Anharmonicity and structural phase transition in the Mott insulator Cu2_2P2_2O7_7

Ab initio investigations of structural, electronic, and dynamical properties of the high-temperature $\beta$ phase of copper pyrophosphate were performed using density functional theory. The electronic band structure shows the Mott insulating state due to electron correlations in copper ions. By calculating phonon dispersion relations, the soft mode at the A point of the Brillouin zone was revealed, showing the dynamical instability of the $\beta$ phase at low temperatures. The double-well potential connected with the soft mode is derived and the mechanism of the structural phase transition to the $\alpha$ phase is discussed. The self-consistent phonon calculations based on the temperature-dependent effective potential show the stabilization of the $\beta$ phase at high temperatures, due to the anharmonic effects. The pronounced temperature dependence and the large line width of the soft mode indicate an essential role of anharmonicity in the structural phase transition

Magnetic behaviour of Mn12-stearate single-molecule magnets Immobilized on the surface of 300 nm spherical silica nanoparticles

The magnetic behaviour of Mn 12 -stearate single-molecule magnets (SMMs) ([ Mn12O12 (CH3(CH2)16CO2)16]⋅2CH3COOH⋅4H2O ) on the surface of 300 nm spherical silica nanoparticles were investigated. The SMMs were bonded at the silica surface with the assumed number of anchoring points, which influenced on their degree of freedom and distribution. In order to check the properties of Mn 12 -stearate molecules separated on the silica surface, and check their interactions, the samples containing four different concentration of spacers per single anchoring unit and variously bonded Mn 12 -stearate particles were prepared. The materials have been examined using Raman spectroscopy, transmission electron microscopy, and SQUID magnetometry. The results of magnetic measurements showed a correlation between the way of single-molecule magnets immobilization onto the silica spheres and the magnetic properties of the obtained hybrid materials

AC Susceptibility Studies of Magnetic Relaxation in Mn12-Stearate SMMs on the Spherical Silica Surface

The study of magnetic relaxations in Mn12-stearate single-molecule magnets deposited on the surface of spherical silica nanoparticles was performed. For such a purpose, the investigation of AC magnetic susceptibility dependence on the frequency and temperature was performed. Based on the Argand plots obtained for different temperatures and temperature dependencies of susceptibility, obtained for different frequencies of AC field, the corresponding relaxation times were derived. Fitting to the Arrhenius law revealed the values of an effective energy barrier and a mean relaxation time, which were consistent for both measuring techniques (Ueff/kB∼ 50 K and τ0∼ 10−7 s) and similar to the corresponding values for the analogous bulk compounds. Additionally, the obtained relaxation parameters for the Mn12-stearate molecules on the spherical silica surface were compared with corresponding values for the Mn12-based single-molecule magnets deposited upon other types of nanostructured silica surface

Influence of Aging on the Structure and Magnetic Properties of Surface-Deposited Single-Molecule Magnets

In this paper, the main issues concerning the possibility of the organization of Mn12-based single-molecule magnets (SMMs) on the surface of silica nanostructures with the preservation of its structure and magnetic properties were summarized. The aging effects on structural and magnetic properties in Mn12-stearate SMMs deposited on the surface of spherical silica nanoparticles were also discussed

Competing Magnetocrystalline and Shape Anisotropy in Thin Nanoparticles

Micromagnetic computations were performed to predict the magnetisation maps in thin elliptically shaped nanoparticles under a variable external magnetic field. Two materials were compared as the constituents of the nanoparticles: permalloy as an example of an isotropic magnet and cobalt, i.e., a hard magnetic material marked with a single easy axis. The interplay of the shape and magnetocrystalline anisotropy gives rise to a variety of switching scenarios, which may be of interest in designing memory storage devices. A fairly periodic shape-induced superlattice-like spin configuration occurs when the shape and magnetocrystalline easy axes are orthogonal. Possible applications as magnonic devices are discussed

Spacing Dependent Mechanisms of Remagnetization in 1D System of Elongated Diamond Shaped Thin Magnetic Particles

Four different switching scenarios have been revealed for a linear chain of flat magnetic particles with long axes perpendicular to the axis of the chain. The diamond-like shape of the particles has been previously shown to be the best to ensure a uniform and stable magnetization within a single particle, that is, to behave as a macrospin. The occurrence of each scenario depends on the distance of the particles in the chain. Whereas long distances favor direct remagnetization of a ferromagnetic configuration “all up” to the one “all down”, a short enough distance allows the system to recover its ground state at a zero field, that is, an antiferromagnetic order. This allows any information stored by a magnetic field to be erased. Vortex-like metastable defects have been noticed for intermediate distances. A longitudinal magnetization component at extremely short distances has been noticed as well as specific systems of domain walls. The hysteresis loops and magnetization maps in the particles have been presented for each scenario. The potential applicability of the findings to the fabrication of memory storage devices has been discussed

