We develop an idea on the origin of a giant dielectric dispersion in relaxors. The dielectric response of relaxors, if represented in terms of the dynamic conductivity, reveals frequency dependences of the shape conventional for many other isolators and known as universal dielectric response (UDR). We suggest a simple phenomenological model of the restricted (local) drift currents, which gives the UDR in the first approximation and a broad-band relaxation when an interaction between the conducting clusters is added.

A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) was held on November 28, 2007 in the conference hall of the P N Lebedev Physical Institute, RAS. following reports were presented at the session: (1) Gulyaev Yu V, Zil'berman P E, Epshtein EM (Institute of Radioengineering and Electronics, RAS, Moscow — Fryazino) structures incorporating ferromagnetic metal layers: new effects due to the passage of a perpendicular current; (2) Zvezdin A K, Zvezdin K A, Khvalkovskiy A V (A M Prokhorov Institute of General Physics, RAS, Moscow) The generalized Landau — Lifshitz equation and spin transfer processes in magnetic nanostructures. An abridged version of these reports is given below. • Nano-sized structures incorporating ferromagnetic metal layers: new effects due to the passage of a perpendicular current, Yu V Gulyaev, P E Zil'berman and E M Epshtein Physics-Uspekhi, 2008, Volume 51, Number 4, Pages 409–412 • generalized Landau — Lifshitz equation and spin transfer processes in magnetic nanostructures, A K Zvezdin, K A Zvezdin and A V Khvalkovskiy Physics-Uspekhi, 2008, Volume 51, Number 4, Pages 412–417

The problem of current-induced motion of a solitary domain wall in a free layer of the spin-valve structure is considered; the current flows perpendicularly to the structure layers. The action of the longitudinal and transverse components of the nonequilibrium polarization of the carriers injected into the free layer on the magnetization is analyzed.

Domain walls (DWs) in strongly correlated ferroics are expected to exhibit rich physical properties due to the competition between ground states that exists in these systems. A typical example is provided by ferromagnetic mixed-valence manganites for which insulating DWs in an otherwise metallic phase have been predicted. Through magnetotransport experiments on a nanopatterned device we have determined the electronic properties of DWs in La2/3Sr1/3MnO3. We find a DW resistance-area (RA) product of similar to 2.5x10(-13) Omega m(2) at low temperature and bias, which is several orders of magnitude larger than the values reported for 3d ferromagnets. However, the current-voltage characteristics are highly linear, which indicates that the DWs are not phase separated but metallic. Remarkably, the DWRA is also found to increase upon increasing the injected current, presumably reflecting some deformation of the wall by spin transfer.

The influence of an electric current flowing through a spin-valve perpendicular to its layers on a domain wall located in the free layer of the spin valve is studied. It is demonstrated that the nonequilibrium spin distribution generated by the current gives rise to a pressure exerted on the domain wall. This pressure is proportional to the current squared, and, for typical values of the magnetic parameters and a current density of 10 7 –10 8 A/cm 2 , its effect is similar to that of a magnetic field of several oersteds to several tens of oersteds. The magnitude and sign of the pressure are strongly dependent on the geometric and physical parameters of the device. The problem is solved using the model of itinerant-electron ferromagnetism. The relation of the discovered effect to experimental data on magnetization reversal induced by a spin-polarized current in such structures is discussed.

We report on the definition of tracks with ∼50-nm wide nanoconstrictions in a manganite epitaxial film, by high-resolution electron beam lithography and ion beam etching. Magnetotransport measurements at low temperature indicate a linear high-field magnetoresistance, with symmetric resistance jumps (1–3%) visible in the 500Oe range. We discuss the origin of this effect in terms of domain-wall scattering in manganites.

The main aim of the present investigation is to develop a technique of 3D computer simulation of SmCo/Fe bilayer exchange-coupled magnets composed of hard and soft magnetic layers. These materials are of great interest now because of the very high values of maximum energy products observed in them; at the same time their computer simulation is rather difficult due to several physical and computational reasons. In present report we review some of these difficulties and propose a technique that may help to go round them.

