1K at P=2.05GPa and the AFM quantum phase transition (QPT) occurs near P=2.1GPa. These results suggest that AFM phase, AFM+SC uniformly coexisting phase, SC phase and paramagnetic phase all contact with each other at Ttetra∼2.1K and Ptetra∼2GPa which evidence the existence of the tetracritical point in the P–T phase diagram of AFM and SC in CeRnIn5.

Novel phase diagram of antiferromagnetism and superconductivity in [formula omitted

We report on the pressure ( P ) -induced phase diagram of antiferromagnetism (AFM) and superconductivity (SC) which emerges at their border at zero magnetic field. The nuclear-quadrupole-resonance (NQR) measurements have revealed that AFM can take place in the superconducting state with T c ∼ 2.1 K at P = 2.05 GPa . The present experiments have, for the first time, demonstrated that AFM phase, AFM + SC uniformly coexisting phase, SC phase and paramagnetic phase all contact with each other at T tetra ∼ 2.1 K and P tetra ∼ 2 GPa which evidence the existence of the tetracritical point in the P – T phase diagram of AFM and SC in CeRnIn 5 .

Publisher's Note: Efficient calculation of the antiferromagnetic phase diagram of the three-dimensional Hubbard model [Phys. Rev. B72, 060411 (2005)

Received 13 September 2005DOI:https://doi.org/10.1103/PhysRevB.72.109902©2005 American Physical Society

Efficient calculation of the antiferromagnetic phase diagram of the three-dimensional Hubbard model

The Dynamical Cluster Approximation with Betts clusters is used to calculate the antiferromagnetic phase diagram of the 3D Hubbard model at half filling. Betts clusters are a set of periodic clusters which best reflect the properties of the lattice in the thermodynamic limit and provide an optimal finite-size scaling as a function of cluster size. Using a systematic finite-size scaling as a function of cluster space-time dimensions, we calculate the antiferromagnetic phase diagram. Our results are qualitatively consistent with the results of Staudt et al. [Eur. Phys. J. B 17 411 (2000)], but require the use of much smaller clusters: 48 compared to 1000.

The phase diagram of antiferromagnetism and superconductivity inCeRhIn5: astudy of 115In NQR under pressure

We report on the pressure (P) versus temperature (T) phase diagram of the P-induced heavy fermion (HF) superconductorCeRhIn5 via nuclear quadrupole resonance (NQR) measurements underP. AtP = 2.1 GPa,the T dependence of the nuclear spin–lattice relaxation rate1/T1 revealed antiferromagnetic critical fluctuations due to the closeness of antiferromagnetism. AsP decreases slightly down to 1.9 GPa, a pseudogap emerges above K, suggesting the appearance of superconducting fluctuations associated with a strongcoupling effect among quasiparticles.

Magnetic and Fermi Surface Properties of an Antiferromagnet Ce3Sn7

We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction of an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4 f -scheme previously proposed by Bonnet et al. in which the two Ce atoms at the 2(a) site possess a magnetic moment of 0.36 µ B /Ce and the one Ce atom at the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn 3 . We also constructed the antiferromagnetic phase diagram for the three principal directions. Furthermore, we carried out the de Haas–van Alphen experiment. Fermi surfaces are many in number but extremely small in volumes, indicating that Ce 3 Sn 7 is a semimetal.

Pressure-temperature phase diagram of antiferromagnetism and superconductivity inCeRhIn5andCeIn3:115In−NQRstudy under pressure

We report the novel pressure($P$) - temperature($T$) phase diagram of antiferromagnetism and superconductivity in CeRhIn$_5$ and CeIn$_3$ revealed by the $^{115}$In nuclear-spin-lattice-relaxation ($T_1$) measurement. In the itinerant magnet CeRhIn$_5$, we found that the N\'eel temperature $T_N$ is reduced at $P \geq$ 1.23 GPa with an emergent pseudogap behavior. In CeIn$_3$, the localized magnetic character is robust against the application of pressure up to $P \sim$ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.

Antiferromagnetic phase diagram based on Hubbard model under external magnetic field

We present a rigorous examination on the behavior of antiferromagnetically correlated electrons under external magnetic field, the suppression of antiferromagnetic order and its reentrant behavior. It is found that these physical properties are explained in terms of the nesting property of Fermi surface both at zero and finite temperatures.