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1.
A four-parameter variational model is used to calculate the properties of stripe domains in uniaxial magnetic films. The width of the stripes and the thickness of the walls between the stripes are allowed to vary. In addition, the effects of the demagnetizing fields across the walls are included by allowing the spins within the walls to twist out of the wall plane. It is shown that the presence of neighboring walls in this model yields a substantially higher wall energy density in most cases of importance to bubble technology than was previously reported by Schlömann for a similar model of an isolated wall, the stripe wall energy density being over 50 percent higher in the case where the dimensionless anisotropy parameterq = K_{u}/2piM^{2}is 1.1 and the film thickness to material length ratioh/lis 9. A critical discussion of the significance of wall energies in such models is given, and a method is discussed by which the stripe-width information from this model may be used in interpreting stripe-width data to obtain material parameters to an accuracy hitherto unavailable.  相似文献   

2.
Static wall coercive force in ferromagnetic thin films   总被引:1,自引:0,他引:1  
The static wall coercive force of thin ferromagnetic films has been calculated from a model of conservative wall energy. The spatial dependence of the wall energy γwis assumed to be given by the mean value of the local anisotropy energy, averaged over a coupling volume of the wall. The result of the calculation shows thatH_{w} propto frac{S}{M_{s}} (frac{D}{W})^{1/2} frac{1}{L}where the structure constantSincludes the local anisotropy,Dis the mean diameter of a region with constant anisotropy (for instance crystallites),Wis the wall width; andLis the coupling length parallel to the wall.  相似文献   

3.
A simple model is presented which allows accurate prediction of bias margins of gap-tolerant half-disk propagation tracks for bubble domains. After this is verified by comparison with experimental margin data, an "isomargin" plot is derived to show how the margin varies as a function ofWandG, whereWis the minimum linewidth andGis the inter-bar gap. The bias margin is shown to decrease along a fairly straight line which goes to zero whenW + Gequals the runout diameter, i.e., whenW+G approx 1.5 W_{s}, where Wsis the bubble stripwidth or average bubble diameter. This agrees with experiment, and means that the minimum resolvable feature for half-disk type patterns must be less than0.75W_{s}, and probably will not be much larger than0.5W_{s}to0.6W_{s}. It is concluded that, if made with perfect Permalloy, T-bars and half-disks should propagate isolated bubbles equally well. The advantages of half-disks over T-bars are 1) the fatal bar-crossing problem of T-bars with multiple bubbles is avoided, 2) the minimum propagation field is lower than for T-bars, and 3) half-disks seem more tolerant of "bad" (e.g., high-coercivity) Permalloy. Also tabulated are the effects on margins of variations in the device parameters of a representative design, as might be encountered in a fabrication process with finite tolerances. A brief discussion of stop-start margins is given in conclusion.  相似文献   

4.
It is widely known that bubble domains can exist when the bias field is between the elliptic instability (runout) field Heand the bubble collapse field Hbc. Values for Heand Hbcwere calculated by Thiele. It is not widely recognized that long stripe domains can also exist in the bottom 20% of this range. Stripes are stable up to the "stripe contraction" field, Hsc, which is about 0.02 M/μ0above Hefor thickness over intrinsic length,h/l, values from 4 to 10. (Hbcis about 0.10 M/μ0above He.) Values for Hscwere calculated by Kooy and Enz of Philips Research Labs. in 1960, although the importance of their result to bubble-domain devices was not apparent at the time. The velocity of the domain tip during stripout and contraction such as occurs during domain detection or transfer is important for calculating maximum circuit speeds. This is given byV = cG (H-H_{sc}), whereHis the field (bias field plus local field from currents or Permalloy elements),Gis the wall mobility, andcis a constant approximately equal to 0.5.  相似文献   

5.
The totaldot{phi}(t)waveform of a square-loop magnetic core switched by MMFF(t)from negative remanencephi = -phi_{r}is composed of elasticdot{phi}_{epsilon}(t), decaying inelasticdot{phi}_{i}(t), and bell-shaped main inelasticdot{phi}_{ma}(t). The worst delta noise in a coincident-current memory core pair is essentiallydot{phi}_{i}(t). The sources of these components and the staticphi(F)curve are explained qualitatively by means of the random variations of the energy gradient vs. domain-wall position: elastic wall displacements and elastic rotation of magnetization inducedot{phi}_{epsilon}(t); minor inelastic wall displacements of essentially constant wall areas inducedot{phi}_{i}(t); and major inelastic wall displacements (involving domain collisions) of varying wall areas inducedot{phi}_{ma}(t). Semiempirical models for thedot{phi}components are based on the characteristics of these displacements. A satisfactory agreement is obtained between these models anddot{phi}(t)oscillograms of a thin ferrite core.  相似文献   

