Ferromagnetic Elements Research Articles

A major problem in strabismus and its possible solution.

One of the challenges in strabismus is to guarantee stability of the surgical corrections. Re-surgeries are often required even after careful diagnosis, planning, and execution. Several factors contribute to this undesired outcome and the existing management strategies are ineffective. The present alternative is to compensate for their consequences. Ocular rotations are evoked by muscular contractions and relaxations (active forces). During eye movement, periocular tissues are stretched, storing part of the kinetic energy, which may be posteriorly recovered (passive forces), whereas the remaining part of the energy is lost via friction and inelastic deformations (dissipative forces). A method for measuring the forces that cause post-surgery eye drift has not been reported. However, this may be indirectly determined as a function of the respective mechanical variables. The estimated ratio between the kinetic energies of a post-surgery eye drift and a normal pursuit eye movement is ~10(-15). Theoretically, it can be expected that the addition of continuously acting forces of such magnitudes to the oculomotor system might prevent the undesired post-surgery eye movement. Several methods for increasing the restraining, dissipative forces to ocular rotations may be conceived. One method is to increase the friction to ocular movements, as for instance, by periocular injection of viscous substances. Another possibility is to use the forces of a magnetic field, which may stabilize the eye in a desired position without avoiding the rotations caused by greater muscular forces acting on it. It has been demonstrated that these forces neutralize the nystagmic movements, whose intensities of mechanical variables are much higher than those of a post-surgery eye drift. Some models of application of this technique are then discussed. Small magnets fixed to the orbit and metallic ferromagnetic elements fixed to the sclera to cover a suitable extension appears to be the best method for providing starting and sliding friction to the oculomotor system. Weak magnetic fields do not cause ocular ill effects. Additionally, the magnetic field may be confined to the elements of the circuit and may not leak. However, the magnetic materials may interfere with magnetic resonance image (MRI) examinations.

Material-inherent Data Storage Using Magnetic Magnesium-cobalt Alloys

Abstract Magnetic magnesium alloys have an inherent load-sensitive behavior. These alloys are manufactured by casting of magnesium alloyed with the ferromagnetic element cobalt. In this context, the magnetoelastic effect can be used in order to measure mechanical loads during the component's service by means of a harmonic analysis of eddy current signals. The utilization of magnetic magnesium as a load-sensitive material in order to measure mechanical loads in structural components has been demonstrated in previous works. Another application is the magnetic labeling of the alloy. In this context the magnetic remanence is a significant characteristic value. A data track can be written directly on the material's surface by means of an electromagnetic write head. The track may contain relevant component-specific information like serial numbers, manufacture date and expected lifetime. This information can be read out by means of a sensor utilizing the giant magnetoresistive (GMR) effect. The magnetic labeling in relation to the manufactured alloy and the cooling rate during the casting process is examined in this work. The magnetic labeling of three alloys based on magnesium, cobalt and zinc has been investigated; these are MgCo4 and MgCo4Zn2. The alloys’ mechanical as well as their magnetic properties are significantly influenced by these additional alloying elements. In order to investigate the alloys’ suitability for magnetic data storage the quality of the data tracks read out using a GMR sensor are compared depending on the alloy composition. The magnetic labeling is influenced by the microstructure regarding solidification and cooling rate. A conical casting geometry with different solidification rates in top and bottom sections was used for an examination of the relationship between the density of the magnetic phases and the quality of the magnetic labeling.

MRI compatible Nb–Ta–Zr alloys used for vascular stents: Optimization for mechanical properties

