Phase Diagram Of Spin-1 Research Articles

Effects of random-crystal-field on the kinetic Blume Capel model

The effects of random crystal field on the stationary states of the kinetic spin-1 Blume Capel model are studied using the Glauber-type stochastic dynamics under the time-dependent oscillating field assumption. Our investigation, based on the equilibrium ground state phase diagram, revealed many interesting phenomena. The known phases, in the equilibrium case, are obtained for high field and are represented by limit cycles. The phase diagram of the pure pure kinetic Ising spin- 1 2 and spin-1 Blume Capel models are deduced as particular cases. First-order, second-order transition lines, dynamical critical and dynamical double critical end points are also obtained.

The Phase Diagrams of Spin-1/2 Ising Model on a Two-Layer Bethe Lattice with AFM/AFM Interactions

The phase diagrams of spin-1/2 Ising model on a two-layer Bethe lattice with antiferromagnetic interactions for each layer and either antiferromagnetic or ferromagnetic interaction between the layers are investigated by using the pairwise approach for given values of coordination number q. The exact expressions of the order-parameters, response functions and free energy are obtained in terms of the recursion relations. The ground-state phase diagrams are calculated for given system parameters of the model. In the guidance of the ground-state phase diagrams, the temperature dependent phase diagrams of the model are also studied in detail for given coordination numbers q = 3, 4 and 6. It was found that the system presents only second-order phase transitions with different thermal behaviors for all values of q. In addition, two Neel temperatures, TN, are found for q = 6 only.

Magnetic phase diagram of the dimerized spin S = 1/2 ladder

The ground-state magnetic phase diagram of a spin $S=1/2$ two-leg ladder with alternating rung exchange $J_{\perp}(n)=J_{\perp}[1 + (-1)^{n} \delta]$ is studied using the analytical and numerical approaches. In the limit where the rung exchange is dominant, we have mapped the model onto the effective quantum sine-Gordon model with topological term and identified two quantum phase transitions at magnetization equal to the half of saturation value from a gapped to the gapless regime. These quantum transitions belong to the universality class of the commensurate-incommensurate phase transition. We have also shown that the magnetization curve of the system exhibits a plateau at magnetization equal to the half of the saturation value. We also present a detailed numerical analysis of the low energy excitation spectrum and the ground state magnetic phase diagram of the ladder with rung-exchange alternation using Lanczos method of numerical diagonalizations for ladders with number of sites up to N=28. We have calculated numerically the magnetic field dependence of the low-energy excitation spectrum, magnetization and the on-rung spin-spin correlation function. We have also calculated the width of the magnetization plateau and show that it scales as $\delta^{\nu}$, where critical exponent varies from $\nu =0.87\pm0.01$ in the case of a ladder with isotropic antiferromagnetic legs to $\nu =1.82\pm0.01 $ in the case of ladder with ferromagnetic legs. Obtained numerical results are in an complete agreement with estimations made within the continuum-limit approach.

Spin instability and phase diagram of v = 2 quantum Hall systems

We present the magnetic phase diagram on the (ra, Ez) plane in the self-consistent Hartree-Fock theory for the ν = 2 quantum Hall system. We show that there is an area on the (rs,Ez) plane where a spiral spin density wave state is the ground state of the system.

Spin Susceptibility, Phase Diagram, and Quantum Criticality in the Eelctron-Doped High Tc Superconductor Ba(Fe1-xCox)2As2

We report a systematic investigation of Ba(Fe 1- x Co x ) 2 As 2 based on transport and 75 As NMR measurements, and establish the electronic phase diagram. We demonstrate that doping progressively suppresses the uniform spin susceptibility and low frequency spin fluctuations. The optimum superconducting phase emerges at x c ≃0.08 when the tendency toward spin ordering completely diminishes. Our findings point toward the presence of a quantum critical point near x c between the SDW (spin density wave) and superconducting phases.

