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

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

Tricritical behaviour in deterministic aperiodic Ising systems

We use a mixed-spin model, with aperiodic ferromagnetic exchange interactions and crystalline fields, to investigate the effects of deterministic geometric fluctuations on first-order transitions and tricritical phenomena. The interactions and the crystal field parameters are distributed according to some two-letter substitution rules. From a Migdal-Kadanoff real-space renormalization-group calculation, which turns out to be exact on a suitable hierarchical lattice, we show that the effects of aperiodicity are qualitatively similar for tricritical and simple critical behaviour. In particular, the fixed point associated with tricritical behaviour becomes fully unstable beyond a certain threshold dimension (which depends on the aperiodicity), and is replaced by a two-cycle that controls a weakened and temperature-depressed tricritical singularity.Comment: Formatting improved. 7 pages, 2 figures (included). Journal reference adde

Diode-pumped 99 fs Yb : CaF2 oscillator

International audienceWe demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF2 crystal. An average power of 380 mW for a 13 nm bandwidth spectrum centered at 1053 nm is obtained. The short-pulse operation is achieved thanks to a saturable absorber mirror and is stabilized by the Kerr lens effect. We investigated the limits of the stabilization process and observed a regime slowly oscillating between mode locking and Q switching