Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites

The effect of an exchange field on electrical transport in thin films of metallic ferromagnetic manganites has been investigated. The exchange field was induced both by direct exchange coupling in a ferromagnet/antiferromagnet multilayer and by indirect exchange interaction in a ferromagnet/paramagnet superlattice. The electrical resistance of the manganite layers was found to be determined by the absolute value of the vector sum of the effective exchange field and the external magnetic field.Comment: 5 pages, 4 figure

Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle

We measure the microwave signals produced by spin-torque-driven magnetization dynamics in patterned magnetic multilayer devices at room temperature, as a function of the angle of a magnetic field applied in the sample plane. We find strong variations in the frequency linewidth of the signals, with a decrease by more than a factor of 20 as the field is rotated from the magnetic easy axis to the in-plane hard axis. Based on micromagnetic simulations, we identify these variations as due to a transition from spatially incoherent to coherent precession.Comment: 15 pages, 5 figure

Magnetic vortex oscillator driven by dc spin-polarized current

Transfer of angular momentum from a spin-polarized current to a ferromagnet provides an efficient means to control the dynamics of nanomagnets. A peculiar consequence of this spin-torque, the ability to induce persistent oscillations of a nanomagnet by applying a dc current, has previously been reported only for spatially uniform nanomagnets. Here we demonstrate that a quintessentially nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale spin valve structure, can be excited into persistent microwave-frequency oscillations by a spin-polarized dc current. Comparison to micromagnetic simulations leads to identification of the oscillations with a precession of the vortex core. The oscillations, which can be obtained in essentially zero magnetic field, exhibit linewidths that can be narrower than 300 kHz, making these highly compact spin-torque vortex oscillator devices potential candidates for microwave signal-processing applications, and a powerful new tool for fundamental studies of vortex dynamics in magnetic nanostructures.Comment: 14 pages, 4 figure

Oscillatory Exchange Coupling and Positive Magnetoresistance in Epitaxial Oxide Heterostructures

Oscillations in the exchange coupling between ferromagnetic $La_{2/3}Ba_{1/3}MnO_3$ layers with paramagnetic $LaNiO_3$ spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an {\it ab initio} calculated band structure of $LaNiO_3$, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance.Comment: 4 pages (RevTeX), 5 figures (EPS

Kinetics of exciton photoluminescence in type-II semiconductor superlattices

The exciton decay rate at a rough interface in type-II semiconductor superlattices is investigated. It is shown that the possibility of recombination of indirect excitons at a plane interface essentially affects kinetics of the exciton photoluminescence at a rough interface. This happens because of strong correlation between the exciton recombination at the plane interface and at the roughness. Expressions that relate the parameters of the luminescence kinetics with statistical characteristics of the rough interface are obtained. The mean height and length of roughnesses in GaAs/AlAs superlattices are estimated from the experimental data.Comment: 3 PostScript figure

Thermomagnonic spin transfer and Peltier effects in insulating magnets

We study the coupled magnon energy transport and collective magnetization dynamics in ferromagnets with magnetic textures. By constructing a phenomenological theory based on irreversible thermodynamics, we describe motion of domain walls by thermal gradients and generation of heat flows by magnetization dynamics. From microscopic description based on magnon kinetics, we estimate the transport coefficients and analyze the feasibility of energy-related applications in insulating ferromagnets, such as yttrium iron garnet and europium oxide.Comment: 6 pages, 2 figure

Current-induced microwave excitation of a domain wall confined in a magnetic wire with bi-axial anisotropy

We studied the current-induced magnetization dynamics of a domain wall confined in a magnetic wire with bi-axial anisotropy. We showed that above the threshold current density, breathing-mode excitation, where the thickness of the domain wall oscillates, is induced by spin-transfer torque. We found that the breathing-mode can be applied as a source of microwave oscillation because the resistance of the domain wall is a function of the domain wall thickness. In a current sweep simulation, the frequency of the breathing-mode exhibits hysteresis because of the confinement.Comment: 5 pages 4 figure

Внедрение норвежской модели организации нефтегазовой отрасли в России: институциональные вызовы

While the Norwegian oil and gas model is a popular reference case in Russia, one should realize that it has developed over time within a specific national, historical and institutional context. The core role in this model belongs to the Norwegian state in terms of resource management, establishing the regulatory framework, massive taxation, and actual involvement in the business, first of all through the national petroleum company Statoil/Equinor. Equinor has evolved since 1972 from a modest carried partner to a large streamlined corporation, operating in 35 countries and focusing heavily on global technological leadership. All investors, either state-owned or private, are put under the same public scrutiny and stimulated with non-fiscal incentives, such as political stability, predictable regulations and abundant geological information. This large scale government intervention relies on proactive, professional and incorrupt bureaucracy enjoying broad powers. Much of this practice is not common and may not be introduced directly in Russia, which tends to limit the role of public servants and rely on big state corporations. However, the Norwegian experience seems very relevant for the urgently needed overhaul of the Russian energy policies, both offshore and in Western SiberiaХотя норвежская нефтегазовая модель является популярным примером успешной организации отрасли, которую многие воспринимают как один из возможных эталонов для внедрения в России, следует понимать, что она развивалась с течением времени в рамках конкретного национального, исторического и институционального контекстов. Ключевая роль в этой модели принадлежит Норвежскому государству с точки зрения управления ресурсами, создания нормативной базы, налогообложения и фактического участия в бизнесе в первую очередь через национальную нефтяную компанию Statoil/Equinor. С 1972 года Equinor превратилась из скромного партнера в крупную корпорацию, работающую в 35 странах и уделяющую большое внимание мировому технологическому лидерству. Все инвесторы, как государственные, так и частные, подконтрольны обществу и стимулируются нефискальными стимулами, такими как политическая стабильность, предсказуемое регулирование и изобилие геологической информации. Такое широкомасштабное государственное вмешательство опирается на активную, профессиональную и неподкупную бюрократию, обладающую широкими полномочиями. Большая часть этой практики не распространена и не может быть внедрена непосредственно в России, которая, как правило, ограничивает роль государственных служащих и опирается на крупные государственные корпорации. Однако норвежский опыт представляется весьма актуальным для срочного пересмотра российской энергетической политики как на шельфе, так и на Востоке Росси