Thermoelectric spin transfer in textured magnets

We study charge and energy transport in a quasi-1D magnetic wire in the presence of magnetic textures. The energy flows can be expressed in a fashion similar to charge currents, leading to new energy-current induced spin torques. In analogy to charge currents, we can identify two reciprocal effects: spin-transfer torque on the magnetic order parameter induced by energy current and the Berry-phase gauge field induced energy flow. In addition, we phenomenologically introduce new $\beta-$like viscous coupling between magnetic dynamics and energy current into the LLG equation, which originates from spin mistracking of the magnetic order. We conclude that the new viscous term should be important for the thermally induced domain wall motion. We study the interplay between charge and energy currents and find that many of the effects of texture motion on the charge currents can be replicated with respect to energy currents. For example, the moving texture can lead to energy flows which is an analogue of the electromotive force in case of charge currents. We suggest a realization of cooling effect by magnetic texture dynamics.Comment: 5 pages, 1 figur

The confinement of phonon propagation in TiAlN/Ag multilayer coatings with anomalously low heat conductivity

TiAlN/Ag multilayer coatings with a different number of bilayers and thicknesses of individual layers were fabricated by DC magnetron co-sputtering. Thermal conductivity was measured in dependence of Ag layer thickness. It was found anomalous low thermal conductivity of silver comparing to TiAlN and Ag bulk standards and TiAlN/TiN multilayers. The physical nature of such thermal barrier properties of the multilayer coatings was explained on the basis of reflection electron energy loss spectroscopy. The analysis shows that nanostructuring of the coating decreases the density of states and velocity of acoustic phonons propagation. At the same time, multiphonon channels of heat propagation degenerate. These results demonstrate that metal-dielectric interfaces in TiAlN/Ag coatings are insurmountable obstacles for acoustic phonons propagation

Properties of ferromagnetic film hysteresis, on the surface of a hard-magnetic antiferromagnet, with a domain structure

This is a theoretical investigation of the exchange bias phenomenon, and the properties of a thin magnetic film's magnetization hysteresis loop, on the rough surface of a hard-magnetic antiferromagnet. An interface model with a periodic structure of atomic steps is presented. These atomic steps are associated with a spatially inhomogeneous distribution of the ferromagnetic film magnetization, akin to a system of domain walls. This structure leads to a complicated external field dependence of magnetization: the hysteresis curve can assume an asymmetrical shape and "fall apart" into two hysteresis loops, divided by a "horizontal plateau," or an area with constant field-independent magnetization. Such field dependence behavior has been recently observed experimentally in different ferro/antiferromagnet systems. The field dependence of magnetization has been obtained analytically using the long-wave approximation for various characteristics of ferromagnetic film (its thickness, values of exchange interaction, and magnetic anisotropy), and the interface (the period of the inhomogeneous structure, and exchange interaction through the interface). The analytical results are confirmed by numerical calculations for the corresponding discrete model with a more complex interface structure

The magnetic structure of a thin ferromagnetic film on the rough surface of an antiferromagnet

The magnetic structure (including domanization) of a thin ferromagnetic film in contact with a rigid antiferromagnet is investigated under the assumption that the interface is rough and contains individual atomic steps of different signs, isolated "dipole of the steps," and a space-ordered periodic system of steps of alternate signs

Exchange bias effect in antiferromagnets containing ferromagnetic clusters

This study offers an explanation for the occurrence of magnetization exchange bias in antiferromagnets with ferromagnetic inclusions during pre-cooling the system in a magnetic field. The ferromagnetic (FM) subsystem ordered in this field at the Néel temperature leads to an inhomogeneous state of the antiferromagnetic (AFM) matrix with the finite mean effective field at the FM/AFM interface. This field causes exchange bias in the dependence M = M(H) during further remagnetization of the heterogeneous system. To describe the proposed scenario for such an effect, a simple model of a two-dimensional system with round inclusions of the FM phase was considered. Using numerical calculations and previously obtained analytical results, the study determines magnetization dependencies on the external field, which qualitatively explains the features of exchange bias in experimentally studied heterogeneous systems

Model of exchange bias in a trilayer FM/AFM/FM structure

A theoretical examination of the properties of the exchange bias phenomenon for sandwich FM/AFM/FM structures, which are actively studied in experiments. Magnetization dependences on the external magnetic field are obtained under the proposed discrete model of ferromagnetic layers of such multilayer structures. It is shown that the magnetization field dependences have a horizontal plateau, a splitting of the hysteresis loop, and asymmetry. We examine the influence of the interface defects on the exchange bias phenomenon and its features. The results are qualitatively consistent with experimental data

Interface-Induced Plasmon Nonhomogeneity in Nanostructured Metal-Dielectric Planar Metamaterial

Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5 nm associated with the development of quantum effects was determined by X-ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal-nitride interfaces was assessed experimentally

Aharonov-Casher effect in a two dimensional hole gas with spin-orbit interaction

We study the quantum interference effects induced by the Aharonov-Casher phase in a ring structure in a two-dimensional heavy hole (HH) system with spin-orbit interaction realizable in narrow asymmetric quantum wells. The influence of the spin-orbit interaction strength on the transport is investigated analytically. These analytical results allow us to explain the interference effects as a signature of the Aharonov-Casher Berry phases. Unlike previous studies on the electron two-dimensional Rashba systems, we find that the frequency of conductance modulations as a function of the spin-orbit strength is not constant but increases for larger spin-orbit splittings. In the limit of thin channel rings (width smaller than Fermi wavelength), we find that the spin-orbit splitting can be greatly increased due to quantization in the radial direction. We also study the influence of magnetic field considering both limits of small and large Zeeman splittings.Comment: 6 pages, 4 figure

Magnon-driven quantum-dot heat engine

We investigate a heat- to charge-current converter consisting of a single-level quantum dot coupled to two ferromagnetic metals and one ferromagnetic insulator held at different temperatures. We demonstrate that this nano engine can act as an optimal heat to spin-polarized charge current converter in an antiparallel geometry, while it acts as a heat to pure spin current converter in the parallel case. We discuss the maximal output power of the device and its efficiency.Comment: 6 pages, 4 figures, published version, selected as Editor's choic