Showing papers on "Saturation (magnetic) published in 1996"

A model of the behaviour of magnetorheological materials

Abstract: Magnetorheological materials are a class of smart materials whose rheological properties may be rapidly varied by application of a magnetic field These materials typically consist of micron-sized ferrous particles dispersed in a fluid or an elastomer A quasi-static, one-dimensional model is developed that examines the mechanical and magnetic properties of magnetorheological materials This model attempts to account for magnetic non-linearities and saturation by establishing a mechanism by which magnetic flux density is distributed within the composite material Experimental evidence of the viscoelastic behaviour and magnetic properties of magnetorheological fluids and elastomers suggests that the assumptions made in the model development are reasonable It is shown that the model is semi-empirical in that it must be fit to the experimental data by adjusting a parameter that accounts for unmodelled magnetic interactions

Method and apparatus for improved fingerprinting and authenticating various magnetic media

Abstract: A method and apparatus is disclosed for determining the remanent noise in a magnetic medium by, for example, DC saturation of a region thereof and measurement of the remaining DC magnetization. A conventional magnetic recording transducer may be used to determine the remanent noise. Upon determination, the remanent noise may then be digitized and recorded on the same magnetic medium to thereby "fingerprint" the magnetic medium. This "fingerprint" may then be later used to verify and authenticate the magnetic medium as being an original. The magnetic medium may be of a type adapted to record information magnetically or, even more broadly, any magnetic surface or substance that can be sensed through its magnetic field. In such manner, any magnetic medium, or any object having an associated magnetic medium, may be "fingerprinted" including credit cards, computer program diskettes, magneto-optic discs, videotapes, cassette tapes, bank checks, stock certificates, etc.

Position encoder using saturable reactor interacting with magnetic fields varying with time and with position

Abstract: A position encoder is provided for indicating the relative position between first and second relatively movable members. One of the members carries a multi-pole magnetic scale which generates a magnetic field whose magnitude and direction vary with position and the other member carries at least one sense conductor. A saturable magnetic element is located in the positionally varying magnetic field of the magnetic scale and an excitation winding is provided which, when energized, generates a magnetic filed which interacts with the positionally varying magnetic field to cause different portions of the saturable magnetic element to saturate and desaturate at different times. The arrangement of the sense conductor is such that as the magnetic element is driven into and out of saturation, it outputs a signal which is indicative of the position of the magnetic scale relative to the sense conductor.

A study on the coercivity and the magnetic anisotropy of the lithium ferrite nanocrystallite

Abstract: Lithium ferrite nanocrystallites ranging from several nanometres to several hundreds of nanometres in size have been prepared by the polyethylene glycol gel method. These nanocrystallites were identified as pure lithium ferrite by x-ray diffraction analysis. Their magnetization and de-magnetization were measured by using a vibrating sample magnetometer at different temperatures. The specific saturation magnetization and the coercivities change with the diameter of these nanocrystallites and with temperature. The effective magnetic anisotropy constants of these samples were deduced by using the law of approach to saturation. It is found that the value of a lithium ferrite nanocrystallite of diameter 9.1 nm is about ten times greater than the magnetocrystalline anisotropy constant of bulk lithium ferrite. The coercivities of these nanocrystallites at different temperatures were calculated by using the mixed coercivity model. The calculated coercivity results are consistent with the experimental ones.

Quantum oscillations of properties in magnetic multilayers (invited)

Abstract: An oscillatory interlayer exchange coupling observed in many sandwich and multilayer films can be understood as an interference effect of electron waves partially reflected at each interface with spin dependent reflection coefficients. Consequently, we might expect all magnetic properties in some way related to the density of states to oscillate as a function of the magnetic and nonmagnetic layer thickness. In order to experimentally test this concept we have measured different magnetic properties of Ni/Au multilayer films prepared by magnetron sputtering on glass substrates. The Ni thickness was kept constant at tNi=(7.3±0.5) A while the Au layer thickness was varied between 4 A and 80 A. The films had a coherent fcc structure with (111) texture. The saturation field and the remanence oscillate as a function of tAu with a period which agrees well with a theoretical value calculated from the bulk Fermi surface of Au and proves that indeed an oscillatory exchange coupling is present. The Curie temperature ...

Complex permeability of demagnetized microwave ferrites near and above gyromagnetic resonance

Abstract: A wide variety of microwave ferrite phase-shifting materials have been measured in the demagnetized state. The relative magnetic permeability and loss factor were determined near and above natural gyromagnetic resonance using H/sub 011/ cylindrical dielectric ring resonators. These low-loss dielectric sleeves were dimensioned for accurate magnetic property measurements of single ferrite rod samples at logarithmically sampled resonant frequencies from 2 GHz to 25 GHz. Permeability and magnetic loss factor are computed from the measured resonant frequencies and Q factors of these resonators, with and without the ferrite sample, using exact eigenvalue equations. Generally, the real part of the complex magnetic permeability increases with decreasing saturation magnetization, while the magnetic loss factor increases nonlinearly with increasing saturation. Schloemann's theoretical model for the real part of initial permeability of a cylindrically symmetric domain configuration in the completely demagnetized state shows excellent agreement with measured data when 2/spl pi//spl gamma//spl mu//sub s///spl omega/<0.75. The data allow design optimization of circulators and dual-mode and polarization-insensitive phasers, which are widely used in antenna array systems.

