Showing papers on "Saturation (magnetic) published in 1989"

Saturation of the light‐induced defect density in hydrogenated amorphous silicon

Abstract: We report new experimental results on the saturation of the light‐induced defect density in hydrogenated (and fluorinated) amorphous silicon. The films were illuminated near room temperature up to 5000 h with bandpass filtered red light at a carrier generation rate G of 5×1020 cm−3 s−1, or up to 20 h with Kr+ laser light (λ=647.1 nm) at G=3×1022 cm−3 s−1. The bulk defect densities Ns saturate in both cases in the vicinity of 1017 cm−3. The saturation values are almost independent either of G or of temperature in the range from room temperature to about 70 °C. The illumination time to reach saturation is approximately proportional to 1/G2. These results are discussed within the framework of existing models for the light‐induced defects.

Half-metallic ferromagnets. I. Structure and magnetic properties of NiMnSb and related inter-metallic compounds

Abstract: The authors present investigations of the crystal structure the microstructure and the magnetic properties of the inter-metallic compounds XMnSb (X=Pt, Ni, Co, Au, Cu) and PtMnSn. It was found that several of these materials contain precipitates of other phases and/or large atomic disorder, which can be influenced by heat treatment. The magnetic properties show an effective paramagnetic moment which differs from the value corresponding to the saturation moment at 0 K. This effect is attributed to a decrease of the conduction electron spin polarisation at high temperature.

Metamagnetism in La2CuO4

Abstract: PHYSICAL REVIEW B VOLUME 39, NUMBER 7 Metamagnetism MARCH 1989 in LazCuO4 S-W. Cheong, J. D. Thompson, and Z. Fisk Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 19 September 1988) A careful study of the metamagnetic transition in single-crystalline La2Cu04 is presented. From magnetic susceptibility measurements the critical exponent (P) of the weak ferromagnetic state, which terminates at a triple point, has been estimated to be P=0. 5+0. 02, a value consistent with mean-field theory. Furthermore, the pressure dependence of the critical magnetic field for the tran- sition has been examined from magnetoresistance measurements under hydrostatic pressure. The magnetic properties of LazCu04 have been exam- ined in detail, ' particularly in an attempt to under- between magnetism stand any possible interrelationship in La2Cu04- found in La2Cu04 and superconductivity based compounds. An anomaly in the susceptibility' of La2Cu04 suggested the presence of an antiferromagnetic phase trarisition, which has been confirmed by neutron- scattering experiments that find three-dimensional Bragg peaks with unit-cell coupling. The Neel temperature sensitive to the oxygen content. ' ( T~ ) is extremely have also established Neutron-scattering experiments the existence of strong two-dimensional (2D) magnetic correlations even far above T&, in addition, two-magnon Raman scattering experiments show the presence of strong, magnetic intralayer coupling. Furthermore, a field-induced transition, which occurs when a magnetic field is applied perpendicular to the CuO planes at a tern- perature below T&, has been reported. The origin of this metamagnetic, field-induced transition is from the cant- ing of Cu spins out of the CuO planes due to the rotation- al distortion of elongated octahedra of oxygen atoms around the divalent Cu ions. The susceptibility peak or- around T& has been attributed to antiferromagnetic in- dering in the presence of the Dzyaloshinski-Moriya teraction which is allowed by the distorted coordination of oxygen atoms. Since the critical behavior around the Neel tempera- ture has not been explored in detail, and the driving force producing the Neel state has not been established well, we have performed careful measurements of the magnetic around Tz on a crystal susceptibility (g)/magnetization of La2Cu04 which exhibits a very sharp susceptibility peak, indicative of a well-ordered homogeneous sample. Large crystals of LazCu04 (as large as 3 X 3 XO. 3 cm ) were grown from a CuO flux. After quenching from high temperatures, crystals were removed from the CuO flux and annealed in an appropriate gas atmosphere according to the oxygen content desired. We found that proper an- nealing is necessary to ensure a sharp magnetic transition and, furthermore, reduces the temperature-independent in y, as well as supp ress es the low- background temperature Curie-tail frequently observed in less well- ordered samples. We observed the peak temperature ( Tz ) in y as high as 326 K in crystals annealed in a nitro- gen atmosphere. The distinction between T& and T will be discussed herein. The data shown here are representa- tive of crystals annealed in air with T -257 K. Suscepti- bility and magnetization were measured with a Quantum superconducting-quantum-interference-device Design susceptometer capable of magnetic fields to 5 T. The temperature-dependent magnetic susceptibility of a La2Cu04 crystal, measured in 0. 2-T magnetic field ap- plied in the CuO-plane direction (yl ) and in the perpen- dicular direction (yi), is displayed in the left panel of Fig. 1. Even though divalent Cu ions are good Heisenberg ions, because of large spin-orbit coupling and the fact that the ground state is a Kramer's doublet, there is ap- preciable susceptibility anisotropy. gz shows a sharper peak, with T =257+0. 5 K, than y~~ and the full width at half maximum of the peak is — 13 K, indicating good homogeneity of oxygen distribution in the sample. The right panel in Fig. 1 exhibits the magnetic field depen- dence of yi (0. 2 T data are the same as shown in the left panel). A clear difference in the two susceptibility curves is evident. We note that in the case of y~~ there is no field dependence except for a slight depression of T . In Fig. 2, we plot isothermal magnetization curves at various temperatures with the applied field perpendicular the field- to the CuO planes. As reported earlier, induced transition, indicated by the deviation from linear shifts to lower-field M(H) behavior found for T Above T„, M(H) values with increasing temperature. curves are linear with a slight tendency toward saturation at high-field values. However, it is not clear, from data like these, precisely at what temperature the jump in M(H) curves disappears. The inset will be discussed later. The critical fields (H, ), defined from the maximum of ~dM/dH~, as a function of temperature are plotted in the left panel of Fig. 3. The right panel displays the tempera- ture dependence of the jump (M, ) in M (H) curves at the critical field values of M, were determined by the difference at H, between smooth extrapolations of low- field and high-field portions of the M(H) curves. We found from careful analysis'that H, (T) does not extrapo- late smoothly to zero at T =257+0. 5 K and that M, ex- trapolates to zero at T =251.5+0. 5 K. This behavior has been observed in a number of samples that show a ( T, The American Physical Society

