arXiv subjects

A. K. Zvezdin

Publications and source records attributed to A. K. Zvezdin.

At least 73 records · Page 4Linked to original sources

arXiv2010

Macroscopic quantum dynamics of toroidal moment in Ising-type rare-earth clusters

We study the quantum dynamics of polygonal rare-earth molecular clusters with Ising-type ion magnetization. It is shown that the ground state of such systems is a non-magnetic quasi-doublet of states with oppositely twisted ion spins. The states differ in sign of toroidal moment, which is a natural physical quantity to characterize the spin chirality of the clusters. The possibility of macroscopic quantum tunneling of toroidal moment between the states is predicted. The effects of an external current is considered, both in equilibrium and in the frames of the Landau-Zener-Stückelberg tunneling model. The special treatment is given for the most important case of triangular rare-earth clusters.

cond-mat.mes-hall↗

arXiv2010

Pinning of magnetic domain walls in multiferroics

The behavior of antiferromagnetic domain wall (ADW) against the background of a periodic ferroelectric domain structure has been investigated. It has been shown that the structure and the energy of ADW change due to the interaction with a ferroelectric domain structure. The ferroelectric domain boundaries play the role of pins for magnetic spins, the spin density changes in the vicinity of ferroelectric walls. The ADW energy becomes a periodical function on a coordinate which is the position of ADW relative to the ferroelectric domain structure. It has been shown that the energy of the magnetic domain wall attains minimum values when the center of the ADW coincides with the ferroelectric wall and the periodic ferroelectric structure creates periodic coercitivity for the ADW. The neighbouring equilibrium states of the ADW are separated by a finite potential barrier.

cond-mat.mtrl-sci↗

arXiv2010

Extraordinary Magnetooptics in Plasmonic Crystals

Plasmonics has been attracting considerable interest as it allows localization of light at nanoscale dimensions. A breakthrough in integrated nanophotonics can be obtained by fabricating plasmonic functional materials. Such systems may show a rich variety of novel phenomena and also have huge application potential. In particular magnetooptical materials are appealing as they may provide ultrafast control of laser light and surface plasmons via an external magnetic field. Here we demonstrate a new magnetooptical material: a one-dimensional plasmonic crystal formed by a periodically perforated noble metal film on top of a ferromagnetic dielectric film. It provides giant Faraday and Kerr effects as proved by the observation of enhancement of the transverse Kerr effect near Ebbesen's extraordinary transmission peaks by three orders of magnitude. Surface plasmon polaritons play a decisive role in this enhancement, as the Kerr effect depends sensitively on their properties. The plasmonic crystal can be operated in transmission, so that it may be implemented in devices for telecommunication, plasmonic circuitry, magnetic field sensing and all-optical magnetic data storage.

cond-mat.other↗

arXiv2010

Exchange interactions and full magnetization process of multispin nanoclaster Mn4

Full magnetization process of magnetic nanocluster Mn4, including all its actual multiplets, is theoretically investigated. The formulas needed to determine the exchange constants of cluster Mn4 from experimental data are obtained. It is shown that quantum jumps of magnetization of this nanocluster are in area of megagauss magnetic fields. Remarkable feature of considered nanocluster Mn4 differing it from other multispin molecules is that its exchange spin Hamiltonian supposes exact diagonalization. This provides a reliable basis for comparison of theoretical predictions with experimental data and is important for development of new experimental techniques of high-spin molecule research.

cond-mat.mes-hall↗

arXiv2010

Bi(1-x)R(x)FeO(3)(R=rare earth): a family of novel magnetoelectrics

Crystals of solid solutions Bi(1-x)R(x)FeO(3),here R= La, Dy, Gd, were obtained with x <=0.7. Solid solutions of the stated rare earths, as x is increased from 0 to 0.7, have one and the same sequence of five crystal structures (rhombohedral C3v 6, triclinic C1 1,orthorhombic D2 6,orthorhombic D2 5, orthorhombic C2v 9). The ferroelectric-paraelectric transition occurs in rhombohedral and triclinic crystals at T=810-560°C.The high temperature modifications are orthorhombic and cubic. The orthorhombic structure C2v 9 holds up to 1180°C.The ferroelectric domain structure was distinguished in all types of crystals. No magnetoelectric effect (MEE) was detected in the orthorhombic crystals with the D2 (222) symmetry class. But the mm2 crystals were found to have both quadratic and linear MEE.The value of the quadratic effect is considerably smaller than that ofthe linear one. Magnetoelectric hysteresis takes place in the crystals. The tensorial properties of the obtained crystals are analyzed from the viewpoint of crystal symmetry.

