Intrinsic spin orbit torque in a single domain nanomagnet

We present theoretical studies of the intrinsic spin orbit torque (SOT) in a single domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using the non-equilibrium Green's function formalism for a model Hamiltonian. We find that, to the first order in SOC, the intrinsic SOT has only the field-like torque symmetry and can be interpreted as the longitudinal spin current induced by the charge current and Rashba field. We analyze the results in terms of the material related parameters of the electronic structure, such as band filling, band width, exchange splitting, as well as the Rashba SOC strength. On the basis of these numerical and analytical results, we discuss the magnitude and sign of SOT. Our results show that the different sign of SOT in identical ferromagnetic layers with different supporting layers, e.g. Co/Pt and Co/Ta, could be attributed to electrostatic doping of the ferromagnetic layer by the support.Comment: 10 pages, 2 figure

Calculations of spin-disorder resistivity from first principles

Spin-disorder resistivity of Fe and Ni is studied using the noncollinear density functional theory. The Landauer conductance is averaged over random disorder configurations and fitted to Ohm's law. The distribution function is approximated by the mean-field theory. The dependence of spin-disorder resistivity on magnetization in Fe is found to be in excellent agreement with the results for the isotropic s-d model. In the fully disordered state, spin-disorder resistivity for Fe is close to experiment, while for fcc Ni it exceeds the experimental value by a factor of 2.3. This result indicates strong magnetic short-range order in Ni at the Curie temperature.Comment: 3 pages, 3 figure

Synthesis and characterization of biodegradable lignin nanoparticles with tunable surface properties

Lignin nanoparticles can serve as biodegradable carriers of biocidal actives with minimal environmental footprint. Here we describe the colloidal synthesis and interfacial design of nanoparticles with tunable surface properties using two different lignin precursors, Kraft (Indulin AT) lignin and Organosolv (high-purity lignin). The green synthesis process is based on flash precipitation of dissolved lignin polymer, which enabled the formation of nanoparticles in the size range of 45–250 nm. The size evolution of the two types of lignin particles is fitted on the basis of modified diffusive growth kinetics and mass balance dependencies. The surface properties of the nanoparticles are fine-tuned by coating them with a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). We analyze how the colloidal stability and dispersion properties of these two types of nanoparticles vary as a function of pH and salinities. The data show that the properties of the nanoparticles are governed by the type of lignin used and the presence of polyelectrolyte surface coating. The coating allows the control of the nanoparticles’ surface charge and the extension of their stability into strongly basic regimes, facilitating their potential application at extreme pH conditions

Measurements of Protein-Protein Interactions by Size Exclusion Chromatography

A method is presented for determining second virial coefficients B_2 of protein solutions from retention time measurements in size exclusion chromatography (SEC). We determine B_2 by analyzing the concentration dependance of the chromatographic partition coefficient. We show the ability of this method to track the evolution of B_2 from positive to negative values in lysozyme and bovine serum albumin solutions. Our SEC results agree quantitatively with data obtained by light scattering.Comment: 18 pages including 1 table and 5 figure

Limiting the resectability in locally advanced primary or rec urrent carcinoma of the colon