With the increased usage of magnetic resonance imaging (MRI) as a diagnostic tool in clinic, the currently-used metals for vascular stents, such as 316L stainless steel (SS), Co–Cr alloys and Ni–Ti alloys, are challenged by their unsatisfactory MRI compatibility, due to their constituents containing ferromagnetic elements. To provide more MRI compatible vascular stents, the Nb–xTa–2Zr (30≤x≤70) series alloys were selected in the current work. Several key properties of these alloys were optimized in terms of stent requirements, including magnetic susceptibility, elastic modulus and tensile properties. In the as-cast state, a single-phase solid solution with bcc structure was formed in the alloys. The volume magnetic susceptibility (χv) and Young's modulus (E) of the alloys scaled linearly with the Ta content. Increasing the Ta content gave rise to the decreased χv and the increased E, together with the elevated yield strength but less-changed elongation. From multiple requirements for the stents, the Nb–60Ta–2Zr alloy exhibits an optimal properties, including the χv of about 3% of the 316L SS, the E of 142GPa superior to pure niobium, high mass density of 12.03g/cm3 favored to the X-ray visibility, yield strength of ~330MPa comparable to the 316L SS and a elongation of ~24%. These remarkable advantages make it quite promising as a new candidate of stent metals.

Magnetic transition in 122 pnictides XFe2As2 (X=Ca, Sr) probed by hyperfine interaction of 66Ga

Employing the time differential perturbed angular distribution (TDPAD) method we have studied the temperature dependence of the magnetic hyperfine field, Bhf for 66Ga in 122 type pnictides, XFe2As2 (X = Ca and Sr). The saturation hyperfine field, Bhf(0) of Ga in Ca(Sr)Fe2As2 have been observed to be 16.2kG and 22kG respectively. Scaled by the hyperfine field of 66Ga in ferromagnetic elements Fe, Co and Ni, our Bhf(0) data indicate small local moments on Fe, consistent with itinerant type magnetism of these materials. The observed temperature dependence of the hyperfine field data suggests second order type magnetic phase transition with a critical exponent β≈0.22(3) indicating quasi-two dimensional magnetic ordering, possibly due to canting of Fe moments out of the ab plane.

High-coercivity ultrafine-grained anisotropic Nd–Fe–B magnets processed by hot deformation and the Nd–Cu grain boundary diffusion process

The grain boundary diffusion process using an Nd70Cu30 eutectic alloy has been applied to hot-deformed anisotropic Nd–Fe–B magnets, resulting in a substantial enhancement of coercivity, from 1.5 T to 2.3 T, at the expense of remanence. Scanning electron microscopy showed that the areal fraction of an Nd-rich intergranular phase increased from 10% to 37%. The intergranular phase of the hot-deformed magnet initially contained ∼55 at.% ferromagnetic element, while it diminished to an undetectable level after the process. Microscale eutectic solidification of Nd/NdCu as well as a fine lamellae structure of Nd70(Co,Cu)30/Nd were observed in the intergranular phase. Micromagnetic simulations indicated that the reduction of the magnetization in the intergranular phases leads to the enhancement of coercivity in agreement with the experimental observation.

Enhancement of coercivity of hot-deformed Nd–Fe–B anisotropic magnet by low-temperature grain boundary diffusion of Nd60Dy20Cu20 eutectic alloy

The coercivity of a hot-deformed Nd–Fe–B magnet was enhanced from 1.6 to 2.6 T by a low-temperature grain boundary diffusion process using a Nd60Dy20Cu20 near-eutectic alloy. The alloy melt infiltrates into the magnet through grain boundaries at the processing temperature of 650 °C. The composition of ferromagnetic elements in the intergranular phase parallel to the c-planes decreases substantially and thin Dy-rich shell surrounds the Nd2Fe14B phase grains after the diffusion process, which explains the large enhancement in coercivity.

Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling

In this paper, we demonstrate that in Ta/MgO/IrMn tunneling junctions, containing no ferromagnetic elements, distinct metastable resistance states can be set by field cooling the devices from above the Néel temperature (TN) along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields, in-plane or out-of-plane. Well below TN, these metastable states are insensitive to magnetic fields up to 2 T, thus constituting robust memory states. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferromagnetic elements and stores the information in an antiferromagnetic active layer.

