Mössbauer effect study of the internal magnetic field in small iron particles

Surface, catalytic and magnetic properties of small iron particles: III. Nitrogen induced surface reconstruction

Mössbauer investigation of supported Fe and FeNi catalysts: II. Carbides formed Fischer-Tropsch synthesis

Preparation and Characterization of Small Iron Particles Supported on MgO

The retention of an iron foreign body within an eye almost always results in progressive iron deposition throughout the eye, cataract formation, glaucoma, and eventually atrophy of all the intraocular tissues. This condition is known as siderosis bulbi.¹To prevent it, any intraocular iron particle must be removed surgically, if possible, even if the surgery itself may result in loss of the eye. Once siderosis is established, surgery seldom helps.²Furthermore, as in two patients seen at the Wilmer Clinic recently, small iron particles may oxidize to nonmagnetic rust which cannot be localized or surgically extracted. Medical therapy of siderosis has been attempted using galvanic deactivation,³intravenous edetic acid,^4,5and subconjunctival edetic acid or adenosine triphosphate.^6,7Edetic acid (formerly known as edathamil), the principal agent studied, has shown a number of toxic effects in humans receiving chronic systemic therapy.^8,9 In 1960, Bickel et al

The influence of carbonyl iron particles sizes on the properties of magneto-rheological fluids (MRFs) were studied. Different-sized carbonyl iron magnetic particles were prepared by ball milling with different milling times. On this basis, different particle MRF were prepared The off-state viscosity and the shear stress of the above MRFs were characterised and studied by an advanced rotational rheometer system. The test results show that the off-state viscosity and the shear stress of single-particle MRFs were enhanced with increasing average carbonyl iron particle size at a constant magnetic field. The shear stresses of MRFs containing two or three different particle sizes were significantly improved compared with the MRFs containing only a single particle size. At a reasonable level of medium and small size carbonyl iron particle spread throughout the structure of the multiple-particle MRFs, the defects in the chain structure were remedied when a chain reaction occurred, and the mechanical properties of MRFs were enhanced. Meanwhile, increased mass fractions of the small size carbonyl iron particle resulted in a reduction in overall average particle size of MRFs, and the mechanical properties of MRFs were also reduced. The mechanical properties of multiple-particle MRFs were observed to be strongly dependent on the size and mass fraction of the medium and small carbonyl iron particles.

Experimental test of a radiative transfer model of the optical effects of space weathering

Local and quasi-local vibrational modes of Si in Ge: S. C. Shen and M. Cardona. Solid St. Commun.36, 327 (1980)

Design of hourglass nanoantenna for magnetic field enhancement

With a modified conception of the Neel sublattices a molecular field theory is developed for small ferromagnetic particles. They are treated as a system of neighboring shells. These are supposed to consist each of atoms with equal average properties and are coupled to the next neighbors by an (exchange-) interaction. To simplify the numerical calculations the model was further modified by taking together all shells of the interior to form a core. Calculations of the temperature dependence of the spontaneous magnetization and of Curie-temperatures have been done for some particle forms and sizes of the f.c.c., b.c.c. and hexagonal lattices. The results are discussed and compared to experimental data of other authors from small particles of nickel, iron and cobalt.

The fluid dynamics of dampers is investigated for the case where the damping fluid flows through passages in which a magnetic field is applied. This is a specific case of a new and promising field of applications that has emerged through the design of devices that take advantage of some properties of the so-called electrorheological fluids and magnetorheological fluids (ERF and MRF). These fluids are created when a base fluid is seed with very small dielectric or iron particles, so that it reacts to electric or magnetic fields by developing some non-Newtonian characteristics, most prominently a yield stress, viscosity change, and also viscoelasticity. These fluid properties can be controlled through control of the electric or magnetic fields’ strength. In this paper, a typical damping load is modeled and related to the required flow of a MRF inside the damper. To this end the fluid is modeled as a Bingham fluid with time-varying yield-stress. The analysis here developed makes it possible to determine the magnetic field variation necessary in order to achieve a specific displacement of the damper’s piston. The flow equations are analytically solved for any time-history of the dimensionless fluid’s yield-stress. Main results are some simplified relationships that correlate damping load and magnetic field time-variations. These results aim at providing analytical tools that may facilitate dampers’ design.

