Mössbauer study of the Ni–Zn ferrite system

1970 ◽  
Vol 48 (4) ◽  
pp. 381-396 ◽  
Author(s):  
J. M. Daniels ◽  
A. Rosencwaig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Full Range ◽  
Zinc Content ◽  
Zero Magnetic Field ◽  
Nickel Zinc ◽  
Zn Ferrite ◽  
Superparamagnetic Clusters ◽  
Ferrite System ◽  
Nuclear Magnetic

Mössbauer spectra of 57Fe in the nickel–zinc ferrite system (ZnO)x(NiO)1−xFe2O3 have been obtained, at room temperature and at 77 °K, in zero magnetic field and also in a longitudinal magnetic field of 13.5 kG, covering the full range of zinc content. The dependence of the isomer shifts, line widths, quadrupole interactions, and nuclear magnetic fields of 57Fe3+ ions in both tetrahedral and octahedral sites has been determined. The principal results of this study are (a) the confirmation of the determination of the nuclear magnetic fields by Abe et al. using NMR, and the extension of these measurements to higher zinc concentrations, (b) an indication that the hypotheses of paramagnetic centers, proposed by Gilleo, and superparamagnetic clusters, proposed by Ishikawa, are not applicable to the nickel–zinc ferrites, (c) evidence of canted spin structures, first proposed by Yafet and Kittel, (d) various effects of chemical disorder in the nickel-zinc ferrites, and (e) an observation of the effect on the Mössbauer spectrum of relaxation in a magnetically ordered iron system.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

ELECTRON AND HOLE EFFECTIVE g FACTORS IN InAs/GaSb QUANTUM WELLS

2003 ◽  
Vol 02 (06) ◽  
pp. 437-444 ◽  
Author(s):  
A. ZAKHAROVA ◽  
S. T. YEN ◽  
K. A. CHAO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Quantum Wells ◽  
Landau Level ◽  
Heavy Hole ◽  
Strong Dependence ◽  
Zero Magnetic Field ◽  
Electron Level ◽  
Hole Level ◽  
G Factors

We investigate the Landau level structures and the electron and hole effective g factors in InAs / GaSb quantum wells under electric and quantizing magnetic fields perpendicular to interfaces. In these structures, the lowest electron level in InAs can be below the highest heavy-hole level in GaSb at zero magnetic field B. Thus the electron and hole levels anticross with the increasing magnetic field and the strong dependence of the Landau level structures as well as g factors on B is obtained. We have found that the voltage across the structure and the lattice-mismatched strain also produce the essential changes in the Landau level structures as well as the electron and hole g factors.

scholarly journals A valley valve and electron beam splitter

Science ◽  
2018 ◽  
Vol 362 (6419) ◽  
pp. 1149-1152 ◽  
Author(s):  
Jing Li ◽  
Rui-Xing Zhang ◽  
Zhenxi Yin ◽  
Jianxiao Zhang ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Beam Splitter ◽  
Transportation Network ◽  
Full Range ◽  
Coherent Beam ◽  
Zero Magnetic Field ◽  
Physical Mechanisms ◽  
Current Transmission ◽  
Two Dimensional Materials

Developing alternative paradigms of electronics beyond silicon technology requires the exploration of fundamentally new physical mechanisms, such as the valley-specific phenomena in hexagonal two-dimensional materials. We realize ballistic valley Hall kink states in bilayer graphene and demonstrate gate-controlled current transmission in a four-kink router device. The operations of a waveguide, a valve, and a tunable electron beam splitter are demonstrated. The valley valve exploits the valley-momentum locking of the kink states and reaches an on/off ratio of 8 at zero magnetic field. A magnetic field enables a full-range tunable coherent beam splitter. These results pave a path to building a scalable, coherent quantum transportation network based on the kink states.

scholarly journals Non-local terahertz photoconductivity in the topological phase of Hg1−xCdxTe

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. S. Kazakov ◽  
A. V. Galeeva ◽  
A. I. Artamkin ◽  
A. V. Ikonnikov ◽  
L. I. Ryabova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Laser Pulses ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Topological Phase ◽  
Non Local ◽  
Dark Signal ◽  
The Magnetic Field

AbstractWe report on observation of strong non-local photoconducitivity induced by terahertz laser pulses in non-zero magnetic field in heterostructures based on Hg1−xCdxTe films being in the topological phase. While the zero-field non-local photoconductivity is negligible, it is strongly enhanced in magnetic fields ~ 0.05 T resulting in appearance of an edge photocurrent that exceeds the respective dark signal by orders of magnitude. This photocurrent is chiral, and the chirality changes every time the magnetic field or the electric bias is reversed. Appearance of the non-local terahertz photoconductivity is attributed to features of the interface between the topological film and the trivial buffer.

