Evolution of atomic and electronic structure of magnetic Gd-doped gold clusters

The evolution of atomic and electronic structure of small Au _n (n = 1–16, and 55) clusters doped with a Gd atom has been investigated using density functional theory within generalized gradient approximation for the exchange–correlation energy. Pure gold neutral clusters with n up to 15 are planar. However, with the doping of a Gd atom, the atomic structure of gold clusters changes, and there is a transition from planar-like structures to three dimensional structures at n = 10. The electronic structure of Gd-doped gold clusters shows a sharp increase in the highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap for certain sizes giving rise to their magic behavior. All clusters are magnetic with large magnetic moments ranging from 6 to 8 μ_B primarily due to the localized 4f electrons on Gd. This makes such clusters with large HOMO–LUMO gaps magnetic superatoms. The main interaction between gold and gadolinium atoms in the clusters is due to hybridization between Au-6s and Gd-5d6s orbitals. Our results indicate the emergence of a wheel structure for Gd@Au₇, a symmetric cage structure at n = 15 for Gd@Au₁₅ and n = 16 for Gd@Au₁₆ ⁺ and Eu@Au₁₆ corresponding to an electronic shell closing at 18 valence electrons leaving aside the f electrons on Gd while for Gd-doped Au₅₅ corresponding to 58 valence electrons, a Au₉Gd@Au₄₆ core–shell structure is obtained in which the Gd atom connects the core of Au₉ with the Au₄₆ shell. The binding energy shows odd–even oscillations with enhancement due to Gd doping compared with pure gold clusters. Such magnetic clusters of gold could have multifunctional biological applications in drug delivery, sensor, imaging, and cancer treatment.     

Strong correlation between the cation ordering and magnetic properties of anodically electrodeposited Mn–Co–O nanocrystals

The rock salt-to-spinel structural transformation that occurs in anodically electrodeposited Mn–Co–O nanocrystals involves a rearrangement of Mn/Co cations from octahedral interstices to tetrahedral interstices. The cation ordering process leads to distinct magnetic properties. Curie temperature (T _C) and blocking temperature (T _B) increase dramatically with annealing temperature (200–400 °C), while the corresponding change in particle size for the oxide nanocrystals is rather small. A strong correlation between the magnetic properties and the cation ordering degree in annealed Mn–Co–O nanocrystals was established. These unique magnetic properties can be attributed to the magnetic moment changes induced by Mn/Co cation ordering from octahedral interstices to tetrahedral interstices in the annealed Mn–Co oxide nanocrystals.     

Analysis of parameters of electric and magnetic phenomena accompanying explosion and shock processes

Parameters of electric and magnetic fields generated by an explosion of chemical explosives and impact of metallic bodies are determined. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 3, pp. 442–449, May–June, 1997.     

Formation of coulomb clusters from charged diamagnetic microparticles in inhomogeneous magnetic field

The possibility of levitating Coulomb clusters formed by charged diamagnetic microparticles in an inhomogeneous magnetic field has been theoretically substantiated and experimentally confirmed. An experimental setup is described, in which the Coulomb clusters can be formed from charged graphite particles 100–300 μm in size and maintained stable between the poles of an electromagnet generating a magnetic field with induction B ∼ 10⁴ G and gradient |∂B| ∼ 10⁵ G/cm.     

One-component cesium magnetometer for measuring the residual magnetic induction in ferromagnetic shields

A simple design for a miniature cesium magnetometer intended for measuring the residual magnetic induction (B ₀≤1000 nT) in ferromagnetic shields of cylindrical shape with an internal diameter ⊘≥15 mm is described. Pis’ma Zh. Tekh. Fiz. 25, 42–46 (May 12, 1999)     

Concerning numerical simulation of the failure of a magnetic-fluid seal with a rotary outer profiled cylinder

The behavior of a circular magnetic fluid seal in the narrow gap between an immovable shaft and a rotary hyperbolic concentrator of the magnetic fluid flow surrounding it is studied. The range of the dimensionless rotation parameter within which the seal is stable is determined. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 105–110, January–February, 1996.     

An analysis of the error in measuring the field of the maximum magnetic permeability of steels

The error δ in measuring the parameters of the field Hμ _m of the maximum magnetic permeability μ _m of steels is estimated. It is established that δ is 5–10 times greater than the error of ±5% in measuring μ _m . It is shown that not all the reference data on μ _m and Hμ _m of steels are reliable. The inadvisability of using Hμ_m in magnetic structural analysis is demonstrated.     

