ISSN:0021-8979    

DOI:10.1063/1.1777164

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1728589

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A broad range of magnetic memories finds extensive use in today's data processing equipment. The most significant factors in evaluating a memory for a given application are reliability, cost, size, speed, and function. Ferrite core memories with capacities of 103to 106bits and with cycle times as short as 0.5 &mgr;sec are in use. Recent developments in this area, including partial switching, 2 cores/bit, and new core fabrication techniques, will be discussed.There have been extensive development efforts recently in many forms of magnetic metal film devices. Many geometries, modes of operation, fabrication techniques, substrate materials, and film compositions are being used. A comparison of some of the resulting devices will be made, and the effects of the factors listed above will be discussed. The application of metal film memory devices will be considered and a comparison drawn with ferrite devices.Techniques for achieving special purpose functions such as nondestructive readout, read‐only and associative memory using magnetic elements, will also be described and compared.

ISSN:0021-8979    

DOI:10.1063/1.1728590

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The use of high magnetic fields as a research tool for a wide variety of physical phenomena is clearly recognized today and the subject of an International Symposium at Cambridge this fall. Another important step in promoting research with the help of large magnetic fields has been the sponsorship of the M. I. T. National Magnet Laboratory by the Air Force. This paper will review the highlights of the conference which included papers on research in plasma physics, low temperatures, solid state and the latest developments for generating high magnetic fields. The plans and objectives of the National Magnet Laboratory and description of the physical facilities will be presented. In addition, a brief review will be given of a number of experiments already performed in the existing Magnet Laboratory at M. I. T.

ISSN:0021-8979    

DOI:10.1063/1.1728591

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Recent development in the theory of screw structure of spins and its modification due to anisotropy energy and applied magnetic field is reviewed, with reference to neutron diffraction work on rare‐earth metals and MnAu2.

ISSN:0021-8979    

DOI:10.1063/1.1728592

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Some transitions between ordered and disordered magnetic states that take place via transitions of first order are tabulated. Among these transitions are some of the order‐disorder type. The theoretical basis for such a transition to occur is indicated using a simple physical model that assumes: (1) a strain dependent exchange interaction and (2) a compressible lattice. The necessary condition for first‐order behavior is determined, and the theory is compared to the behavior of a real material, MnAs. It is found to be in substantial agreement with the behavior of that compound. The system represented by the simple model employed here possesses ferro‐, antiferro‐, and paramagnetic states. The equilibrium boundaries between these states are determined in the pressure‐temperature plane as an illustration of the possible transitions that may be observed with this model.

ISSN:0021-8979    

DOI:10.1063/1.1728593

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The recent discovery that Nb3Sn remains superconducting in magnetic fields exceeding 88 kgauss while carrying current densities in excess of 100 000 amp/cm2has stimulated widespread activity directed toward the construction of superconducting magnets and the understanding of ``hard'' superconductivity. Some of the relevant events that have transpired since the discovery of superconductivity by Onnes in 1911 are reviewed. The critical current versus magnetic field (IcvsH) characteristics of several materials are discussed and the justification of using such measurements on small samples as a basis for magnet design is presented. Nb‐Zr alloys appear useful for magnets capable of fields as large as 80–100 kgauss while Nb3Sn appears to be useful for fields of 200 kgauss. Superconducting magnets of Nb3Sn and of Nb‐Zr have been constructed and tested by several laboratories. Fields as large as about 70 kgauss have been generated with Nb3Sn magnets and 60 kgauss with Nb‐Zr magnets. Fields exceeding 100 kgauss have been attained by augmenting the field produced by a superconducting Nb3Sn magnet with the field from a conventional Bitter solenoid. Superconducting magnets capable of fields of at least 100 kgauss are almost a certainty and it is quite likely that magnets will eventually be constructed to produce fields of 200 kgauss. Fields of several hundred kgauss are an intriguing possibility.

ISSN:0021-8979    

DOI:10.1063/1.1728594

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A switching threshold relaxation effect has been observed which is detrimental to high‐speed selection of partially switched (time‐limited switching) ferrite memory cores. This paper discusses this threshold effect as determined by measurements on cores of 1‐ to 5‐oe coercivity. Two aspects of switching threshold are observed: A static threshold (Hf) which is effective at a time long after switching, and a relaxation effect which is a reduction in threshold immediately after switching. The reduction is considerable and may limit the amplitude of the digit‐disturb field that a core may withstand to a small fraction of the coercive force. A first approximation to the switching threshold dependence on time may be given as:Ht=Hf(1‐e−3t/&tgr;) fort>0. This representation is reasonably accurate for most ferrite cores, although a sum of exponentials is necessary for an improved description. The ratio of the static threshold to the coercivity (Hf/Hc) is influenced by the duration and polarity (relative to the switching field) of the disturb field, the amplitude of the switching field, the flux state, the ambient temperature, and the ferrite composition. The static threshold of a core switched to the 50% flux state by a 10‐nsec pulse may be only half the value of the threshold after switching to the 50% state with a 2‐&mgr;sec pulse. The relaxation time also depends on the above mentioned parameters (except relative polarity) and, in addition, is influenced by the coercivity of the sample, lower coercivity samples having longer relaxation times. Measurements at ambient temperatures ranging from −195°C to near the Curie temperature (+250°C) show the product of coercivity and relaxation time to be nearly constant for a given core. The relaxation time is a maximum at the 40–50% flux state and approaches zero at the major loop remanent flux states.

ISSN:0021-8979    

DOI:10.1063/1.1728595

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The technique of using magnetic thin films in computer memory devices is reviewed, and conclusions drawn as to the properties of the film that are required for successful operation of a memory. A description is then given of a series of experiments which were designed to determine the best compromise in properties. Particular importance is attached to the easy axis dispersion, and it is claimed that the addition of a small quantity of cobalt to the nickel iron alloy reduces this despersion by about a factor 3.

ISSN:0021-8979    

DOI:10.1063/1.1728596

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A technique employing the Kerr magneto‐optic effect has been used for measuring switching times as short as 10 nsec in thin ferromagnetic films, both individually and when coupled together in a sandwich structure. The switching speed of individual 1‐mm‐diam Permalloy bits has been found to be dependent on film thickness, the thicker bits switching more slowly. It was further observed that the time to switch 90% of a film is much more sensitive to film thickness than the time to switch 50% of the same film. When two similar films, magnetized in a head‐to‐tail fashion, are placed on either side of a drive line strip, the time to switch 50% of the films is essentially the same as for individual bits. However, the time required to switch 90% of the material is considerably shorter for sandwich elements than for the corresponding single bits. These results suggest that the slower switching of thick bits may be attributed to an incoherent rotational mechanism associated with the inhomogeneous demagnetizing field.

ISSN:0021-8979    

DOI:10.1063/1.1728597

出版商:AIP    

年代:1962

数据来源: AIP