Ferronematics with soft particle anchoring in magnetic and laser fields

The influence of a magnetic field and an optical laser field on the orientational behavior of a ferronematic with positive magnetic and dielectric anisotropy is investigated. A slow transition from the homeotropic to the distorted alignment of the nematic director is found when the field strengths exceed certain threshold values. A correlation between the threshold values of the two fields is obtained and a phase diagram for this transition is determined. It is also found that in the presence of the two fields the distorted arrangement is more stable than the homeotropic one (its free energy per unit area is smaller).     

Magnetic properties of soft magnetic composites prepared with crystalline and amorphous powders

Physical properties of soft magnetic composites prepared with a mixture of amorphous (FeSiBC) and crystalline (Fe) powders coated with distinct electrical insulator contents are reported. Density, saturation polarization, permeability and coercivity of the cores reduce linearly with the increase of the softer magnetic phase amount and a general relation can be expressed by a rule of mixtures. The behavior of the coercivity, as a function of the magnetic phase content, differs from that previously reported for magnetic composites prepared with equal amounts of magnetic and non-magnetic phases. For frequencies upto 1 kHz the magnetic losses of the cores are constant, following the same behavior of the coercivity. A qualitative explanation of the behavior of the latter is addressed based on an expression applicable for crystalline and amorphous materials.     

Magnetic and structural properties of iron phosphate-phenolic soft magnetic composites

This work focuses on the effect of phosphate modification on the magnetic and surface properties of iron-phenolic soft magnetic composite materials. Fourier transform infrared (FTIR) spectra, EDX analysis, distribution maps, X-ray diffraction pattern and density measurements show that the particles surface layer contains a thin layer of nanocrystalline/amorphous phosphate with high coverage of powders surface. Magnetic measurements show that phosphating treatment decreases the loss factor, imaginary part of permeability, increases the electrical resistivity and operating frequencies by decreasing the effective particle size. The operating frequency increases from 200 kHz for uncoated-powders samples to 1 MHz for phosphated-powders samples at optimum concentration. Phosphated iron powders that are covered by 0.7 wt% of phenolic resin exhibits lower magnetic loss and higher frequency stability. The minimum loss factor and maximum permeability at each frequency can be obtained for 0.01 g/ml orthophosphoric acid concentration in comparison with other concentrations including 0.005 and 0.04 g/ml.     

Stable static structures in models with higher-order derivatives

We investigate the presence of static solutions in generalized models described by a real scalar field in four-dimensional space–time. We study models in which the scalar field engenders higher-order derivatives and spontaneous symmetry breaking, inducing the presence of domain walls. Despite the presence of higher-order derivatives, the models keep to equations of motion second-order differential equations, so we focus on the presence of first-order equations that help us to obtain analytical solutions and investigate linear stability on general grounds. We then illustrate the general results with some specific examples, showing that the domain wall may become compact and that the zero mode may split. Moreover, if the model is further generalized to include k-field behavior, it may contribute to split the static structure itself.     

Magnetized Domain Walls Cosmological Model in General Relativity

A non-static Bianchi type-III domain walls cosmological models in presence and absence of magnetic field are investigated in general theory of relativity. We assume that F ₁₂ is only the non-vanishing component of F _ij . To obtain deterministic model, we assume relations B=C ⁿ and ρ=p. Some physical properties of these models are discussed.     

Interaction of ultrasonic waves with domain walls on nanocrystalline YIG

The nanocrystalline YIG samples with different particle sizes (20–40 nm) has been prepared using microwave–hydrothermal method. As synthesized powders were characterized using XRD and TEM. The powders were pressed and sintered at three different temperatures i.e., 700 °C/30 min, 800 °C/30 min, 900 °C/30 min, using microwave furnace. The sintered samples were characterized using XRD and TEM. The sintered samples are monophasic in nature with average grain size ranging in between 72 nm and 90 nm. The thermal variation of ultrasonic velocities [longitudinal (V_l) and transverse (V_S)] and longitudinal attenuation (α_l) has been measured on sintered samples by the pulse transmissionmethod at 1 MHz, in the temperature range of 300–600 K. The room temperature velocity is found to be grain size dependent and decreases with increasing temperature, except near the Curie temperature, T_C, where a small anomaly is observed. The longitudinal attenuation (α₁) at room temperature is also found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation exhibits a sharp maximum just below Curie temperature (T_C). The above observations were carried on in the demagnetized state, on the application of a saturation field of 380 mT, the anomaly observed in the thermal variation of velocities (longitudinal and transverse) and attenuation is found to disappears. The observed interaction of ultrasonic velocity with domain walls has been qualitatively explained with the help oftemperature variation of magneto-crystalline anisotropy constant (k₁) and Landau’s theory.     