scholarly journals SPECIFIC HEAT OF Mg11B2 IN MAGNETIC FIELDS: TWO ENERGY GAPS IN THE SUPERCONDUCTING STATE

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3180-3183
Author(s):  
R. A. FISHER ◽  
F. BOUQUET ◽  
N. E. PHILLIPS ◽  
D. G. HINKS ◽  
J. D. JORGENSEN
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Normal State ◽  
Energy Gap ◽  
Zero Magnetic Field ◽  
Energy Gaps ◽  
State Electron ◽  
Electron Contribution ◽  
Semi Empirical

We present specific-heat measurements on Mg 11 B 2 in magnetic fields to 9 T. The anomaly at Tc is rapidly broadened and attenuated in fields, as expected for an anisotropic, randomly oriented superconductor. At low temperature there is a strongly field-dependent feature that shows the existence of a second energy gap. The Sommerfeld constant, γ, increases rapidly and non-linearly with magnetic field, which cannot be accounted for by anisotropy. It approaches γn = 2.6 mJ K -2 mol -1, the coefficient of the normal-state electron contribution, asymptotically for fields greater than 5 T. In zero magnetic field the data can be fitted with a phenomenological two-gap model, a generalization of a semi-empirical model for single-gap superconductors. Both of the gaps close at the same Tc; one is larger and one smaller than the BCS weak coupling limit, in the ratio ~ 4:1, and each accounts for ~ 50% of the normal-state electron density of states. The parameters characterizing the fit agree well with those from theory and are in approximate agreement with some spectroscopic measurements.

MÖSSBAUER EFFECT STUDIES ON LITHIUM FERRITE SUBSTITUTED WITH CHROMIUM AND ANTIMONY

2003 ◽  
Vol 17 (02) ◽  
pp. 67-73 ◽  
Author(s):  
RADHAPIYARI LAISHRAM ◽  
CHANDRA PRAKASH ◽  
SUMITRA PHANJOUBAM ◽  
H. N. K. SARMA
Keyword(s):  
Magnetic Field ◽  
Quadrupole Splitting ◽  
Cation Distribution ◽  
Room Temperature ◽  
Hyperfine Interactions ◽  
Lithium Ferrite ◽  
Mossbauer Effect ◽  
Chromium Level ◽  
Ferrite System ◽  
Nuclear Magnetic

The effect of Cr 3+ concentration on the various hyperfine interactions for the ferrite system Li 0.5+t Cr x Sb t Fe 2.5-2t-x O 4, 0.0 ≤ x ≤ 1.0, x in steps of 0.2 and t = 0.1, have been studied at room temperature using Mössbauer spectroscopy. The isomershift and the quadrupole splitting are almost negligibly influenced by the change in chromium level. The internal nuclear magnetic field, as determined from the Mössbauer spectra and the linewidth are also studied with the variation of composition. The results have been explained on the basis of various models and a cation distribution has been worked out.

scholarly journals Fabrication and Characterisation of Magnetorheological Shear Thickening Fluids

2020 ◽  
Vol 7 ◽  
Author(s):  
Vladimir Sokolovski ◽  
Tongfei Tian ◽  
Jie Ding ◽  
Weihua Li
Keyword(s):  
Magnetic Field ◽  
Shear Rate ◽  
Magnetic Fields ◽  
Applied Magnetic Field ◽  
Iron Concentration ◽  
Shear Thickening ◽  
Zero Magnetic Field ◽  
Iron Particles ◽  
Shear Thickening Fluid ◽  
Iron Concentrations

In this article, a magnetorheological shear thickening fluid (MRSTF) was fabricated based on magnetorheological (MR) material and shear thickening fluid (STF). The STF was firstly fabricated as the liquid phase, and carbonyl iron particles were then mixed with the prefabricated STF to synthesise a series of MRSTFs with various iron concentrations. Then, a rheometer was used to measure their viscosities by varying the shear rate under various magnetic fields. Both static and dynamic tests were conducted to study the rheology of MRSTFs under different magnetic fields. The tested results revealed that the MRSTF showed shear thickening under zero magnetic field and MR effect with increasing applied magnetic field. It was also noted that the viscosity of the MRSTFs can be controlled by both shear rate and the applied magnetic field. The concentration of iron particles played an important role in the MRSTFs’ rheological properties. The MRSTFs with higher iron particle concentrations revealed lower shear thickening effects but higher MR effects, which means the MRSTF with higher iron concentration can be treated as an effective MR fluid. Meanwhile, the MRSTF with low iron concentration displays good shear thickening effect under weak magnetic field. To summarise the behavior of MRSTFs with various iron concentrations and under different magnetic fields, three regions were proposed to provide guidelines to design MRSTFs and assist in their applications.

scholarly journals Dynamical simulations of magnetically channeled line-driven stellar winds