cond-mat.mtrl-sci↗

arXiv2010

Effect of magnetoelectrical interactions on multiferroic domain walls

The antiferromagnetic domain structure of a multiferroic has been investigated in the presence of a ferroelectric domain structure. It has been demonstrated that an inhomogeneous magnetoelectric (flexomagnetoelectric) interaction leads to pinning of antiferromagnetic domain walls at the walls of the ferroelectric domains and to a change in the structure of antiferromagnetic domain walls.

cond-mat.mtrl-sci↗

arXiv2010

On surface plasmon polariton wavepacket dynamics in metal-dielectric heterostructures

The WKB equations for dynamics of the surface plasmon polariton (SPP) wavepacket are studied. The dispersion law for the SPP in the metal-dielectric heterostructure with varying thickness of a perforated dielectric layer is rigorously calculated and investigated using the scattering matrix method. Two channels of the SPP wavepacket optical losses related to the absorption in a metal and to the SPP leakage are analyzed. It is shown that change of the dielectric layer thickness acts on the SPP as an external force leading to evolution of its quasimomentum and to the wavepacket reversal or even to the optical Bloch oscillations (BO). Properties of these phenomena are investigated and discussed. Typical values of the BO amplitude are about tens of microns and the period is around tens or hundreds of femtoseconds.

cond-mat.other↗

arXiv2009

Interacting antiferromagnetic and ferroelectric domain structures

The correlation between antiferromagnetic and ferroelectric domain structures in multiferroics has been studied. The role of magnetoelectric interactions in a formation of antiferromagnetic domain structure has been analysed. It has been shown the major physical mechanism binding antiferromagnetic domains to ferroelectrics ones is inhomogeneous flexomagnetoelectric interaction of the Pz((lgrad)lz-lz(divl)) type. The dependences illustrating rearrangement of antiferromagnetic domain pattern together with change of ferroelectric domains thickness has been performed.

cond-mat.mtrl-sci↗

arXiv2008

Phase transitions in multiferroic BiFeO3 crystals, thin-layers, and ceramics: Enduring potential for a single phase, room-temperature magnetoelectric 'holy grail'

Magnetic phase transitions in multiferroic bismuth ferrite (BiFeO3) induced by magnetic field, epitaxial strain, and composition modification are considered. These transitions from a spatially modulated spin spiral state to a homogenous antiferromagnetic one are accompanied by the release of latent magnetization and a linear magnetoelectric effect that makes BiFeO3-based materials efficient room-temperature single phase multiferroics.

cond-mat.str-el↗

arXiv2008

Flexomagnetoelectric effect in bismuth ferrite

There is a profound analogy between inhomogeneous magnetoelectric effect in multiferroics and flexoelectric effect in liquid crystals. This similarity gives rise to the flexomagnetoelectric polarization induced by spin modulation. The theoretical estimations of flexomagnetoelectric polarization agree with the value of jumps of polarization in magnetoelectric dependences (~20muC/m^2) observed at spin cycloid suppression at critical magnetic field 200kOe.

cond-mat.str-el↗

arXiv2008

Quadratic Magnetoelectric Effect and Magnetic Field Induced Pyroelectric Effect in Multiferroic BaMnF4

The experimental studies of magnetoelectric effects in pulse magnetic field up to 250 kOe and their theoretical analysis on the basis of magnetic symmetry consideration are carried out. It is shown that the nonvanishing components of quadratic magnetoelectric effect tensor corresponding to the electric polarization along b- and c-axes point out the triclinic distortion of the crystal symmetry. Anomalous temperature dependence of magnetically induced polarization Pa(Hb) testifies to the magnetically induced pyroelectric effect. The torque curves measurements show the deflection of the spin orientation from the b-axis at 9 degrees of arc.

cond-mat.str-el↗

arXiv2008

High domain wall velocities due to spin currents perpendicular to the plane

We consider long and narrow spin valves composed of a first magnetic layer with a single domain wall (DW), a normal metal spacer and a second magnetic layer that is a planar or a perpendicular polarizer. For these structures, we study numerically DW dynamics taking into account the spin torques due to the perpendicular spin currents. We obtain high DW velocities: 50 m/s for planar polarizer and 640 m/s for perpendicular polarizer for J = 5*10^6 A/cm^2. These values are much larger than those predicted and observed for DW motion due to the in-plane spin currents. The ratio of the magnitudes of the torques, which generate the DW motion in the respective cases, is responsible for these large differences.

