ISSN:0021-8979    

DOI:10.1063/1.2000401

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A simple and powerful new method for the treatment of spin wave interactions is introduced and used toobtain the corrections to the energy and magnetization of ferromagnets, antiferromagnets and ferrimagnets.The results previously obtained by Dyson and by Oguchi using complicated analysis are reproduced andextended by means of elementary considerations which throw light on the physical interpretation of thecorrections. In the case of a ferromagnet the validity of the random phase approximation is discussed, andthe properties of the continuous medium model are calculated: in particular, the spin wave exchange-collisioncross section is obtained in a simple way.

ISSN:0021-8979    

DOI:10.1063/1.2000447

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The ferromagnetic rare-earth metals show the magnetic transition from the ferromagnetic state to theantiferromagnetic state. The possibility of this kind of magnetic transition between spin arrangements isdiscussed on the basis of the spin wave approximation. It is shown that the transition from the ferromagneticto the helical spin arrangement which has recently been observed in dysprosium and holmium can occurwhen a large axial anisotropy field exists. The temperature dependence and the field dependence of thepitch of the helical structure are calculated on the same standpoint of the spin wave theory.

ISSN:0021-8979    

DOI:10.1063/1.2000511

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

An investigation of the ground state of the classical Heisenberg exchange energy in spinels has led toseveral new results. By means of a recent generalization of the method of Luttinger and Tisza, we haverigorously obtained the ground state in part of the exchange parameter space defined by nearest neighborABandBBinteractions for tetragonally distorted spinels. The regions in this space where the Ne´el andYafet-Kittel configurations minimize the energy are much smaller than predicted by the Yafet-Kittel six-sublatticetheory. Outside of these regions, there exists a domain where the ground state is an antiferromagneticspiral similar to those recently introduced in the literature. In still other regions, the ground stateis a new type of spiral which is ferrimagnetic. An investigation of a parameter region including cubic spinelsshows that such a ferrimagnetic spiral yields an appreciably lower energy than that given by the Yafet-Kittelmodel and is locally stable up to a specified ratio ofBBtoABinteractions. The generalized Luttinger-Tiszamethod shows it to be the best possible ferrimagnetic spiral up to and beyond the point of instability, butfails to prove it to be the ground state. An examination of small deviations at the point of instability indicatesthe existence of spin configurations much more complex than the magnetic spirals proposed here.

ISSN:0021-8979    

DOI:10.1063/1.2000376

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

This is the summary of a paper which discussed neutron diffraction techniques as applied to helicaltype and related spin structures, and illustrated these techniques with results from recent investigationsonMnAu2and metallic holmium.

ISSN:0021-8979    

DOI:10.1063/1.2000405

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The behavior of a helical spin configuration of a hexagonalcrystal in an applied field is discussed for the case where the axisof the helix is identical with the hexagonalcaxis and the magnetizationvector in each layer is parallel to the basal plane. In a smallfield applied parallel to the basal plane, a slight deformation ofthe helix occurs resulting in a small increase in over-all magnetization.If the field surpasses a certain critical value, the helix changesabruptly into a state with high resulting magnetization. In thisstate the spin directions are oscillating about the direction of theapplied field, the magnetization being about 85% of the saturationvalue. In still higher fields, saturation is reached completely. Ahelical spin configuration has been found inMnAu2by Herpin,Me´riel, and Villain. We have investigated the properties of thehexagonal oxide(Ba,Sr)2Zn2Fe12O22which is of the Y-type. TheBa-rich composition is ferrimagnetic and has a preferential planefor the magnetization at all temperatures. The Sr-rich compositionhas no spontaneous magnetization, but a magnetization equal tothe one in the Ba case can easily be induced by an applied field.This behavior can be explained by the assumption of a helicalspin configuration. As an other example, we show that the magneticproperties of dysprosium as investigated by Behrendt,Legvold, and Spedding can be explained by assuming a helicalspin configuration between 85°K and 178°K. The angle betweentwo neighboring layers is equal to zero at 85°K, the ferromagneticCurie temperature, and increases at higher temperatures. Themagnetization process mentioned above is modified slightly indysprosium by the presence of a strong magnetic anisotropy in theplane. In the presence of this anisotropy the transition betweenthe ferromagnetic state and the helical state turns out to be afirst-order transition, which explains the observed specific heat.

ISSN:0021-8979    

DOI:10.1063/1.2000413

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A sequential logic circuit must have a capacity for memory, unidirectionality, and gain. The problemof obtaining these features in magnetic components is considered, and a number of approaches are described.The organization of a circuit using multiapertured cores is discussed, and a method for introducing addedcombinational logic in a compatible manner is described. The status of these techniques is summarized.

ISSN:0021-8979    

DOI:10.1063/1.2000436

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The storage of binary information in twistor wire is complicated by the presence of demagnetizing fieldsresulting from the open flux path structure of this device. These fields modify the writing threshold of eachbit and contribute an interaction with neighboring bits on the same wire. The effect of these demagnetizingfields has been measured with a search-coil technique. A simple procedure consisting of a coincident-currentbit select followed by a single-current read select is used to form and “erase” the magnetized regions. It isfound that the shape of the magnetized regions thus formed are a complex function of the two currents usedand that the bits are not fully erased by the single current. The results suggest that demagnetization mustbe reduced by reducing thickness and/or bit density unless a more complex solenoid structure can be foundto control the magnetization of the bit regions.

ISSN:0021-8979    

DOI:10.1063/1.2000468

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Computer solutions of a pair of differential equations based on the Landau-Lifshitz model indicate thatwith passive loading, magnetic film devices may be used as storage and logical elements in digital computers.Experimental models of a flipflop consisting of anR-C-Lloaded film device show that successive 20-oe,0.1-&mgr;sec drive field pulses can switch the magnetization in the film alternately from one rest orientationto the other with repetition rates of the drive on the order of106 pps. A nondestructive readout memoryelement consisting of anR-Lloaded thin film device is shown which allows films withHkon the order of3 oe to be driven in the hard direction by 15-oe, 0.05-&mgr;sec field pulses without destroying the stored information,resulting in output voltages of about 25 mv per winding turn. Fabrication by evaporation techniquesof a memory employing such elements is discussed.

ISSN:0021-8979    

DOI:10.1063/1.2000474

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

This paper describes the flux distribution in a ferrite core after partial switching to the same flux densityby three different methods: (1) by applying a fixed pattern of alternate-polarity pulses with diminishingamplitude, (2) by amplitude limiting, and (3) by time limiting. Discontinuities in the residual magnetizationcurve in the first case show the existence of regions of oppositely-directed magnetization. A comparison ofthe curves shows that the time-limited state can be represented by a model consisting of a large numberof regions magnetized in alternate directions.

ISSN:0021-8979    

DOI:10.1063/1.2000485

出版商:AIP    

年代:1961

数据来源: AIP