Showing papers on "Saturation (magnetic) published in 1975"

Magnetic annealing of amorphous alloys

Abstract: Amorphous alloys with nominal composition of Ni 40 Fe 40 P 14 B 6 are shown to respond to annealing in a magnetic field. Coercive forces are reduced by a factor of 10 to 50 during annealing of straight ribbons to values of 0.003 Oe, as low as ever reported for potentially useful materials. Concurrently the ratio of the magnetization in 1 Oe applied field, to saturation, increases from about 0.5 to 0.95. These changes during annealing correlate with measured stress relief changes. It thus appears that most of the strain-magnetostriction contribution to the anisotropy is removed during annealing. Magnetic annealing at temperatures as low as 100°C results in noticeable changes in properties. From measurements transverse to the magneticaliy induced anisotropy axis, the induced anisotropy is calculated to be about 800 ergs/cm3, considerably smaller than obtained in crystalline Ni 50 Fe 50 . This field-induced anisotropy is reversible in direction and magnitude by reheating the sample to its Curie temperature and then cooling in a field. Annealing of 1.5 cm diameter toroids, made from 50 μm thick tapes, increases the initial permeability by more than a factor of 10 and decreases losses by more than a factor of 10. Losses and permeabilities after heat treatment compare favorably to the Permalloys with similar saturation magnetizations.

An analysis for the circular mode of magnetization in short wavelength recording

Abstract: It has been deduced from the analysis of recording demagnetization mechanism in magnetic recording that in short wavelengths the remanent magnetization exhibits a closed-loop structure in the recording medium. In this paper a novel experimental method is presented to confirm the existence of such structure (a circular magnetization mode) and to investigate its mechanism for usual recording medium and heads. The transformation of magnetization from a circular mode to a perpendicular mode is also discussed.

Observation of hole burning and cross relaxation effects in ruby

Abstract: In this paper we report, for the first time, the observation of optical hole burning in a solid, ruby. In addition, we describe experimental results which show that optical saturation of the inhomogeneously broadened ${R}_{1}$ line in ruby at 4.2\ifmmode^\circ\else\textdegree\fi{}K occurs not only for ions in resonance with the saturating radiation but also for ions at frequencies up to about 50 MHz away from the radiation frequency. This result and others are consistent with a model in which cross relaxation occurs in the ground-state levels between ions in resonance with the laser beam and nonresonant ions.

Low−field magnetic properties of ferromagnetic amorphous alloys

Abstract: The low−field magnetic properties of some amorphous magnetic alloy ribbons have been measured. The as−prepared specimens have low coercive field but rather low remanence. The application of elastic stress greatly increases the remanence, and can also decrease the coercive field. Some of the improvement due to stress can be made permanent by annealing under stress. These alloys should be useful in various magnetic devices.

Magnetic properties of rare earth-cobalt phases R 5 Co 19

Abstract: Phases with the stoichiometry R 5 Co 19 have been observed in the rare earth-cobalt systems with R = La, Ce, Pr, and Nd. These phases may play a significant role in the development of coercive force in RCo 5 -based permanent magnets containing the light rare earths, particularly mischmetal. The present paper reports Curie temperatures, saturation magnetizations, and the results of anisotropy field measurements made on alloy powders of these phases.

Magnetization reversal behavior in an amorphous alloy

Abstract: Metglas amorphous Fe-Ni base alloy ribbons supplied by Allied Chemical Co., Morristown, N.J., while mechanically strong, are magnetically very soft, with H c around 20-100 mOe. About 20 Oe H is necessary to saturate the material in strip form. The remanence is on the order of 1/3 the saturation. Elastic tensile stress of a few N/mm2greatly increases the magnetization in low fields. The stress resulting from winding the ribbon into a toroidal sample changes its behavior, giving a much slower approach to saturation and an increase in H c . Thus properties achieved in a strip cannot be maintained on simply winding it into a toroid. Reversal takes place in a series of discontinuous jumps, at fields depending on the previous magnetizing field, just as in cobalt-rare-earth particles. Elastic torsion greatly increases H c and produces a perfectly rectangular loop, again characteristic of nucleation-dominated reversal.

Magnetostriction of some cubic rare earth-Co2 compounds in high magnetic fields

Abstract: Magnetostriction measurements have been carried out in the cubic Laves phase compounds DyCo2, HoCo2 and ErCo2 from 10K to well above their respective Neel temperatures TN. The observed magnetostrictions are very large ( approximately 10-3). The measurements confirm the extremely high anisotropy of these materials. The expected values of the saturation magnetostriction at 0K are similar in sign and magnitude to those found in the corresponding rare earth metals. This fact and the scaling of magnetostriction with rare earth sublattice magnetization indicates that the rare earth ion is the main source of the magnetostriction. The metamagnetic transition above TN has been studied, the relation between critical field and temperature being nonlinear for HoCo2 and ErCo2. The compounds are highly anisotropic above TN and all the features indicate that the field-induced phases are likely to be ferrimagnetic.

