Langevin simulations of a model for ultrathin magnetic films

Nicolao, Lucas; Stariolo, Daniel A.

doi:10.1103/physrevb.76.054453

Cited by 31 publications

(36 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This opens the possibility for the second scenario predicted by Abanov et al 14 of an intermediate perpendicular nematic phase, with long range orientational order but without positional order. Evidence for this phase comes also from simulations of the Ising dipolar model 9 and a recent theoretical model for the nematic transition in two dimensional systems with competing interactions 12,13 .…”

Section: A Stripes-tetragonal Transitionmentioning

confidence: 95%

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

et al. 2008

Self Cite

View full text Add to dashboard Cite

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 with 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 a paramagnetic gap in between in a finite region in 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, 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.

show abstract

Section: A Stripes-tetragonal Transitionmentioning

confidence: 95%

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

et al. 2008

Self Cite

View full text Add to dashboard Cite

show abstract

“…In this sense there are broken symmetry phases but with an intermediate degree of symmetry, higher than the less symmetric stripe phases in which both orientational and positional orders are present. Nematic phases associated with intermediate stripelike order are present in many quasi-two-dimensional (2D) systems like ultrathin ferromagnetic films [2,25,27] and electronic liquids in which they may be relevant to understand high-temperature superconductivity [28][29][30]. The conditions under which a system can sustain a nematic phase of this kind are still not completely clear.…”

Section: Introductionmentioning

confidence: 99%

Nematic phase in theJ1−J2square-lattice Ising model in an external field

2015

Self Cite

View full text Add to dashboard Cite

The J 1 -J 2 Ising model in the square lattice in the presence of an external field is studied by two approaches: the cluster variation method (CVM) and Monte Carlo simulations. The use of the CVM in the square approximation leads to the presence of a new equilibrium phase, not previously reported for this model: an Ising-nematic phase, which shows orientational order but not positional order, between the known stripes and disordered phases. Suitable order parameters are defined, and the phase diagram of the model is obtained. Monte Carlo simulations are in qualitative agreement with the CVM results, giving support to the presence of the new Ising-nematic phase. Phase diagrams in the temperature-external field plane are obtained for selected values of the parameter κ = J 2 /|J 1 | which measures the relative strength of the competing interactions. From the CVM in the square approximation we obtain a line of second order transitions between the disordered and nematic phases, while the nematic-stripes phase transitions are found to be of first order. The Monte Carlo results suggest a line of second order nematicdisordered phase transitions in agreement with the CVM results. Regarding the stripes-nematic transitions, the present Monte Carlo results are not precise enough to reach definite conclusions about the nature of the transitions.

show abstract

“…The pictures from top to bottom are characteristic of the stripes, nematic and isotropic phases respectively. Taken from [19]. The three figures represent the structure factor of a model for ultrathin magnetic films with strong perpendicular anisotropy, which has short range ferromagnetic interactions competing with long range dipolar interactions [19].…”

Section: The Nematic Order Parametermentioning

confidence: 99%

“…Taken from [19]. The three figures represent the structure factor of a model for ultrathin magnetic films with strong perpendicular anisotropy, which has short range ferromagnetic interactions competing with long range dipolar interactions [19]. The top figure shows C( k) for a very low temperature, where the equilibrium state of the system presents almost perfectly straight stripes of up and down magnetization.…”

Section: The Nematic Order Parametermentioning

confidence: 99%

Orientational order in systems with competing interactions

Stariolo

Barci

2010

J. Phys.: Conf. Ser.

View full text Add to dashboard Cite

Abstract. Quasi two dimensional systems with competing interactions usually display complex patterns in the relevant order parameter. In many cases these patterns are analog to liquid-crystal phases, showing smectic, nematic or hexatic order. We show that order parameters suitable for the characterization of these phases in systems with nearly isotropic competing interactions emerge naturally from an analysis of a Landau model. We describe with some detail the nematic case, which characterizes orientational order of striped domain walls. The Landau model presents an isotropic-nematic transition of the Kosterlitz-Thouless type. Although for the perfectly isotropic model long range nematic order is absent in infinite systems, we show that in real systems of finite size nematic order of domain walls can be observed. IntroductionIn many natural systems complex patterns originate due to the presence of competing interactions at different scales. Examples range from classical systems like magnetic ultrathin films [1], diblock copolymers [2] and colloidal suspensions [3], to quantum systems like quantum Hall samples [4] and high T c superconductors [5]. These pattern forming systems may present positional as well as orientational order, the origin of which depends on microscopic interactions. In the case of magnetic ultrathin films, of a few atomic monolayers thick, strong anisotropy perpendicular to the film plane forces the magnetization to be out of plane. In this case short range ferromagnetic interaction competes with antiferromagnetic dipolar interaction. As a consequence, the system shows ordered striped phases, of alternating magnetization along one direction, as is seen in Figure 1.In Figure 2 similar patterns can be observed in a completely different system, a block copolymer. In this case, elongated polymer chains with different types of building "blocks" compete between them and produce phase segregation, giving rise to complex patterns in two and three dimensions. Figure 3 shows a schematic representation of microemulsion phases. Microemulsions are mixtures of anfiphilic molecules which have an hydrophilic head and an hydrophobic tail. When in contact with water and oil, as depicted in the figure, they tend to phase separate giving rise to different kinds of ordered patterns with an order similar to liquid crystals [7,8].

show abstract

Langevin simulations of a model for ultrathin magnetic films

Cited by 31 publications

References 30 publications

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

Spin reorientation transition and phase diagram of ultrathin ferromagnetic films

Nematic phase in theJ1−J2square-lattice Ising model in an external field

Orientational order in systems with competing interactions

Contact Info

Product

Resources

About