Evidence for a bicritical point in the XXZ Heisenberg antiferromagnet on a simple cubic lattice

The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. Analyzing, especially, various staggered susceptibilities and Binder cumulants, we present clear evidence for the meeting point of the antiferromagnetic, spin--flop, and paramagnetic phases being a bicritical point with Heisenberg symmetry. Results are compared to previous predictions based on various theoretical approaches.Comment: 4 pages, 6 figures (to appear in the Phys. Rev. E (2011)

Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy

The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy, the XXZ model, and competing planar single-ion anisotropy in a magnetic field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. The biconical (supersolid) phase, bordering the antiferromagnetic and spin-flop phases, is found to become thermally unstable well below the onset of the disordered, paramagnetic phase, leading to interesting multicritical points

Anomalies in the antiferromagnetic phase of metamagnets

Motivated by recent experiments on the metamagnet FeBr2, anomalies of the magnetization and the specific heat in the antiferromagnetic phase of related spin models are studied systematically using Monte Carlo simulations. In particular, the dependence of the anomalous behavior on competing intralayer interactions, the spin value and the Ising-like anisotropy of the Hamiltonian is investigated. Results are compared to experimental findings on FeBr2.Comment: 19 pages, 15 figures, submitted to Phys. Rev.

Finite-size effects in the rough phase of the 3d Ising model

Using Monte Carlo simulations, finite-size effects of interfacial properties in the rough phase of the Ising on a cubic lattice with $L\times L\times R$ sites are studied. In particular, magnetization profiles perpendicular to the flat interface of size L$\times$R are studied, with $L$ being considerably larger than $R$, in the (pre)critical temperature range. The resulting $R$-dependences are compared with predictions of the standard capillary-wave theory, in the Gaussian approximation, and with a field theory based on effective string actions, for $L$=$\infty$.Comment: 6 pages, 3 figure

Interfacial adsorption in Potts models on the square lattice

We study the effect of interfacial phenomena in two-dimensional perfect and random (or disordered) $q$-state Potts models with continuous phase transitions, using, mainly, Monte Carlo techniques. In particular, for the total interfacial adsorption, the critical behavior, including corrections to scaling, are analyzed. The role of randomness is scrutinized. Results are discussed applying scaling arguments and invoking findings for bulk critical properties. In all studied cases, i.e., $q = 3$, $4$, and $q = 8$, the spread of the interfacial adsorption profiles is observed to increase linearly with the lattice size at the bulk transition point.Comment: 6 pages, 6 eps figures, 1 table, minor corrections, accepted for publication in Eur. Phys. J.

Particles, string and interface in the three-dimensional Ising model

We consider the three-dimensional Ising model slightly below its critical temperature, with boundary conditions leading to the presence of an interface. We show how the interfacial properties can be deduced starting from the particle modes of the underlying field theory. The product of the surface tension and the correlation length yields the particle density along the string whose propagation spans the interface. We also determine the order parameter and energy density profiles across the interface, and show that they are in complete agreement with Monte Carlo simulations that we perform

Structure of interfaces at phase coexistence. Theory and numerics

We compare results of the exact field theory of phase separation in two dimensions with Monte Carlo simulations for the q-state Potts model with boundary conditions producing an interfacial region separating two pure phases. We confirm in particular the theoretical predictions that below critical temperature the surplus of non-boundary colors appears in drops along a single interface, while for q > 4 at critical temperature there is formation of two interfaces enclosing a macroscopic disordered layer. These qualitatively different structures of the interfacial region can be discriminated through a measurement at a single point for different system sizes

Horse portraiture and blazing saddles - research report on the artist Emil Volkers (1831-1905)

Emil Volkers was a popular 19th century German horse portraitist. After Dresden Art Academy, he developed a unique style, and aristocrats provided commissions. He became "court painter" to Prince Charles of Romania, and was commissioned by William I to paint him on horseback. His paintings were popular with European rulers, as horses were important to their lifestyle. Volkers also painted rural and historical scenes. It is surprising that he is not generally acknowledged in art history literature, which contrasts with the number of his paintings sold today, and the number in private collections compared with the few held publicly. Lack of official recognition may be due to the few surviving documents plus the number of unknown collectors, which makes it difficult to produce an academic monograph. This paper aims to introduce Volkers to the international research community under the aforementioned aspects