The magnetic structure of a plane nanobridge consisting of two ferromagnetic film electrodes connected by a nanosized crossbar of the same material is studied. Due to their magnetoresistive properties, such bridges are of considerable interest for microelectronics. Using a numerical micromagnetics method, it is shown that a domain wall is displaced from the center of the bridge crossbar as the anisotropy constant of the system decreases and reaches a critical value. A phase diagram is constructed, which makes it possible to determine the possible magnetic states of real nanobridges. The mechanism of the phase transformation is described in terms of an analytical model. This model explains the shape of the phase diagram of the nanobridge. Formally, the transformations of the magnetic structure of the nanocontact can be described in terms of the Landau theory of phase transitions in a certain range of parameters of the system.

Nanobridge (NB) is a single-layer ferromagnetic film structure composed of two wide leads connected by a nanometer channel; due to its magnetic and magnetoresistive properties NBs are considered attractive from fundamental point of view and for applications. In the present report the dependence of the domain wall (DW) specific resistance on the position within the crossbar is obtained within the frame of the spin-accumulation model. It was revealed that the DW specific resistance diminishes appreciably if DW approaches one of the leads. Consequences of this result are discussed.

Nanobridge is a single-layer ferromagnetic film structure composed of 2 wide platforms connected by a narrow channel, due to the magnetoresistive and magnetic properties nanobridges are considered to be very attractive for various spintronic applications. In this article, we present the results of study of the frequency response of this device. The investigation is performed in the frame of the Valet-Fert theory.

Bridge-shaped magnetic nanowires have been designed and patterned in half-metallic La2/3Sr1/3MnO3 thin films, using a thick negative-tone electron beam lithography (EBL) process. EBL was performed in the high resolution hydrogen silsesquioxane (HSQ) inorganic resist. This paper reports on the optimization of EBL, for which both electron beam proximity effects and pre-bake annealing temperatures have been studied. To take benefit of the proximity effects, a special bridge geometry is proposed. Hundred nanometre-wide nanowires with large aspect ratio (⩾2) have been successfully patterned and transferred in LSMO.

We present the results of the study of transport and magnetic properties of magnetic planar nanobridges. A nanobridge (NB) is a single-layer ferromagnetic film structure composed of two wide platforms connected by a narrow channel. Investigation of the magnetic and magnetoresistive properties of the device shows that NB may be useful for spintronic applications. Except the NBs based on conventional ferromagnetics, semiconductor NB is of great interest as combining both spintronic effects and semiconductor technology; besides, quantum ballistic transport effects may appear in it. Magnetic structure of semiconductor NB is also studied.

Large values of magnetoresistance experimentally observed in magnetic nano-contacts and nano-wires are explained in terms of spin accumulation. The investigation of the spin-accumulation effect in magnetic nano-contacts (Phys. Rev. Lett. 82 (1999) 2923) and nano-bridges (JETP Lett. 75 (10) (2002) 613), which are considered to be very promising for various spintronic applications, is presented. The two-dimensional spin-diffusion problem in a magnetic nano-bridge is solved. Dependences of the specific resistance of the domain wall and of the distribution of non-equilibrium spin density on the nano-bridge geometry and the material parameters are obtained.

A new design of spin transistor based on half-metallic ferromagnets (referred to as a spin half-metallic transistor) is suggested, and its current-voltage characteristics are studied theoretically. Like a bipolar transistor, the new device can amplify current. At the same time, the properties of a spin half-metallic transistor depend considerably on the mutual orientation of the magnetizations of its three contacts. We also propose a device based on an F↑-F↓ junction. This device consists of two single-domain half-metallic parts with opposite magnetizations. There is a range of voltages where the current-voltage characteristics of an F↑-F↓ junction and a semiconductor diode are similar. The behavior of an F↑-F↓ junction under different conditions is studied.

A new construction of the spin transistor is proposed and its volt–ampere characteristics (VAC) are theoretically investigated. It is based on the ferromagnetic half-metals and is referred to as a spin half-metallic transistor (SHMT). SHMT is revealed to amplify electric current as a bipolar transistor. At the same time, its properties drastically depend on the reciprocal orientation of magnetizations of its three junctions; so SHMT can be used as a switching device. Also properties of an “F↑–F↓ junction” are considered. This device consists of two half-metallic electrodes with antiparallel magnetizations. Its VAC reminds VAC of a diode in some voltage range. Behavior of the F↑–F↓ junction under different conditions is considered.