Structure and anisotropic compensation of Tb 1− xPr x(Fe 0.4Co 0.55B 0.05) 1.93 (0 ≤ x ≤ 1) magnetostrictive alloys

Structural, magnetic and magnetostrictive properties of Tb 1− x Pr x (Fe 0.4Co 0.55B 0.05) 1.93 (0 ≤ x ≤ 1) alloys have been investigated. The (Tb,Pr)(Fe,Co,B) 2 compounds are found to stabilize in a cubic Laves-phase structure. The lattice parameter increases with increasing Pr content and obeys the linear Vegard's law. The spin phase diagram for the compounds is constructed to illustrate both the composition dependence of the Curie temperature ( T C) and spin reorientation temperature ( T SR) and the arrangement for the easy magnetization direction (EMD). It is found that T C decreases, while T SR increases as increasing Pr content. The saturation magnetization ( M S) decreases to reach a minimum when x ≤ 0.50, and then increases with further increasing Pr content. The composition for magnetic-moment compensation is about x comp = 0.55. The magnetostriction (λ a ) decreases with increasing Pr content when 0 ≤ x ≤ 0.50, then increases with a further increasing x and exhibits a peak in the range of 0.50 ≤ x ≤ 1.0. Both the magnetization and the magnetostriction analyses show that Tb 1− x Pr x (Fe 0.4Co 0.55B 0.05) 1.93 is an anisotropy compensation system and the compensation point is close to x = 0.80.

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

We show results from Monte Carlo simulations of a two-dimensional Heisenberg model for ultrathin films with perpendicular anisotropy. A complete phase diagram is obtained as a function of anisotropy and temperature, spanning a wide range of behavior. We discuss our results in relation to experimental findings in different ultrathin films. We observe and characterize a line of spin reorientation transitions. This transition from out-of-plane stripe order to in-plane ferromagnetic order presents an intermediate paramagnetic gap in a finite region of parameter space, as reported in experiments. For large anisotropies, direct transitions from a low temperature stripe phase to a paramagnetic or tetragonal phase with dominant perpendicular magnetization is observed, which is also in agreement with experiments. We also show the phase diagram for a system without exchange, i.e., with pure dipolar and anisotropy interactions. It shows a similar behavior to the ferromagnetic case with antiferromagnetic instead of stripe phases at low temperatures. A spin reorientation transition is also found in this case.

Quantum corrections of the Dzyaloshinskii-Moriya interaction on the spin- $\frac{1}{2}$ AF-Heisenberg chain in an uniform magnetic field

We have investigated the ground state phase diagram of the 1D AF spin-\(\frac{1}{2}\) Heisenberg model with the staggered Dzyaloshinskii-Moriya (DM) interaction in an external uniform magnetic field H. We have used the exact diagonalization technique. In the absence of the uniform magnetic field (H=0), we have shown that the DM interaction induces a staggered chiral phase. The staggered chiral phase remains stable even in the presence of the uniform magnetic field. We have identified that the ground state phase diagram consists of four Luttinger liquid, staggered chiral, spin-flop, and ferromagnetic phases.

Magnetic Phase Diagram of Spin-1/2 Two-Leg Ladder with Four-Spin Ring Exchanges

We study a spin-1/2 two-leg Heisenberg ladder with four-spin ring exchanges under a magnetic field. We introduce an exact duality transformation, which is an extension of the spin-chirality duality developed previously and yields a new self-dual surface in the parameter space. We then determine the magnetic phase diagram using the numerical approaches of the density-matrix renormalization-group and exact diagonalization methods. We demonstrate the appearance of a magnetization plateau and a Tomonaga–Luttinger liquid with a dominant vector-chirality quasi-long-range order for a wide parameter regime of strong ring exchange. A “nematic” phase, in which magnons form bound pairs and magnon-pairing correlation functions dominate, is also identified.

Singlet–triplet transition of a two-electron quantum ring in magnetic and electric fields

We present an exact numerical calculation of the spin phase diagram of a two-electron quantum ring as a function of an applied in-plane electric field E and a perpendicular magnetic field B. In general, large E and B favour, respectively, singlet and triplet states. At low fields, however, the spin phase diagram shows singlet–triplet oscillations and the formation of spin islands surrounded by the complementary phase. Calculations of the density dipole excitation spectrum as a function of the electric field are also reported.

