摘要:

A simple model is suggested which enables the calculation of the relationship between the domain length and the domain wall spacing in constructional steel. The magnetic interaction between domain in neighboring grains is measured from the observed domain patterns, and a coefficient is proposed which makes possible such a calculation for antiparallel domains. The calculated results compare favorably with experiments. However, the observed scatter of experimental results is due to the complex magnetic interaction of ferrite grains with pearlite, cementite and nonmetallic inclusions.

ISSN:0021-8979    

DOI:10.1063/1.334625

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The dynamics of the magnetization process of a ferromagnetic material is in general strongly influenced by interactions between Bloch walls, brought about by internal fields. The resulting stochastic character of the magnetization process has, together with many other effects, an important role in producing the so called excess magnetic loss, found in practically all the ferromagnetic materials undergoing a cyclic magnetization process. Recently an optical technique has been developed which makes use of the Kerr effect, on suitably prepared specimens, to study the Bloch wall dynamics in a wide frequency range (0–100 kHz). Through this technique, and by means of mathematical developments allowing one to evaluate local magnetic losses from the analysis of the optical signal, a rather large amount of information has been obtained on the magnetization dynamics and loss mechanisms in monocrystalline, polycrystalline, and amorphous materials. In particular, in the case of grain‐oriented Fe–Si laminations, the correlation existing between Bloch wall interactions and deviations from the Pry and Bean theory of losses, even in well‐oriented grains, showing a regular antiparallel domains structure, has been clearly evidenced. In the present paper, this technique, whose main advantage is connected with the possibility of visualizing the domain structure of the region under study, will be described and discussed, together with some of the main results obtained until now.

ISSN:0021-8979    

DOI:10.1063/1.334626

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new method for observing magnetic domain structures with a scanning electron microscope has been realized in which the image video signal is the spin polarization of secondary electrons. Examples of domain structure images are presented and the potential of this method is discussed.

ISSN:0021-8979    

DOI:10.1063/1.334627

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Ribbon‐form 13% Al–Fe alloy was prepared by a rapid quenching single roller method. The ribbon obtained had dimensions of 50–60 &mgr;m thick, 1–3 mm wide, and a few meters long. The annealing temperature dependence of magnetic, electrical, and mechanical properties were examined from 900 to 1200 °C. After annealing at 1000 °C for one hour in vacuum of 1×10−5Torr, the best magnetic properties were obtained: the saturation magnetostriction was 52×10−6, the coercive force was 0.8 Oe, and the initial permeability was about 500. The electric resistivity was as high as 105–110 &mgr;&OHgr; cm. The ribbon was notably flexible and could be wound around a rod of 0.5 mm diameter.

ISSN:0021-8979    

DOI:10.1063/1.334628

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The effective permeability ( &mgr;eff) of the ring Sendust alloys (Fe‐9–10 wt. % Si‐5–7 wt. %Al), molded with Epoxy resin, was measured in the temperature range of −10 to 70 °C. The &mgr;effof the alloys in molded condition measured at 20 °C is smaller than that in unmolded condition. The high values of the &mgr;effat 20 °C of the molded alloys were obtained from the alloys in which magnetostriction constants (&lgr;s) were close to zero. The temperature dependencies of the &mgr;efffor the studied alloys in the unmolded condition are very similar, but after molding they are classified into four variations depending on the value of &lgr;s. When the alloys have large positive or negative values of &lgr;s, the &mgr;effincreases or decreases monotonically with increasing temperatures, but for the alloy with &lgr;s&bartil;0, the &mgr;efftemperature dependence is complex. These behaviors of the &mgr;effwith temperature are interpreted on the basis of the induced stress, initiating from the differences in thermal expansion between alloys and Epoxy resin. The &mgr;effof the molded alloys was mainly dominated by the induced uniaxial magnetic anisotropy (Ku) by the tangential and axial compressive stresses in the molded ring alloys.