cond-mat.mtrl-sci↗

arXiv2008

Electric Field Induced Transformation of Magnetic Domain Structure in Magnetoelectric Iron Garnet Films

The room temperature magnetoelectric effect was observed in epitaxial iron garnet films that appeared as magnetic domain wall motion induced by electric field. The films grown on gadolinium-gallium garnet substrates with various crystallographic orientations were examined. The effect was observed in (210) and (110) films and was not observed in (111) films. Dynamic observation of the domain wall motion in 400 V voltage pulses gave the value of domain wall velocity in the range 30-50 m/s. The same velocity was achieved in magnetic field pulse about 50 Oe.

cond-mat.mtrl-sci↗

arXiv2008

Magnetoelectric Control of Domain Walls in a Ferrite Garnet Film

The effect of magnetic domain boundaries displacement induced by electric field is observed in epitaxial ferrite garnet films (on substrates with the (210) crystallographic orientation). The effect is odd with respect to the electric field (the direction of wall displacement changes with the polarity of the voltage) and even with respect to the magnetization in domains. The inhomogeneous magnetoelectric interaction as a possible mechanism of the effect is proposed.

cond-mat.mtrl-sci↗

arXiv2006

Magnetic Magnetoelectric and Magnetoelastic Properties of new multiferroic material NdFe3(BO3)4

Complex experimental and theoretical study of the magnetic, magnetoelectric, and magnetoelastic properties of neodymium iron borate NdFe3(BO3)4 along various crystallographic directions have been carried out in strong pulsed magnetic fields up to 230 kOe in a temperature range of 4.2-50 K. It has been found that neodymium iron borate, as well as gadolinium iron borate, is a multiferroic. It has much larger (above 3 10^(-4) C/m^2) electric polarization controlled by the magnetic field and giant quadratic magnetoelectric effect. The exchange field between the rare-earth and iron subsystems (~50 kOe) has been determined for the first time from experimental data. The theoretical analysis based on the magnetic symmetry and quantum properties of the Nd ion in the crystal provides an explanation of an unusual behavior of the magnetoelectric and magnetoelastic properties of neodymium iron borate in strong magnetic fields and correlation observed between them.

cond-mat.mtrl-sci↗

arXiv2006

Extraordinary magnetooptical effects and transmission through the metal-dielectric plasmonic systems

We report on significant enhancement of the magnetooptical effects in gyrotropic systems of a metallic film perforated by subwavelength hole arrays and a uniform dielectric film magnetized perpendicular to its plane. Calculations, based on a rigorous coupled-wave analysis, demonstrate the Faraday and Kerr effect spectra having several resonance peaks in the near infrared range, some of them coinciding with transmittance peaks. Qualitative analysis revealed that magnetic polaritons being coupled magnetic-film waveguiding modes with surface plasmons play a crucial role in the observed effect.

cond-mat.mtrl-sci↗

arXiv2004

Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets

The properties of antiferromagnetic materials with violated space-time parity are considered. Particular attention is given to the bismuth ferrite BiFeO3 ferroelectric magnet. This material is distinguished from other antiferromagnets in that the inversion center is absent in its crystal and magnetic structures. This circumstance gives rise to the diversified and unusual properties, namely, to the appearance of a spatially modulated spin structure and to the unique possibility of the linear magnetoelectric effect coexisting with a weak ferromagnetic moment. The magnetic-induced phase transitions accompanied by the suppression of the modulated spin structure and appearance of a number of new and unusual effects are considered. These are the linear magnetoelectric effect and the appearance of a toroidal moment and a weak ferromagnetic moment of the magnetoelectric nature.

cond-mat.mtrl-sci↗

arXiv2003

Giant Keplerate molecule Fe30 - the first octopole magnet

The multipole expansion technique is applied to one of the largest magnetic molecules, Fe30. The molecule's dipole, toroid and quadrupole magnetic moments are equal to zero (in the absence of magnetic field) so the multipole expansion starts from the octopole moment. Probably the Fe30 molecule is the most symmetrical magnetic body synthesized so far. The magnetization process is considered theoretically in different geometries. Some components of the octopole moment experience a jump while the magnetization rises linearly up to its saturation value. An elementary octopole moment consisting of four magnetic dipoles is proposed as a hint for designing of an experiment for measurement of octopole magnetic moment components.

cond-mat.mes-hall↗