Effects of exchange and weak Dzyaloshinsky–Moriya anisotropies on thermodynamic characteristics of spin-gapped magnets

We study the modification of low-temperature properties of quantum magnets such as magnetization, heat capacity, energy spectrum and densities of condensed and noncondensed quasiparticles (triplons) due to anisotropies in the framework of mean-field- based approach. We show that in contrast to exchange anisotropy (EA) interaction, Dzyaloshinsky–Moriya (DM) interaction modifies the physics dramatically. Particularly, it changes the sign of the anomalous density in the whole range of temperatures. Its critical behavior is slightly modified also by the EA. We have found that the shift of the critical temperature of phase transition (or crossover caused by DM interaction) is positive and significant. Using the experimental data on the magnetization of the compound TlCuCl3, we have found optimal values for the strengths of EA and DM interactions. The spectrum of the energy of low lying excitations has also been investigated and found to develop a linear dispersion similar to Goldstone mode with a negligibly small anisotropy gap.

Thermal entanglement in a mixed spin Heisenberg XXX chain with DM interaction

We consider a one-dimensional, mixed spin Heisenberg XXX model with an homogeneous external magnetic field and Dzyaloshinskii–Moriya interaction. Alternating spin-[Formula: see text] and spin-1 particles are forming the chain. The effect of the different parameters of the system on the bipartite thermal entanglement is studied. The type of chain used (mixed) and the size of the chain ([Formula: see text]) allow to study three types of bipartite entanglement, the qubit–qubit, qubit–qutrit and qutrit–qutrit thermal entanglement.

Effects of hybrid comprehensive telerehabilitation on cardiopulmonary capacity in heart failure patients depending on diabetes mellitus: subanalysis of the TELEREH-HF randomized clinical trial

Background Type 2 diabetes mellitus (DM) is one of the most common comorbidities among patients with heart failure (HF) with reduced ejection fraction (HFrEF). There are limited data regarding efficacy of hybrid comprehensive telerehabilitation (HCTR) on cardiopulmonary exercise capacity in patients with HFrEF with versus those without diabetes. Aim The aim of the present study was to analyze effects of 9-week HCTR in comparison to usual care on parameters of cardiopulmonary exercise capacity in HF patients according to history of DM. Methods Clinically stable HF patients with left ventricular ejection fraction [LVEF] < 40% after a hospitalization due to worsening HF within past 6 months were enrolled in the TELEREH-HF (The TELEREHabilitation in Heart Failure Patients) trial and randomized to the HCTR or usual care (UC). Cardiopulmonary exercise tests (CPET) were performed on treadmill with an incremental workload according to the ramp protocol. Results CPET was performed in 385 patients assigned to HCTR group: 129 (33.5%) had DM (HCTR-DM group) and 256 patients (66.5%) did not have DM (HCTR-nonDM group). Among 397 patients assigned to UC group who had CPET: 137 (34.5%) had DM (UC-DM group) and 260 patients (65.5%) did not have DM (UC-nonDM group). Among DM patients, differences in cardiopulmonary parameters from baseline to 9 weeks remained similar among HCTR and UC patients. In contrast, among patients without DM, HCTR was associated with greater 9-week changes than UC in exercise time, which resulted in a statistically significant interaction between patients with and without DM: difference in changes in exercise time between HCTR versus UC was 12.0 s [95% CI − 15.1, 39.1 s] in DM and 43.1 s [95% CI 24.0, 63.0 s] in non-DM, interaction p-value = 0.016. Furthermore, statistically significant differences in the effect of HCTR versus UC between DM and non-DM were observed in ventilation at rest: − 0.34 l/min [95% CI − 1.60, 0.91 l/min] in DM and 0.83 l/min [95% CI − 0.06, 1.73 l/min] in non-DM, interaction p value = 0.0496 and in VE/VCO2 slope: 1.52 [95% CI − 1.55, 4.59] for DM vs. − 1.44 [95% CI − 3.64, 0.77] for non-DM, interaction p value = 0.044. Conclusions The benefits of hybrid comprehensive telerehabilitation versus usual care on the improvement of physical performance, ventilatory profile and gas exchange parameters were more pronounced in patients with HFrEF without DM as compared to patients with DM. Trial registration: ClinicalTrials.gov Identifier: NCT02523560. Registered 3rd August 2015. https://clinicaltrials.gov/ct2/show/NCT02523560?term=NCT02523560&draw=2&rank=1. Other Study ID Numbers: STRATEGME1/233547/13/NCBR/2015

Индуцированные флуктуациями фазовые переходы и скирмионы в сильно коррелированных Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si с нарушенной кристаллической структурой типа В20

Concentration and temperature transitions in strongly correlated Fe1-хCoxSi alloys with the Dzyaloshinsky-Moriyya (DM) interaction are considered within the framework of the spin-fluctuation theory and taking into account the results of LDA+U+SO calculations of the density of electronic states. It is shown that order-order concentration transitions with a change in the sign of the left-handed spin chirality (at x <0.2) to right-handed (at 0.2≤x<0.65), and again to left-handed, are associated with a change in the sign of the intermode interaction parameter. At the same time, it was indicated that in the region of compositions Fe1-хCoxSi 0.2≤x<0.65, temperature-prolonged first-order phase transitions appear, accompanied by the appearance of an intermediate temperature region of spin short-range order with uncompensated local magnetization and DM interaction. In an external magnetic field in this temperature range at 0.2<x<0.65, skyrmion microstructures appear. At x=0.65, the intermode interaction parameter becomes zero, and the long-range order becomes ferromagnetic (since the experiment implies compensation for the DM interaction). Instead of a prolonged first-order transition, a second-order temperature transition occurs at х=0.65. The constructed (h-T) diagrams of the magnetic states of Fe1-хCoxSi agree with the experiment.