Negative magnetoresistance in organic ionic semiconductor:TTFCOONH3Ph

TTFCOONH3Ph is a recently synthesized open-shell ionic semiconductor, the electronic state of which differs from that of typical organic closed-shell semiconductors. Magnetotransport properties were examined using a single-crystal sample, and found to exhibit small negative magnetoresistance (∼0.2%) for 9T at room temperature (rt). The magnetization curve verifies the existence of a ferromagnetic (35%) and a paramagnetic (65%) component at rt, which is very similar to that of diluted magnetic semiconductors, despite the absence of any ferromagnetic metal elements. Electron spin resonance reveals weak localization of paramagnetic molecular spins, and moreover, ferromagnetic resonance confirms the existence of magnetically ordered spins in addition to the paramagnetic ones. The origin of the spin-polarized transport is discussed.

Estimation of error fields from ferromagnetic parts in ITER

Error fields in tokamaks are small departures from the exact axisymmetry of the ideal magnetic field configuration. Their reduction below a threshold value by the error field correction coils is essential since sufficiently large static error fields lead to discharge disruption.The error fields are originated not only by magnets fabrication and installation tolerances, by the joints and by the busbars, but also by the presence of ferromagnetic elements. It was shown that superconducting joints, feeders and busbars play a secondary effect; however in order to estimate of the importance of each possible error field source, rough evaluations can be very useful because it can provide an order of magnitude of the correspondent effect and, therefore, a ranking in the request for in depth analysis. The paper proposes a two steps procedure. The first step aims to get the approximate magnetization state of ferromagnetic parts; the second aims to estimate the full 3D error field over the whole volume using equivalent sources for magnetic masses and taking advantage from well assessed approximate closed form expressions, well suited for the far distance effects.

Single-domain shape anisotropy in near-macroscopic Ni80Fe20 thin-film rectangles

Shape anisotropy provides a simple mechanism to adjust the local bias field in patterned structures. It is well known that for ellipsoidal particles <1 μm in size, a quasi-single domain state can be realized with uniform anisotropy field. For larger patterned ferromagnetic thin-film elements, domain formation is thought to limit the effectiveness of shape anisotropy. In our work, we show that very soft lithographically patterned Ni80Fe20 films with control of induced magnetic anisotropy can exhibit shape anisotropy fields in agreement with single-domain models, for both hysteresis loop measurements at low field and ferromagnetic resonance measurements at high field. We show the superiority of the fluxmetric form over the magnetometric form of anisotropy estimate for thin films with control dimensions from 10 μm to 150 μm and in-plane aspect ratios above 10.

SiO2-supported ferromagnetic catalysts for hydrogen generation from alkaline NaBH4 (sodium borohydride) solution

Ferromagnetic elements Fe, Ni and Co were immobilized on the porous SiO2 to catalyze the hydrogen generation from aqueous alkaline NaBH4 (sodium borohydride). The porous SiO2 was prepared by silica-surfactant self-assembly and the ferromagnetic catalyst was prepared by chemical reduction. The ferromagnetic catalysts were characterized using TG/DTA (Thermogravimetry/differential thermal analysis), BET, XRD (X-ray powder diffraction), ESEM/EDS (environmental scanning electron microscope/energy dispersive spectroscopy), XPS (x-ray photoelectron spectroscopy) and VSM (vibration sample magnetometer) measurements. The surface area of porous SiO2 was affected by the molecular weight of surfactant. The relative catalytic activities in the generation of hydrogen from alkaline NaBH4 solution follow the order Co/SiO2 > Ni/SiO2 > Fe/SiO2. The rates of hydrogen generation using Co/SiO2, Ni/SiO2 and Fe/SiO2 catalysts in 20 ml of 5 wt.% NaBH4 solution at 313 K were 8701, 307 and 130 ml min−1 g−1-metal, respectively. It is found that the degree of metal-oxidation and crystal structure affected the catalytic activity. The hydrogen generation of NaBH4 in alkaline solution increased with increasing cobalt loading, of which the activation energy was 59 ± 2 kJ mol−1.

