Magnetic properties of 3D nanocomposites consisting of an opal matrix with embedded spinel ferrite particles

The magnetic properties of 3D nanocomposites representing Mn–Zn, Ni–Zn, Co–Zn, La–Co–Zn, and Nd–Co–Zn spinel ferrite particles embedded in the interspherical spaces of opal matrices are studied. Experimental data are obtained in the temperature interval 2–300 K by measuring the magnetization at a static magnetic field strength of up to 50 kOe and the ac magnetic susceptibility at an alternating magnetic field amplitude of 4 kOe and a frequency of 80 Hz.     

Effects of magnetic field on shape evolution of Fe–Co particles in a Cu matrix

The effects of magnetic field on the shape evolution of ferromagnetic fcc Fe–Co particles in Cu–0.83 at.% Fe–1.37 at.% Co alloy single crystals were examined using magnetic anisotropy measurements. The Cu–Fe–Co single crystals were aged at 993 K for 2 h to 24 h under a magnetic field of 10 T parallel to either the [001] or [011] direction. The magnetic anisotropy was examined by measuring magnetic torque around the (100) plane. It was found that the fcc Fe–Co particles are elongated in the direction parallel to the magnetic field. Furthermore, the elongation along [001] is more remarkable than that along [011]. The results are explained quantitatively by considering the minimization of the sum of the interface energy, elastic strain energy and magnetostatic energy of spheroidal particles.     

Decrease in the Particle Size and Coercivity of Self‐Assembled CoNi Nanoparticles Synthesized Under a Repulsive Magnetic Field

Towards the challenge for synthesis of smaller‐sized heterostructures and hybrid composites for nanomagnets and magnetic fluid applications. Here, a novel method is reported to reduce the particle size of Cobalt–Nickel (CoNi) magnetic nanoparticles by placing them between a static, repulsive magnetic field (N–N/S–S) during synthesis in contrast to the conventional method of applying an attractive (N–S) magnetic field. The obtained smaller sized‐CoNi nanoparticles (≈40 nm) possess a uniform size, an excellent monodispersity, and outstanding magnetic properties. The results clearly demonstrate that the size and morphology change of CoNi nanoparticles have great influence on their magnetic properties. This study provides a footprint to design new heterostructured magnetic nanomaterials under the same‐poled magnetic field for potential applications in magnetic fluids, spintronics, and other related industries.     

Electromagnetic waves reflection,transmission and absorption by graphene–magnetic semiconductor–graphene sandwich-structure in magnetic field: Faraday geometry

Electrodynamic properties of the graphene–magnetic semiconductor–graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene–semi-infinte magnetic semiconductor and graphene–magnetic semiconductor–graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene–magnetic semiconductor–graphene sandwich-structure by an external magnetic field has been shown.     

Superior values of the initial permeability for electrodeposited Ni–Co–P-BaFe12O19 composite films

In this research, we detected superior values of the initial magnetic permeability for electrodeposited Ni–Co–P-M-type BaFe₁₂O₁₉ (BaM) composite films as magnetic soft–hard composites with a large amount of entrapped BaM particles. Furthermore, the initial magnetic permeability of Ni–Co–P-BaM composite films is significantly large and is comparable with corresponding values of the excellent corresponding values for permalloys, Sendust, Co-based amorphous alloys, nanocrystalline (Fe-based) and commercially sintered MnZn ferrite cores. Therefore, Ni–Co–P-BaM composite films are very attractive for magnetic devices, such as magnetic inductors, transformers, and magnetic recording heads.     

Formation of the magnetic domain structure and properties of magnetic cores under conditions of ordered laser deformations

The methods of laser processing and mechanical scribing are used for improving the functional characteristics of transformer magnetic cores from anisotropic Fe–3%Si alloys. The effect is achieved due to controlling the micromagnetic state of elements of the magnetic core by optimizing the type, the dimensional characteristics of their domains, and the magnetic-anisotropy type. These results lead to a substantial decrease in magnetic losses by 9–12% and, with subsequent thermal or thermomagnetic processing, by 14–16% due to decreasing the vortex-current component of magnetic losses.     

A new non-destructive method for estimating the remanent life of a turbine rotor steel by reversible magnetic permeability

We present a new magnetic and non-destructive procedure to evaluate the remanent life of 1Cr–1Mo–0.25V steel using the value of reversible magnetic permeability. The method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive force. The measurement principle is based on the foundation harmonics voltage induced in a coil using a lock-in amplifier tuned to a frequency of the exciting one. Results obtained for reversible magnetic permeability and Vickers hardness on the aged sample show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of 1Cr–1Mo–0.25V steel.     