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C,B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn₅₅Al₄₅ based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal ε crystal structure. Phase transformations between the ε and the L1₀ (τ) phase are of interest. The ε → τ transformation occurred at ~500 °C and the reversed τ → ε transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L1₀ τ-phase and improved the hard magnetic properties. The Curie temperature T _C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T _C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially J_S. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the ε phase or the L1₀ hard magnetic τ phase.     

Superconducting gap function and upper critical field in the presence of inhomogeneous magnetic order

Rare earth ternary superconductors are known to exhibit oscillatory magnetic orders below their superconducting transition temperatures. The study of behaviour of superconducting electrons in an inhomogeneous magnetic field is therefore important for such systems. We report here the results of our theoretical study of superconducting gap function Δ(T) and upper critical fieldH _c2 (T). The results are applied to analyse and explain the variation of Δ(T) andH _c2 (T) in case of NdRh₄B₄.     

Influence of the concentration of a dispersed phase and of the magnetic field on the attenuation of ultrasonic waves in magnetic fluids

The regularities of the propagation of elastic waves of ultrasonic range in magnetic fluids have been experimentally established. The influence of relaxation processes — nonlocal heat exchange and viscous dissipation — on the coefficient of attenuation of sound has been revealed and a comparison to the existing theoretical data has been made. The dependences (anisotropic in form) of the attenuation of the wave’s amplitude on the value and direction of the magnetic field have been determined and an interpretation of the results obtained has been proposed. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 5, pp. 133–140, September–October, 2007.     

Effect of magnetic anisotropy on the mobility of the boundaries in thin magnetic films

This paper discusses the effect of magnetic crystallographic anisotropy on the mobility of the domain walls in thin magnetic films with an easy axis in the plane of the film. It shows that the stable configuration of a domain wall is a single-vortex Bloch domain wall. Besides this, there are two metastable states of the domain wall—a Néel domain wall and a domain wall with two magnetic vortices along the normal to the plane of the film. It is also shown that the mobilities of the single-vortex and Néel domain walls and the domain wall with two vortices decrease as the anisotropy constant increases and tend to the same value. Pis’ma Zh. Tekh. Fiz. 24, 42–46 (January 26, 1998)     

Diffraction of light by agglomerates in a layer of magnetic fluid situated in a magnetic field parallel to the plane of the layer

Previously unknown behavior observed when laser radiation propagates through a layer of magnetic fluid with and without an external magnetic field are established for the first time and their physical nature is explained. Pis’ma Zh. Tekh. Fiz. 23, 64–67 (February 12, 1997)     

Effects of magnetic fields on flexural properties of a longitudinal polymer liquid crystal

We have placed a copolymer of poly(ethylene terephthalate + 0.6 mole fraction of p-hydroxybenzoic acid) in magnetic fields up to 1.8 Tesla, heated it to the molten state (at several temperatures in the range 240–315 °C) and cooled to the room temperature under the field to maintain the orientation so acquired. Then the extent of the orientation has been determined with an anisotropy parameter a based on the ultrasound critical–angle reflectometry (UCR); the parameter is calculated from the ratio of the maximum velocity to the minimum velocity of the reflected wave at critical incidence angles at which total internal reflection occurs. A significant orientation effect is found. As expected, anisotropy increases with time, magnetic field strength and to a lesser extent with the temperature. Large changes in the extent of the anisotropy are connected to phase transitions determined before. The Freederickscz transition is observed. The influence of the orientation effect on the mechanical properties of samples has been established by flexural tests. The strengthening observed has been explained using an extension of the statistical–mechanical theory of Flory in terms of channeling of flexible sequences in the polymer liquid crystals (PLC) and changes in phase structures under the magnetic field. The strengthening effect depends strongly on the presence, size and distribution of liquid crystal (LC) islands in the material. The islands act similarly as dispersoids in other types of materials. Maxima of the strengthening effect with respect to the alignment are found and related to the size of LC-rich islands in the structure. Electronic Publication     

Nonequilibrium processes in Hg1−x CdxTe n +−p junctions in a magnetic field

The results of measurements of the relaxation and current-voltage characteristics of Hg_{1− x} Cd_xTen ⁺−p junctions in a magnetic field are presented. It is shown that the lifetime of the nonequilibrium electrons in the p-type region undergoes an increase in a magnetic field, which can be associated with the heterogeneous distribution of defects from the junction boundary. The current-voltage characteristics in a magnetic field exhibit suppression of the diffusion component of the current and an increase in the contribution of the generation-recombination channel, as well as the appearance of shunting channels, which are associated with the influence of the surface. Pis’ma Zh. Tekh. Fiz. 23, 88–94 (October 26, 1997)     