Anharmonicity and structural phase transition in the Mott insulator Cu2P2O7

Ab initio investigations of the structural, electronic, and dynamical properties of the high-temperature 0 phase of copper pyrophosphate were performed using density functional theory. The electronic band structure shows the Mott insulating state due to electron correlations in the copper ions. By calculating phonon dispersion relations, the soft mode at the A point of the Brillouin zone was revealed, showing the dynamical instability of the 0 phase at low temperatures. The double-well potential connected with the soft mode is derived and the mechanism of the structural phase transition to the & alpha; phase is discussed. The self-consistent phonon calculations based on the temperature-dependent effective potential show the stabilization of the 0 phase at high temperatures, due to the anharmonic effects. The pronounced temperature dependence and the large linewidth of the soft mode indicate an essential role of anharmonicity in the structural phase transition.Web of Science10810art. no. 10410

The Separation of the Mn₁₂ Single-Molecule Magnets onto Spherical Silica Nanoparticles

The Mn12 single-molecule magnets (SMMs) could be attached to the surface of spherical silica for the first time with a high probability. This allowed separation of the individual molecular magnets and direct microscopic observation of the SMMs. We described in detail how to fabricate such a composite material. The synthesis procedure proposed here is simple and efficient. We confirmed the efficiency of the method by transmission electron microscopy (TEM): single-molecule magnets were visible at the surface of a silica substrate. Based on TEM observation, we described how the molecules anchor to the surface of silica (the geometry of the magnetic molecule in regard to the surface of the substrate). The SQUID magnetometry showed that single-molecule magnet behaviour is kept intact after grafting. The attachment of the single-molecule magnets to the surface of silica allows to investigate their properties as separate molecules. This is particularly important in the analysis of magnetic properties such as magnetic states of the separated SMMs, their mutual interactions, and the influence of a silica support

Application of neural networks to ensure the efficiency of industrial enterprises'activity in the process of their internationalization

Здійснено оцінювання ефективності діяльності промислових підприємств у процесі їх інтернаціоналізації за допомогою засобів штучного інтелекту. Досліджено переваги застосування методу нейромережового моделювання для вирішення економічних завдань та обгрунтовано доцільність його використання у проведенні даного дослідження. На основі даних експертного оцінювання та фінансової звітності десяти промислових підприємств за допомогою лінійного коефіцієнта кореляції Пірсона встановлено значущість кожного із 25 параметрів (субкритеріїв), які впливають на ефективність діяльності промислових підприємств. Визначено, що 10 із них мають найбільшу значущість. На основі визначення значущості субкритеріїв розроблено програмну систему інтелектуальних агентів (нейронних мереж) для підтримки прийняття управлінських рішень в умовах невизначеності щодо інтернаціоналізації промислових підприємств з метою забезпечення ефективності їх діяльності. Для програмної системи інтелектуальних агентів застосовано метод машинного навчання багатошарового персептрону (БШП). Розраховано значення середньої абсолютної помилки (MAPE) оцінки якості програмної системи інтелектуальних агентів, яке становить 1,2%, що свідчить про високу точність отриманих результатів. Встановлено, що розроблений програмний продукт можна застосовувати для вирішення також інших проблем у діяльності підприємства.The effectiveness of industrial enterprises activities in the process of their internationalization with the help of artificial intelligence tools is measured in the article. The advantages of using the method of neural network modeling for solving economic problems and the expediency of its use in conducting this research are explored. Based on the expert estimation and financial data of ten industrial enterprises, using the linear Pearson correlation coefficient, the significance of each of the 25 parameters (subcriteria) that affect the performance of industrial enterprises is established. It is determined that 10 of them have the greatest significance. On the basis this determination a software system of intellectual agents (neural networks) is developed to support the decisionmaking process under uncertain conditions which are directed on the internationalization of industrial enterprises in order to ensure effectiveness of their activities. For the software system of intelligent agents, the method of machine learning of multilayer perceptron (MLP) is used. The value of the average percentage error (MAPE) for estimating the quality of the software system of the intelligent agents is calculated and is equal to 1,2%, which indicates the high accuracy of the obtained results. It is determined that the developed software product can be used to solve other problems in enterprise activit

Generalization of Ohta's Model for Description of Multilayer Josephson Junctions.

У статті зроблено узагальнено напівкласичну модель Охти для використання її для дослідження n послі- довно розміщених тунельних надпровідних контактів. Використавши запропоновану загальну схему макро- скопічного аналізу таких систем, отримано аналітичний результат для залежності надпровідного струму від різниці фаз параметрів упорядкування в крайніх надпровідниках. ; The effect of tunneling in many layers Josephson junction was analyzed. Modification of Ohta’s model for investigation equilibrium current states in many layers superconducting structures was also proposed. The expression for the dependence of current from phase difference in many barrier contacts was received