2003 ◽  
Vol 212 ◽  
pp. 247-248
Author(s):  
Asif ud-Doula ◽  
Stanley P. Owocki
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Magnetic Fields ◽  
Full Range ◽  
Flow Speed ◽  
Magnetic Equator ◽  
Field Energy ◽  
Kinetic Energy Density ◽  
X Rays ◽  
Full Account

We present numerical magnetohydrodynamic simulations of the effect of stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, the simulations here take full account of the dynamical competition between field and flow, and thus apply to a full range of magnetic field strength, and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless, ‘wind magnetic confinement parameter’, η* = B2eqR2*/Mv∞, which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind. For weak confinement η* ≤ 1, the field is fully opened by the wind outflow, but nonetheless for confinements as small as η* = 1/10 can have a significant back-influence in enhancing the density and reducing the flow speed near the magnetic equator. For stronger confinement η* > 1, the magnetic field remains closed over a limited range of latitude and height about the equatorial surface, but eventually is opened into a nearly radial configuration at large radii. Within closed loops, the flow is channeled toward loop tops into shock collisions that are strong enough to produce hard X-rays, with the stagnated material then pulled by gravity back onto the star in quite complex and variable inflow patterns. Within open field flow, the equatorial channeling leads to oblique shocks that are again strong enough to produce X-rays, and also lead to a thin, dense, slowly outflowing ‘disk’ at the magnetic equator. The polar flow is characterized by a faster-than-radial expansion that is more gradual than anticipated in previous 1d flow-tube analyses, and leads to a much more modest increase in terminal speed (< 30%), consistent with observational constraints. Overall, the results here provide a dynamical groundwork for interpreting many types of observations, e.g., UV line-profile variability; red-shifted absorption or emission features; enhanced density-squared emission; and X-ray emission, that might be associated with perturbation of hot-star winds by surface magnetic fields.

Absorption Component of the Magnetic Susceptibility in Superconducting YBa2Cu3O7

1987 ◽  
Vol 99 ◽  
Author(s):  
R. Durny ◽  
S. Ducharme ◽  
J. Hautala ◽  
O. G. Symko ◽  
P. C. Taylor ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Magnetic Fields ◽  
Characteristic Temperature ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Dc Voltage ◽  
Absorption Component ◽  
Field Dependent ◽  
Absorption Measurements

ABSTRACTMicrowave absorption measurements from 20 to 80 K in magnetic fields up to 12 kG are reported. Below a certain characteristic temperature T* = 80 ± 2 K < Tc the absorption in magnetic-field-cooled samples is smaller and broader in comparison to the zero-field-cooled samples. The incident microwave radiation induces a dc voltage across the sample which is also magnetic field dependent and peaks at zero magnetic field.

scholarly journals MAGNETOCALORIC EFFECT AND HEAT CAPACITY OF MAGNETIC FLUIDS

2020 ◽  
Vol 63 (5) ◽  
pp. 12-18
Author(s):  
Viktor V. Korolev ◽  
Anna G. Ramazanova ◽  
Olga V. Balmasova ◽  
Matvey S. Gruzdev
Keyword(s):  
Magnetic Field ◽  
Heat Capacity ◽  
Magnetic Fields ◽  
Specific Heat ◽  
Magnetocaloric Effect ◽  
Specific Heat Capacity ◽  
Magnetic Fluids ◽  
Zero Magnetic Field ◽  
Extreme Character ◽  
Temperature Dependences

The magnetic fluids based on magnetite nanoparticles were synthesized using mixed surfactants (oleic acid/alkenyl succinic anhydride) dispersed in different carrier media (polyethylsiloxane and dialkyldiphenyl). The physicochemical properties of magnetic fluids (density, viscosity, saturation magnetization, magnetic phase concentration, magnetic core size) were determined. Magnetic fluids are stable in a wide temperature range. All the samples of the magnetic fluids exhibit typical superparamagnetic behavior. The magnetocaloric effect and the specific heat capacity of the magnetic fluids were first direct determined at 288–350 K in a magnetic field of 0–1.0 T. The field dependences of the magnetocaloric effect have a classic linear form. The temperature dependences of the magnetocaloric effect of magnetic fluids in magnetic fields have an extreme character. Thermodynamic parameters of magnetic fluids (magnetization namely enthalpy/entropy change) were determined. The specific heat capacity of magnetic fluid samples in a zero magnetic field was obtained at different temperatures (at 278–350 K) on a differential scanning calorimeter and on the original microcalorimeter. The temperature dependences of the heat capacity of magnetic fluids in magnetic fields have an extreme character. It was established that the difference in heat capacity values obtained in and without the magnetic field is within the experimental error. The extreme character of the heat capacity is reflected in the magnetocaloric effect temperature dependences.

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