Ferromagnetic signature in nanoparticles of diluted magnetic semiconductors of ZnO:V

Nanoparticles of ZnO:V prepared using sol–gel method are investigated for the magnetic properties. The particles of them possess polycrystalline and hexagonal wurtzite structure. The average size of particles is found to be around 60 nm. In the optical absorption study of the samples, a red shift of optical band edge and a narrowing of the optical band gap are observed when vanadium concentration is increased. The observed non-zero magnetization and coercive field determined from magnetic hysteresis loops indicate the exchange and anisotropy effects developed in nanoparticles of ZnO:V. EPR measurements provide substantial evidence for the presence of defect sites.     

A mathematical model of the identification of the magnetic field of a flowmeter

The construction of a mathematical model of the magnetic field in the measurement channel of an electromagnetic flowmeter by an identification method is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 55–58, October, 2006.     

Preparation and characterization of temperature-responsive magnetic composite particles for multi-modal cancer therapy

The temperature-responsive magnetic composite particles were synthesized by emulsion-free polymerization of N-isopropylacrylamide (NIPAAm) and acrylamide (Am) in the presence of oleic acid-modified Fe₃O₄ nanoparticles. The magnetic properties and heat generation ability of the composite particles were characterized. Furthermore, temperature and alternating magnetic field (AMF) triggered drug release behaviors of vitamin B₁₂-loaded composite particles were also examined. It was found that composite particles enabled drug release to be controlled through temperature changes in the neighborhood of lower critical solution temperature. Continuous application of AMF resulted in an accelerated release of the loaded drug. On the other hand, intermittent AMF application to the composite particles resulted in an “on–off”, stepwise release pattern. Longer release duration and larger overall release could be achieved by intermittent application of AMF as compared to continuous magnetic field. Such composite particles may be used for magnetic drug targeting followed by simultaneous hyperthermia and drug release.     

Effect of composition on the crystallization and magnetic properties of Fe–Co–Si–B–Nb amorphous alloys

The crystallization behavior and magnetic properties of Fe₆₂Co₁₀Si_15−x B_18−y Nb_{(x + y)−5} amorphous alloys with x = 0–5 and y = 0–5 were examined. Primary crystallization temperature of Fe₆₂Co₁₀Si_15−x B₁₃Nb _x and Fe₆₂Co₁₀Si₁₀B_18−y Nb _y alloys increased with the addition of Nb. The primary and secondary crystallization temperatures were well separated when the Nb content is above 4 at%. The alloys with 15–18 at% B showed a distinct supercooled region. The Nb addition decreased the Curie temperature as well as room temperature saturation magnetization. The glassy-type Fe₆₂Co₁₀Si₁₀B₁₈ alloy exhibited good soft magnetic properties as well as a supercooled liquid region of 39 K. The finding of the glassy-type Fe-based alloy without Nb element exhibiting high Bs above 1.4 T is promising for future use as a soft magnetic glass material.     

Effects of Co, Mo, and Ni on magnetic properties in 3Si–0.1Sn–0.08Sb alloyed non-oriented electrical steels

With the addition of Co, Mo and Ni to high-alloyed non-oriented electrical steels with 3Si–0.1Sn–0.08Sb, Ni increased grain size more than Co and Mo. A very low level of core loss (W _15/50 = 2.2 W/kg) and high magnetic induction (B ₅₀ = 1.7 T) were obtained in the Ni added steel. However, Co and Mo deteriorated the magnetic properties substantially. With respect to the texture effect on magnetic properties, core loss decreased and magnetic induction increased proportionally to texture factor (ratio of the sum of cube and Goss texture to γ fiber), while correlations of anisotropies of core loss and magnetic induction to the texture factor appeared parabolic.     

Optically pumped quantum magnetometer employing two components of magnetic moment precession signal

The new scheme of a combined quantum magnetometric device is proposed that represents a fast M _X magnetometer, in which the phase of M _X signal detection is corrected with respect to the maximum of the variable component of the atomic magnetic moment. The device combines a high response speed (τ ≤ 0.1 s) with high precision, which is determined by the resolving power of the quantum M _X magnetometer for a time of an order of 100 s. The reproducibility of field measurements is on a level of 2–3 pT.