Collective motion of magnetization in two-dimensional arrays of square elements

The resonance in a two-dimensional array of square ferromagnetic elements has been experimentally investigated. The magnetization of the elements is shown to be in the vortex state. The resonance peak splitting in the array with increasing density of the elements has been established. The explanation of this phenomenon is proposed and eigenfrequencies of the collective modes are theoretically estimated. Different combinations of polarities and chiralities of the nearest elements in the array are examined.     

Formation of two-dimensional lattices of magnetic domains in a harmonic magnetic field

New configurations of two-dimensional lattices of magnetic domains with symmetry described by the P2 and Cmm2 space groups are revealed in studying the formation of domain structures in a harmonic magnetic field. Two-dimensional lattices belonging to five space groups of the orthorhombic and hexagonal systems are observed in a single iron garnet film. Changes in the lattice configurations and in the lattice elements occur upon the variation of only one parameter of the applied magnetic field, namely, its frequency.     

Persistent currents and magnetization in two-dimensional magnetic quantum systems

Persistent currents and magnetization are considered for a two-dimensional electron (or gas of electrons) coupled to various magnetic fields. Thermodynamic formulae for the magnetization and the persistent current are established and the “classical” relationship between current and magnetization is shown to hold for systems invariant both by translation and rotation. Applications are given, including the point vortex superposed onto an homogeneous magnetic field, the quantum Hall geometry (an electric field and an homogeneous magnetic field) and the random magnetic impurity problem (a random distribution of point vortices).     

Collective diffusion in a two-dimensional liquid composed of Janus particles

The collective diffusion of anisotropic particles in liquids plays a crucial role in many processes, such as self-assembly. The patchy particle, which is usually nearly spherical in shape, is an important anisotropic particle with different properties from other anisotropic particles like the ellipsoid liquid crystal particles. In the present study, molecular dynamics simulations are performed to study the collective diffusion of a two-dimensional anisotropic liquid system composed of Janus particles. The static structures and diffusion behaviours of anisotropic and isotropic Lennard-Jones liquids are compared. The long-time diffusion behaviour of an anisotropic liquid of nearly spherical Janus particles is found to be similar to that of an isotropic liquid because the orientation of the particles disappears over long-term averaging. The anisotropic properties of the Janus particles are mainly reflected in the spatial correlation of particle orientations and mid-time diffusion behaviour. The difference between nearly spherical anisotropic particles and rod-like particles is also discussed in this paper.     

Contrasting magnetic behavior of fine particles of some Kondo lattices

We have investigated the magnetic behavior of ball-milled fine particles of well-known Kondo lattices, CeAu₂Si₂, CePd₂Si₂ and CeAl₂, by magnetization and heat-capacity studies in order to understand the magnetic behavior when the particle size is reduced. These compounds have been known to order antiferromagnetically in the bulk form near ($T_N=$) 10, 10 and 3.8 K respectively. We find that the features due to magnetic ordering get suppressed to temperatures below 1.8 K in the case of fine particles of ternary alloys, though trivalence of Ce as inferred from the effective moment remains unchanged. In contrast to this, in CeAl₂, there appears to be a marginal enhancement of $T_N$, when the particle size is reduced to less than a micron. These results can be consistently understood by proposing that these compounds move toward left in the Doniach magnetic phase-diagram, for instance, due to relatively more 4f-localization, as the particle size is reduced.     

二维正方格子磁性光子晶体的界面传导模

采用平面波展开加超元胞方法计算了二维正方格子磁性光子晶体的光子带隙结构，其中散射子的形状分别为长方形，正方形，六角形和圆形.结果表明绝对带隙宽度和其宽高比远大于同种结构的非磁性光子晶体.在此基础上，构成了混合型异质结，并计算了相应的传导模，发现了理想的界面传导模，而且当磁性散射子为长方形、圆形、六角形散射子时产生传导模都不需要晶格畸变，这也是磁性光子晶体异质结所具备的优点. 关键词： 光子晶体 光子带隙结构 传导模     

Perturbation of magnetization of a magnetic fluid by ultralow thermal fluctuations accompanying a sound wave

The paper presents the results of theoretical and experimental research of the the effect of perturbation of the magnetization of a magnetic fluid caused by thermal fluctuations in an adiabatic sound wave in the initial area of the magnetization curve. Measurements are conducted on samples of a magnetic colloid with various viscosity of the dispersion medium in the frequency range of 20–60 kHz. In this frequency range, the studied samples are characterized by the absence of thermal relaxation of magnetization. Comparison of the conclusions of the thermal magnetization relaxation model with the results of experiment make it possible to obtain information on the rheological features of the neareast molecular environment of a particle, i.e., nanorheology.     

On the magnetization curves of bubble lattices

The paper presents magnetization curves of bubble lattices in garnet samples of composition (YSmLuCa)₃(FeGe)₅O₁₂, in which we observed a discontinuity in the magnetization at a certain negative value of the external magnetic field applied normal to the sample surface. This points to an anomaly in the behaviour of the existing honeycomb domain structure. The proposed theoretical interpretation of this behaviour is based on the interaction of closely spaced pairs of Bloch walls.     

