Normal Magnetization Curve Research Articles

Isochronal Recovery of the Shape of the Normal Magnetization Curve of Nickel Shocked at 400 kbar

The recovery of the shape of the normal magnetization curve of high-purity polycrystalline nickel shock loaded to 400 kbar has been studied using an isochronal annealing technique. It was found that gross shape recovery occurs after annealing at temperatures in excess of 400°C. Lower-temperature annealing does not effect the shape of the normal magnetization curve significantly but lower-temperature annealing processes are reflected in the value of the field strength associated with the maximum susceptibility.

Magnetic and Magneto-Optical Properties of Fe-Doped EuO Films

EuO films with ∼8-wt% Fe have saturation magnetic moments of about 180 emu/g at 4.2°K and Curie temperatures (Tc) as high as 200°K (for pure EuO, σ=232 emu/g, Tc=69.5°K). The temperature dependence of the magnetization does not scale relative to pure EuO but deviates from the normal magnetization curve in that it exhibits a long tail extending from about 100°K up to Tc. Optical absorption data at 6°K in the range 0.3–2.5 μ indicate a characteristic peak at λ=0.6 μ (due to the 4f-5d transition) with α=2.2×105/cm, about 50% higher than pure EuO. The wavelength dependence of the normal Faraday rotation at 4.2°K is similar in shape to pure EuO; both peak at 0.7 μ but the peak rotation of the Fe-doped film (6×105 deg/cm) is about 30% lower than pure EuO. Mössbauer measurements of 151Eu show mainly Eu+ + with an isomer shift of −12.25 mm/s as in bulk EuO. At 4.2°K the 151Eu hyperfine field is 280.8±5.6 kOe (pure EuO≈300 kOe). The isomer shift of the doublet observed on the 57Fe resonance at 300°K is characteristic for metallic iron. We conclude that only a small fraction of the Fe is effectively doping the EuO films.

Effect of shock waves on the residual magnetic properties of armco iron

Abstract The effect of shock waves on the residual magnetic properties of Armco iron is determined by measuring the magnetic hysteresis and the normal magnetization curves after shock deformation. The pressure range investigated is from 73 to 250 kilobars. It is observed that all structure sensitive properties change and these changes are related to the peak pressure associated with the shock wave. The data are discussed in terms of magnetic domain theory. Functional expressions are presented for both the change in coercive force and the change in the area of a hysteresis loop with pressure. It is noted that a minimum occurs in the pressure dependence of the residual magnetization near the pressure required for the α→ε phase transformation.

Specification, treatment and properties of soft irons for electromagnetic relays

Electromagnetic relays deteriorate in service. Part of this deterioration is due to ageing of the iron employed in the magnetic circuit, and, in particular, to the use of annealing atmospheres, such as cracked ammonia, which contain nitrogen. If such atmospheres are unavoidable, then, for most practical purposes, ageing can be eliminated by the use of irons containing about 0.1 % of aluminium. Silicon, in the iron initially or available in the furnace lining, increases nitrogen ageing. The best properties are obtained by annealing in a furnace lined with alumina, in an atmosphere of wet hydrogen and with an iron free from additions. The properties obtained by treatments at high temperatures are not always unique: they can sometimes be obtained by more prolonged treatment at a lower temperature. Nitrogen-aged piece-parts can be salvaged and restored to a condition better than new by reannealing in hydrogen.The magnetic circuit of a relay must be able to lift and to release its springset load when needed. The first requirement depends on the normal magnetization curve, and the second on the coercive force. Nevertheless, relays are manufactured without sufficient consideration of the properties of the iron necessary for the performance of specific functions. An experimental technique has been devised for the retrospective determination of the requisite properties. The significance of the normal magnetization curve is ascertained by studying the alteration in load-lifting ability as the (field-dependent) permeability is systematically degraded, starting with a ‘better-than-necessary’ material. This is done by reducing the cross-section of the magnetic circuit in such a way that the configuration of leakage paths is not altered. The relation between release m.m.f. and coercive force is approached by first considering the change to be expected in the hysteresis loop for a uniform ring when a gap is introduced, and then examining the relationship between this changed loop and the release of a uniform and of a non-uniform relay.

Parallel-Connected Magnetic Amplifier

A mathematical analysis of parallel-connected magnetic amplifiers with an inductive and capacitive load is presented. The analysis is based on the representation of the normal magnetization curve of the core material by polynomials of third and fifth degree respectively.