Effect of external actions on the magnetic properties and corrosion resistance of Co<Subscript>70.5</Subscript>Fe<Subscript>0.5</Subscript>Cr<Subscript>4</Subscript>Si<Subscript>7</Subscript>B<Subscript>18</Subscript> amorphous alloy

Variations in the magnetic characteristics (specific saturation magnetization and coercive force) of Co–Fe–Cr–Si–B amorphous alloy (AA) are studied after high-pressure torsion (HPT) and heat treatment. The behavior of AA magnetic properties is analyzed with respect to structural transformations caused by external actions. The corrosion resistance of AA upon transitioning from an amorphous to a crystalline state is investigated. The established optimum annealing and HPT conditions yield a satisfactory combination of the magnetic properties and corrosion resistance of the investigated alloy.     

Size effects in parameters of both interatomic exchange interactions in Fe–Pt alloy nanoparticles and their superparamagnetism

The objective of this study is to calculate the parameters of strong exchange interactions within magnetic nanoparticles and weak (dipolar + anisotropic) interactions for the patterns of nanoparticles injected into non-magnetic substrate. The Fe–Pt magnetic system was chosen as the best applicable for this purpose. However, computations done in this work may be extended to the other f.c.c. magnetic systems. In this paper, we estimated the parameters of exchange interactions within the magnetic Fe–Pt nanoparticles close to equiatomic composition with 4–10 nm in diameter. Size effect for exchange interaction parameters was found. Temperature dependences of spontaneous magnetizations for Fe and Pt subsystems of nanoparticles with different sizes at fixed equiatomic composition were obtained. Total magnetic energies of weak interactions between Fe and Pt nanoparticles injected different matrixes were also estimated. Magnetic moment ordering temperature was evaluated within the simple model for ordered and disordered Fe–Pt nanoparticles of various sizes (4–10 nm) separated by different interparticle distances (30–50 nm).     

Tuning of exciton states in a magnetic quantum ring

The exciton states in a CdTe quantum ring subjected to an external magnetic field containing a single magnetic impurity are investigated. We have used the multiband approximation which includes the heavy hole–light hole coupling effects. The electron–hole spin interactions and the s, p–d interactions between the electron, the hole and the magnetic impurity are also included. The exciton energy levels and optical transitions are evaluated using the exact diagonalization scheme. We show that due to the spin interactions it is possible to change the bright exciton state into the dark state and vice versa with the help of a magnetic field. We propose a new route to experimentally estimate the s, p–d spin interaction constants.     

Investigation of microwave absorbing properties for magnetic nanofiber of polystyrene–polyvinylpyrrolidone

Aligned magnetic blend of polystyrene–polyvinylpyrrolidone (PS–PVP) nanofibers were prepared by this method. First, polystyrene–polyvinylpyrrolidone (PS–PVP) blend solution in THF was synthesized. Then magnetic of PS–PVP–Fe₃O₄–polyethylene glycol (PEG) was prepared by masking method. Finally, magnetic nanofiber of PS–PVP–Fe₃O₄–PEG was prepared by electrospinning method, too. An electric potential difference of 25 kV was applied between the collector and a syringe tip, and the distance between the collector and the tip was 13 cm. Fe₃O₄ is exhibit various magnetic properties of which the complex permeability and the permittivity, in particular, are important in determining their high frequency characteristics. The magnetic oxide particles and nanofiber of nanometer size were characterized by TEM and SEM respectively. The thermal properties of nanofibers were determined by TGA and DSC. The magnetic characterization of the fibers was also performed by VSM and AFM techniques. On the other hand, nanofiber with diameters ranging from 30 to 40 nm, showing at room temperature, coercive field values of around 25 kV and saturation magnetization was 1.1 emu/g. Microwave reflection loss of the sample was tested at 8–12 GHz microwave frequencies and the results showed that magnetic nanofiber possessed the microwave absorbing properties.     

Preparation of magnetic poly(methylmethacrylate–divinylbenzene–glycidylmethacrylate) microspheres by spraying suspension polymerization and their use for protein adsorption

Moderately uniform magnetic poly(methylmethacrylate–divinylbenzene–glycidylmethacrylate) microspheres (poly(MMA–DVB–GMA) microspheres) were prepared by spraying suspension copolymerization of methyl methacrylate, divinylbenzene and glycidyl methacrylate in the presence of Fe₃O₄ magnetic fluid. A protein adsorption assay indicated that these magnetic microspheres could significantly improve the capacity of protein adsorption.     