Rapid magnetization reversal in magnetic small particles induced by non-static bias field

Magnetization reversal processes by a switching field in single-domain nano-sized magnetic particles in the presence of a small transverse non-static bias field are studied. Applying an oscillating bias field instead of a static field, the reversal time becomes much shorter when the switching field is slightly stronger than the effective anisotropy field. A pulsed bias field of a suitably chosen duration in the nanosecond scale is found to induce a rapid switching, even when the switching field is smaller than the anisotropy field. The dependence of the reversal time on the frequency of an oscillating bias field and the duration of a pulsed bias field are studied. The present work thus complement the earlier studies on switching in the presence of a static bias field.     

Collective effects in the transport properties of two-dimensional electron systems

The results of the experimental study of the nontraditional manifestations of collective effects in the transport properties of two-dimensional electron systems are reported.     

Collective effects by agglomerated debris particles in the backscatter

We present an analysis of backscattered light by agglomerated debris particles whose size is comparable with the wavelength. We consider agglomerates that consist of one or two large central particles and a few relatively small fragments surrounding the particles. We find that for the particles we studied, the attachment of small fragments onto the particles leads to a decrease of the negative polarization branch (NPB) at small phase angles in comparison with the branch produced by the isolated particles. For relatively large agglomerates (with size parameters x about 25) the internal scatter in the agglomerates may produce a secondary minimum of the NPB. In this case the second order of scatter between constituents of aggregates plays the dominant role.     

Singularities of the magnetization of a two-dimensional diluted magnetic semiconductor with strong spin-orbit interaction

The properties of the bound states of magnetic impurities and localized carriers in two-dimensional semiconductor systems with strong Rashba spin-orbit interaction have been investigated. The peculiar behavior of the bound states of an electron in such a system leads to the dependence of the ground state of polarons on the external magnetic field. This results in a jump in the dependence of the magnetization on the applied field.     

Interaction effects observed in the magnetization of a bilayer two-dimensional electron system

We present magnetization measurements of a bilayer two-dimensional electron system with strong coupling between the wells. Magnetization steps related to transitions of the chemical potential between Landau levels and between anti-symmetric and symmetric states are observed; however, the step sizes do not fit into a simple single-particle figure. A further indication of interaction effects is a peculiar magnetization peak that arises on top of the magnetization step associated with the transition to the lowest Landau level.     

A novel type of domain walls with two-dimensional magnetization distribution in magnetic triaxial films

On the basis of numerical minimization of total energy in magnetic triaxial ferromagnetic films with a surface of a (1 1 0)-type, we investigated two-dimensional structures of domain walls within a rigorous micromagnetic approach that takes into account all the main interactions including the dipole–dipole one. Novel two-vortex and three-vortex domain wall structures are established to exist. The profiles of domain wall structures and their stability regions are studied.     

Oscillatory magnetization of two-dimensional electron gas

Diamagnetic moment of the two-dimensional electron gas is calculated for finite temperature using a simple energy band model and assuming no collisional broadening of Landau levels. Numerical results are presented for GaAs band parameters. The diamagnetic moment oscillates around zero value as a function of magnetic field strength and tends to zero at low fields. It is concluded that both the diamagnetic and the paramagnetic susceptibilities of the 2D electron gas vanish in the low field limit.     

Studies of two-dimensional lattices using ferrofluid

By exerting a magnetic filed H normal to a ferrofluid layer, a triangular lattice of droplets is formed when H exceeds a characteristic critical field. The lattice may be “heated” by reducing H and the effects of dislocations and disclinations may be studied. This offers a new experimental system for direct visual observations of phenomena related to two-dimensional melting.     

Dual-negative-refraction and imaging effects in normal two-dimensional photonic crystals with hexagonal lattices

A novel dual-negative-refraction (DNR) effect is studied in two types of normal two-dimensional photonic crystals (2DPCs) with hexagonal lattices. Systematical analyses of the band structures and equifrequency surfaces indicate that the DNR may be realized when the overlapping second and third bands with relatively flat shapes and only a slight separation are available at some frequencies close to the band's peak of 2DPCs. Further simulations have not only confirmed the DNR and corresponding dual-imaging effects in normal 2DPCs with hexagonal lattices but also revealed some relative rules to the dual images. In particular, the thickness as well the cutoff value at terminations of PCs can strongly influence the performance of dual images and even determine whether the dual images would appear. Moreover, a relatively low working frequency is recommended to minimize the distortion degree of dual images.     

Acoustic studies of metal-ceramic composites with meso- and nanosize particles

The elasticity moduli and absorption coefficients of longitudinal ultrasonic waves with a frequency of 2–50 MHz depending on the steel concentration and sintering temperature of 1400–1700°C in vacuum were studied in samples of cermet-type composites on the basis of corundum and stainless steel. The results were discussed from the point of view of the elastic waves propagating in the fine-disperse two-phase medium at the presence of the intergrain and interphase boundaries, noticeably affecting the physical properties of the composite.     

Magnetization anomalies of nanosize zinc ferrite particles prepared using electrodeposition

Nanosize zinc ferrite particles have been prepared for the first time using electrodeposition. Zinc and iron are deposited on the cathode from a common bath containing the salts of zinc and iron. The deposited materials were forced to undergo electrochemical oxidation in a strong alkaline solution (1 M KOH) to convert them into oxides. Crystallization in ZnFe₂O₄ structure was obtained by heating the deposited material at appropriate temperature. X-ray diffraction pattern confirmed that the procedure leads to the formation of pure phase of ZnFe₂O₄. The magnetization value for the smallest size ZnFe₂O₄ is much smaller than that for the ZnFe₂O₄ made by most of the other methods although it shows a nice hysteresis shape. The magnetization shows very little variation with size in the range studied.