The "M\"ossbauer" technique was used to measure the internal magnetic fields and isomer shifts of ${\mathrm{Fe}}^{57}$ atoms residing at various sites in the FeSi series. The relative abundances of the various sites present in a given alloy were obtained by measuring the relative intensities of the components in the resolved spectrum of the alloy. Alloys with Si content varying from 0 to \ensuremath{\sim}27 at.% were studied. In the disordered region (10 at.% Si) three different type sites were observed. These corresponded to Fe atoms having 8, 7, and 6 nearest-neighbor Fe atoms. The internal field decreased by $0.08 {H}_{\mathrm{Fe}}$ for each Si nearest neighbor. In the ordered region the alloys try to go into a ${\mathrm{Fe}}_{3}$Al type structure. Sites having 8 through 3 nearest-neighbor iron atoms were observed. For $A$-type sites (4 nearest-neighbor Fe atoms and 4 nearest-neighbor Si atoms at 25 at.% Si), the internal field decreased by $0.14 {H}_{\mathrm{Fe}}$ for each Si nearest neighbor. Over the whole series the isomer shift indicated that there was progressively less electronic charge density at the origin as the number of nearest-neighbor Si atoms increased. A measure of the relative intensities of the various magnetic field components in the spectra of an alloy series is shown to give direct evidence on the type of ordering. No tendency to form intermediate compounds other than ${\mathrm{Fe}}_{3}$Si was observed. An average internal magnetic field for each alloy could be obtained from the data. This average internal field does not vary in the same way as the magnetization on the FeSi series.

A passive DC magnetic concentrator is designed with transformation optics (TO) and realized by meta-materials. The passive DC magnetic concentrator based on space compression transformation can greatly enhance the magnetic field in a free space region and can be used for e.g., improving the sensitivity of magnetic sensors and increasing the efficiency of wireless energy transmission. The magnetic property of the medium obtained by TO is extremely anisotropic. To solve this, we use magnetic metamaterials made of alternated high-permeability ferromagnetic (HPF) materials and high-temperature superconductor (HTS) materials. We optimize our structure by conducting simulations using the finite element method (FEM) and experimentally demonstrate a strong, 4.74-time enhancement of the DC magnetic field by our meta-material magnetic concentrator. We also demonstrate that a simplified structure with only HPF materials working at room temperature can still gives 3.84-time enhancement of the DC magnetic field. The experimental results are in good agreement with the numerical simulations based on FEM.

Mechanical properties of polymer composite materials, containing ferromagnetic small dispersed particles of carbonyl iron that create structures along force lines of the magnetic field have been investigated. In paper the influence of the polymer matrix material and the orientation of ferromagnetic particles inside it on the properties of polymer composites are considered in the regimes of horizontal shear, vertical shear and periodical (sinusoidal) deformation of the samples. Magnetic properties at the change of magnetic field induction B in the range of 0 to 1 T are determined.

The reconstruction of Mercury’s internal magnetic field enables us to take a look into the inner heart of Mercury. In view of the BepiColombo mission, Mercury’s magnetosphere is simulated using a hybrid plasma code and the multipoles of the internal magnetic field are estimated from the virtual spacecraft data using three distinct reconstruction methods: the truncated singular value decomposition, the Tikhonov regularization and Capon’s minimum variance projection. The study shows that a precise determination of Mercury’s internal field beyond the octupole, up to the dotriacontapole is possible and that Capon’s method provides the same high performance as the Tikhonov regularization, which is superior to the performance of the truncated singular value decomposition.

The internal magnetic fields and isomer shifts of ${\mathrm{Fe}}^{57}$ nuclei in a number of iron-rich bcc binary alloy systems were measured by the M\ossbauer technique. The added solute atoms Al, Si, Mn, Cr, or V give structure to the individual lines of the spectra indicating that their effects are quite localized. These line shapes were analyzed by a computer program which interpreted them in terms of the effects of the solute atoms in the first five neighbor shells. It appears justifiable to attribute the observed hyperfine-field shifts in the FeAl series to the spatial variation of the spin polarization of the $4s$ conduction electrons around an Fe atom in pure iron. The observed $4s$ spin-polarization variation with distance had oscillations with a ${k}_{F}\ensuremath{\simeq}(1.0\ensuremath{-}1.2)\ifmmode\times\else\texttimes\fi{}{10}^{8}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ corresponding to 0.4-0.6 electrons/atom in the $4s$ conduction band. These oscillations are compared with those obtained by recent improved calculations of the indirect exchange polarization which take into account the full $k$ dependence of the conduction-electron wave functions. For all the alloy series reported here, internal field shifts at the first and second nearest neighbors decreased the internal field. This indicates that the $4s$ electrons produce an antiferromagnetic contribution to the magnetic coupling in iron. The average internal field of each alloy was also obtained, and for all the alloy series described here this quantity decreases more rapidly than the moment per Fe atom as a function of solute-atom concentration. The isomer shifts due to solute atoms in the first three neighbor shells are also reported.