Electron transport at high fields in a‐SiO2

Abstract: An iterative‐integral technique is used to determine the velocity of hot electrons in a‐SiO2. Deviations from linearity begin for fields above 8×105 V/cm, and saturation of the velocity‐field curve sets in for fields above 1×106 V/cm.

Computation of the magnetic field of permanent magnets in iron cores

Abstract: A method for computing the magnetic field of permanent magnets in the presence of iron cores is described. The method makes use of finite elements and allows for nonuniform magnetisation in the magnet and saturation in the iron if required. Two possible representations of the field in the magnet are compared. Some, simple examples are used in a study of the rate of convergence to a solution.

Saturation spectrum of the parametric decay instability in the presence of an external magnetic field

Abstract: The effects of an external magnetic field on the saturation spectrum of parametric instabilities are calculated and are discussed in the context of ionospheric heating experiments.

Magnetic susceptibility and magnetization of the ionic ferromagnets dipotassium, dirubidium, and dicaesium tetrachlorochromate(II)

Abstract: High-temperature (300–80 K) susceptibility data are reported for polycrystalline samples of the ionic ferromagnets M2CrCl4(M = K, Rb, or Cs) and interpreted using the high-temperature series-expansion method for the quadratic-layer Heisenberg S= 2 ferromagnet to yield estimates of 7·0, 8·5, and 6·5 cm–1 for the nearest-neighbour exchange integrals. Low-temperature (80–4·2 K) magnetization measurements are also reported for polycrystalline Rb2CrCl4 and Cs2CrCl4. In both compounds the magnetization obeys the equation {1 –[M(T)/M(0)]}=CTγ with γ= 1·54 up to 60 K, i.e. ca 0·9 Tc. Saturation magnetizations are ca 0·4 B.M. lower than expected for S= 2 ions.

Magnetic properties of amorphous magnetic alloys

Abstract: Low-field magnetic properties of amorphous ferromagnetic alloys have been previously reported mainly at d.c. The alloys in ribbon form generally show square hysteresis loops, with coercive fields less than 0.1 Oe, and with saturation magnetization up to 17000 G. Maximum magnetization is obtained in low fields only when the ribbons are under tensile stress. This paper reports further measurements on amorphous magnetic alloys, including differential scanning calorimeter data on the crystallization of three compositions and a variety of a.c. measurements on toroidal samples at frequencies up to 2000 Hz. The coercive fields and magnetic losses under a.c. excitation are disappointingly high. This is attributed to an increase in coercive field when straight ribbon is wound into toroidal form, and to a further increase in H c with frequency due to an apparent decrease in the number of domain walls participating in the magnetization reversal. Neither effect is necessarily inherent in amorphous magnetic materials.

Effective magnetic moments of the europium-monochalcogenides

Abstract: We have measured the paramagnetic susceptibility and the saturation magnetic moment of a number of polycrystalline samples of all four europium monochalcogenides. Many of them exhibit a negative susceptibility at 2 K and magnetic fields of 70 kOe, rather than the expected saturation behaviour. These anomalies are believed to be due to lattice defects. Reproducible saturation moments have been obtained after subtraction of this linear high field magnetization. Since all materials were nonstoichiometric to within a few percent, the ratio between the Curie-Weiss constantC and the saturation momentM0 has been evaluated in order to eliminate the unreliably known numberN of the Eu+ + ions. The quantityR = gJ(J+1) extracted in this way should have the valueR0 = 9.00 forg = 2 andJ ≡S = 7/2. The measured values, 9.72, 9.33, 9.32 and 9.50 for EuO, EuS, EuSe and EuTe, respectively, can be correlated directly with the magnetic hyperfine fields, which are − 305, − 330, − 328 and − 315 kOe in the ferromagnetic aligned states. Both results together lead to the assumption that the magnetic moment per Eu-ion is enhanced over the8S7/2-value by spin contributions of outer 5d or 6s electrons.

Nuclear magnetic resonance of 59Co in (FE1-xCox)2B ferromagnetic borides

Abstract: Measurements are presented of the nuclear resonance frequency of 59Co in (Fe1-xCox)2B ferromagnetic borides at 4.2K for 0.1

Saturation and recovery of the direct interband absorption in semiconductors

Abstract: We report observation of dynamical saturation of the optical absorption in direct band−gap semiconductors using mode−locked pulses from a Nd: glass laser. The alloys were of the types InAsxP1−x and Ga1−yInyAs, with x or y chosen so that the direct band gap at room temperature was about 10 meV less than the laser photon energy. Increases in the transmission coefficient of epitaxial thin films by more than 4 orders of magnitude above the equilibrium value have been observed. Using a probe pulse with variable delay with respect to the strong bleaching pulse, we have studied the time dependence of the recovery of the absorption following bleaching and find it to be as short as 30 psec. Thus such alloys may be useful as saturable absorbers for mode locking visible and infrared lasers.

