Showing papers on "Saturation (magnetic) published in 1979"

Effect of gain saturation on injection laser switching

Abstract: Gain saturation is introduced into the laser‐coupled rate equations. Numerical and analytical solutions show considerable damping of relaxation oscillations for small amounts of saturation.

A Theory of Nearly Ferromagnetic Semiconductors

Abstract: Magnetic and thermal properties of nearly ferromagnetic semiconductors are investigated on the basis of our spin fluctuation theory of itinerant electron systems. The couplings among the spin fluctuation modes of general amplitudes are taken into account by using a functional integral formalism within a local approximation, introducing a simple model for the local density of states. The negative mode-mode coupling at low temperatures and the saturation of the amplitude of local spin fluctuations at high temperatures seem to explain peculiar magnetic and thermal properties reported on FeSi.

Micromagnetism in Amorphous Alloys

Abstract: Brown's micromagnetic equations are derived for the case of dipolar and "magnetocrystalline" fluctuations in amorphous ferromagnetic alloys. The influence of these fluctuations and the effects of internal stresses of so-called quasi-dislocation dipoles on the law of approach to ferromagnetic saturation is discussed in detail. It is shown that intrinsic fluctuations of magnetic properties lead to a 1/\sqrt{H} -term in the high-field range whereas internal stresses give rise to 1/H - and 1/H^{2} -power laws. A quantitative analysis of experimental results indicates that internal stresses dominate the effects of intrinsic fluctuations considerably.

Mössbauer effect and magnetic studies of secondary iron oxides in soils

Abstract: Summary Simple, rapid and non-destructive measurements of magnetic properties (magnetic susceptibility, saturation isothermal remanent magnetization and coercivity of isothermal remanence) coupled with more time consuming and sophisticated analyses such as thermomagnetic and Mossbauer effect studies, provide a basis for identifying forms of iron oxide present in the soil. At two of the sites studied, Caldy Hill, Merseyside, and Llyn Bychan, N. Wales, the secondary ferrimagnetic oxide formed in surface soil as a result of recent forest fires is shown to be non-stoichiometric magnetite approximating to the formula Fe2. 904. No evidence for the presence of maghemite was found in any of the soil samples from these sites or in soils from the Annecy region of S.E. France.

Further Investigations on Magnetic Properties of Co(S x Se 1− x ) 2 , (0≤ x ≤1)

Abstract: Further investigations, succeeding to the works of J. Phys. Soc. Japan 26 (1969) 631 and 29 (1970) 323, on the magnetic properties of Co(S x Se 1- x ) 2 in the whole concentration ranges (0≤ x ≤1) were performed by means of high magnetic field, electrical resistivity and low temperature X-ray diffraction measurements. The first kind magnetic transition was found in the ferromagnetic phase except CoS 2 . The metamagnetic behaviors were observed in the ferromagnetic (0.89< x <1.0) as well as paramagnetic ( x <0.89) phases. The saturation moment per Co atom was obtained to be 0.855 µ B for CoS 2 and it decreased gradually with increasing Se content. The electrical resistivity in low temperatures showed a T 2 -dependence. It was concluded that the itinerant electron model base on the spin fluctuation theory is more adequate than models based on a localized spin scheme.

Effect of silicon addition on the magnetic properties of Fe‐B‐C amorphous alloys

Abstract: The effect of compositions on the saturation magnetization, Curie temperature and coercivity of the amorphous Fe‐B‐C alloys has been investigated in a wide range of B and C concentration. The C addition less than 7 at.% to Fe‐B alloys increases the saturation magnetization at the room temperature. The highest magnetization, σs = 178 emu/g, with the lowest coercive force, Hc = 22 mOe, has been obtained for the Fe81B12‐C7 alloy annealed in a magnetic field. In order to obtain further desirable soft magnetic properties, the effect of the addition of other elements to the Fe‐B‐C based amorphous alloys has been studied. The best properties are σs (R.T.) = 176 emu/g, Hc = 8 mOe, Br/B100 = 0.88 and the core loss W/f = 8×10−4 watt. sec/kg (at 12.5 kG and 50 Hz) for the magnetically annealed Fe81B13C2Si4 alloy. As a result, it has been found that the addition of Si is most effective in reducing the coercive force and core loss as well as an improving the magnetic stability during aging at low temperatures.

