Enhancement of incorporated ferromagnetic nanoparticles content in nanocomposite electrodeposited coatings by gradient magnetic field

Electrodeposited NiCoMnP coatings incorporating ferromagnetic nanoparticles demonstrate excellent magnetic properties compared with plain metal and alloy. However, improving the weight per cent of ferromagnetic nanoparticles incorporated into nanocomposite coatings is still a challenge. In this paper, a gradient magnetic field has been applied to enhance the nanoparticles’ incorporation during composite electrodepositing. Both experimental and theoretical investigations on the effect of magnetic field on the content of nanoparticles incorporated into nanocomposite coatings were carried out. The results show that gradient magnetic field is favourable for incorporating ferromagnetic nanoparticles into coatings, and uniform or static magnetic field has almost no effect for enhancing codeposition of ferromagnetic nanoparticles into coatings. With gradient magnetic field, a maximum nanoparticles incorporation of 8·08 wt-%BaFe₁₂O₁₉ is observed in CoNiMnP–BaFe₁₂O₁₉ nanocomposite coatings deposited with a BaFe₁₂O₁₉ nanoparticles bath concentration of 40 g L^?1 at a current density of 2 A dm^?2.     

Change of the equilibrium state of ferromagnetic MnBi by high magnetic fields

Differential thermal analysis was carried out for ferromagnetic material MnBi in the temperature range 300-773 K in magnetic fields up to 45 T to investigate the effect of high magnetic fields on its decomposition process and corresponding phase diagram. The decomposition temperature T_t (MnBi → Mn_1.08Bi + liquid Bi) increases from 632 K (at a zero field) to 714 K by applying a magnetic field of 45 T. Furthermore, the magnetocaloric effect of MnBi is observed in 11.5-45 T in the vicinity of 689 K, showing that a field-induced composition process occurs. The obtained results show that the equilibrium state of MnBi can be controlled by a high magnetic field.     

Dynamics of a lattice of magnetic nanoparticles under action of a pulse of a magnetic field

Processes of quasistatic and dynamic magnetization reversal have been studied for the case of planar 6 × 6 lattices of magnetic nanodipoles that possess a cubic crystallographic anisotropy. The response of the total magnetic moment to a magnetic-field pulse of various duration and polarization have been determined for different equilibrium configurations of the lattices. Along with the in-plane configurations of magnetic moments, configurations with one and two dipoles oriented perpendicular to the plane of the lattices have been considered.     

Fabrication and magnetic force microscopy (MFM) observation of nano scale ferromagnetic nanodot arrays

A novel electron beam lithography technique was utilized to fabricate nano scale magnetic dots array with high periodicity. C₆₀ film (fullerine) was used as an electron beam sensitive resist for electron beam patterning carried out under a high accelerating voltage of 200 kV in a transmission electron microscope with a scanning mode. 50 nm sized permalloy (Py) nanodot arrays were successfully fabricated using the method followed by ion-milling. An array of Co nanodots having a size of 100×70 nm was alternatively prepared by liftoff instead of ion milling so as to prevent surface damage by ion milling. Lift-off does not yield any surface roughness, which is important for device fabrication. Magnetic force microscopy (MFM) observations were carried out on the fabricated Co nanodot arrays. A single domain state could be realized in patterned Co nanodots. MFM tip induced magnetization effects were also clearly demonstrated in the array of Co nanodots.     

Evaluation of residual stress in ferromagnetic steels based on residual magnetic field measurements

The paper presents a residual stress evaluation method using the gradients of the residual magnetic field (RMF) components. Distributions of the RMF components were measured on the surface of samples with a various degree of plastic strain. The finite element method was used to model residual stress in samples. The impact of residual stress on changes in the residual magnetic field was shown. A very good qualitative correlation was found between places with residual stress and areas with increased values of the gradients of the RMF components. An algorithm was developed and verified for steel T/P24 to make a quantitative evaluation of residual equivalent (von Mises) stress based on the gradients of tangential component dH_T,Y/dx and field gradient dH/dx. Directions of further research were formulated, which included the validation of the method and which took into consideration the factors affecting its accuracy. The developed algorithm can be a significant complement to the Metal Magnetic Memory (MMM) method.     

