Landau-Ginzburg-Devonshire theory for electromechanical hysteresis loop formation in piezoresponse force microscopy of thin films

Electromechanical hysteresis loop formation in piezoresponse force microscopy of thin ferroelectric films is studied with special emphasis on the effects of tip size and film thickness, as well as dependence on the tip voltage frequency. Here, we use a combination of Landau-Ginzburg-Devonshire (LGD) theory for the description of the local polarization reversal with decoupling approximation for the calculation of the local piezoresponse loops shape, coercive voltages and amplitude. LGD approach enables addressing both thermodynamics and kinetics of hysteresis loop formation. In contrast to the "rigid" ferroelectric approximation, this approach allows for the piezoelectric tensor components dependence on the ferroelectric polarization and dielectric permittivity. This model rationalizes the non-classical shape of the dynamic piezoelectric force microscopy (PFM) loops.Comment: 23 pages, 5 figures, 1 appendix,to be submitted to J. Appl. Phy

Magnetic Moment Softening and Domain Wall Resistance in Ni Nanowires

Magnetic moments in atomic scale domain walls formed in nanoconstrictions and nanowires are softened which affects dramatically the domain wall resistance. We perform ab initio calculations of the electronic structure and conductance of atomic-size Ni nanowires with domain walls only a few atomic lattice constants wide. We show that the hybridization between noncollinear spin states leads to a reduction of the magnetic moments in the domain wall. This magnetic moment softening strongly enhances the domain wall resistance due to scattering produced by the local perturbation of the electronic potential.Comment: 4 pages, 5 figure

Taking Distributions Seriously: On the Interpretation of the Estimates of Interactive Nonlinear Models

This is the final version. Available on open access from Cambridge University Press via the DOI in this recordData Availability Statement; Replication code for this article is available at Zhirnov, Moral, and Sedashov (Reference Zhirnov, Moral and Sedashov2022) at https://doi.org/10.7910/DVN/ZJCYGP.In recent decades, political science literature has experienced significant growth in the popularity of nonlinear models with multiplicative interaction terms. When one or more constitutive variables are not binary, most studies report the marginal effect of the variable of interest at its sample mean while allowing the other constitutive variable/s to vary along its range and holding all other covariates constant at their means, modes, or medians. In this article, we argue that this conventional approach is not always the most suitable since the marginal effect of a variable at its sample mean might not be sufficiently representative of its prevalent effect at a specific value of the conditioning variable and might produce excessively model-dependent predictions. We propose two procedures to help researchers gain a better understanding of how the typical effect of the variable of interest varies as a function of the conditioning variable: (1) computing and plotting the marginal effects at all in-sample combinations of the values of the constitutive variables and (2) computing and plotting what we call the “Distribution-Weighted Average Marginal Effect” over the values of the conditioning variable

Thermodynamics of nanodomain formation and breakdown in Scanning Probe Microscopy: Landau-Ginzburg-Devonshire approach

Thermodynamics of tip-induced nanodomain formation in scanning probe microscopy of ferroelectric films and crystals is studied using the Landau-Ginzburg-Devonshire phenomenological approach. The local redistribution of polarization induced by the biased probe apex is analyzed including the effects of polarization gradients, field dependence of dielectric properties, intrinsic domain wall width, and film thickness. The polarization distribution inside subcritical nucleus of the domain preceding the nucleation event is very smooth and localized below the probe, and the electrostatic field distribution is dominated by the tip. In contrast, polarization distribution inside the stable domain is rectangular-like, and the associated electrostatic fields clearly illustrate the presence of tip-induced and depolarization field components. The calculated coercive biases of domain formation are in a good agreement with available experimental results for typical ferroelectric materials. The microscopic origin of the observed domain tip elongation in the region where the probe electric field is much smaller than the intrinsic coercive field is the positive depolarization field in front of the moving counter domain wall. For infinitely thin domain walls local domain breakdown through the sample depth appears. The results obtained here are complementary to the Landauer-Molotskii energetic approach.Comment: 35 pages, 8 figures, suplementary attached, to be submitted to Phys. Rev.

Параметры периферической крови как маркеры неспецифического адаптационного ответа при острых инфекционных заболеваниях с синдромом тонзиллита