Presence of stable carbon centric free radicals and ferromagnetic elements in the antennae and the wings of nocturnal silk moth: A magnetic nanostructure for magneto sensing

This work addresses an interesting, interdisciplinary problem of nature- “the mechanism by which animal senses the earth's magnetic field and navigate”. Currently there are two existing theories trying to explain, “How the animal senses the magnetic field of earth”. One theory is based on the presence of biogenic magnetic materials in the body of the animals. Such magnetic materials which are present inside the body, orients itself according to the earth's weak magnetic field and convey the information to the nervous system to develop the navigational map. The second theory is based on a light dependent photochemical reaction. A photochemical reaction leads to the generation of radical pairs, which helps in sensing the weak magnetic field of the earth. In this work, we are proposing a new model of magnetoreception. Unlike the existing radical pair system of magnetoreception, where a light-dependent reaction is essential to generate free radicals, here we show the presence of a large pool of stable carbon-centric free radicals in the nano-domains of the antennae and the wings of silk moth. This stable pool of carbon-centric free radicals is intrinsic in the nano-domains of these anatomical structures and responds to weak magnetic fields similar to that of Earth's (50 μT) even in the absence of light. Hence we are proposing that nocturnal animals in their navigation could utilize such a light independent mechanism. We further observed the presence of ferromagnetic elements (Fe, Ni, Co, Mn) in these structures. In conclusion, we have discussed how carbon centric free radicals along with other ferromagnetic components present in the antennae and the wings of the nocturnal silk moth, might help them to avoid the bats.

Radiation stability of nanoscale ferromagnetic memory elements

Computer-simulation data on the radiation-induced processes in nanoscale ferromagnetic clusters exposed to charged and neutral particles are presented. An instability-zone radius that characterizes the material’s radiation stability is estimated for an atom knocked out from a lattice site. Temperature and thermoelastic effects in the clusters and their influence on the defect structure of the irradiated objects are considered.

Influence of cobalt on the properties of load-sensitive magnesium alloys.

In this study, magnesium is alloyed with varying amounts of the ferromagnetic alloying element cobalt in order to obtain lightweight load-sensitive materials with sensory properties which allow an online-monitoring of mechanical forces applied to components made from Mg-Co alloys. An optimized casting process with the use of extruded Mg-Co powder rods is utilized which enables the production of magnetic magnesium alloys with a reproducible Co concentration. The efficiency of the casting process is confirmed by SEM analyses. Microstructures and Co-rich precipitations of various Mg-Co alloys are investigated by means of EDS and XRD analyses. The Mg-Co alloys' mechanical strengths are determined by tensile tests. Magnetic properties of the Mg-Co sensor alloys depending on the cobalt content and the acting mechanical load are measured utilizing the harmonic analysis of eddy-current signals. Within the scope of this work, the influence of the element cobalt on magnesium is investigated in detail and an optimal cobalt concentration is defined based on the performed examinations.

Publisher's Note: Ferromagnetic elements by epitaxial growth: A density functional prediction [Phys. Rev. B85, 024407 (2012)

Publisher's Note: Ferromagnetic elements by epitaxial growth: A density functional prediction [Phys. Rev. B85, 024407 (2012)

Competing interactions at the interface between ferromagnetic oxides revealed by spin-polarized neutron reflectometry

We have investigated the magnetization profiles in superlattices composed of the two ferromagnets La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ and SrRuO${}_{3}$ using spin-polarized neutron reflectometry. In combination with magnetometry, the neutron data indicate a noncollinear spin configuration where orientation of the Ru moments changes from in plane at the interface to out of plane deep inside the SrRuO${}_{3}$ layers. The spin structure originates in a competition between antiferromagnetic exchange interactions of Mn and Ru moments across the interface, and the magnetocrystalline anisotropy of the Ru moments, and it is closely related to the ``exchange spring'' structures previously observed in multilayers composed of ferromagnetic elements and alloys.