Calculation of magnetic leakage field from a surface defect in a linear ferromagnetic material: an analytical approach

A novel analytical approach for calculating the magnetic leakage field from surface defects is proposed and demonstrated for the case of a linear ferromagnetic material. The novelty of the theory is that it relates the distribution of induced magnetic charges to the surface shape. An excellent agreement between the analytical and numerical results is shown. The functional relations between different magnetic field components are discussed.     

Three-dimensional constitutive equations of ferromagnetic materials with magnetoelastic coupling: Determination of elastic coefficients under magnetic field

This paper determines the elastic coefficients in the constitutive equations of typical ferromagnetic materials. The constitutive equations are given by rate-type equations for the magnetization and the strain expressed in terms of the magnetic field and the stress. The authors have shown that the constitutive equations can describe the stress-dependent hysteretic magnetization curve, the stress magnetization effects, the stress-dependent magnetostriction curve, etc. They have determined the coefficients except the elastic coefficients as functions of the magnetization and the stress for typical ferromagnetic materials. In this paper, we attempt to obtain the elastic coefficients depending on the magnetization and the stress. To do it, applying the magnetoacoustic effect, we measure the stress–strain curves and the speeds of the longitudinal and the transverse ultrasonic waves under the magnetic field.     

An alternating magnetic field in a conducting composite with magnetic fibers

The distribution of an ac magnetic field in a conducting fiber composite of a finite length with components differing in their magnetic and electrical properties has been found. The geometry of the skin layer has been determined, and the degree of homogeneity of the magnetic field in samples representing a system of fibers regularly arranged in the matrix has been evaluated. The specific features of the distribution of the magnetic field and eddy currents caused by the presence of interfaces between unlike materials, magnetic properties, dimensions, and the mutual location of inclusions have been analyzed.     

Electrochemical synthesis of polyaniline nanoparticles in the presence of magnetic field and erbium chloride

The uniform polyaniline nanoparticles with size of about 80 nm were electropolymerized using the method of constant potential of 0.7 V. The effects of erbium chloride and magnetic field on properties of polyaniline deposited on two different platinum electrodes were investigated. The resulting films were characterized by FT-IR, UV–vis spectra and scanning electron microscope (SEM). The experimental results show that the magnetic field has an orientation effect on polyaniline chain and there exists the interaction between Er³⁺ and polyaniline chain due to the electrostatic interaction. The longer polymerization time and the higher concentration of erbium chloride can lead to the more distinct morphology of polyaniline films.     

铁磁性激光熔覆层应力的金属磁记忆评价

基于压磁理论,探讨激光熔覆层应力的磁记忆评价机理.基于激光熔覆层SEM观察对磁记忆法向分量H_p(y)信号进行分析.结果表明,随应力增大,激光熔覆层磁记忆法向分量H_p(y)曲线以过零点为中心呈逆时针转动,磁畴由无序向有序转变使得H_p(y)曲线斜率逐渐变大,当应力达到520 MPa(小于试样屈服强度)时,再随应力的增大,H_p(y)曲线斜率逐渐变小.分析认为,激光熔覆层的快速凝固各向异性组织及其中界面导致激光熔覆层呈不均匀塑性变形过程是引起上述结果的主要原因,也是应力小于试样屈服极限时,H_p(y)曲线斜率随应力增大呈减小趋势变化的原因之一.     

Preparation of Y2BaCuO5 nanoparticles by a co-precipitation process with the aid of ultrasonic irradiation

Y₂BaCuO₅ nanocrystallites were prepared by a co-precipitation method with the aid of ultrasonic irradiation using Y₂O₃, CuCl₂ and BaCl₂ as source materials. The crystallization and morphologies of as-prepared nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results show that Y₂BaCuO₅ monophase can be prepared at the calcining temperature up to 900 °C with NaOH and Na₂CO₃ mixtures as precipitator. Particle size of Y₂BaCuO₅ crystallites decreases with the increase of sonicating power. Around 30 nm Y₂BaCuO₅ crystallites can be achieved when sonicating power is increased to 300 W.     