Magnetic, transport, and thermal properties of ferromagnetic EuB6

Abstract: Magnetic measurements on Al‐flux grown EuB6 crystals show that this material orders ferromagnetically with a transition temperature Tc=13.7 K. The effective moment derived from paramagnetic susceptibility measurements gives μeff=7.76 μB, and the saturation magnetization extrapolated to 0 K is within 10% of the theoretical value of 7 μB expected for Eu+2. The magnetic order, however, cannot be that of a simple colinear ferromagnet because the magnetic specific heat in zero applied magnetic field shows a broad maximum centered about 9 K rather than the expected λ‐like anomaly at 13.7 K. Finally, transport measurements suggest that EuB6 is an intrinsic semimental.

Magnetization of Co(S x Se 1− x ) 2 under High Magnetic Field Up to 500 kOe

Abstract: Proceeding the previous paper (J. Phys. Soc. Jpn. 46 (1979) 1474) the high field magnetization process of Co(S x Se 1- x ) 2 system for 0.70 ≤ x ≤1.00 has been investigated by means of pulse fields up to 500 kOe at fixed temperatures. The metamagnetic behaviors were observed and the phase diagram between the transition field and temperature was given. The saturation moment seemed to disappear at x ≃0.6.

Soft magnetic properties of metallic glasses—recent developments

Abstract: Two major aspects of the soft magnetic properties of metallic glasses, i.e., high magnetic permeability and high saturation induction, are discussed. Recent development in the area of high permeability materials is centered around the zero‐magnetostriction Co‐rich metallic glasses having Si and B as metalloids. The heat treated materials studied thus far show low‐field magnetic properties comparable or superior to those of commercial supermalloy. A typical example includes an effective permeability at l kHz exceeding 50,000. Attractive high saturation induction metallic glasses are found in the series Fe82B18−xSix. Typical dc results for field‐annealed samples of this glass with x=8 are Hc=0.03 Oe, Br=12 kG and μ (20) =8,000. Core loss under sine flux conditions at 60 Hz is 0.24 watts/kg at 16 kG. This value is nearly five times lower than that of the widely used power transformer material grade M‐4 Si/Fe (1.3 watts/kg) and well below that of Fe‐B glass. The stability against crystallization of Fe82B10Si8 is higher than that of Fe80B20.

Saturation Magnetostriction and Volume Magnetostriction of Fe-Ni-Co Amorphous Ribbons(Metallurgy)

Abstract: The saturation magnetostriction and the volume magnetostriction in amorphous ribbons of Fe-Ni-Co system were measured from 77K to room temperature, by a three terminal capacitance method. The ternary diagram were given of the saturation magnetostriction and volume magnetostriction in (Fe x Co y Ni 1-x-y ) 78 Si 8 B 14 system. It was found that the largest saturation magnetostriction constant is 36×10-6for the composition Fe 65 Co 13 Si 8 B 14 at room temperature. The temperature dependence of the saturation magnetostriction and the volume magnetostriction in Fe-Ni-Co system were not a simple function of the temperature. The maximum value of volume magnetostriction δω/δH was observed for Fe 78 Si 8 B 14 to be 24×10-10Oe-1at room temperature.

Sputtered multilayer films for digital magnetic recording

Abstract: Layered films of cobalt over chromium deposited by dc sputtering onto heated substrates exhibit magnetic properties suitable for digital saturation recording. A cobalt layer of a few tens of nanometers thickness deposited over a chromium layer of several hundred nanometers has coercivity between 1100 and 300 Oe and remanence-thickness product between 0.014 and 0.07 G.cm with squareness between 0.7 and 0.95. Additional alternate layers of chromium and cobalt can increase remanent flux without reduction of coercivity. Magnetic properties can be tailored to specific needs by varying layer thicknesses.

Fe‐B‐C amorphous alloys with room‐temperature saturation induction over 17.5 kG

Abstract: Amorphous alloys of Fe86B14−xCx (5⩽x⩽7) were found to have room‐temperature saturation induction approaching 18 kG after appropriate heat treatment. The alloys possess excellent soft‐magnetic properties with the ac loss less than 0.5 W/kg at 17 kG and 60 Hz. It is expected that the application of these alloys to power transformers will produce very large savings of energy.

The magnetic properties and stability of a ferrofluid containing Fe3O4 particles

Abstract: A study has been made of a commercial 200 gauss ferrofluid + consisting of Fe 3 O 4 particles of ≈75 A diameter in a diester carrier. The stability of the fluid was monitored during the course of investigation by observing the real part of the susceptibility function x ′( f ) of the fluid using an L-C resonance circuit. The size distribution of the particles was calculated from magnetic measurements, from magneto-optical (birefringence) data and from electron micrographs. The median diameters obtained from birefringence and microscope data are found to be equal (100 A) but larger than that obtained from magnetic measurements (75 A). The saturation magnetisation has been measured between 4.2 K and 300 K, which covers the change from liquid to solid phase of the carrier. The interpretation of magnetisation measurements is consistent with the presence of particle associations, probably in the form of chains. This is reflected in an increase both in coercivity and remanence with increasing field. From the variation of remanence with temperature in zero field a value of 2.7 x 10 5 erg/cm 3 is obtained for the anisotropy constant K .