The Effect of Resonant Light Pressure in Saturation Spectroscopy

Abstract: We report on line-shape modifications in optical saturation spectroscopy on an atomic gas, which are caused by resonant light pressure: Asymmetries and line shifts occur as a result of the small modification of the atomic velocity distribution that is caused by the spontaneous scattering force of the saturating light field. In addition to a detailed theoretical description, we report on the observation of this phenomenon in atomic Yb vapor. Our measurements clearly show the expected light-pressure-induced modifications of both absorptive and dispersive saturation signals and demonstrate the significance of the phenomenon for high-resolution laser spectroscopy.

Magnetic properties of aerosol synthesized barium ferrite particles

Abstract: Barium ferrite fine particles have been synthesized from ferric nitrate and barium nitrate aqueous solution by an aerosol technique. The as-received particles showed a spin-glass behavior with a history-dependent low-field magnetization below 180 K. An exothermic peak with an initial crystallization temperature of 687 degrees C was found by DSC (differential scanning calorimetry) analysis. Heat treatments above this temperature greatly changed the magnetic properties and morphologies without changing the Ba/Fe atomic ratio, which was 1/12. Heat-treated samples had coercivities and saturation magnetizations as high as 5360 Oe and 70.6 emu/g, respectively. >

Optical and magnetic properties of a nonconjugated conducting polymer

Abstract: The magnetic and optical properties of a nonconjugated conducting polymer (1,4 cis‐polyisoprene) at different doping levels of iodine are discussed in this report. The EPR and static magnetic susceptibility measurements show that cation radical (spin 1/2) species are generated as a consequence of doping. The concentration of the cation radicals increases approximately linearly with the dopant concentration until saturation. The magnetic susceptibility has a Curie‐like temperature dependence as anticipated. The optical measurement of doped samples show two absorption peaks—one at ∼4.27 eV and the other at ∼3.3 eV. The first peak is attributed to the excitation of the cation radicals (comparable to ethylene ions) and the second one is interpreted as due to charge transfer between localized states. These results are fully consistent with the electrical properties and the structure of the system.