Nuclear magnetic resonance in magnets with a helicoidal magnetic structure in an external magnetic field

In this review, the static and dynamic properties of a magnet with a helicoidal magnetic structure placed in an external magnetic field are discussed. The results of the investigation of its ground state and spectra, as well as the amplitudes of the spin excitations are presented. The temperature and field dependences of the basic thermodynamic characteristics (heat capacity, magnetization, and magnetic susceptibility) have been calculated in the spin-wave approximation. The results of calculating the local and integral dynamic magnetic susceptibility are given. This set of data represents a methodical basis for constructing a consistent (in the framework of unified approximations) picture of the NMR absorption in the magnet under consideration. Both local NMR characteristics (resonance frequency, line broadening, enhancement coefficient) and integral characteristics (resultant shape of the absorption line with its specific features) have been calculated. The effective Hamiltonian of the Suhl-Nakamura interaction of nuclear spins through spin waves has been constructed. The second moment and the local broadening of the line of the NMR absorption caused by this interaction have been calculated. The role of the basic local inhomogeneities in the formation of the integral line of the NMR absorption has been analyzed. The opportunities for the experimental NMR investigations in magnets with a chiral spin structure are discussed.     

Reliability of automatic eddy-current equipment with a rotating magnetic field

This paper presents a method for estimating the reliability of eddy-current nondestructive inspection by using the rotating magnetic field method. The results of the inspection are considered as memory-less stochastic processes, with the possibility of representation in a bi-dimensional space: ‘good product’ and ‘bad product’. The general formulae are calculated by using the master equation for the time behaviour of the probabilities, the numerical data used for results estimation being obtained by means of an automatic eddy current installation with rotating magnetic field. The samples used had 20 μm, 40 μm and 98 μm deep artificial faults, and the control speed ranged between 0.05 and 1 m s⁻¹.     

Stress dependence of the spontaneous stray field signals of ferromagnetic steel

Measuring spontaneous stray field signals provides a promising tool to analyze the stress in ferromagnetic materials. However, strong initial stray field signals on the surface of ferromagnetic materials originating from various manufacturing processes can disturb stress-induced stray field signals. Consequently, it is necessary to conduct a study that will clarify the stress dependence of spontaneous stray field signals by eliminating initial random signals. In the present work, the focus is placed on sheet specimens that have a clean initial magnetic state by means of vacuum heat treatment. Measurements of the normal component H_p(y) signals of stray field were performed during the whole tensile test. The results showed that the stress-induced H_p(y) signal curve had good linearity after loading, i.e., the slope coefficient K_s increased continuously in the elastic deformation stage but decreased slightly during the plastic deformation stage. This phenomenon was discussed and explained from both the stress-induced effective magnetic field and residual compressive stress viewpoints.     

Effective magnetic permeability of ferromagnetic composites. Theoretical description and comparison with experiment

Two analytical methods based on the so-called local linearization of magnetostatic properties of composite materials with ferromagnetic inclusions in a non-magnetic matrix are described. These methods are applied to the experimental data obtained in Gorkunov et al. [Russ. J. Nondestruct. Test. 3 (2001) 186]. A qualitative agreement is obtained for the concentration values reported in that paper and a quantitative agreement is achieved at slightly different value of concentration. The conclusions are supported by direct numerical modeling.     

Dynamics of a spiral magnetic structure in an external magnetic field

Static and dynamic properties of a magnet with an easy-plane anisotropy with a spiral magnetic structure placed in an external magnetic field have been analyzed. The energy spectrum and the amplitudes of linear spin excitations have been calculated for this structure. Their field dependences have been analyzed in detail. Tensors of the local and integral dynamic magnetic susceptibilities have been derived. The spin-wave contributions to the temperature-field dependence of the magnetization have been calculated. The possibility of applying the results obtained to the study of NMR in magnets with a spiral magnetic structure is discussed.     

On the influence of the magnetic field upon hydrogasdynamic processes in a boiling magnetic fluid

The processes of the growth and separation of the vapor bubbles in a boiling magnetic liquid were experimentally and theoretically modeled. Experimental results of the influence of a homogeneous constant magnetic field upon the volume and departure frequency of magnetic fluid drops from a horizontal surface in a transparent nonmagnetic liquid are presented. The mechanism of the influence of the magnetic field upon the volume and departure frequency of the magnetic fluid drops is explained. The shape and volume of a magnetic liquid drop placed in a nonmagnetic environment are theoretically calculated for various values of the magnetic field intensity the drop is exposed to.