Value Of Frustration Parameter Research Articles

Observation of Griffiths phase, spin glass behaviour and magnetocaloric effect in frustrated Ga2Mn2-xCrxO7 (x = 0, 0.1, 0.3, 0.5) pyrochlore compounds

New series of pyrochlore compounds Ga2Mn2-xCrxO7 (x = 0–0.5) has been synthesized by conventional solid-state reaction method. The X-ray diffraction analysis confirms a single-phase cubic structure of the prepared compounds. All compounds undergo a paramagnetic-antiferromagnetic transition at the Néel transition temperature, close to 42 K. Below ∼12 K temperature, magnetization measurements reveal a glassy behaviour. The value of frustration parameter indicates the presence of a spin frustration. All the compounds exhibit the Griffiths phase. The Arrott's plots confirmed a second-order magnetic phase transition. Moreover, under 5 T applied magnetic field, the maximum value of magnetic entropy change −ΔS was 1.36 J/kg.K for Ga2Mn2O7 compound, which slightly increased to 1.47 J/kg.K for the compound with x = 0.5. At 21 K, the relative cooling power value enhanced from 42.96 J/kg to 47.73 J/kg with Cr4+-ion content changing from x = 0 to x = 0.5.

Thermodynamics properties of copper-oxide superconductors described by an Ising frustrated model

In this work we will study the thermodynamics properties of the quenched decorated Ising model with competitive interactions through the effective field theory (EFT) of a one-spin cluster. This model is used here to describe the thermodynamics properties of the cooper-based oxide superconductors compounds in its insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically (JA<0) with their nearest-neighbors and ferromagnetically (JF>0) with the spins that decorated the bonds, which are quenched randomly distributed over the two-dimensional lattice. The planes interact antiferromagnetically with weak exchange interaction (i.e., JA′=λJA, λ=10−5). By using the framework of an effective-field theory, based on the differential operator technique, we discuss beyond thermodynamics properties the antiferromagnetic-phase stability limit in the temperature-decorated bond concentration space (T×p), for λ=10−5 and various values of frustration parameter (α=JA/JF), magnetic field (H) and concentration parameter (p). For certain range of the parameter α we observe a reentrant behavior in low-temperature that it reflects in the properties behavior itself.

Dynamical percolation transition in the two-dimensional ANNNI model

The dynamical percolation transition of the two-dimensional axial next nearest-neighbor Ising model due to a pulsed magnetic field has been studied by finite size scaling analysis (by Monte Carlo simulation) for various values of frustration parameters, pulse width and temperature (below the corresponding static transition temperature). It has been found that the size of the largest geometrical cluster shows a transition for a critical field amplitude. Although the transition points shift, the critical exponents remain invariant for a wide range of frustration parameters. They are also the same as those obtained for the 2d Ising model. This suggests that although the static phase diagrams of these two models differ significantly in various aspects, the dynamical percolation transitions of these models belong to the same universality class.

Frustrated model to describe reentrant behavior in copper oxide superconductors

The quenched decorated Ising model with competitive interactions is used here to described the magnetic properties of the copper oxide superconductors compounds in the insulating phase (antiferromagnetic). The model consists of planes in which the nodal spins interact antiferromagnetically ( J A < 0 ) with their nearest-neighbors, and ferromagnetically ( J F > 0 ) with the spins that decorate the bonds, which are quenched and distributed randomly over the two-dimensional lattice. The planes interact antiferromagnetically with weak-exchange interaction (i.e., J A ′ = λ J A , λ = 10 - 5 ). By using the framework of an effective-field theory, based on the differential operator technique, we discuss the antiferromagnetic-phase stability limit in the temperature-decorated bond concentration space ( T - p ), for λ = 10 - 5 and various values of frustration parameter α = J A / J F . For certain region range of the parameter α we observe a reentrant behavior at low-temperature. We also discuss the critical behavior of T N versus α for some values of decorated bond concentrations and reentrant phenomena is observed. We calculate the dependence of the staggered magnetization as a function of the temperature to analyze the reentrant behavior observed in the phase diagrams.