Field and concentration dependence of chain formation in magnetic fluids

Abstract: The field and concentration dependence of chain formation in magnetic fluids is investigated. The results show that the chain length increases rapidly with the field and then continues to increase gradually at higher fields approaching saturation. Moreover, the results show that the chain length at a given field is linear with the concentration of the fluid. The correlation between chain formation and some magneto-optic effects is discussed.

Texture and Magnetic Properties

Abstract: The magnetic properties of ferromagnetic materials are closely related to the crystallographic texture, i.e. the orientation distribution of the crystallites, they are, however, not uniquely determined by the texture. Higher order “textural quantities” such as, for instance, orientation correlation functions are additionally needed for a more complete description.The properties in saturation are uniquely determined by the texture. They can be expressed by a fourth—or sixth—order approximation of the texture function which can be obtained by “low resolution” texture measurements.On the other hand, magnetic anisotropy measurements can only provide a low-resolution approximation to the texture function and not the complete function.The distribution of magnetization directions can be described by a “magnetic texture” which can be calculated from pole figures measured by neutron diffraction using the method of superposed pole figures.

Fe-based soft magnetic alloy

Abstract: An Fe-based soft magnetic alloy essentially consisting of an Fe-based alloy including fine crystal grains used for such as a magnetic core. An average size of the fine crystal grains is controlled to 300 Å or less. Each of the fine crystal grains is composed of a body-centered cubic phase at least partially including a super lattice. This alloy has a high saturation flux density and excellent soft magnetic characteristics such as a low iron loss and a high magnetic permeability.

Magnetic and structural investigation of the composition dependence of the local order in amorphous Tb-Fe

Abstract: The properties of ferrimagnetic amorphous Tb-Fe prepared by magnetron cosputtering over a range of composition from 9 to 40 at. % Tb have been extensively examined. No sign of crystallinity is found for any of these samples by transmission electron microscopy or x-ray diffraction. The gross properties such as saturation moment and Curie temperature are well behaved over this entire range. However, the magnetic anisotropy, which is an extremely sensitive probe of local structure, exhibits a relatively abrupt transition at 22 at. % Tb, the magnetic compensation composition. No change in such properties as anisotropy is expected to occur at the magnetic compensation composition, and indeed results to be described below suggest that this coincidence is simply accidental. Deposition parameters are varied in an attempt to understand the unexpected transition in the local structural order.

Nonlinear resonant absorption effects on the design of resonance fluorescence lidars and laser guide stars

Abstract: Saturation effects may significantly reduce the backscattered signal expected for resonance fluorescence lidar systems. Saturation arises when the laser energy density within the layer is large enough to significantly alter the population densities of the atomic states within the layer. These altered state populations lead to nonlinear absorption of the laser energy resulting in reduced rate of fluorescence and increased rate of stimulated emission. The level of saturation is determined by the laser pulse length, pulse energy, beam-width, and linewidth. Analysis reveals that the saturation effects can be characterized by two parameters: the saturation time τs and the rms laser linewidth Δωrms.The saturation time is the characteristic time of stimulated emission and is an indication of the level of saturation. The saturation time depends on pulse energy, pulse length, and beamwidth. The laser linewidth is important since it determines the effective absorption cross section of the atoms and also the percentage of atoms illuminated for an inhomogeneously broadened absorption line. The impact of saturation on lidar design is also examined. Design examples, including lidar systems for atmospheric research and laser guide stars for adaptive imaging applications in astronomy are studied in detail.

