Two-dimensional behavior of the sublattice magnetization in three-dimensional Ising antiferromagnets

A three-dimensional layered Ising-Antiferromagnet with a ferromagnetic intra-layer coupling to z neighbors, zJ > 0, and an antiferromagnetic interlayer coupling to z' neighbors, z'J' < 0, is investigated by Monte Carlo simulations on a hexagonal lattice. The physical nature of the anomalous temperature bahavior of the sublattice magnetizations, which is found for certain values of r=zJ/z'J' and z' in magnetic fields is explained in terms of successive phase transitions. They take place on the ferromagnetic 2-dimensional spin-down sublattice at T = T_c^{2d}, smeared by a finite stabilizing molecular field, and on both antiferromagnetically coupled sublattices at T_c^{3d} > T_c^{2d}.Comment: 8 pages (TeX), 6 figures (eps), submitted to World Scientific: Proceedings SDHS'99 Duisbur

Critical behavior at edge singularities in one dimensional spin models

In ferromagnetic spin models above the critical temperature ($T > T_{cr}$) the partition function zeros accumulate at complex values of the magnetic field ($H_E$) with a universal behavior for the density of zeros \rho (H) \sim | H - H_E |^{\sg}. The critical exponent \sg is believed to be universal at each space dimension and it is related to the magnetic scaling exponent $y_h$ via \sg = (d-y_h)/y_h. In two dimensions we have y_h=12/5 (\sg = -1/6) while y_h=2 (\sg=-1/2) in $d=1$. For the one dimensional Blume-Capel and Blume-Emery-Griffiths models we show here, for different temperatures, that a new value y_h=3 (\sg =-2/3) can emerge if we have a triple degeneracy of the transfer matrix eigenvalues.Comment: to appear in Phys. Rev. E, 16 pages, 3 figure

Light diffraction by field-induced non-periodic magnetic domain structures in FeCl2

The magnetic-field-induced mixed phase of the meta magnet FeCl2 gives rise to reduced transmittivity of circularly polarized light. Within the framework of the diffraction theory of thin random magnetic phase gratings and the assumption of field-dependent refractive indices of the antiferromagnetic domains the field dependence of the transmission is perfectly modeled

Exchange Bias in a generalized Meiklejohn-Bean approach

A generalized Meiklejohn–Bean model is considered in order to derive an analytic expression for the dependence of the previous exchange bias term field on the layer thickness involved in ferromagnetic/antiferromagnetic heterosystems, on the orientation of the applied magnetic field with respect to the magnetic easy axes and on the quenched magnetization MAF of the antiferromagnetic pinning layer. While MAF is a well-known feature of field-cooled dilute antiferromagnets, it seems to occur quite generally also in pure AF pinning substrates. The new analytic expressions are successfully compared with recent experimental results and Monte Carlo investigations

Extrinsic control of the exchange bias

A new control mechanism for the exchange bias effect in magnetic heterostructures is proposed. It takes advantage of the magnetoelectric effect which takes place in the antiferromagnetic pinning layer. In contrast with the pioneering AC measurements of the magnetoelectric effect, we investigate the magnetic response of the prototypical magnetoelectric compound Cr2O3 on static electric fields. The linear dependence of the magnetic moment on the applied axial electric field and the temperature dependence of the corresponding slopes αshort parallel are measured by DC SQUID magnetometry. The contribution of the field-induced surface magnetization and its impact on the exchange bias effect is estimated

BROWSERSPOT – MULTIFUNKCJONALNE NARZĘDZIE DO TESTOWANIA FRONT-ENDU STRON INTERNETOWYCH ORAZ APLIKACJI SIECIOWYCH

The article presents the multifunctional BrowserSpot tool, which serves as an automated environment for testing websites and web applications for Android and iOS systems. It highlights and describes the individual stages of research and development work, the issues with solutions currently available on the market, as well as the project's results. The article also discusses the reasons for undertaking work on the tool, its functionalities, and the methods of its usage.W artykule zaprezentowano multifunkcyjne narzędzie BrowserSpot stanowiące zautomatyzowane środowisko do testowania stron internetowych oraz aplikacji webowych dla systemów Android i iOS. Wyróżnione i opisane zostały poszczególne etapy prac badawczo rozwojowych, problemy aktualnych rozwiązań dostępnych na rynku, a także rezultaty projektu. Przedstawiono również powody podjęcia się prac nad narzędziem, funkcjonalności narzędzia, oraz sposoby jego użytkowania

Electric Control of Exchange Bias Training

Voltage-controlled exchange bias training and tunability are introduced. Isothermal voltage pulses are used to reverse the antiferromagnetic order parameter of magnetoelectric Cr2O3, and thus continuously tune the exchange bias of an adjacent CoPd film. Voltage-controlled exchange bias training is initialized by tuning the antiferromagnetic interface into a nonequilibrium state incommensurate with the underlying bulk. Interpretation of these hitherto unreported effects contributes to new understanding in electrically controlled magnetis

Ising metamagnets in thin film geometry: equilibrium properties

Artificial antiferromagnets and synthetic metamagnets have attracted much attention recently due to their potential for many different applications. Under some simplifying assumptions these systems can be modeled by thin Ising metamagnetic films. In this paper we study, using both the Wang/Landau scheme and importance sampling Monte Carlo simulations, the equilibrium properties of these films. On the one hand we discuss the microcanonical density of states and its prominent features. On the other we analyze canonically various global and layer quantities. We obtain the phase diagram of thin Ising metamagnets as a function of temperature and external magnetic field. Whereas the phase diagram of the bulk system only exhibits one phase transition between the antiferromagnetic and paramagnetic phases, the phase diagram of thin Ising metamagnets includes an additional intermediate phase where one of the surface layers has aligned itself with the direction of the applied magnetic field. This additional phase transition is discontinuous and ends in a critical end point. Consequently, it is possible to gradually go from the antiferromagnetic phase to the intermediate phase without passing through a phase transition.Comment: 8 figures, accepted for publication in Physical Review

Boundary magnetization properties of epitaxial Cr2−xAlxO3 thin films

The magnetoelectric antiferromagnet α-Cr2O3 (chromia) is known to possess a roughness insensitive net equilibrium magnetization at the (0001) surface, called boundary magnetization (BM), which is coupled to the bulk antiferromagnetic order parameter. In order to verify whether this symmetry sensitive BM persists in alloys, we investigate the impact of diamagnetic dilution on chromia thin films alloyed with the isostructural α-Al2O3 (alumina). Single-crystalline Cr2−xAlxO3 thin films with (0001) surface orientation and varying stoichiometry have been grown by sputter codeposition in the concentration range between x = 0 and x = 0.6. For these samples, we find the corundum crystal structure, the antiferromagnetic ordering, and the boundary magnetization to be preserved. We also find that the critical temperature TN can be tuned by alloying with α-Al2O3, using the BM as a probe to study the magnetic phase transition. Furthermore, we were able to evaluate the critical exponent and the absolute BM values for different samples. Both properties corroborate that the observed magnetic signals originate from the BM rather than the bulk of the samples