Purpose: The terms of ‘unresectable`, ‘inoperable` and ‘incurable` cancer/patient are widely used but not clearly defined and thus subject to significant subjectivity. Where is the limit of ‘resectability` of colorectal cancer - the criteria are variable and not precisely defined yet. Locally advanced lesion may vary from visible intimately adhered to the surrounding tissue, i.e. marginal, ‘border` resectable tumour to one that directly macroscopically engages adjacent critical structures. This paper presents the experience of other foreign authors with their results in the determination of the tumour as resectable or unresectable as well as own clinical experience in this field.Material and methods: The study covered the patients with colorectal cancer who were operated in the Clinic of Surgery during a period of 9 years and retrospectively analyzed.Results: Out of a total of 1051 surgeries on the occasion of colorectal cancer, advanced disease constituted 28,6% or 301 patients. Of them, 52,5% were localized in different parts of the colon. Fifty-eight combined resections were performed as in 7 of them (recurrent tumours) R1 was accomplished, i.e. a non-radical result. A total of 117 cases were assessed intraoperatively as non-radical surgery and palliative procedures were performed such as resections (with or without restoration of the intestinal passage, but in the case of M1), bypass anastomoses, or simple interruption of the passage. .Conclusion: Many of the world`s leading surgical centres adopt the tactics of ‘adequate aggressive behaviour` for locally advanced primary and recurrent colorectal cancer. In determining the reasonable balance between aggressive approach and the so-called meaningless ‘surgical exorbitance` there is strive to adhere to the view that failure to achieve R0-resection planed in such an operation as well as leading performance or a combination of factors such as advanced age, severe co-morbidities, presence of complicated forms of colorectal cancer, urgent intervention and data of generalization of the malignant process undermine the performance of aggressive block removal of tumour formation. However, adequate pre- and intraoperative assessment and surgical experience should avoid ‘exaggerated` intraoperative status of locally advanced tumou

Ferroelectric Dead Layer Driven by a Polar Interface

Based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As a representative model, we consider a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces that serve as doping layers. We find that the polar interfaces create an intrinsic electric field that is screened by the electron charge leaking into the BaTiO3 layer. The amount of the leaking charge is controlled by the boundary conditions which are different for three heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. Our first-principles and model calculations demonstrate that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces.Comment: 33 Pages, 5 figure

The Origin of Tunneling Anisotropic Magnetoresistance in Break Junctions

First-principles calculations of electron tunneling transport in Ni and Co break junctions reveal strong dependence of the conductance on the magnetization direction, an effect known as tunneling anisotropic magnetoresistance (TAMR). The origin of this phenomenon stems from resonant states localized in the electrodes near the junction break. The energy and broadening of these states is strongly affected by the magnetization orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias voltage on a scale of a few mV. Our results bear a resemblance to recent experimental data and suggest that TAMR driven by resonant states is a general phenomenon typical for magnetic broken contacts and other experimental geometries where a magnetic tip is used to probe electron transport.Comment: 4 pages, 3 figure

Effect of oxygen vacancies on spin-dependent tunneling in Fe/MgO/Fe

First-principles calculations based on density functional theory are used to elucidate the effect of O vacancies, forming F centers, on spin-dependent tunneling in Fe/MgO/Fe(001) magnetic tunnel junctions. O vacancies produce occupied localized s states and unoccupied resonant p states, which is consistent with available experimental data. The authors find that O vacancies affect the conductance by nonresonant scattering of tunneling electrons causing a substantial reduction of tunneling magnetoresistance (TMR). Improving the quality of the MgO barrier to reduce O vacancy concentration would improve TMR in these and similar junctions

Controlled interfacial assembly of 2D curved colloidal crystals and jammed shells

Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional micro-crystalline materials useful in fields as diverse as biomedicine1, materials science2, mineral flotation3 and food processing4. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials employed5-9. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.Comment: 18 pages, 5 figure

FLORA, MYCOTA AND VEGETATION OF KUPENA RESERVE (RODOPI MOUNTAINS, BULGARIA)

The paper represents results from recent complex studies of flora, mycota and vegetation within the Kupena Reserve (Rodopi Mts, Bulgaria). Twenty three species, referred to 2 divisions, 4 classes and 16 families are recorded for the bryoflora. The vascular flora is presented by 368 species from 57 families, 121 of which are considered as medicinal plants. Eighty seven species of larger ascomycetes and basidiomycetes are found and reported for first time in the reserve. Four of them are of a high conservation value. The vegetation cover is consisted of mixed and monodominant deciduous and coniferous forests, as well as of mire, riverbank and mesic grasslands. Thirteen types of habitats according to the Habitats Directive classification have been recorded within the reserve