Macroparticle filtering of high-current vacuum arc plasmas

Abstract: The transport of vacuum arc plasmas through a 90/spl deg/ curved magnetic macroparticle filter was investigated using a high-current pulsed arc source with a carbon cathode. The peak arc current was in the kiloampere range, exceeding considerably the level of what has been reported in the literature. The main question investigated was whether magnetic macroparticle filters could be scaled up while maintaining the transport efficiency of small filters. In front of the cathode, we found that arc current dependent total ion saturation currents were in the range from 10% to 23% of the arc current. The best relative transmission was 25% (time integrated output/time integrated input) at a duct wall bias of 12.5 V and at an axial magnetic field of about 100 mT. The measured relative transmission of the used high-current arrangement is comparable to what has been observed with other low-current filters. The absolute measurable ion saturation currents at the filter exit reached 70 A at an arc current of about 1000 A.

Magnetic moment (saturation) measurements on hardmetals

Abstract: This note summarises the background to the use of appropriate units for the measurement of magnetic moment (saturation) in hardmetals. It also discusses the methods used for correlating composition/structure with magnetic properties and indicates the theoretical ranges likely to be obtained in typical industrial products. It includes comparative data obtained on two different measurement systems on both hardmetals and synthetic Co, Co-Ni and Ni alloys containing W and C in solution.

Saturation effects in Z-scan measurements

Abstract: We investigate the behavior of the Z-scan technique in the case where the phase of the electric field departs from a Gaussian due to the saturation of the optical nonlinearity. The usual Gaussian decomposition theoretical approach cannot describe experimental results obtained with well-characterized chromium-doped saturable absorbers: ruby and alexandrite. This aim can be accomplished by extending the theory based on the Hankel transformation of the electric field through the inclusion of the phase saturation. As in the case of Kerr media, the nonlinear refractive index can be obtained from the measurement of the transmittance difference between peak and valley.

Metal-in-gap thin film magnetic head employing Ni45 Fe55

Abstract: The present invention provides a novel high magnetic moment material for the pole pieces as well as a metal-in-gap configuration for the pole tips of either an inductive magnetic head only or the inductive portion of a MR head. The novel material is Ni45 Fe55. In the MIG configuration each pole piece of the inductive head or the inductive head portion of a MR head has a combination of layers, each combination of layers including a first layer of high magnetic moment material Ni45 Fe55 adjacent to a transducing gap and a second layer of low magnetic moment material such as Permalloy (Ni81 Fe19) further away from the gap. Since both layers are made of NiFe all the desirable properties of this type of material can be employed as well as simplifying its construction with similar plating baths. The saturation of the first layers is 50 to 60 percent higher than the saturation of the second layers. The present invention avoids effects of magnetostriction in spite of the high magnetic moment of the first layers. By appropriately selecting the thickness ratio of the second layer with respect to the first layer the magnetostriction of the laminated structure can be reduced substantially to zero. When this thickness ratio is in the order of five to nine the magnetostriction is reduced to, or slightly below, zero. If the inductive head is employed for write functions only then the second pole tip or both pole tips can be constructed of the high moment Ni45 Fe55 material without any thickness ratio or MIG configuration constraints.

Amorphous and nanocrystalline glass-covered wires

Abstract: The invention refers to amorphous and nanocrystalline magnetic glass-covered wires. The wires consist of a metallic amorphous or nanocrystalline core with diameters by the order of 10−6 m, having compositions based on transition metal-metalloids and other additional metals and a glass cover, having a thickness of the wall by the same order of magnitude. The wires present high or medium saturation inducation, positive, negative or nearly zero magnetostriction and values of the coercive field and of the magnetic permeability in function of the requested applications in a field of electronics and electrotechnics to achieve sensors, transducers, inductive coils, trnasformers, magnetic shields, devices working on the basis of the correlation between the magnetic properties of the metallic core and the optical properties of the glass cover.

Highly precise non-contact instrumentation for magnetic measurement of mechanical stress in low-carbon steel wires

Abstract: The magnetoelastic properties of steel wires are used for measuring a mechanical load in tension. A microcomputer-controlled measuring instrument was designed. The dependence of magnetic behaviour on a previous state is eliminated by the suggested method of commutated measurement of amplitude permeability from saturation to the demagnetizing state. It was observed that the change of permeability with tension was linear during technical saturation of the specimen: low-carbon steel wire used in building industry. Temperature influenced the permeability curve and was found to be positive. The effect decreased with magnetizing field, but it increased under mechanical loading. The coefficient of relative change of permeability with both tension and temperature was compared. The resolution and the reproducibility of the method is described. The dispersion of magnetic properties of specimens has been shown to be less than 1.5% in the determination of resulting stress. Because of the internal stress of specimen evaluation this method allows one to measure the tension of loaded wire, especially in civil engineering applications.

