ISSN:0021-8979    

DOI:10.1063/1.1657795

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Magnetism applications permeate our whole modern society in its basics of electric power, communications, and information storage. Although the general public is mostly unaware of its role, magnetism has an economic impact of over 1% of the Gross National Product. The annual direct magnetic materials market is currently estimated at 650 million dollars, with dollar leadership shared by electrical steels and recording tape, followed by soft ferrites, magnetic disk packs and drums, permanent magnets, and nickel‐iron alloys. The magnetism market is also described with reference to the role of research leading to quality improvement and to a growing list of new applications. It is estimated that the cost of basic and applied research (U.S.) is about 5% of the direct magnetics market. The world output of publications on magnetics has increased sixfold over the past decade after a plateau during the 1950's. During this same period magnetism has become more popular relative to a total science publication base and its scope has broadened in research, in discovery, and in application.

ISSN:0021-8979    

DOI:10.1063/1.1657796

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Magnetic memory cells meet the essential logical and economic requirements1,2of a memory cell and presently play a dominant role in electronically and mechanically accessed computer memories.3,4Electronically addressed magnetic memories typically are arranged in 3D, 2D, or 2½Dorganizations.5–9Progress in electronically addressed magnetic memories has resulted from a number of basic discoveries and developments in the threshold and switching properties of ferrite cores,10–12planar thin films,13–15and plated wires.16As recently summarized,17,18mechanically accessed memories such as tapes, drums, disks and data cells have had continual improvements in magnetic materials and in cell density. Present magnetic cells typically do not approach the limits set by thermal noise,19,9and, as a consequence, a substantial increase in density is possible. The number of magnetic memory cells produced each year is increasing by more than 30% per year3and continued growth can be anticipated.

ISSN:0021-8979    

DOI:10.1063/1.1657797

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The functions of ferrite components in advanced microwave systems are briefly outlined, and the principal requirements described. The successful development of these sophisticated devices is the cumulative result of contributions from many areas of basic research and technology. As an example of the dependence of device performance on diverse efforts, the status and evolution of ferromagnetic digital phasers are reviewed. In this instance, materials research, ceramic technology, methods of numerical analysis, and the understanding of basic damping mechanisms have all contributed to the realization of practical devices. The application of ferrite devices to microwave integrated circuits is also outlined and some recent experimental results given. Other new trends in the field of microwave ferrite devices are briefly mentioned, as are areas most in need of further research.

ISSN:0021-8979    

DOI:10.1063/1.1657798

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Magnetism has played a vital role in the development of basic concepts of solid‐state physics. Early research in magnetism was concerned largely with the reaction of the magnetization on external applied static and electro‐magnetic fields. Indeed, technological developments in magnetism have utilized such behavior highly successfully. Today's trend in basic magnetics research emphasizes the interrelation of magnetism with other physical properties of solids. For example, magneto‐electronic, ‐optical, and ‐electric properties of materials, the magnitude of the interaction, and how external fields coupled to the magnetization influence other properties is the subject of many of the basic papers in this Conference. This paper reviews current magnetics research with emphasis on the experimental observations. These effects provide a wealth of new material on which to base future technological applications.

ISSN:0021-8979    

DOI:10.1063/1.1657799

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Direct measurements of the direction and strength of the earth's magnetic field have provided a knowledge of the field's form and behavior during the last few hundreds of years. For older times, however, it has been necessary to measure the magnetism of certain rocks to learn what the geomagnetic field was like. For example, when a lava flow solidifies (at temperatures near 1000°C) and cools through the Curie point of the magnetic minerals contained in it (around 500°C) it acquires a remanent magnetism that is (1) very weak, (2) very stablel, (3) paralle to the direction of the ambient geomagnetic field, and (4) proportional in intensity to the ambient field. Separating, by various analytical means, this magnetization from other ``unwanted'' magnetizations has allowed paleomagnetists to study the historical and prehistorical behavior of the earth's field. It has been learned, for example, that the strength of the field was almost twice its present value 2000 years ago and that it has often completely reversed its polarity. Paleo‐magnetists have also confirmed that most oceans are, geologically speaking, relatively new features, and that the continents have markedly changed their positions over the surface of the earth.

ISSN:0021-8979    

DOI:10.1063/1.1657800

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The use of magnetic fields as a tool for control and measurement has important medical applications. Present devices include magnets to remove objects from the eye and to facilitate the withdrawal of swallowed safety pins and similar objects, ensuring that the sharp end points backwards. In more sophisticated applications magnetic materials are purposely introduced into the body to accomplish various tasks. Magnetically guided catheters have been used to negotiate the tortuous passageways of blood vessels. Ferrite powders may replace barium sulfate for gastrointestinal x‐ray diagnosis in some applications. Magnetic fields have also been used for various measurements, employing not only fields due to small amounts of material artificially introduced into the body but also the extremely weak fields produced by the electrical or electromagnetic activity of the body itself.

ISSN:0021-8979    

DOI:10.1063/1.1657801

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The consequences of a simple type of exchange interaction between charge carriers in a broad energy band and localized magnetic moments will be discussed for a ferromagnetic semiconductor. The interaction causes (1) a splitting of the energy band into two bands for the different spin directions, (2) spin disorder scattering of the charge carriers. The calculated temperature and field dependence of the magnetoresistance are compared with experimental data of CdCr2Se4. The magnetoresistance of compoundsMeCr2S4,Me=Fe, Co, Cd was measured. Forn‐type CdCr2S4and forp‐type FeCr2S4andp‐type CoCr2S4, the magnetoresistance −&Dgr;&rgr;/&rgr;0was found to be 0.78, 0.05, and 0.05, respectively, at 12 kOe nearTc, whereasn‐type FeCr2S4and CoCr2S4show no effect. The magnetoresistance of the system Fe1−xCdxCr2S4was also measured. The temperature dependence of the polar magneto‐optical Kerr effect of CdCr2Se4is discussed in connection with the described model for the energy bands.

ISSN:0021-8979    

DOI:10.1063/1.1657802

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

In the last few years intense interest has developed in the nature of second‐order phase transitions. Experimental and theoretical investigations have centered primarily on equilibrium properties. Transport or nonequilibrium properties are only now beginning to be intensively studied. Thus far there exists only very limited theoretical work in this area, and little experimental data for comparison. We review the theoretical and the experimental situation (excluding neutron diffraction) as it applies to magnetic systems. Scaling‐law theory is summarized and the importance of the dynamic‐scaling hypothesis is emphasized. An attempt is made to relate existing experiments to these scaling laws. We conclude that the closest contact between scaling theory and experiment at present comes in the prediction and observation of transitional behavior between the hydrodynamic regime far from the critical point, and the critical regime in which the fluctuation range becomes large compared to other characteristic lengths.

ISSN:0021-8979    

DOI:10.1063/1.1657803

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A method of recording digital information on a thin magnetic film is described. The change of magnetization in the film is accomplished by a coincidence of a high‐power optical beam from a laser and a magnetic field. Films having coercive force ratiosHc(25°C)/Hc(150°C) of at least 3 were used as the media. Information was recorded with a 1 W Argon‐Ion laser beam controlled by an electrooptic switch to provide spots down to 3.5&mgr; diam. Photographs and electrical readout of tracks of written bits are presented.

ISSN:0021-8979    

DOI:10.1063/1.1657804

出版商:AIP    

年代:1969

数据来源: AIP