Structure of magnetic amorphous alloys studied by energy dispersive X‐ray diffraction

Abstract: Recent advances in the technique of energy dispersive X‐ray diffraction (EDXD) have made it possible to study the atomic structure of amorphous solids with greater accuracy. This paper reviews the techniques involved in the successful utilization of the EDXD method. Also the structural relaxation of amorphous alloys which was recently clearly resolved by the EDXD technique is discussed, as well as the structure of the Fe‐B‐C amorphous alloys, which were found to have the highest room‐temperature saturation induction among the Fe based amorphous alloys.

Saturation magnetostriction and its annealing behavior of Fe100−xBx and Co100−xBx amorphous alloys

Abstract: Boron content dependences of saturation magnetostriction λs at room temperature in as‐quenched and annealed Fe100−xBx (15?x?25) and Co100−xBx (19?x?24) amorphous alloys were measured. The value of λs in Fe‐B alloys peaks at x=20, while λs in Co‐B alloys decreases with increasing boron content. For two series of alloys, nearly quadratic relations between magnetostriction and saturation magnetization σs were found. After 1 hour annealing at 250° C, both λs and σs in Fe‐B and Co‐B alloys increased. The increase in λs of Fe‐B alloys was within 8%, and was larger than that of Co‐B alloys. For annealed Fe‐B and Co‐B alloys, quadratic relations were also observed, which suggests that the increase in magnetostriction arises from the increase in magnetization.

High-efficiency free-electron laser

Abstract: The electronic conversion efficiency of a free-electron laser using an intense relativistic electron beam in a rippled magnetic field as its active medium is limited mainly by the destruction of the coherent slow space-charge wave through particle trapping and the depletion of the available beam energy. It is shown that by proper stepping up of the ripple magnetic field strength prior to electrostatic wave saturation, the efficiency can be substantially increased along with some bandwidth improvement and shortening of the device length.

Micromagnetics of curling configurations in magnetically soft cylinders

Abstract: The response of an ideally soft magnetic cylinder is calculated by approximating magnetostatic interactions while taking into account the exchange energy of curling patterns with point singularities. Detailed calculations of the magnetic surface charge distribution of paramagnetic materials are used as a guide in parameterizing an approximate charge distribution suitable for applying the Ritz method to the micromagnetic problem of ferromagnetic materials without anisotropy or magnetostriction. Numerical results are given for a cylinder with L/D=1 for fields below saturation illustrating how remanence and coercivity depend on the ratio of the exchange length A/M2o to sample dimensions. The role of point singularities in remanence, coercivity, nucleation and irreversibility is outlined.

Temperature dependence of magnetization of amorphous Fe‐B‐C alloys

Abstract: Temperature and magnetic field dependence of amorphous Fe‐B‐C alloys obtained by splat cooling were measured and compared with those of Fe‐B alloys. It was found that the effect of replacing boron by carbon in Fe86B14 alloy was to change significantly the temperature dependence of magnetization in the direction of increasing spin‐wave stiffness, and to reduce the saturation susceptibility. The high value of room temperature saturation induction found in Fe‐B‐C alloy is therefore attributed to a change in the temperature dependence of magnetization, rather than to change in the magnetic moment at 0 K.

Saturation effects in transient stimulated Raman scattering

Abstract: The evolution of the Stokes pulse generated by transient stimulated Raman scattering is considered for the case of ultrashort incident pulses. A model is proposed which allows for the effects of either depletion of the laser pump pulse or saturation of the non-linear medium.

Strain-induced anisotropy in amorphous alloys and the effect of toroid diameter on magnetic properties

