Surface phase diagram of the Ising model with modified surface-bulk coupling

The phase diagram of the three-dimensional Ising system with intrasurface Js and surface-bulk J^ interactions modified with respect to the bulk exchange interaction Js is studied by the use of an effective field method within the framework of a single-site cluster theory. In this investigation, the new parameter J^ strongly affects the phase diagram obtained recently in the case J^=Js. Indeed, our calculations reveal some qualitatively interesting features for the surface when the bulk is ordered or disordered. Surface magnetisations are also investigated for different values of the ratio R=Js /JBThe phase diagram of the three-dimensional Ising system with intrasurface Js and surface-bulk J^ interactions modified with respect to the bulk exchange interaction Js is studied by the use of an effective field method within the framework of a single-site cluster theory. In this investigation, the new parameter J^ strongly affects the phase diagram obtained recently in the case J^=Js. Indeed, our calculations reveal some qualitatively interesting features for the surface when the bulk is ordered or disordered. Surface magnetisations are also investigated for different values of the ratio R=Js /J

Mixed spin Ising model with four-spin interactions and crystal field

A mixed spin Ising model consisting of spin-1/2 and spin-1 with four-spin interactions and crystal field anisotropy is studied by the use of the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the square lattice. It has been shown that the phase diagram of the system depends on the strength of four-spin interaction and exhibits a variety of interesting features.A mixed spin Ising model consisting of spin-1/2 and spin-1 with four-spin interactions and crystal field anisotropy is studied by the use of the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the square lattice. It has been shown that the phase diagram of the system depends on the strength of four-spin interaction and exhibits a variety of interesting features

Phase diagram of the mixed spin transverse Ising model with four-spin Interactions

The two dimensional mixed spin system consisting of spin-1/2 and spin-1 with four-spin interactions exhibits tricritical behaviour. The influence of a transverse field on this behaviour is studied with the finite cluster approximation based on a single-site cluster theory. The state equations are derived for the square lattice. It has been shown that the system keeps its tricritical behaviour, but when the strength of the transverse field approaches a critical value, all transitions become of second-order for any value of four-spin interaction

Bond diluted surface phase diagrams of the transverse Ising model

The effects of diluted surface on the phase diagram of the transverse Ising spin model is studied by the use of an effective field method within the framework of single-site cluster theory. The state equations are derived using the differential operator technique. The complete phase diagrams are investigated when the exchange interactions JijS at the surface, is randomly distributed. JijS is in competition with the bulk interactions. In particular, the influence of the surface transverse field and the dilution parameter on the three-dimensional transverse Ising model is examined in detail.The effects of diluted surface on the phase diagram of the transverse Ising spin model is studied by the use of an effective field method within the framework of single-site cluster theory. The state equations are derived using the differential operator technique. The complete phase diagrams are investigated when the exchange interactions JijS at the surface, is randomly distributed. JijS is in competition with the bulk interactions. In particular, the influence of the surface transverse field and the dilution parameter on the three-dimensional transverse Ising model is examined in detail

The transverse mixed spin Ising model in a longitudinal random field

The transverse mixed spin Ising system consisting of spin-1/2 and spin-1 with a longitudinal random field is studied within the finite cluster approximation based on single-site cluster theory. The equations are derived using a probability distribution method based on the use of Van der Waerden identities. In the absence of the transverse field, the complete phase diagram in the case of simple cubic lattice is investigated and exhibits interesting behaviours, where the longitudinal field is bimodally and trimodally distributed. The influence of the transverse field on these behaviours are also examined.The transverse mixed spin Ising system consisting of spin-1/2 and spin-1 with a longitudinal random field is studied within the finite cluster approximation based on single-site cluster theory. The equations are derived using a probability distribution method based on the use of Van der Waerden identities. In the absence of the transverse field, the complete phase diagram in the case of simple cubic lattice is investigated and exhibits interesting behaviours, where the longitudinal field is bimodally and trimodally distributed. The influence of the transverse field on these behaviours are also examined

Disordered mixed spin Ising system in a random field

The diluted mixed spin Ising system consisting of spin-1/2 and spin-1 in a random field is studied by the use of finite cluster approximation the framework of a single-site cluster theory. The equations are derived using a probability distribution method based on the use of Van der Waerden identities. The complete phase diagrams are investigated in the case of the simple cubic lattice (z=6), where the random field is bimodally and trimodally distributed. In particular, the influence of the magnetic sites concentration on the tricritical behaviour is examined in detail.The diluted mixed spin Ising system consisting of spin-1/2 and spin-1 in a random field is studied by the use of finite cluster approximation the framework of a single-site cluster theory. The equations are derived using a probability distribution method based on the use of Van der Waerden identities. The complete phase diagrams are investigated in the case of the simple cubic lattice (z=6), where the random field is bimodally and trimodally distributed. In particular, the influence of the magnetic sites concentration on the tricritical behaviour is examined in detail

Phase diagram of the mixed spin Ising model with four-spin interaction and nextnearest neighbor couplings

The phase diagrams of the ferromagnetic two-dimensional mixed spin-1 and spin-1/2 Ising model with four-spin interaction J4 and next-nearest couplings J’ are investigated by the use of the finite cluster approximation based on single-site cluster theory. The state equations are derived for the two-dimensional square lattice. The phase diagram is qualitatively and quantitatively different from that obtained when the interaction J’ is ignored. In fact, the system exhibits a variety of interesting features resulting from the introduction of the next-nearest neighbor interaction (NNN). It undergoes two kinds of behavior according to the negative and the positive value of J’. In particular, for J4/J2=-4, the system keeps the coexistence of the two ground state up to J’-dependent finite temperature

The critical Ising lines of the d=2 Ashkin-Teller model

The universal critical point ratio $Q$ is exploited to determine positions of the critical Ising transition lines on the phase diagram of the Ashkin-Teller (AT) model on the square lattice. A leading-order expansion of the ratio $Q$ in the presence of a non-vanishing thermal field is found from finite-size scaling and the corresponding expression is fitted to the accurate perturbative transfer-matrix data calculations for the $L\times L$ square clusters with $L\leq 9$.Comment: RevTex, 4 pages, two figure

Mode-locked operation of a diode-pumped femtosecond Yb : SrF2 laser

International audienceFemtosecond mode-locked operation is demonstrated for the first time, to our knowledge, with a Yb:SrF2 crystal. The shortest pulse duration is 143 fs for an average power of 450 mW. The highest average power is 620 mW for a pulse duration of 173 fs. Since Yb:SrF2 corresponds to the longest-lifetime Yb-doped crystal with which the mode-locking operation has been achieved, a detailed analysis is carried out to characterize the quality of the solitonlike regime