Development of Simple-Structure Magnetic Membrane Actuator for Synthetic Jet Application

In this work, a magnetic membrane actuator that involves simple fabrication process and low cost is developed based on electroplating technique, and its dynamic performance is examined. The magnetic actuator consists of an element of soft ferromagnetic material embedded in PDMS circular membrane. It is driven by attracting the soft ferromagnetic element using external magnet that is attached on a shaft of electrical motor. When the shaft is rotated, the magnet will move back and forth towards the membrane. In this study, the nickel element as a soft ferromagnetic material is designed as a simple circular disk with four straight arms, and it is fabricated into three different thicknesses, i.e. 49±3, 70±7 and 100±6 μm, while PDMS thickness is fixed at 280±33 µm. The dynamic performances of 2-cm membrane actuators are examined using a capacitive sensor in the actuating frequency range of 40-240 Hz. The experimental results show that there are two motion patterns, i.e. small and strong oscillations, where the transition frequency is approximately at 100 Hz. In addition, with the increment of nickel element’s thickness, gain and peak frequency, where gain peaks occur, increase while peak-to-peak amplitude decreases.

A Low-Field Magnetically Affected Reaction Yield (MARY) Spectrometer with Spectral Fluorescence Resolution

A novel spectrometer for low-field studies in magnetically affected reaction yield (MARY) spectroscopy with fluorescence detection is described. The spectrometer is based on a yoke-free magnetic system containing no ferromagnetic elements, uses X-ray or optical excitation, and includes a monochromator to analyze the spectral composition of luminescence. Using the new setup, the effect of transversal residual magnetic field on zero field MARY line is illustrated, formation of exciplexes under X-irradiation in a naphthalene/N,N-dimethylaniline solution in alkane is demonstrated, a magnetic field effect on the emission spectrum is shown in field-cycling mode, and modulated MARY spectra in the exciplex and the intrinsic luminophor bands are compared to show that magnetic field sensitivity here is provided at the stage of the recombining radical ion pair, while exciplex formation only transforms the luminescence properties.

Method of synthesis of axially symmetric magnetic field sources with ferromagnetic elements

У роботі запропоновано метод ефективного проведення оптимального параметричного синтезу аксіально-симетричних джерел магнітного поля з феромагнітними елементами. Задача синтезу вирішується з урахуванням лінійних та нелінійних магнітних властивостей феромагнетику.

Multidipoles model of ship's magnetic field

Ships made of ferromagnetic metals interfere with Earth's magnetic field in their surrounding. The disturbance of the magnetic field makes possible localization and even identification of the ship, which could determine a threat to the ship. The measurement of the magnetic field around the ship enables to determine its magnetic signature. The paper presents a multidipoles model of the ship magnetic field, which allows to determine parameters of the ship magnetic signature. The ship built of ferromagnetic elements disrupts Earth's magneticfield in its surrounding. This disor- der is defined as the ship's own magnetic field. This field contains constant and induced components(2). Thecharacteristicfeaturesofthe ship'sownmagneticfield are called magnetic signature(2,4). Magnetic signature allows to specify the distribution of the magnetic field around the ship. Magnetic signature can be determined using numerical modeling or the measurement method (3). The numerical modeling of the ship's magnetic field with commercial software has limited capacity, because the thickness of ship's metal sheets is very small in comparison with its size (3). That makes it necessary to use a dense grid of a huge number of finite elements. Additionally, the existence of the ship's permanent magnetism complicates the numerical modeling. The paper proposes a new computational method for measuring anddeterminingthe magneticsignatureofa ship, whichis basedon measurementof themagneticfieldin selected points in space around the ship, and then on creating a model of the multidipoles magnetic field of the ship. In the multidipoles model of magneticfield, a certain numberof magnetic dipoles distributed in space inside the ship are assumed. Subsequently, the spatial distribution, the values and directions of the magnetic dipole moments are found using the optimization method. The multidipoles model allows to reconstruct the ship's multidipoles magnetic field distribution in the ship's surrounding (2,4). 2. The own ship's magnetic field Measurements of the ship magnetic flux density are carried out on the measuring range. In practice, the magnetic field distribution is measured along a certain trajectory around the ship at one depth. Due to the passive protection of the ship, knowledge of the distribution of the magnetic field across the lower half-spaceinthevicinity oftheshipisrequired. Thereforeoneneedsaneffectivemethodfordetermining