The optical tweezer of skyrmions

In a spin-driven multiferroic system, the magnetoelectric coupling has the form of effective dynamical Dzyaloshinskii–Moriya (DM) interaction. Experimentally, it is confirmed, for instance, for Cu2OSeO3, that the DM interaction has an essential role in the formation of skyrmions, which are topologically protected magnetic structures. Those skyrmions are very robust and can be manipulated through an electric field. The external electric field couples to the spin-driven ferroelectric polarization and the skyrmionic magnetic texture emerged due to the DM interaction. In this work, we demonstrate the effect of optical tweezing. For a particular configuration of the external electric fields it is possible to trap or release the skyrmions in a highly controlled manner. The functionality of the proposed tweezer is visualized by micromagnetic simulations and model analysis.

Quantum heat engine based on spin isotropic Heisenberg models with Dzyaloshinskii–Moriya interaction

A quantum heat engine (QHE) model by considering as working substance two spins (spin-1, spin-[Formula: see text]) is proposed. It consists of using different Heisenberg models with the Dzyaloshinskii-Moriya (DM) interaction in the presence of magnetic field [Formula: see text]. The proposed model contains four stroke two isochoric and two others adiabatic. A comparison of different models such that [Formula: see text], [Formula: see text] and [Formula: see text] is examined for various thermodynamics quantities, especially the efficiency [Formula: see text] and work [Formula: see text]. Finally, discussion and interpretation all results are given in the last section.

Skyrmions and Spin Waves in Magneto–Ferroelectric Superlattices

We present in this paper the effects of Dzyaloshinskii–Moriya (DM) magneto–electric coupling between ferroelectric and magnetic interface atomic layers in a superlattice formed by alternate magnetic and ferroelectric films. We consider two cases: magnetic and ferroelectric films have the simple cubic lattice and the triangular lattice. In the two cases, magnetic films have Heisenberg spins interacting with each other via an exchange J and a DM interaction with the ferroelectric interface. The electrical polarizations of ±1 are assumed for the ferroelectric films. We determine the ground-state (GS) spin configuration in the magnetic film and study the phase transition in each case. In the simple cubic lattice case, in zero field, the GS is periodically non collinear (helical structure) and in an applied field H perpendicular to the layers, it shows the existence of skyrmions at the interface. Using the Green’s function method we study the spin waves (SW) excited in a monolayer and also in a bilayer sandwiched between ferroelectric films, in zero field. We show that the DM interaction strongly affects the long-wave length SW mode. We calculate also the magnetization at low temperatures. We use next Monte Carlo simulations to calculate various physical quantities at finite temperatures such as the critical temperature, the layer magnetization and the layer polarization, as functions of the magneto–electric DM coupling and the applied magnetic field. Phase transition to the disordered phase is studied. In the case of the triangular lattice, we show the formation of skyrmions even in zero field and a skyrmion crystal in an applied field when the interface coupling between the ferroelectric film and the ferromagnetic film is rather strong. The skyrmion crystal is stable in a large region of the external magnetic field. The phase transition is studied.

Time evolution of entanglement in a four-qubit Heisenberg chain

The phenomenon of quantum entanglement has a very important role in quantum mechanics. Particularly, the quantum spin chain provides a platform for theoretical and experimental investigation of many-body entanglement. In this paper, we investigate time evolution of entanglement in a four-qubit anisotropic Heisenberg XXZ chain with nearest neighboring (NN), the next nearest neighboring (NNN), and the Dzialoshinskii-Moriya (DM) interactions. Calculations of the entanglement evolution of the Werner state carried out in terms of concurrence for selected ranges of control parameters such as DM interaction, frustration, etc. The results show that for the Werner state, DM interaction and the frustration parameters play important roles. Furthermore, results show that the time evolution of the Werner state entanglement may be useful to capture the quantum phase transitions in quantum magnetic systems.

Traveling skyrmions in chiral antiferromagnets

Skyrmions in antiferromagnetic (AFM) materials with the Dzyaloshinskii-Moriya (DM) interaction are expected to exist for essentially the same reasons as in DM ferromagnets (FM). It is shown that skyrmions in antiferromagnets with the DM interaction can be traveling as solitary waves with velocities up to a maximum value that depends on the DM parameter. Their configuration is found numerically. The energy and the linear momentum of an AFM skyrmion lead to a proper definition of its mass. We give the details of the energy-momentum dispersion of traveling skyrmions and explore their particle-like character based on exact relations. The skyrmion number, known to be linked to the dynamics of topological solitons in FM, is, here, unrelated to the dynamical behavior. As a result, the solitonic behavior of skyrmions in AFM is in stark contrast to the dynamical behavior of their FM counterparts.

Influence of He+-ion beam induced effect on ultrafast quantum spin-state switching dynamics in exchange bias Co–Mn FM/AFM systems

A study of magnetic or spin logic appears as an appealing alternative due to its nonvolatile character, which can boost up switching on/off. The influences of Dzyaloshinskii–Moriya (DM) interaction on non-classical correlations play an important role in foundations of quantum technologies such as quantum information and quantum computation. We have considered the anisotropic general spin Hamiltonian (GSH) model in presence of DM interaction in addition to the Landau–Lifshitz–Gilbert (LLG)-model in a pulse magnetic field. For study of ultrafast spin dynamics in exchange bias Co–Mn FM/AFM systems, we present some quantum circuits for a deterministic quantum computing in Co–Mn FM/AFM systems.