Low Temperature Magnetic Properties of Amorphous Ferromagnetic Fe–Si–B Glass-Coated and Glass Removed Microwire

This work presents results of investigations of low temperature magnetic properties of microwires, fabricated by the Ulitovsky–Taylor method from Fe–Si–B alloy. Influence of the glass coating presence on the magnetostatic properties was shown at room temperature and at 2 K. Conclusions about the peculiarities of temperature dependence of the magnetic moment, measured in low and high magnetic fields (10 Oe–5 kOe) in the temperature range from 2 to 300 K for a sample with partially reduced fabricated processinduced stress by removing the glass, were made.     

Controllable magnetic solitons excitations in an atomic chain of spinor Bose–Einstein condensates confined in an optical lattice

We propose an experimental scheme to show that the nonlinear magnetic solitary excitations can be achieved in an atomic spinor Bose–Einstein condensate confined in a blue-detuned optical lattice. Through exact theoretical calculations, we find that the magnetic solitons can be generated by the static magnetic dipole–dipole interaction (MDDI), of which the interaction range can be well controlled. We derive the existence conditions of the magnetic solitons under the nearest-neighboring, the next-nearest-neighboring approximations as well as the long-range consideration. It is shown that the long-range feature of the MDDI plays an important role in determining the existence of magnetic solitons in this system. In addition, to facilitate the experimental observation, we apply an external laser field to drive the lattice, and the existence regions for the magnetic soliton induced by the anisotropic light-induced dipole–dipole interaction are also investigated.     

Neutrino induced magnetic moment and spin precession

When propagating through a dispersing medium, a massive neutrino acquires an induced magnetic moment that may give rise to a helicity flip in an external magnetic field with a larger probability than that caused by the anomalous magnetic moment. This phenomenon is investigated in the framework of relativistic quantum mechanics and of the generalized Bargmann–Michel–Telegdi equation.     

Low-energy relation for the trace of the energy–momentum tensor in QCD and the gluon condensate in a magnetic field

The nonperturbative QCD vacuum in a magnetic field has been studied. A low-energy relation for the trace of the energy–momentum tensor in the magnetic field has been obtained. It has been shown that the derivatives of the quark and gluon contributions to the trace of the energy–momentum tensor with respect to the magnetic field coincide with each other. The magnetic field dependence of the gluon condensate has been calculated in the limits of strong and weak fields.     

Resistance oscillations in junctions of superconductor–magnetic system

Resistance oscillations as a function of magnetic field were observed in superconductor–magnetic tunnel junctions of Nb–Fe–FeO_x–SiO₂–Au–Nb. Junctions involving superconductor–magnetic layer superconductor system are exciting because for certain regime of ferromagnetic layer thickness, a Josephson coupling with an intrinsic phase difference of π might be stabilized. For fabrication of the tunnel junctions the thin films were deposited by RF/DC magnetron sputtering. Using photolithography and reactive ion etching, square junctions of size varying from 50 μm to 250 μm were defined. I–V characteristics and R vs. H characteristics were studied at 4.2 K. When the magnetic field is applied parallel to the junction plane, measurements of the junction resistance as a function of magnetic field at a fixed temperature show resistance peaks whenever the total magnetic flux through the junction equals an integral multiple of flux quantum. The penetration depth of the superconducting electrodes was estimated from the positions of the resistance peaks.     

Effect of Rashba spin–orbit coupling on the spin polarized transport in diluted magnetic semiconductor barrier structures

We investigate theoretically the effects of Rashba spin–orbit coupling on the spin dependent transport through diluted magnetic semiconductor single and double barrier structures in the presence of a magnetic field. We find that the Rashba spin–orbit coupling gives rise to an enhancement of the negative tunnelling magnetoresistance of the diluted magnetic semiconductor single barrier structure and a pronounced beating pattern in the tunnelling magnetoresistance and spin polarization of the diluted magnetic semiconductor double barrier structure.     

High-frequency magnetic permeability of nanocomposite film

The high-frequency magnetic permeability of nanocomposite film consisting of the single-domain spherical ferromagnetic particles in the dielectric matrix is studied. The permeability is assumed to be determined by rotation of the ferromagnetic inclusion magnetic moments around equilibrium direction in AC magnetic field. The composite is modeled by a cubic array of ferromagnetic particles. The magnetic permeability tensor is calculated by solving the Landau–Lifshits–Gilbert equation accounting for the dipole interaction of magnetic particles. The permeability tensor components are found as functions of the frequency, temperature, ferromagnetic inclusions density and magnetic anisotropy. The obtained results show that nanocomposite films could have a rather high value of magnetic permeability in the microwave range.