摘要:

Evidence is presented to support the assumption of spin‐triplet p‐wave Cooper pairing in the A and B phases of3He, and the particular form of the order parameter in each phase follows from available experimental data. Leggett’s description of the spin dynamics shows that the macroscopic condensate qualitatively alters the NMR properties, for the spin density experiences an additional coherent torque that depends on the orientation of the orbital angular momentum of the Cooper pairs. This torque produces many new phenomena, including a temperature‐dependent shift in the transverse CW resonance signal away from the Larmor frequency, resonant absorption in longitudinal CW excitation, and ringing behavior following a sudden perturbation in the applied magnetic field.

ISSN:0094-243X    

DOI:10.1063/1.30584

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The observed spin down rates of pulsars (rapidly spinning isolated neutron stars) imply that their stellar surface magnetic fields exceed 1012G. In such superstrong fields atoms shrink in each dimension by over an order of magnitude and the binding energy of atoms into molecular chains can exceed that of all the electrons in an isolated atom. The stellar surface layer forms a dense (104−105g cm−3) tightly bound (10 kev/atom) anisotropic conductor which gives the star a sharp edge even at temperatures of 107°K.Strong magnetospheric electric fields are insufficient to pull ions from such a surface. Instead they generate electron‐positron discharges in the 1012G field of the near magnetosphere. These particles are probably the source of current flow in the magnetosphere and of many of the observed properties of pulsar radiation.

ISSN:0094-243X    

DOI:10.1063/1.30474

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

We review briefly the experimental and theoretical literature on the contribution from spin‐spin interactions to the thermal boundary conductance (Kapitza conductance) between liquid He3and solids. This contribution to the boundary conductance has its origin in the interaction of the He3nuclear magnetic moment with electron spins in solids. We summarize some new predictions of the behavior of the magnetic boundary conductance at temperatures below the onset of superfluid order in He3. Also, we present initial results of our study of the longitudinal relaxation of liquid He3nuclear spins in dipolar contact with electron spins in a paramagnet.

ISSN:0094-243X    

DOI:10.1063/1.30521

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Geomagnetism is the most familiar example of astrophysical magnetic field production. Our current understanding of the principles of magnetic field generation is briefly reviewed and the major outstanding problems are outlined, with particular emphasis on the Earth. The geomagnetic reversal phenomenon is an important feature of the field’s behavior. Several possibilities for the origin of geomagnetic reversals are discussed.

ISSN:0094-243X    

DOI:10.1063/1.30540

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

In this talk, the more fundamental issues confronting magnetic recording theory will be reviewed in a fashion which should be of interest to both recording specialists and other magneticians. The absence of a usable, microscopic, vector model of the recording medium magnetization is the principal theoretical problem in both recording and other magnetic studies. M‐H curve fitting or, better, the Preisach function approach1yields only limited information on the recorded signal and none on the medium noise. In contrast, the theory of recording head fringing fields appears to be nearly complete; recent results on narrow pole‐tip heads2and on pole‐tip partial saturation effects3will be reviewed. After a brief discussion of theory of the anhysteretic4and thermo‐remanent processes, some results of large scale modeling5of the write process will be presented. A salient finding of these experiments is a rotating vector magnetization pattern which may not be understood fully without a vector M‐H presciption; the rotating magnetization patterns give rise to curious symmetries6of the medium flux. Whereas the minimum additive noise due to the particle statistics in the medium may be deduced from first principles7, multilplicative (or modulation) noises due to physical aggregations or magnetic collective behavior of particles presently defy simple prediction. It is possible to conclude, however, that provided such aggregations are small in comparison with the trackwidth, the signal‐to‐noise ratio (SNR) will decrease by only 3 dB per halving of the trackwidth but by 6 dB per halving of the wavelength. More information per unit area can, therefore, be recorded by using narrow tracks and low linear densities than with wide tracks and high linear density. With current &ggr;‐Fe3O3media, the SNR8 limited areal densities are somewhat above 107bits/sq. in.8, a factor of ten higher than in current practice.