Temperature Dependence of the Magnetic Properties of Nickel-Iron Alloys

The effect of temperature on the magnetic properties of six commercially available nickel-iron alloys is reported for the temperature range −60°C to +250°C. The trade names of the alloys are: Hipernik, Deltamax, Hipernik V, Supermalloy, 4-79 Mo-Permalloy, and Hymu 80. The temperature dependence of both ac and dc magnetic properties was determined experimentally over the temperature range. Dc properties were measured by the standard ballistic testing method. At each test temperature sufficient data was taken to plot a normal magnetization curve. Remanent induction and coercive force were also determined at each temperature, these properties being measured relative to magnetizing forces in excess of 100 oersteds. Ac properties were measured by means of a modified Hay bridge, the tests being conducted at frequencies of 60, 400, and 1000 cps. At each test temperature, and for each frequency, total core loss was measured at various inductions in the range characteristic of the alloy being tested. The data presented are the average of the results of tests on six samples of each alloy.

A Mathematical Analysis of an Inductively Loaded Parallel-Connected Magnetic Amplifier

A mathematical analysis of a parallel-connected magnetic amplifier with an inductive load is presented. The analysis is based on the representation of the normal magnetization curve of the core material by a polynomial of the fifth degree. The load current is expressed in terms of the magnetic intensity of one of the cores. The magnetic intensity is shown to satisfy a nonlinear differential equation and an approximate solution of this equation is obtained by an iterative procedure. An estimate of the response time of the amplifier is determined and the steady-state response of the amplifier is obtained.

Transient response of magnetic amplifiers

THE TRANSIENT RESPONSE of magnetic amplifiers with cores of gradually varying incremental permeability can be analyzed with methods already applied in previous articles. For this, the alternating component of core fluxes is assumed to vary sinusoidally and the normal magnetization curve is approximated by a hyperbolic sine function of the type H = U sinh uB. A straightforward integration of the differential equations of the control circuits for a step change of the signal voltage becomes hereby possible, at least for “slow” transients lasting over a few cycles of the a-c source frequency, and curves representing the output current (rms or rectified average) during the transient can be calculated.

ROTATIONAL MAGNETIZATION IN POLYCRYSTALLINE FERROMAGNETICS

In the attempts to derive from theory the magnetization curve, in the region of rotational magnetization, for well annealed ferromagnetic polycrystals, a generally recognized complication is the possible existence of internal fields caused by the out of alignment of the magnetization vectors of the grains. However, if such internal fields do not really exist, a simple deduction by the usual formal treatment predicts that the magnetization curves of polycrystals, of the same crystalline structure and having the same sign for the values of the principal anisotropy constant, can be brought into coincidence by expressing the intensity of magnetization and the field in proper reduced units'. This prediction is checked experimentally by measurements on iron and an iron alloy containing 15 percent cobalt by weight. In each case, it is found that the normal magnetization curves for various temperatures can be brought into coincidence in the manner as indicated. It is therefore concluded that the effect of internal fields on the process of magnetization in the case of polycrystals cannot be any greater than that in the case of single crystals. The absence of wide spread internal fields of magnetic origin in polycrystals during rotational magnetization is then discussed in the light of recent developments in the domain theory.

General Characteristics of Magnetic Amplifiers

A general analysis of basic types of magnetic amplifiers without and with feedback is presented in dimensionless form. The use of a simplified approximation of the normal magnetization curve with a hyperbolic sine function permits a comparatively simple treatment of a most comprehensive nature on a purely analytical basis. General dimensionless characteristics are obtained which apply, without need for further calculations, to any kind of design specifications and to any core material of not too abruptly varying incremental permeability. Thus the influence of factors of design and materials on the performance is made evident. This approach also yields a practical method of accounting for the simultaneous conduction of the feedback rectifiers (commutation) in terms of a correction factor which is applied to the feedback ratio. Numerical values of this correction factor are calculated for some significant instances.

Magnetization and Hysteresis in Hematite Crystals

Magnetization and Hysteresis in Hematite Crystals; Experimental Procedure.---In a previous paper, the author has given the results of an investigation of the magnetic properties of crystallized hematite, the measurements being of the force exerted upon a sphere when it is placed in a non-uniform magnetic field. The present paper contains some results obtained by measuring the couple exerted when a hematite sphere is suspended in a uniform magnetic field. The couple in a uniform field measures the component of magnetization perpendicular to the field; the force measures the component parallel to the field.Experimental Data.---The paper contains (1) magnetization curves (Fig. 4) for two specimens of hematite; (2) hysteresis loops at fields from 9.5 to 1020 gausses, some obtained with a rotating field (Figs. 6, 7, 8, 9, 11), the others with an alternating field (Figs. 10, 11); (3) a graph representing components of magnetization parallel and perpendicular to the field (Fig. 12).Deduction, The normal magnetization curve of hematite consists of a sharp rise followed by a slow increase, which is proportional to the field strength. The hysteresis energy loss increases with an increase in the maximum field applied up to a certain field, and thereafter the area of the hysteresis loop remains constant. For the specimen on which most of the present measurements were made, the hysteresis loss is constant for field strengths above about 150 gausses.