Multicritical phase diagrams of the ferromagnetic spin- [formula omitted] Blume–Emery–Griffiths model with repulsive biquadratic coupling including metastable phases: The cluster variation method and the path probability method with the point distribution

We study the thermal variations of the ferromagnetic spin- 3 2 Blume–Emery–Griffiths (BEG) model with repulsive biquadratic coupling by using the lowest approximation of the cluster variation method (LACVM) in the absence and presence of the external magnetic field. We obtain metastable and unstable branches of the order parameters besides the stable branches and phase transitions of these branches are investigated extensively. The classification of the stable, metastable and unstable states is made by comparing the free energy values of these states. We also study the dynamics of the model by using the path probability method (PPM) with the point distribution in order to make sure that we find and define the metastable and unstable branches of the order parameters completely and correctly. We present the metastable phase diagrams in addition to the equilibrium phase diagrams in the ( kT/ J, K/ J) and ( kT/ J, D/ J) planes. It is found that the metastable phase diagrams always exist at the low temperatures, which are consistent with experimental and theoretical works.

Spin phase diagram of theνe=4∕11composite fermion liquid

Spin polarization of the ``second-generation'' ${\ensuremath{\nu}}_{e}=4∕11$ fractional quantum Hall state (corresponding to an incompressible liquid in a one-third-filled composite fermion Landau level) is studied by exact diagonalization. A spin phase diagram is determined for GaAs structures of different widths and electron concentrations. Transition between the polarized and partially unpolarized states with distinct composite fermion correlations is predicted for realistic parameters.

The spin- [formula omitted] bilayer Bethe lattice with crystal field

The phase diagrams of the bilayer spin- 3 2 Ising model on the Bethe lattice is analyzed by taking into account the intralayer coupling constants of the two layers ( J 1 , J 2 ) , interlayer coupling constant between the layers ( J 3 ) and crystal field interaction ( D) for the coordination number q = 3 by using the exact recursion equations. First, the distinct ground state phase diagrams of the model are obtained on the ( J 2 / | J 1 | , J 3 / q | J 1 | ) plane with J 1 > 0 for given crystal field values. Then, the phase diagrams of the system are obtained on the ( kT / J 1 , J 3 / J 1 ) planes for given values of the crystal field and α = J 2 / J 1 on the honeycomb lattice, i.e., q = 3 . It was found that the system presents both first- and second-order phase transitions, therefore, tricritical points, and splitting of the critical lines at negative values of the crystal field. The paramagnetic phases are also classified by studying the thermal variations of the quadrupolar moments.

Confinement versus deconfinement of Cooper pairs in one-dimensional spin-3∕2fermionic cold atoms

The phase diagram of spin-$3∕2$ fermionic cold atoms trapped in a one-dimensional optical lattice is investigated at quarter filling (one atom per site) by means of large-scale numerical simulations. In full agreement with a recent low-energy approach, we find two phases with confined and deconfined Cooper pairs separated by an Ising quantum phase transition. The leading instability in the confined phase is an atomic-density wave with subdominant quartet superfluid instability made of four fermions. Finally, we reveal the existence of a bond-ordered Mott insulating phase in some part of the repulsive regime.

Field-induced supersolid phase in spin dimer [formula omitted] systems

We study the ground state phase diagram of the two-dimensional spin S = 1 2 dimer model with an anisotropic intra-plane coupling. A supersolid phase characterized by a non-uniform bose condensate density that breaks translational symmetry is found when the anisotropy 4 ≳ Δ ≳ 3 . The rich phase diagram contains a checkerboard solid and two different types of superfluid phase with finite staggered magnetization in z -axis and in-plane direction, respectively. We show that the model can be realized if next nearest neighbor (n.n.n.) coupling among dimers is taken into account.