ISSN:0094-243X    

DOI:10.1063/1.30567

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The dc and ac Josephson effects and the behavior of the current‐voltage characteristics of Josephson junctions are briefly reviewed. The Josephson junction cryotron is described. Two cryotrons have been incorporated into a NDRO memory cell with a switching time of 80ps, a power‐delay product of 10−16J, and an area of 900&mgr;m2. DRO memory cells involving the storage of a single flux quantum have estimated switching speeds of 50ps and a dissipation in continuous operation of 40nW. Latching logic elements with a switching time of 200ps and a power‐delay product of 5fJ have been built. Non‐latching devices and the flux shuttle are described. The use of dc and rf SQUIDS in conjunction with flux transformers for magnetic measurements is discussed. Presently achieved sensitivities are: magnetic field, 10−15THz−1/2, magnetic field gradient, 10−13Tm−1Hz−1/2; magnetic susceptibility, 2×10−11e.m.u. for 1cm3at 10−1T; voltage, 10−15VHz−1/2. The highest energy resolution reported for a SQUID‐transformer combination is 8×10−30JHz−1in a frequency range from 2×10−2Hz to 1kHz. At lower frequencies the noise power spectrum is 1/f. The performance of the computer and measuring devices is compared with that of conventional (non‐superconducting) devices.

ISSN:0094-243X    

DOI:10.1063/1.30572

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The design of a pickax replicate/transfer gate has been reported.1Here we report on the operation of this element with respect to variations in the current pulse parameters (amplitude A, width tw, and position tp), inplane drive field amplitude and bias field. This element was operated at 100 KHz on (YSm)3(FeGa)5O12garnet with a nominal bubble diameter of 5 &mgr;m and was configured in the major loop to detector path on a major/minor loop chip. The following values of pulse parameters provide replicate and transfer bias field margins equal to that of loop propagation (16 Oe) while maintaining acceptable tolerances: Replicate: A=75 mA, tw=2.0 &mgr;sec and tp=5.4 &mgr;sec (zero &mgr;sec corresponds to the inplane field parallel to the long axis of the pickax element); Transfer: A=75 mA, tw=4.0 &mgr;sec and tp=3.8 &mgr;sec. With these pulse parameters, reducing the drive field amplitude from 40 to 25 Oe reduces the bias field margin for replicate and transfer by 3 and 2 Oe, respectively.

ISSN:0094-243X    

DOI:10.1063/1.30605

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

For the first time the distribution of normal (perpendicular to the elements plane) component of magnetization M in T and I bars of efficient bubble domain propagation circuits at various orientations and values of external magnetic field H has been studied by means of magnetooptic micromagnetometer method, where previously measurements of horizontal component of magnetization M have been obtained.*Parts have been discovered, where M emerges from the plane of bars, which are magnetostatic wells for the bubble. While H is oriented along I, two parts with M have been registered with dimensions of about 1/8 that of I. When H is oriented perpendicularly to a short section of T, one magnetostatic well is observed in its centre, and when H is oriented at an angle of 45° to the short section of T, three magnetostatic wells appear. The distribution of M in the short section of T in case of longitudinal magnetization is similar to that of M in I. It has been found that M in the whole range of operate fields does not exceed O, IMs.

ISSN:0094-243X    

DOI:10.1063/1.30617

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

To better understand how bubbles affect a resistance change in a Permalloy chevron stretcher detector, a more detailed knowledge of the magnetoresistive properties of such elements in the absence of bubbles is required. Results of systematic resistance measurements on a single element as a function of magnitude, H, and direction of an inplane dc magnetic field are presented for 10 Oe<H<10,000 Oe.

ISSN:0094-243X    

DOI:10.1063/1.30624

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The &ohgr;−2&ohgr; transition1in the magnetoresistance waveform at 100 KHz was investigated for a long Permalloy chevron stretcher detector in the absence of bubbles propagating through the structure. When the Permalloy is demagnetized by decreasing the rotating inplane field, H, in the absence of any dc fields, the waveform of the resistance variation is 2&ohgr; for 0<H<40 Oe, where &ohgr; is the angular frequency of rotation. When the Permalloy is ac demagnetized in the presence of a small dc field applied along the long axis of the detector element, the resulting waveform has an &ohgr; dependence for 0<H≲20 Oe, becoming 2&ohgr; for 20<H<40 Oe. In the &ohgr; regime, the phase angles of the rotating inplane field at which resistance maxima occur depend on the direction in which the dc field was applied during demagnetization. A domain model based on magnetization fanning is proposed to explain these results.

ISSN:0094-243X    

DOI:10.1063/1.30635

出版商:AIP    

年代:1976

数据来源: AIP