E. A. Kravtsov

Bio: E. A. Kravtsov is an academic researcher from Ural Federal University. The author has contributed to research in topics: Neutron reflectometry & Magnetization. The author has an hindex of 11, co-authored 67 publications receiving 450 citations. Previous affiliations of E. A. Kravtsov include Argonne National Laboratory & Ural State Technical University.

Low Temperature Catalytic Decomposition of Hydrogen Sulfide into Hydrogen and Diatomic Gaseous Sulfur

Abstract: A new catalytic reaction of hydrogen sulfide decomposition is discovered, the reaction occurs on metal catalysts in gas phase according to equation $$2{\text{H}}_{2} {\text{S}} \leftrightarrow 2{\text{H}}_{2} + {\text{S}}_{2}^{{({\text{gas}})}}$$ to produce hydrogen and gaseous diatomic sulfur, conversion of hydrogen sulfide at room temperature is close to 15 %. The thermodynamic driving force of the reaction is the formation of the chemical sulfur–sulfur bond between two hydrogen sulfide molecules adsorbed on two adjacent metal atoms in the key surface intermediate and elimination of hydrogen into gas phase. “Fingerprints” of diatomic sulfur adsorbed on the solid surfaces and dissolved in different solvents are studied. In closed vessels in adsorbed or dissolved states, this molecule is stable for a long period of time (weeks). A possible electronic structure of diatomic gaseous sulfur in the singlet state is considered. According to DFT/CASSCF calculations, energy of the singlet state of S2 molecule is over the triplet ground state energy for 10.4/14.4 kcal/mol. Some properties of gaseous diatomic sulfur are also investigated. Catalytic solid systems, both bulk and supported on porous carriers, are developed. When hydrogen sulfide is passing through the solid catalyst immersed in liquid solvent which is capable of dissolving sulfur generated, conversion of hydrogen sulfide at room temperature achieves 100 %, producing hydrogen in gas phase. This gives grounds to consider hydrogen sulfide as inexhaustible potential source of hydrogen—a very valuable chemical reagent and environmentally friendly energy product.

Complementary polarized neutron and resonant x-ray magnetic reflectometry measurements in Fe/Gd heterostructures: Case of inhomogeneous intralayer magnetic structure

Abstract: A unified approach combining polarized neutron and resonant x-ray magnetic reflectometry has been applied to determine the magnetic structure in an ${[\text{Fe}(35\text{ }\text{\AA{}})/\text{Gd}(50\text{ }\text{\AA{}})]}_{5}$ multilayer as a function of temperature and magnetic field. Simultaneous self-consistent refinement of neutron and x-ray data made it possible to resolve the element-specific magnetization profile in the multilayer with unprecedented accuracy. It is shown that the small number of bilayer periods together with the asymmetric termination (Fe-top, Gd-bottom) lead to unique low-temperature magnetic phases characterized by significant twisting of Fe and Gd magnetic moments and nonuniform distribution of vectorial magnetization within Gd layers. A twisted magnetic state was found to be stable at small magnetic fields and at a low temperature of 20 K, which is well below the compensation temperature of this artificial ferrimagnetic system.

Magnetic off-specular neutron scattering from Fe/Cr multilayers

Abstract: The magnetic structure of a [Cr(9 A)/ 57 Fe (68 A)]×12 multilayer on sapphire substrate has been studied with polarized neutron reflectometry. The intensity distribution was measured over a broad range of incident and outgoing angles with spin analysis. The specular and off-specular intensities of the first and second-order Bragg-peaks (determined by the bi-layer thickness) and those at the half-order positions (due to an antiferromagnetic coupling) were measured. Off-specular scattering arranged into sheets running across the antiferromagnetic half-order positions is spread over an appreciable range perpendicular to the specular line. It consists of almost totally spin-flip scattering. Nearly no experimental evidence of the peak at the position of antiferromagnetic superstructure is found in the spin-flip specular channel. The intensity of the diffuse scattering scales with the intensity of the Bragg peaks, which is a function of the external magnetic field. These findings result in a picture of antiferromagnetic domains, rather than in the model of homogeneous magnetized neighbouring layers with a magnetization coupling angle.

Element- and site-specific oxidation state and cation distribution in manganese ferrite films by diffraction anomalous fine structure

Abstract: Epitaxial manganese ferrite thin films were studied by x-ray diffraction anomalous fine structure to obtain element-specific and site-specific information on site occupancy, local structure, and valency. These properties were introduced to molecular field theory to reproduce thermomagnetization curves and determine superexchange energy, Neel temperature, and spin canting angle.

Perpendicular giant magnetoresistance of magnetic multilayers

Abstract: The theoretical and experimental studies of the giant magnetoresistance effect in metallic magnetic multilayers with measuring current perpendicular to the interface planes are reviewed. Theoretical formalisms of electronic transport in the inhomogeneous electron gas are critically compared with emphasis on the perpendicular magnetoresistance in multilayers. The effects of interface roughness, potential steps at the interfaces, and realistic band structures are addressed. The experimental determination of the perpendicular resistance of metallic multilayers requires either low-resistance measurement techniques or microfabricated samples with enhanced resistances. The experimental methods known at present are discussed and, where possible, compared with each other.

The defining length scales of mesomagnetism: a review

Abstract: This review is intended as an introduction to mesomagnetism, with an emphasis on what the defining length scales and their origins are. It includes a brief introduction to the mathematics of domains and domain walls before examining the domain patterns and their stability in 1D and 2D confined magnetic structures. This is followed by an investigation of the effects of size and temperature on confined magnetic structures. Then, the relationship between mesomagnetism and the developing field of spin electronics is discussed. In particular, the various types of magnetoresistance, with an emphasis on the theory and applications of giant magnetoresistance and tunnelling magnetoresistance, are studied. Single electronics are briefly examined before concluding with an outlook on future developments in mesomagnetism.

A review of high magnetic moment thin films for microscale and nanotechnology applications

Abstract: The creation of large magnetic fields is a necessary component in many technologies, ranging from magnetic resonance imaging, electric motors and generators, and magnetic hard disk drives in information storage. This is typically done by inserting a ferromagnetic pole piece with a large magnetisation density MS in a solenoid. In addition to large MS, it is usually required or desired that the ferromagnet is magnetically soft and has a Curie temperature well above the operating temperature of the device. A variety of ferromagnetic materials are currently in use, ranging from FeCo alloys in, for example, hard disk drives, to rare earth metals operating at cryogenic temperatures in superconducting solenoids. These latter can exceed the limit on MS for transition metal alloys given by the Slater-Pauling curve. This article reviews different materials and concepts in use or proposed for technological applications that require a large MS, with an emphasis on nanoscale material systems, such as thin and ultra-thin films. Attention is also paid to other requirements or properties, such as the Curie temperature and magnetic softness. In a final summary, we evaluate the actual applicability of the discussed materials for use as pole tips in electromagnets, in particular, in nanoscale magnetic hard disk drive read-write heads; the technological advancement of the latter has been a very strong driving force in the development of the field of nanomagnetism.

Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

Abstract: The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors.