摘要:

Impulse selection is a scheme for operating ferrite cores which have low values of coercive force. Twodifferent threshold properties of a core are utilized. One threshold is the dc coercive force, which can bechanged electrically. The other threshold results from the inertial magnetic effects within the core whichare predominant when pulses of very narrow widths are applied. The switching behavior of ferrite coresis discussed when two threshold currents, a low amplitude current and an impulse of current, are combined.The application of this property to core logic is considered.

ISSN:0021-8979    

DOI:10.1063/1.2000489

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A systematic theoretical study of a saturation type of recordingand reproduction in digital magnetic tape systems was undertakenso that the details of these processes could be more clearly understood.The dependence of tape magnetization and of output signalpulse width and amplitude on the major system parameters hasbeen investigated and determined. These parameters are themagnetic field distribution of the recording head, write currentwaveform, tape thickness and hysteresis characteristics, head-to-tapespacing, reading gap length, and bit density. A portion ofthis study is presented here, concerning the extension of thesinusoidal theory to include the reproduction of signals resultingfrom saturation recording. This is done by a Fourier analysis ofthe tape magnetization and a term-by-term summation of harmonicresponses to obtain the resultant signal. The results showwhy high writing field gradients, high tapeB-H“squareness,”and thin tapes are needed for high-density recording. They indicatepossible reasons for emf pulse peak position asymmetries duringreadback. Two examples of output calculations are included. Oneshows the signal amplitude and pulse width vs bit density, comparedwith experimental measurements. The other presents thefield distribution above the magnetized tape, indicating the influenceof the presence of the read head.

ISSN:0021-8979    

DOI:10.1063/1.2000490

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Thin films of ferrites, of the order of 1000 A thickness, have been prepared by vacuum evaporation of themetals, and subsequent high-temperature oxidation. Films of iron, nickel, cobalt, magnesium, and copperferrites, mixed ferrites, and mixed ferrite-aluminates, as well as yttrium iron garnet, have been prepared.X-ray powder diffractometry indicates that the ferrite films are single-phase spinels, while the garnet showsthe garnet structure. In many respects, the properties of the films are the same as those of bulk ferrites ofsimilar composition. The resistivity of the films can be controlled by proper oxidizing procedures. X-bandmagnetic resonance measurements indicate that the saturation magnetizations of the films are comparableto those of the corresponding bulk ferrites, though the films show larger resonance linewidths. It has beenpossible to prepare magnesium ferrite films with magnetizations from 2200 gauss to less than 500 gauss byproper annealing and quenching. The possible advantages of thin films are that they allow optical studiesof the material by transmission, and should permit determination of magnetic exchange constants throughobservation of spin wave resonances.

ISSN:0021-8979    

DOI:10.1063/1.2000491

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Thin films of ferrites of various compositions have been prepared.Two methods have been developed, both involving a spraytechnique whereby hot suspensions of hydroxides are directedonto a heated substrate. The ferrite films are formed essentiallythrough a coprecipitation mechanism. X-ray diffraction has shownthat the films have a cubic spinel structure. Various compositionshave been attained; magnetite, nickel ferrous ferrite, a magnetite-zincferrite series, and other mixed ferrites. Coercive force measurementswere made from hysteresis loops obtained on a 1000-cycleloop tracer. The films are magnetically isotropic and have a highsquareness ratio. Film thicknesses have been varied from a fewhundred A to about 1 &mgr;. Relative film thicknesses were estimatedby using a spectrophotometric technique. For a fixed composition,coercive force decreases with increasing thickness. Magnetitefilms had coercive forces varying from 170 to 300 oe depending onthickness. A nickel ferrous ferrite series had coercive forces varyingfrom 225 oe for thick films to 400 oe for a very thin one. Coerciveforce measurements are related to composition variations in aseries of zinc ferrous ferrite films.

ISSN:0021-8979    

DOI:10.1063/1.2000492

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Neutron diffraction measurements on a single crystal of dysprosium show that the magnetic structurein the antiferromagnetic region between 179° and 87°K closely resembles a helical-type arrangement of theatomic moments. In this arrangement the moments within a hexagonal layer are aligned parallel and pointin a direction perpendicular to thecaxis of the crystal. The moment direction in adjacent layers is rotatedby a specific angle which is dependent on the temperature of the sample. A slight modification of thisstructure exists below about 140°K, and a transition to ferromagnetism occurs at 87°K.

ISSN:0021-8979    

DOI:10.1063/1.2000493

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Neutron diffraction measurements were made on erbium single crystals in the temperature range 298°–4.2°K.The material is antiferromagnetic below 80°K and ferromagnetic below 20°K. In the antiferromagneticregion, the magnetic scattering consists of satellite reflections corresponding to a modulation of themagnetic scattering amplitude along thecaxis. The spacing and intensity distribution of these satellitesshow two distinct subregions of antiferromagnetism. In the upper region, between 80° and 52°K, the datasuggest a sinusoidal modulation of the magnitude of thec-axis component of magnetic moment with aperiod of3.5 c0. Between 52° and 20°K the wavelength of the modulation varies continuously from3.5° c0to4.0 c0. In addition, there is a squaring up of the modulation and a simultaneous ordering of the componentof the moment normal to thecaxis. Below 20°K the material is basically ferromagnetic with a momentof 7.2 &mgr;B directed parallel to thecaxis.

ISSN:0021-8979    

DOI:10.1063/1.2000494

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Low-temperature magnetic isotherms of &agr;-Mn and its alloys with Fe, N, and H have been examined.Hysteresis loops and effects of cooling in an applied field are reported. Similar properties are found forsingle crystals of Cu-Mn. It is pointed out that the spin density wave mechanism of antiferromagnetism,proposed by Overhauser, provides explanations for these phenomena. Neutron diffraction data are reinterpretedand provide further evidence for spin density waves in &agr;-Mn and its alloys.

ISSN:0021-8979    

DOI:10.1063/1.2000495

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The nature of the interaction between Mn atoms which is responsible for the helical magnetic structureand the metamagnetic behavior ofAu2Mnis examined by analyzing the magnetic behavior of Au-Mnsystem in general. From the comparison of the magnetic structure ofAu2Mnand that ofAu4Mn, themagnetic dipole interaction is suggested as one of the possible main weak interactions which connects thesuccessive layers of Mn atoms ofAu2Mn.

ISSN:0021-8979    

DOI:10.1063/1.2000496

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Compounds of the formMn2−xCrxSbshow a first-order ferrimagnetic to antiferromagnetic phase transitionwith decreasing temperature. Sublattices composed of the three adjacent ferrimagnetically aligned (001)planes Mn(II)-Mn(I)-Mn(II) are ferromagnetically ordered above the transition temperatureTsandantiferromagnetically ordered belowTs. The exchange interaction between these sublattices changes signat a critical interlayer distance. The discontinuous change in interlayer distance atTsis proportional to thesquare of the magnetization of the sublattice in agreement with Kittel's conclusions.

ISSN:0021-8979    

DOI:10.1063/1.2000497

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Magnetic anisotropy and electrical resistivity have been determined for several materials of compositionMn2−xCrxSb, which exhibit a ferrimagnetic to antiferromagnetic phase transformation with decreasingtemperature. Magnetocrystalline anisotropy is similar in its temperature behavior to that ofMn2Sbwithslight differences attributed to changes in magnetic moment of the Mn sublattices. Resistivity is attributedto electron-magnon scattering. The magnetocrystalline anisotropy at the two Mn sites of nearly equalmagnitude but opposite sign is consistent with the small anisotropy of the magnetoresistance.

ISSN:0021-8979    

DOI:10.1063/1.2000498

出版商:AIP    

年代:1961

数据来源: AIP