Influence of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites

This paper investigates the effect of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites (50 Hz-1000 kHz). The results showed that the optimum amount of phenolic resin to attain maximum permeability and minimum loss factor at 10 kHz is 0.7 wt% for samples containing iron powder with average particle size ∼150 μm compacted at 800 MPa. In accordance with this resin content, at high frequencies (>300 kHz), the sample with lower particle size ∼10 μm exhibits higher magnetic permeability, higher operating frequencies and lower imaginary part of permeability. With increase in the compaction pressure, specific resistivity decreases and imaginary and real parts of permeability increase at low frequencies.     

LETTER: Gauge Field Corrections to Domain Walls

Gauge field corrections to domain walls are obtained by making use of perturbation method on the usual flat domain wall. The gauge vector field introduces a damping term and an external force on the motion equation for the perturbed domain wall. A thin domain wall approximation solution is found. The vector gauge field also introduces a gauge mass term correction into the perturbed Lagrangean.     

A Higher Dimensional Cosmic Domain Wall in Brans-Dicke Theory of Gravitation

Five dimensional Kaluza-Klein Space-time is considered in the presence of thick domain walls in the scalar-tensor theory formulated by Brans and Dicke (Phys. Rev. 124:925, 1961). Exact cosmological model, in this theory, is presented with the help of special law of variation proposed by Berman (Nuovo Cim. B 74:182, 1983) for Hubble’s parameter. Some physical and kinematical properties of the model are also discussed.     

ICF玻璃靶丸化学镀磁性Ni-P涂层的研究

 采用化学镀方法对ICF空心玻璃微球靶丸进行处理,使其表面均匀包覆一层磁性Ni-P合金镀层,从而使得ICF玻璃靶丸具有一定的磁性,可望用于进行磁悬浮ICF定位打靶实验研究。用X射线衍射仪、扫描电子显微镜和振动样品磁强计对涂层的组成、结构、形貌及磁性能进行了表征。结果表明：对 ICF玻璃靶丸进行化学镀处理,其球形度、同心度和壁厚均匀性都与化学镀前未发生明显改变,其饱和磁化强度和矫顽力分别为3.883×10^-3 A/g和1.046×^-3 T。     

On the thickness of domain walls in ferroelectrics and ferroelastics

Ferroelastic and ferroelectric domain walls are commonly described by wall profiles of the tanh(x/w)-type. We argue that this profile is still a good approximation if higher-order gradient energies are considered. Such energies are relevant for phase transitions close to structural incommensurations and also for phase transitions with dominant elastic interactions. Their effect on the wall profile is to influence the effective wall thickness. Positive gradient energies tend to widen domain walls beyond the values predicted in classic Landau-Ginzburg theory.     

Domain wall propagation in Permalloy nanowires with a thickness gradient

The magnetization reversal behavior of Permalloy nanowires has been investigated using a magneto-optic Kerr effect setup. Nanowires with various widths, w=250$w=250$ nm to 3 μm and a thickness of t=10$t=10$ nm were fabricated by electron-beam lithography and subsequent lift-off. Furthermore, similar nanowires but with a thickness gradient along the nanowire axis have been prepared to investigate the influence of the gradient on the magnetic domain wall propagation. Magnetization hysteresis loops recorded on individual nanowires without a gradient are compared to corresponding wires with a thickness gradient. The dependence of the coercive field, _Hc$H_c$ vs. t/w$t/w$ shows a linear behavior for wires without a gradient. However, wires with a gradient display a more complex crossover behavior. We find a plateau in the _Hc$H_c$ vs. t/w$t/w$ curve at values of w$w$, where a transformation from transverse to vortex domain wall type is expected.     

Magnetic symmetry of the plain domain walls in ferro- and ferrimagnets

Magnetic symmetry of all possible plane domain walls in ferro- and ferrimagnets is considered. Magnetic symmetry classes of non 180° (including 0°) domain walls are obtained. The domain walls degeneracy is investigated. The symmetry classification is applied for research of all possible plane domain walls in crystals of the hexoctahedral crystallographic class.     

Theoretical study of the temperature dependence of the width of magnetic domain walls

The temperature dependence of magnetic domain walls in ferromagnetic systems with strong exchange coupling and weak lattice anisotropy is studied assuming that the thermal influence results mainly from the temperature dependence of the magnetization. We obtain that in lattices with an uniaxial symmetry like Co the wall width increases with temperature, but stays finite up to the Curie temperature T_c. In contrary, for a cubic lattice like Fe the wall width diverges for T → T_c, if only the lattice anisotropy is taken into account. The shape of the domain walls is not conserved, since at T_c the wall is determined only by the lowest order of anisotropy. In addition, the temperature dependence of a domain wall width for a thin magnetic film is determined. Using a special symmetry, we obtain a diverging wall width at a temperature markedly lower than T_c. However, the consideration of additional domain wall modes should modify this result.     

