摘要:

This paper extends the theory of magnetic domains with emphasis on recent developments in ``hard bubbles''. A spin configuration of a planar Bloch wall containing periodic Bloch lines is presented which minimizes the magnetostatic energy to first order in the parameter2&pgr;Ms2/Kufor arbitrary period. The form of this solution is found to suggest the form of the dynamic breakdown of this spin configuration. The remainder of the paper consists of applications of the gyrocoupling force and vector, fg= g × v and g = − (Ms/|&ggr;|)sin&thgr;(▿&thgr;) × (▿&phgr;), respectively, and the dissipation force and dyadic, fa= d · v and d = − &agr;(Ms/|&ggr;|)[(▿&thgr;)(▿&thgr;) + sin2&thgr;(▿&phgr;)(▿&phgr;)]. The use of fgand faproduces results with fewer assumptions and with less calculation than with previous methods. The magnitude of g is found to be an invariantlocalmeasure of the ``hardness'' of the domains. Integrating fgand f&agr;produces a general planar wall response function from which the hard bubble dynamic equation is obtained. It is found that the difference between the hard bubble and normal bubble damping parameters can be accounted for by examination of the hard bubble spin‐wave spectrum. An estimate of the velocity required for the production of horizontal Bloch lines is made using fg. This velocity is a substantial fraction of the Walker velocity. The vector g is used as an aid in the visualization of the mechanism by which ion implantation suppresses hard bubbles. From the point of view of both mobility and hard bubble suppression, materials having a large in‐plane anisotropy are found to be desirable.

ISSN:0021-8979    

DOI:10.1063/1.1662989

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Calculations are made for the motion of a domain wall surrounded by a perturbed region of current density resulting from the action of the magnetic field of the domain on a uniform impressed current density. The perturbed region follows the motion of the domain wall and produces a magnetic field which causes the domain to propagate. In particular, a ferromagnetic layer containing a cylindrical domain, with a Hall‐effect overlayer, is considered.

ISSN:0021-8979    

DOI:10.1063/1.1662991

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The electromagnetic interaction between a wall separating two magnetic domains and an impressed electric current is studied in quasistatic approximation. In this case, unlike the related eddy‐current loss problem, the wall velocity calculation requires explicit consideration of magnetic losses which limit the wall velocity, otherwise the wall velocityvwould reach the carrier drift velocityvD. For a magnetic bubble in a material having wall mobility &mgr;&ohgr;and coercive forceHc, we calculate&ngr;=[1−(4/&pgr;)(Hc/Hd0)]&ngr;D&ngr;m/(&ngr;D+&ngr;m), whereHd0is a calculated drive field and&ngr;m=&mgr;&ohgr;Hd0.

ISSN:0021-8979    

DOI:10.1063/1.1662992

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The Faraday‐rotation technique in combination with high‐speed cinephotography has been used to study flux kinetics and heat flow associated with flux jumps in type‐II superconductors. It has been shown that at ``runaway'' velocities, flux motion can be better described in terms of an exponential rather than a diffusion law. Transients observed to exist in the flux‐penetrated region and thought to represent a flux relaxation or redistribution following the jump have been shown to be associated with heating effects in the Faraday glass. Heat flow and its relationship to the flux kinetics was studied for the particular case of a Nb&sngbnd;25%Zr disk sample at 1.4 K in different thermal environments; that is, in a vacuum or immersed in liquid‐helium II. In the latter case, heat transfer to the bath was about three orders of magnitude more important than thermal conduction within the sample. Nevertheless, the assumption that flux jumps take place under essentially adiabatic conditions, made for purposes of analysis, turns out to be approximately correct; this supports the theoretical treatments of Swartz and Bean and Wipf.

ISSN:0021-8979    

DOI:10.1063/1.1662993

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A general two‐dimensional analytical solution is presented for the problem of transport current injection from a normal conductor into a superconductor and collection back into a normal conductor. The current distribution is solved for the general case which takes in the full range from essentially point source to full‐width injection and collection. The current distribution also represents that in a split‐ring superconductor joined by a link of variable width, such as that in a Josephson junction. A comparison is made with current injection into and collection from a normal conductor. Computer calculations are included showing a virtual anomaly which is reconciled. Speculation is made regarding the formation of transport current vortices in an initially simply connected superconductor.