ISSN:0021-8979    

DOI:10.1063/1.335475

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This paper describes a material and new method of processing that yields pressed compacts magnetically suitable for a variety of ac applications. Small rectangular plain‐carbon steel particles with dimensions 2.0×0.51×0.15 mm are decarburized, individually insulated and uniaxially pressed using typical powder‐metallurgical techniques. In this condition the 60‐Hz losses are somewhat higher than conventional carbon steel sheet while at higher frequencies the losses are lower. This loss behavior is due to the large hysteresis‐to‐eddy current ratio,>9. The permeability of the compacts is poorer than that of carbon steel sheet. Attempts to reduce the core loss by lowering the hysteresis loss component through a series of stress‐relief annealing experiments resulted in exceptionally high losses. These high losses were attributed to large circulating eddy currents caused by local particle‐to‐particle sintering. Subsequent repressing, either uniaxial or cold isostatic, resulted in a dramatic reduction in the eddy current loss component and a total core loss superior to that of conventional carbon steel sheet. The variations in magnetic performance are related to the sample density, initial core pressing pressure, the annealing parameters, and the repressing method and pressure.

ISSN:0021-8979    

DOI:10.1063/1.335473

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The ternary alloy family Fe–Co–Al is studied in the body‐centered cubic (&agr;) phase for the behavior of structure‐insensitive magnetic parameters, out to compositions of 13 wt. % Al and 50 wt. % Co. Interest in this family on the potentially practical side derives from the properties of its separate iron binary systems. Iron–aluminum alloys have been investigated since before the turn of the century and there have been several efforts at commercialization as soft magnetic material. Iron–cobalt alloys have received special attention because of their high saturation magnetization (exceeding that the Fe), as well as for their very high Curie temperatures. However, the ternary system has received only sporadic attention, starting with the phase diagram and Curie point work of Ko¨ster one‐half century ago and resumed largely for scientific interest in the electronic properties of transition metal alloys. Room‐temperature magnetizations on a mass basis and on the more practical volume basis are presented. These expand upon earlier low temperature results. The presence of a broad maximum in magnetization in the Fe–Co binary does not persist beyond about 5 wt. % Al in the ternary family. Curie point results add to the data base and confirm those of Ko¨ster including an anomalous increase of Curie point with Al dilution for a certain range of composition. This feature is explained in terms of the bcc–fcc (&agr;–&ggr;) structure transition and the stabilization of the &agr;‐phase by Al additions.

ISSN:0021-8979    

DOI:10.1063/1.334578

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Ferrohydrodynamics treats the flow and thermodynamics of magnetically polarizable fluid in response to applied magnetic field. Following its introduction twenty years ago, ferro‐hydrodynamics has developed as a branch of mechanics similar to magnetohydrodynamics and electrohydrodynamics. Unique phenomena of ferrofluids and related media are manifested in hydrostatics, inviscid and viscous flows, magnetically induced flow instability, magnetic stabilization of flow, generation of antisymmetric stress, and magnetic multiphase flow. Certain of the phenomena serve as bases of developed technology in seals, dampers, accelerometers, and cooling techniques with new applications under active development in tribology, acoustics, printing, instrumentation, and other areas. Ferrohydrodynamic principles underlie also the development of magnetic multiphase systems yielding turbulence prevention of moving‐bed operations in the process industry. Major concepts and advances of the field are presented in the context of the continuum mechanical framework.

ISSN:0021-8979    

DOI:10.1063/1.334579

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A Monte Carlo technique is used to predict the influence that magnetic dipolar interations have on thermodynamic ordering in dispersions of fine magnetic particles. The interactions give rise to Curie–Weiss‐like behavior with an ordering temperature that is found to vary linearly with particle concentration. The dependence of the ordering temperature on packing fraction is in agreement with predictions from analytical treatments. These observations have important implications in the characterization of magnetic liquids. In particular it confirms that many of the techniques used to calculate particle size distribution parameters will give misleading results unless the measurements are made on very dilute systems.

ISSN:0021-8979    

DOI:10.1063/1.334580

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A theory is presented which explains the observed birefringence of colloidal dispersions of fine magnetic particles. The system is assumed to consist of pairs of interacting particles, interactions between pairs being negligible. A pair of particles approximates to a single particle with a high degree of optical anisotropy. Application of a magnetic field to the colloid has the effect of aligning the axes of the pairs, resulting in the measured birefringence. On the basis of this model, the birefringence of a magnetic colloid is calculated. The form of the numerical results is consistent with experimental data. In particular it is shown that in small fields the birefringence is proportional to H2.

ISSN:0021-8979    

DOI:10.1063/1.334581

出版商:AIP    

年代:1985

数据来源: AIP