Role of anisotropy on the domain wall properties of ferromagnetic nanotubes

In this paper we investigate the role of magneto-crystalline anisotropy on the domain wall (DW) properties of tubular magnetic nanostructures. Based on a theoretical model and micromagnetic simulations, we show that either cubic or uniaxial magneto-crystalline anisotropies have some influence on the domain wall properties (wall size, propagation velocity and energy barrier) and then on the overall magnetization reversal mechanism. Besides the characterization of the transverse and vortex domain wall sizes for different anisotropies, we predict an anisotropy dependent transition between the occurrence of transverse and vortex domain walls in tubular nanowires. We also discuss the dynamics of the vortex DW propagation gradually increasing the uniaxial anisotropy constant and we found that the average velocity is considerably reduced. Our results show that different anisotropies can be considered in real samples in order to manipulate the domain wall behavior and the magnetization reversal process.     

Magnetic anisotropy and domain patterns in electrodeposited cobalt nanowires

The magnetic anisotropy and domain structure of electrodeposited cylindrical Co nanowires with length of 10 or 20 μm and diameters ranging from 30 to 450 nm are studied by means of magnetization and magnetic torque measurements, as well as magnetic force microscopy. Experimental results reveal that crystal anisotropy either concurs with shape anisotropy in maintaining the Co magnetization aligned along the wire or favours an orientation of the magnetization perpendicular to the wire, hence competing with shape anisotropy, depending on whether the diameter of the wires is smaller or larger than a critical diameter of 50 nm. This change of crystal anisotropy, originating in changes in the crystallographic structure of Co, is naturally found to strongly modify the zero (or small) field magnetic domain structure in the nanowires. Except for nanowires with parallel-to-wire crystal anisotropy (very small diameters) where single-domain behaviour may occur, the formation of magnetic domains is required to explain the experimental observations. The geometrical restriction imposed on the magnetization by the small lateral size of the wires proves to play an important role in the domain structures formed. Received 14 September 2000     

Magnetic and microstructural properties of the Ti-doped Barium hexaferrite

A study of the magnetic and microstructural properties of the M-type Ti⁴⁺-doped Barium hexaferrite according to the stoichiometric formulation BaFe_{(12−(4/3)x)}Ti_xO₁₉ with x=0, 0.6, 0.8 and 1.0, has been reported. The XRD and magnetic analysis show a variation of the host lattice parameters and a decrease in the values of remnant magnetization and magnetic anisotropy with Ti⁴⁺ content. The behavior of magnetic properties of materials is explained by the combined effect of the coherent rotation of the magnetic domains and the replacements of Fe³⁺ by Ti⁴⁺ ions in the octahedral and tetrahedral sites.     

Magnetic properties of mechanically alloyed Co–Ti powder

An amorphous phase containing traces of non-transformed Co and Ti powders was obtained by mechanical alloying nominal compositions of Co₆₇Ti₃₃ and Co₅₀Ti₅₀ in a high-energy ball-mill. These alloys were prepared from elemental powders of Co and Ti. The heat treatment of Co₆₇Ti₃₃ at 573, 873 and 1173 K crystallized nanoparticles of Co₂Ti and Co₃Ti compounds, while the same treatments conducted on Co₅₀Ti₅₀ resulted in the formation of Co₂Ti and CoTi nanoparticles. The saturation magnetizations reached a maximum value in the amorphous state and they decreased when the temperatures of the heat treatment rose. Demagnetizing interparticle interaction effects were estimated through hysteresis loops and initial magnetization curves using the Fourier technique.     

Magnetic properties of ErN films

We report a magnetization study of stoichiometric ErN nanocrystalline films grown on Si and protected by a GaN passivating layer. According to the temperature dependence of the resistivity the films are heavily doped semiconductors. Above 100 K the magnetization data fit well to a Curie-Weiss behavior with a moment expected within the free-ion Er³⁺ multiplet. Below 50 K the Curie-Weiss plot steepens to an effective moment corresponding to that in the crystal-field determined quartet ground state, and develops a clear paramagnetic Curie-Weiss temperature of about 4.5 K. Zero-field- and field-cooled magnetization curves and the AC susceptibility firmly establish a ferromagnetic ground state within that multiplet below a Curie temperature of . Due to the (1 1 1) texture of the film the comparison between the magnetization behavior, when the field is applied parallel and perpendicular to the film plane, gives new information about the magnetic structure. An arrangement of the moments according to the model derived from neutron diffraction for bulk HoN is strongly suggested.     

Five Dimensional Domain Walls in a Scalar-Tensor Theory of Gravitation

Five dimensional Kaluza-Klein space-time is considered in the presence of thick domain walls in the framework of scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, [1986]). Exact cosmological model, which represents a stiff domain wall, is presented. Some physical and kinematical properties of the model are also discussed.