Method and apparatus for producing semiconductor layers composed of amorphous silicon-germanium alloys through glow discharge technique, particularly for solar cells

Abstract: A method and apparatus are provided for improving the dangling-bond saturation in amorphous silicon-germanium semiconductor layers. The deposition from the vapor phase of germane, silane, and hydrogen proceeds on the basis of different plasma excitations in the same reactor, that are spatially separated. Capacitive and inductively coupled plasmas are generated at different locations, in such a manner that the two plasmas superimpose in a central substrate region. For increasing the ionization density, the inductively excited plasma has a dc magnetic field for resonance excitation superimposed on it perpendicular to the radio frequency magnetic field. Amorphous silicon-germanium layers containing hydrogen are produced that have a low density of states and are particularly suitable for thin-film tandem solar cells.

Magnetism in very thin films of permalloy measured by spin polarized cascade electrons

Abstract: The spin polarizationP of the low energy cascade electrons excited with a primary unpolarized electron beam is measured with ultrathin films of permalloy (Ni80Fe20) as a function of film thickness, external magnetic field, and temperatureT. Surface adsorbates of small concentrations of less than 10% of a monolayer can change the Curie point and the saturation value ofP 0(T→0) by as much as 30%. The Ta-substrate induces a magnetically dead region in permalloy. Conventional spin wave theory cannot account for the observed smallT-dependence of the magnetizationM. Films on a nonmagnetic substrate are compared to similar films coupled to bulk permalloy over an interface of Ta. TheT-dependence ofM with the coupled films can be explained by spin wave theory. At lowT, the films coupled to the bulk exhibit a faster decrease ofM than the uncoupled films. We propose that this thermal stabilization of the magnetization in very thin ferromagnetic films is due to quenching of the long wavelength spin modes.

Deuterium magnetic resonance and permeability in porous media

Abstract: Deuterium nuclear magnetic resonance relaxation studies were performed on sandstones, carbonates, and synthetic porous samples. The magnetization decay in the rotating frame T1ρ is a stretched exponential in rock samples.The relaxation time in porous media is related to the absolute permeability by the relation k=C(T1ρ)2φ2. We show that T1ρ is proportional to the width of the pore size distribution and the permeability, and is proportional to the water saturation in partially saturated rock. These results provide new methods for estimating absolute permeability and saturation.

Magnetic Properties of Fe-Based Binary Crystalline Alloys Produced by Vapor Quenching

Abstract: Structure and magnetic properties of Fe-M (M=Ti, Zr Hf, Nb or Ta) alloy films produced by rf sputtering haye been investigated in Fe-rich compositional ranges below 10 at%M. These alloy films have a nonequilibrium bcc phase with lattice parameters larger than that of pure Fe. They exhibit high saturation magnetization and soft magnetic properties. In particular, the bcc Fe94Zr6 film annealed at 673 K for 1 h exhibits a saturation magnetization of 2 T and a magnetostriction less than 1×10-6.

Three-dimensional antiferromagnetic ordering in the light rare-earth high-T c superconductor NdBa2Cu3O6.86

Abstract: Powder neutron diffraction investigations performed in the temperature range from 20 mK to 300K prove that the magnetic Nd moments of the superconductor NdBa2Cu3O6.86 withTc=88 K order three-dimensionally (3D) antiferromagnetic belowTN=(551±10) mK. As in similar Gd and Dy compounds the corresponding wave vector isk=[1/2, 1/2, 1/2]. In approximate agreement with crystal field calculations the ordered magnetic moment of Nd amounts at saturation to (1.14±0.06) μB and at 25 mK the magnetic moments are oriented parallel [0,0,1]. The transition to the magnetically ordered state corresponds to the Landau type critical exponent β≈0.5, in contrast to the predominant 2D character of such heavy rare-earth systems. The crystal structure of NdBa2Cu3O6.86 is orthorhombic similar to the one of YBa2Cu3O7−x.

Magnetic susceptibility of some materials used for apparatus construction (at 295 K)

Abstract: The magnetic susceptibility, χ, at 295 K of a wide variety of common laboratory construction materials has been carefully measured. Only materials with well‐characterized compositions are included in the final data. Materials such as Cu alloys and filled epoxies showing ferromagneticlike saturation behavior are listed with the recognition that workers will probably want to use these with great caution in precision experiments where magnetic effects may be a source of error. Susceptibility values are given for over 30 materials for which χ values are not available in the literature and which exhibit χ independent of H.