Multilayer thin-film for magnetoresistive device

Abstract: A multilayer thin-film structure comprises at least one layered structure formed by depositing a nonmagnetic layer, a first ferromagnetic layer of a ferromagnetic metal or alloy having a positive saturation magnetostriction constant, a nonmagnetic layer and a ferromagnetic layer of a ferromagnetic metal or alloy having a negative saturation magnetostriction constant in that order, and a uniaxial stress is induced in the multilayer thin-film structure. The multilayer thin-film structure for magnetoresistive devices, comprises the magnetic layers which could not have been used for forming the prior art structures and having similar compositions which could not have been used for forming the prior art structure, has an MR ratio in the range of 10 to 20%, does not need the use of antiferromagnetic materials unsatisfactory in corrosion resistance and environment resistance, does not require the turning of a magnetic field when forming the thin films and does not require expensive manufacturing systems.

Characterization of magnetic materials by Mössbauer spectroscopy

Abstract: Since its discovery the Mossbauer effect has been a powerful probe of iron in magnetic materials and, together with neutron scattering and magnetic resonance, complements measurements of magnetic susceptibility and magnetization. The magnetic hyperfine splitting of the spectrum gives a measure of the magnetic moment on the iron atoms, and the line intensities enable the orientation of the magnetic moments to be determined. By applying external magnetic fields the local susceptibility of the iron atoms in paramagnets can be determined, and in magnetically ordered crystals magnetic phase changes may be induced and may be used to measure the magnetic anisotropy. In the early days this was used to determine the magnetic structure of crystalline ferromagnets, ferrimagnets and antiferromagnets. More modern applications include the study of amorphous and disordered crystalline materials (speromagnets, spin glasses, cluster glasses), incommensurate spin structures, fine particle magnets (superparamagnets and superferromagnets), magnetic multilayers, high flux density permanent magnet alloys (e.g. ) and high- superconductors.

Observation of perpendicular anisotropy in granular magnetic solids

Abstract: Granular Co‐Ag materials with low Co contents exhibit giant magnetoresistance and single‐domain magnetic properties. In this paper, we discuss unusual hysteresis behavior that we have observed in Co‐rich samples, where the magnetization is approximately linear with the applied field up to saturation, and the coercivity and remnant magnetization are both nearly zero. We attribute this unusual behavior to a perpendicular anisotropy that depends on the nanostructure in the phase‐segregated materials. These results are corroborated by magnetic domain imaging using scanning electron microscopy with polarization analysis.

Sensitivity and spatial resolution for electron-spin-resonance detection by magnetic resonance force microscopy

Abstract: The signal intensity of electron spin resonance in magnetic resonance force microscopy (MRFM) experiments employing periodic saturation of the electron spin magnetization is determined by four parameters: the rf field H1, the modulation level of the bias field Hm, the spin relaxation time tau1, and the magnetic size R([partial-derivative]H/[partial-derivative]z) of the sample. Calculations of the MRFM spectra obtained from a 2,2-diphenyl-1-picrylhydrazyl particle have been performed for various conditions. The results are compared with experimental data and excellent agreement is found. The systematic variation of the signal intensity as a function of H1 and Hm provides a powerful tool to characterize the MRFM apparatus.

Analysis of stability in two-mode laser systems

Abstract: Stability in two-mode laser systems is analyzed by considering both the gain saturation and the absorption saturation. The analysis shows that the two-mode laser systems could exhibit new types of stability other than previously predicted and have at most triple stable steady states. The influences of the saturation coefficients on the stability are studied. The cross saturation of the gain and that of the saturable absorber are found to have an opposite influence on the stability. Analysis also shows that an increasing ratio of the self-saturation coefficient of the saturable absorber to that of the gain favors the new types of stability, including the tristability.

Soft magnetic thin film, and magnetic head and magnetic recording device using the same

Abstract: Corrosion resistance of a magnetic film composed mainly of Fe is maintained while keeping its magnetic properties. A magnetic head having a magnetic core is formed in part of the magnetic thin film, which contains not only an alloy of Fe-metalloid series but also (Al, Ru) or (Al, Rh) and which is thermally treated at a constant temperature to develop the soft magnetic properties. The deterioration of the saturation magnetization and the soft magnetic properties is suppressed by adding (Al, Ru) or (Al, Rh) together. The magnetic film has a high saturation magnetization and excellent soft magnetic properties and is excellent in corrosion resistance and hardness.