ISSN:0021-8979    

DOI:10.1063/1.1662994

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Propagation losses are calculated for magnetostatic surface waves in slabs of YIG and LiFe5O8. A phenomenological (Gilbert) magnetic damping is assumed and known magnetic parameters are used. The propagation loss factorL(dB/&mgr;sec) is calculated as a function of frequency. At high frequencies we find thatLis proportional to frequency with a slope of 4&pgr;(76.4&lgr;/&ggr;2M), where &lgr; is the damping parameter, &ggr; is the gyromagnetic ratio, andMis the magnetization. At low frequencies,Lapproaches a limiting value of 4&pgr;(76.4&lgr;/&ggr;). The quantityLis independent of slab thickness, although both loss and delay time are functions of thickness for a given slab length. Our calculatedLis in reasonable agreement with recent measurements. As expected, magnetic anisotropy has a greater effect onLfor LiFe5O8than for YIG.

ISSN:0021-8979    

DOI:10.1063/1.1662995

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Nb3Sn alloyed with Si, Ti, V, Ta, Bi, or Mo has been grown from the vapor phase on stainless‐steel (Hastelloy) ribbon substrates. Compared to a value of 185 kOe observed for unalloyed Nb3Sn, 1.3% Si increasedHc2to 225 kOe, while 0.002% Bi or 0.05% V raisedHc2to about 215 kOe. Whereas 0.0006% Ti or 3.7% Ta did not affectHc2appreciably, 0.4% Mo decreasedHc2to 140 kOe. Diffusion of Ni from the stainless‐steel substrate into the Nb3Sn layer appears to be responsible for the observedHc2value of 196 kOe for the unalloyed (but carbon doped) ribbon since the same Nb3Sn layer on a Nb substrate has anHc2value of 225 kOe. The effect of the Ni outdiffusion onHc2can be reduced by reducing the Nb3Sn growth temperature or by increasing the Nb3Sn layer thickness.Hc2does not appear to correlate directly withTcsinceTcis about 15.5°K for both the Si‐ and Mo‐alloyed Nb3Sn, as well as for the unalloyed Nb3Sn deposited on a Nb substrate, whileHc2ranges from 140 to 225 kOe. The intermediate phase region between the Nb3Sn layer and the stainless‐steel substrate consists of a rich variety of phases including NbNi, NbNi3, Ni3Sn, Ni3Sn2, and MoNi. Alloying Nb3Sn with Bi, Ti, V, and Mo reducesJcby a factor of 2 to 4 compared to the unalloyed sample. Ta does not significantly affectJcand Si significantly increasesJcabove 120 kOe. CO2or C2H6additions can increaseJcfor the alloy ribbons by up to a factor of 8, but not to values greater than observed for unalloyed Nb3Sn doped with carbon. Si alloys doped with carbon are an exception and have higherJcvalues above 120 kOe than the carbon‐doped unalloyed ribbon.

ISSN:0021-8979    

DOI:10.1063/1.1662996

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The critical current of an asymmetrical Josephson junction as a function of magnetic field has been computed for junction lengths of 2&lgr;Jand 6&lgr;J. The boundary conditions for the asymmetrical and cross junction (with an assumed current distribution) are derived. Similarity between the computed asymmetrical junction diffraction patterns and experimental patterns for the cross junction plus identical boundary conditions indicate that the current flow in the cross junction is the same as in the asymmetrical junction. Profiles of the current density in the linear and asymmetrical Josephson junctions are compared.

ISSN:0021-8979    

DOI:10.1063/1.1662997

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The propagation characteristics of magnetoelastic (ME) Rayleigh waves on a YIG substrate are treated for theparallel bias configuration, wherein the bias field is tangential to the substrate and parallel to the direction of propagation. The YIG surface is considered to be mechanically free and either adjoined to vacuum (unmetallizedconfiguration) or electrically shorted by a thin perfectly conducting metallic film (metallizedconfiguration). The ME Rayleigh waves are found to be bound surface waves outside of a spectrum of frequencies given approximately by the magnetostatic bulk‐wave spectrum, and of the leaky type within it. By varying the frequency (or equivalently the bias field) over the leaky‐wave spectrum, the direction of energy leakage into the substrate may be controlled over an angle of 180° from the direction of surface‐wave propagation.

ISSN:0021-8979    

DOI:10.1063/1.1662999

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The occurrence of new metallurgical phases and enhanced superconductivity in a number of sputtered transition‐metal alloy films has been studied as a function of substrate temperature during deposition. Results indicate that such new phases are readily produced in the temperature range 200–1000°C by this technique and that these new phases are accompanied by marked changes in the superconducting transition temperature. The findings show how easily the more complex transition‐metal alloys, particularly &sgr; phase, can be modified at low temperatures, and demonstrate the importance of structural instability, vis‐a`‐vis composition, in determining the superconducting transition temperature.

ISSN:0021-8979    

DOI:10.1063/1.1663000

出版商:AIP    

年代:1974

数据来源: AIP