Zinc-doping of

Abstract: Zinc-doping into (511)A (AI0.6Ga0.4)0.5In0.5P layers using atmospheric metalorganic vapour phase epitaxy is investigated and compared to that into (100) layers. The doping efficiency is an order of magnitude higher for (511)A layers. Saturation in hole concentration begins at around 15×1018cm−3 in (511)A crystals, but at 4×1017cm−3 in (100) crystals.

A new type of fluxgate magnetometer using apparent coercive field strength measurement

Abstract: A novel fluxgate magnetometer is introduced which employs the measurement of the change of the apparent coercive field strength derived from the magnetizing current. The external magnetic field is periodically measured at a frequency which is the same as that of the magnetizing current of the sensor. The magnetometer shows a standard deviation of the relative nonlinearity of less than 0.01% and a resolution of 0.1 nT, and it can measure transient external magnetic fields with a 100-kHz sampling rate. >

Optimization of the efficiency in gyrotron backward‐wave oscillator via a tapered axial magnetic field

Abstract: The efficiency of a gyrotron backward‐wave oscillator (gyro‐BWO) in the presence of a tapered axial guide magnetic field is calculated from a three‐dimensional self‐consistent theory. The saturation efficiency has a low value in the range 10–15% when the external magnetic field is uniform. However, the efficiency can be enhanced to over 30% by a small taper in the magnetic field. Numerical results are shown for operation in the TE11 mode of a cylindrical waveguide.

Magnetization and domain structure of cylinders and spheres in subsaturating fields

Abstract: We explore the magnetization patterns and domain walls which may occur in ferromagnetic cylinders and spheres in a certain range of sizes, placed in a uniform external magnetic field below saturation. The solutions found are field‐free inside the sample. The analysis is explicitly carried out for circular and elliptic cylinders and spheres, and may be extended to general ellipsoids.

A novel method for measurement of the saturation magnetostriction of amorphous ribbons

Abstract: A novel method for measurement of the saturation magnetostriction constant of metallic glass ribbons is described. The magnetostriction constant is calculated from the change of the effective anisotropy field induced by a tensile stress applied to the ribbon. The determination of the effective anisotropy field makes use of the measurement of the biased transverse susceptibility. The new method is applicable to both high and low magnetostrictive metallic glasses and it is especially appropriate for wider ribbons.

Surface crystallization and magnetic properties of iron-based metallic glasses

Abstract: We have studied surface crystallization of amorphous Fe78Si9B13 and its consequences on the magnetic properties. Thin crystalline surface layers on both ribbon sides were induced in various thicknesses by suitably annealing at elevated temperatures. As a consequence an out-of-plane anisotropy K developed in the amorphous bulk; the magnitude of K being proportional to the thickness of the crystallized surface layer. The temperature variation of K was studied from room temperature up to Curie temperature Tc and was predominantly determined by the one of saturation magnetostriction; a further contribution was due to the different thermal expansion of crystallized surface and amorphous bulk. The magnetization in the surface layer, finally, could be separated from that of the bulk by recording magnetization loops around Tc. The experimental results are in good agreement with a recently proposed theory which is based on the calculation of the internal stress distribution generated by the crystallized surface.

Thin film magnetic head with laminated metal and non magnetic film

Abstract: A thin film magnetic head adapted for recording and/or reproducing signals at a frequency of 1 MHz or higher, in which a soft magnetic film having uniaxial magnetic anisotropy is used as a magnetic pole film material and the direction of the magnetic path of the magnetic circuit of the head is arranged to be substantially orthogonal to the axis of easy magnetization, wherein a magnetic pole film constituting the magnetic path is formed as a lamination of at least two, particularly four soft magnetic films, with an intervening nonmagnetic film between the adjacent soft magnetic films, the length W of the magnetic pole film along the direction of the axis of easy magnetization is 30 μm≦W≦300 μm, and the uniaxial magnetic anisotropy constant Ku is Ku≦300 J/m 3 . This provides a relative permeance of at least 1000.