Evaluation of nonspecific adaptive response of the body in children with acute infectious diseases associated with tonsillitis syndrome was the aim of this research. This prospective study included clinical, anamnestic and laboratory examination of children with acute infectious diseases with tonsillitis syndrome. A systemic multiple factor analysis was conducted (significance level р<0.05). The evaluation of peripheral blood parameters (specific gravity of lymphocytes and indices of reactive protective potential (RPP) - specific immune lymphocytic-monocytic parameter (SILMP) and coefficient of phagocytic defense (CPD)) gives the possibility to determine the condition of nonspecific adaptation in children with acute infectious diseases associated with tonsillitis syndrome. Children with tonsillitis syndrome show significant increase of integral RPP parameters, i.e. decrease of RPP, which is more pronounced on discharge (on admission - in 57% of children, on discharge - in 87%). The most unfavourable initial nonspecific adaptative body response (NABR) (according to the percentage of lymphocytes) is the reaction of increased activation, as it is associated with the transition to the overactivation by the time of discharge (37% of children). Systemic multiple factor analysis determined which peripheral blood parameters have more influence on children’s adaptation during the course of infectious disease: RPP indices showed high influence coefficients in all diseases (CPD was the highest in bacterial infection - Рi 198.3; SILMP was the highest in viral infection - Рi 147.81; in mixed infection CPD and SILMP were roughly the same - Рi – 107.25 and Рi - 78.11, respectively), which proves the feasibility of RPP evaluation for prognostic purposes in the treatment of this category of patients.Целью настоящего исследования явилась оценка неспецифической адаптационной реакции организма у детей с острыми инфекционными заболеваниями, ассоциированными с синдромом тонзиллита. Данное проспективное исследование включало клинико-анамнестическое и лабораторное обследование детей с острыми инфекционными заболеваниями с синдромом тонзиллита. Проведен системный многофакторный анализ (уровень значимости р<0,05). Оценка показателей периферической крови (удельного веса лимфоцитов и показателей реактивно-протективный потенциал (РПП) - специфического иммунного лимфоцитарно-моноцитарного параметра (ИЛМП) и коэффициента фагоцитарной защиты (КФЗ) дает возможность определить состояние неспецифической адаптации у детей с острыми инфекционными заболеваниями, ассоциированными с синдромом тонзиллита. У детей с синдромом тонзиллита отмечается достоверное повышение интегральных показателей РПП, т. е. снижение РПП, которое более выражено при выписке (при поступлении - у 57% детей, при выписке - у 87%). Наиболее неблагоприятной исходной неспецифической адаптационной реакцией организма (по проценту лимфоцитов) является реакция повышенной активации, так как она связана с переходом к гиперактивации к моменту выписки (37% детей). Системный многофакторный анализ определил, какие показатели периферической крови оказывают большее влияние на адаптацию детей в течение инфекционного заболевания: показатели РПП показали высокие коэффициенты влияния при всех заболеваниях, что доказывает целесообразность оценки РПП в прогностических целях при лечении данной категории больных

First-principles investigation of 180-degree domain walls in BaTiO_3

We present a first-principles study of 180-degree ferroelectric domain walls in tetragonal barium titanate. The theory is based on an effective Hamiltonian that has previously been determined from first-principles ultrasoft-pseudopotential calculations. Statistical properties are investigated using Monte Carlo simulations. We compute the domain-wall energy, free energy, and thickness, analyze the behavior of the ferroelectric order parameter in the interior of the domain wall, and study its spatial fluctuations. An abrupt reversal of the polarization is found, unlike the gradual rotation typical of the ferromagnetic case.Comment: Revtex (preprint style, 13 pages) + 3 postscript figures. A version in two-column article style with embedded figures is available at http://electron.rutgers.edu/~dhv/preprints/index.html#pad_wal

Application of elastostatic Green function tensor technique to electrostriction in cubic, hexagonal and orthorhombic crystals

The elastostatic Green function tensor approach, which was recently used to treat electrostriction in numerical simulation of domain structure formation in cubic ferroelectrics, is reviewed and extended to the crystals of hexagonal and orthorhombic symmetry. The tensorial kernels appearing in the expressions for effective nonlocal interaction of electrostrictive origin are derived explicitly and their physical meaning is illustrated on simple examples. It is argued that the bilinear coupling between the polarization gradients and elastic strain should be systematically included in the Ginzburg-Landau free energy expansion of electrostrictive materials.Comment: 4 page

Electron Spin for Classical Information Processing: A Brief Survey of Spin-Based Logic Devices, Gates and Circuits

In electronics, information has been traditionally stored, processed and communicated using an electron's charge. This paradigm is increasingly turning out to be energy-inefficient, because movement of charge within an information-processing device invariably causes current flow and an associated dissipation. Replacing charge with the "spin" of an electron to encode information may eliminate much of this dissipation and lead to more energy-efficient "green electronics". This realization has spurred significant research in spintronic devices and circuits where spin either directly acts as the physical variable for hosting information or augments the role of charge. In this review article, we discuss and elucidate some of these ideas, and highlight their strengths and weaknesses. Many of them can potentially reduce energy dissipation significantly, but unfortunately are error-prone and unreliable. Moreover, there are serious obstacles to their technological implementation that may be difficult to overcome in the near term. This review addresses three constructs: (1) single devices or binary switches that can be constituents of Boolean logic gates for digital information processing, (2) complete gates that are capable of performing specific Boolean logic operations, and (3) combinational circuits or architectures (equivalent to many gates working in unison) that are capable of performing universal computation.Comment: Topical Revie

Er:Yb phosphate glass laser with nonlinear absorber for phase-sensitive optical time domain reflectometry

A novel laser for phase-sensitive optical time-domain reflectometry (Φ-OTDR) is presented. The advantages of a compact solid-state laser are listed, current problems are shown. Experiments with a microchip single-optical-element laser, from setup construction to usage in Φ-OTDR system, are presented. New laser scheme with two-photon intracavity absorber is suggested and its advantages are described