Abstract: The magnetic properties of toroids wound from amorphous Fe-B-Si alloy ribbons has been examined as a function of toroid diameter and for ribbon widths from 0.1 cm to 2.5 cm. For the smallest ribbon widths, as the diameter decreased from 20 cm to 1 cm, the magnetic coercivity before annealing increased by a factor of ten and the remanence-to-saturation ratio decreased from ∼0.7 to less than 0.4. After annealing in a field, the coercivity still increased with decreasing diameter by a factor of ten and the ratio of remanence-to-saturation dropped from ∼0.9 to ∼0.45. The losses after annealing similarly increased by a factor of ten and the permeability decreased. These lowest losses, obtained from large diameter toroids, are below those of the best commercial alloys (Supermalloy, 4-79 Mo-Permalloy, and Deltamax) and are well below any previously reported amorphous alloy. Toroids made from wider tapes, 1 cm and 2.5 cm in width, of similar Fe-B-Si compositions, were found to have properties essentially independent of their diameter. This difference in behavior between narrow and wide tapes can be understood on the basis of their differences in strain distribution. The approach to saturation after annealing was found to improve with increasing nickel in the amorphous alloys Fe x Ni 80-x B 20 . This is attributed to the decrease in magnetostriction which decreased the anisotropy arising from strain induced ordering. This assumption was confirmed when it was noted that the approach to saturation became much easier when the inner half of the thickness of an annealed toroid tape was etched away removing material with annealed in strain induced ordering. The impairment in properties of toroids with decrease in diameter is thus attributed to the increase in the strain induced ordering anisotropy. In order to eliminate the effect of toroid diameter on the magnetic properties we wound the toroids with sufficient tension to overcome the compressive forces developed in the tapes due to their radius of curvature. Rather than improving the properties, winding with tension significantly deteriorated the properties. This is believed to be due to the radial forces introduced by the winding tension. The effects of tensional loads and of compressive loads on the surface of straight ribbons were studied and confirmed the results obtained in the toroids.

Magnetic properties of zero magnetostrictive amorphous Fe‐Co‐Si‐B alloys

Abstract: The metalloid content dependence of zero magnetostrictive composition of an amorphous (FexCo1−x)100−y(Si0.4B0.6)y alloy in an as‐quenched state is experimentally determined. The iron content (x) of the zero magnetostrictive composition was found to decrease with an increase in the metalloid content (y). The Curie temperature and saturation magnetization decrease with an increase in the metalloid content, while crystallization temperature increases. With an increase in the saturation magnetization of the present alloys the coercive force increases as Hc∝M3s.

Power loss measurements in amorphous alloys

Abstract: A method for measuring magnetic losses in amorphous alloys is described.It is based on the use of a lock‐in amplifier to determine the magnitude and phase of the fundamental component of magnetic field H when the induction B is forced to vary sinusoidally with time. The method is applicable to very small samples in the form of straight lengths or of toroids, and gives satisfactory results at flux levels approaching saturation if the flux wave form can be held sinusoidal. Data are presented on several amorphous alloy compositions as a function of peak induction and of frequency. Annealing effects have been investigated.

Magnetic properties of amorphous ribbon

Abstract: The magnetic properties of transition-metal amorphous alloys are discussed, with emphasis on methods to increase the value of the saturation induction at room temperature, and on the factors that control the low-field magnetic properties that are important in most engineering applications.

Spin excitations in amorphous transition‐metal boron glasses

Abstract: Magnetic inelastic neutron scattering studies have been performed on ribbon specimens of amorphous Fe83B16.5Si0.5 and Fe20Ni60B19P1. The samples were prepared from isotopically enriched B to reduce the neutron absorption. The Curie temperatures for the two materials are 613 K and 410 K respectively, and the room temperature saturation magnetizations 4πMs are 16.0 kG and 5.1 kG. In the Fe20Ni60B19P1 specimen, well‐defined spin waves were observed at room temperature for neutron wave‐vector transfers in the range q=0.06 A−1 to q=0.20 A−1. After correcting for instrumental resolution, the data obeyed a quadratic dispersion law with spin stiffness D=80 meV‐A2. Spin waves in the Fe83B16.5Si0.5 amorphous alloy exhibited a D=125 meV‐A2 consistent with the higher Tc of this alloy.

Magnetization of a two-component Stoner-Wohlfarth particle

Abstract: The free energy of an arbitrary two-component Stoner-Wohlfarth particle is derived and general criteria for stable states of magnetization are established. Hysteretic properties of coaxial prolate spheroids composed of γ-Fe 2 O 3 coated iron particles are calculated numerically and the specific extension to epitaxial cobalt ferrite γ-Fe 2 O 3 particles amongst other two-component systems is indicated.

Method of finishing ferromagnetic articles by ferromagnetic abrasive powders in magnetic field

Abstract: A method of finishing of ferromagnetic articles by means of ferromagnetic abrasive powders in a magnetic field formed by electromagnets of opposite polarities, wherein a ferromagnetic abrasive powder and a ferromagnetic article are first magnetized to the saturation induction, then the ferromagnetic article is placed into an external magnetic field so as to form a working gap between said ferromagnetic article and the poles of electromagnets, the total magnetic field produced therein being the sum of the external magnetic field and the field of said magnetized ferromagnetic articles. The ferromagnetic powder is finally introduced into the working gap to form a cutting "brush" and the article and the external magnetic field are brought into relative motion.