Phase transitions and multicritical points in the mixed spin- [formula omitted] and spin-2 Ising system with a single-ion anisotropy

The effect of a single-ion anisotropy on the phase diagram of the mixed spin- 3 2 and spin-2 Ising system is investigated by the use of a mean-field theory based on the Bogoliubov inequality for the free energy. Topologically different kinds of phase diagrams are achieved by changing values of the parameter in the model Hamiltonian. Besides second-order transitions, lines of first-order transitions terminating either at a tricritical point or an isolated critical point, are found.

Quantum Hall Ferrimagnetism in Lateral Quantum Dot Molecules

We demonstrate the existence of ferrimagnetic and ferromagnetic phases in a spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall regime. The spin phase diagram is determined from the Hartree-Fock configuration interaction method as a function of electron number N and magnetic field B. The quantum Hall ferrimagnetic phase corresponds to spatially imbalanced spin droplets resulting from strong interdot coupling of identical dots. The quantum Hall ferromagnetic phases correspond to ferromagnetic coupling of spin polarization at filling factors between nu=2 and nu=1.

Supersolid Phase in Spin DimerXXZSystems under a Magnetic Field

Using quantum Monte Carlo method, we study, under external magnetic fields, the ground state phase diagram of the two-dimensional spin $S$=1/2 dimer model with an anisotropic intra-plane antiferromagnetic coupling. With the anisotropy $4 \gtrsim \Delta \gtrsim 3$, a supersolid phase characterized by a non-uniform bose condensate density that breaks translational symmetry is found. The rich phase diagram also contains a checkerboard solid and two different types of superfluid phase formed by $S_z=+1$ and $S_z=0$ spin triplets, with finite staggered magnetization in z-axis and in-plane direction, respectively. As we show, the model can be realized as a consequence of including the next nearest neighbor coupling among dimers and our results suggest that spin dimer systems may be an ideal model system to study the supersolid phase.

Experimental studies of spin reorientations inEr2−xPrxFe14B

57Fe Mössbauerspectroscopy, x-ray diffraction and magnetic measurements have been used to study the polycrystallineEr2−xPrxFe14B (x = 0.25,0.5, 0.75, 1.0, 1.5) compounds. Special emphasis was put on the spin reorientation phenomena(change of spin orientation from planar to axial arrangement) occurring in this series. Thespin reorientation in each compound has been investigated mainly by means of narrow steptemperature scanning in the neighbourhood of the spin reorientation temperature,TSR.Initial magnetization versus temperature measurements allowed us to establish thetemperature regions of reorientations and also the Curie temperatures of the compounds.Mössbauer temperature scanning was performed with a step of 2 K in the vicinity ofTSR. The spectra obtained were analysed by using a procedure of simultaneousfitting and the transmission integral approach. Consistent fits were obtained;TSR and the composition dependences of hyperfine interaction parameters were derived from fitsfor all compounds studied.The TSR values obtained with both methods were compared and the spin phase diagram for theseries was constructed.

Spin configuration and magnetostrictive properties of Laves compounds TbxDy0.7−xPr0.3(Fe0.9B0.1)1.93(0.10⩽x⩽0.28)

The spin configuration and magnetostrictive properties of TbxDy0.7−xPr0.3(Fe0.9B0.1)1.93 (0.10⩽x⩽0.28) Laves compounds are investigated. The spin phase diagram for the compounds is constructed to illustrate both the composition dependence of the Curie point TC and spin reorientation temperature TSR and the arrangement for the easy magnetization direction (EMD). It is found that when x is increased from 0.16 to 0.28, TC increases from 617to623K, while TSR decreases from 375to160K at which the EMD reorients from ⟨100⟩ to ⟨111⟩ axis. The magnetization and magnetostriction of the compounds are measured as a function of applied field. The magnetocrystalline anisotropy constant K1 and the ratio λa∕K1 reach a minimum and a maximum value at x=0.22, respectively. The single phase Tb0.22Dy0.48Pr0.3(Fe0.9B0.1)1.93 compound has the lowest magnetocrystalline anisotropy, the highest magnetostriction to anisotropy ratio, and a large spontaneous magnetostriction λ111 of ∼1500ppm at room temperature. In view of these properties, the compound is a promising magnetostrictive material.