The beneficiation of clay using a superconducting magnetic separator

Abstract: This paper describes the reduction of the concentration of iron and potassium from a slurry of English Clay using a high intensity superconducting magnetic separator It was found that for magnetic fields greater than about 2T, the performance of the filter depended on H o V o where H o is the applied field and V o is the entrance velocity to the filter in agreement with theory For fields less than 2T there is a slightly enhanced performance which is again in agreement with theory Although in this region the theory may not be valid because particle size and shape effects become important

Pulse magnetization measurements in ferrofluids

Abstract: A pulsed-field (1 μ sec to 3 m sec) inductive magnetometer has been constructed that measures the magnetic moment of a ferrofluid as a function of time. After the applied field is removed, the magnetization is characterized by a fast decay (< 1 μ sec) and a gradual decay that can be as long as 4 msec. The fast component of magnetization varies from about 50% to nearly 100% of the total and we conclude it is due to magnetization processes within the particle. The slow component of magnetization is believed to be due to particle rotation and can be related to particle size through a model developed by Janak.

The replay signal from a tape with magnetization components parallel and normal to its plane

Abstract: A simple formula is given which describes the magnetization distribution recorded in magnetic tapes. This is more realistic than the usual M = M_{o}\sin wx in that it contains both longitudinal and normal components of magnetization. The corresponding output voltages are shown to be higher while the self-demagnetizing fields are lower than in the usual case.

Magnetic properties and pressure dependence of the Curie temperature of LaCo5xCu5−5x

Abstract: The magnetic properties of the series LaCo5xCu5−5x were studied. All compounds were found to crystallize in the hexagonal CaCu5 structure type. As a function of composition x the following properties were determined: the lattice constants, the Curie temperatures and their pressure dependence up to 40 kbar, the anisotropy fields, the saturation moments at 4.2 K, and the initial compressibilities. Attempts have been made to explain the variation of the magnetic properties in terms of the collective electron model with a 3d band shape that depends on Cu concentration, taking account, however, of a certain extent of localization of the 3d electrons.

Magnetic properties of amorphous Gd‐Co‐Au films

Abstract: Magnetization as a function of temperature (4.2–300 °K) for the amorphous ferrimagnetic Gd‐Co‐Au alloys is analyzed by using a two‐sublattice model. The magnetization behavior is discussed in terms of the cobalt spin value, and the intersublattice and intrasublattice exchange constants. Magnetic domain wall properties are considered in an attempt to estimate the growth‐induced uniaxial perpendicular anisotropy.

Saturation effects in a tunable coherent near-infrared source

Abstract: A saturation effect in a tunable infrared source utilizing four‐wave parametric conversion in potassium vapor is reported and is shown to be the result of parasitic oscillations. A hundredfold increase over previously attained power levels has been effected via elimination of these oscillations.

The initial Matteucci effect

Abstract: The magnetoelastic anisotropy introduced by torsional twist in ferromagnetic wires allows the measurements of the circular magnetization Mphi as a function of the longitudinal magnetic field Hz and the longitudinal magnetization Mz as a function of the circular magnetic field Hphi . For two types of samples, twisted to saturation the Mphi -Hz and Mz-Hphi curves were obtained. These curves show two different types of behaviour.

Influence of zinc on cobalt substituted magnetic recording media

Abstract: The instability of magnetic properties of cobalt substituted acicular iron oxides can be reduced without losing the desirable properties in their application as high energy magnetic recording media. It is shown that by introducing small amounts of zinc into these oxides, they become chemically and magnetically stable. This stabilizing effect is produced by the ability of zinc to decrease the crystal anisotropy of the cobalt substituted iron oxides. The degree of chemical stability and the degree of magnetic stability is dependent not only on the zinc content but also on the zinc to cobalt ratio. In addition, tapes prepared from these powders do not show magnetostrictive losses under pressure, as is the case with cobalt substituted iron oxides.

Switching properties of epitaxial planar transistors operating in saturation

Abstract: In an epitaxial transistor operating in saturation, charge is stored not only in the active and passive base regions but also in the region bounded between the collector junction and n - n + interface. The saturation operation of a transistor switch is characterized by a single most fundamental parameter, the saturation time constant, which may be related to the intrinsic physical structure of the transistor. In this paper, an attempt has been made to correlate the saturation behaviour of an epitaxial planar transistor with its physical structure. The analysis takes into account the effects of n - n + interface in the collector and the retarding-accelerating built in field for the minority carriers in the base, both of which so far have been subject to gross simplifications. The theoretical conclusions have been verified experimentally for some typical epitaxial planar transistors.