6.
The magnetic coupling between the magnetization in two nonmagnetostrictive Ni-Fe layers separated by a SiO layer has been investigated by means of a transverse susceptibility measurement. The main results are that 1) the coupling energy Ec per Unit area of the multilayered film has a form ofE_{c}= -A cos (phi_{1}-phi_{2}), wherephi_{1}-phi_{2}is the angle between the magnetization vectors in the two Ni-Fe layers, and 2) the dependence of the coupling constant on the thickness b of the intermediate SiO layer can be interpreted quantitatively by the combination of the coupling energy due to Néel's topography model and that due to the magnetostatic interaction between the magnetic free poles appearing at the edges of the two Ni-Fe layers. The former coupling energy is given byE_{c1} = -frac{p}{2sqrt{2}}omega^{2}M^{2} exp(-sqrt{2}pb) cos (phi_{1}-phi_{2})wherep=2pi/LandLandware the wavelength and the amplitude of the undulation of the interface between Ni-Fe and SiO layers, respectively. The latter is given byE_{c2} = frac{2M^{2}D^{2}}{R} ln (frac{R}{D+b}) cos (phi_{1}-phi_{2})whereDis the thickness of each Ni-Fe layer, andRis the radius of the film.  相似文献   

7.
The movement of an individual Bloch wall in a single-crystal picture frame of silicon iron was studied. By using an electronic apparatus the wall velocity was held constant during the magnetization reversal. It was possible to control the wall velocity down to 10-2mm/s. Even at these low velocities the relationship between the wall velocityvand the driving magnetic fieldHis precisely linear:v = const . (H-H_{0}). This is to be expected under the given experimental conditiondB/dt = const.  相似文献   

8.
Dielectric behaviour of a ferrofluid subjected to a uniform magnetic field   总被引:2,自引:0,他引:2  
The electric susceptibility of samples of ferrofluids subjected to a uniform magnetic fieldHwas measured. The electric susceptibilitychiis dependent on the magnitude of the magnetic field and on the relative direction between the electric fieldEand the magnetic fieldH. 1) WhenEis perpendicular toH, frac{partialchi_{perp}}{partialH} < 02) WhenEis parallel toH, frac{partialchi_{parellel}}{partialH} > 0These results have been interpreted as a magneto-electric directive effect. A model is proposed, based on the assumption that the magnetic particles are roughly ellipsoidal and conducting grains.  相似文献   

9.
In Goss-oriented SiFe laminations, regions exist with a significant normal magnetization component arising from dip misorientation of the crystallites. It has recently been suggested by Imamura and co-workers that this normal magnetization can make a major contributionP_{perp}to the eddy current losses incurred during cyclic magnetization along the texture axis.P_{perp}is calculated for three distinct domain models of the magnetization process in laminar crystallites with modest dip misorientation. Contrary to the Imamura work,P_{perp}is found to be practically negligible for a simple slab domain structure without closure domains. This is because the normal demagnetizing field restricts normal induction to the neighborhood of the domain walls and ensures that its volume average is practically zero. In a second model monotonic reversal of normal magnetization in closure domain structures is also shown to give rise to rather low normal lossP_{perp}. A third model concerns how closure domains may interact with the major boundaries between slab domains and be swept along with them. Quite substantial lossesP_{perp}are predicted if all closure domains in a zone extending a distance rather greater than the sheet thickness either side of the major domain wall are displaced in this way. However, even this mechanism can explain only a small part of the marked increase in eddy loss with dip misorientation reported, and it is concluded that normal flux is probably not primarily responsible.  相似文献   

10.
A new process-an electron-"radiomagnetic" treatment-for obtaining high-remanence, low-coercive-force loops in magnetic alloys was recently announced. As an example, 2-MeV electron irradiation of 6-mil-thick ring laminations of polycrystalline 5-80 Mo Permalloy with 1017e/cm2in an applied circumferential magnetic field of 0.2 Oe atsim100degC produced record highs in remanence (∼6700 G) for this material. Additional studies of this process have been made to determine some of the controlling factors and the range of application. In particular, the effects of the dose (number of e/cm2) and of the preirradiation magnetic properties were examined. The results show that: 1) for a given dose of1.1 times 10^{17}2-MeV e/cm2, the relative change in remanence (DeltaB_{r}/B_{r}) is always positive, ranging from 10 to 50 percent, but varies inversely with the preirradiation value of remanence (Br); 2) for the same dose, the relative change in coercive force (DeltaH_{c}/H_{c}) also depends upon the preirradiation value of remanence, but in a different way. ForB_{r} < 5000G,DeltaH_{c}/H_{c}is either negative or zero. ForB_{r} > 5000G,DeltaH_{c}/H_{c}is positive, ranging from 20 to 150 percent, and increases linearly withB_{r}; 3) if the dose is reduced tosim0.8 times 10^{17}e/cm2, thenDeltaH_{c}/H_{c}is reduced to a tolerable level (∼10 percent) with no significant sacrifice in the positive gain in remanence and rectangularity. Hence, there are optimum dose ranges in the "radio-magnetic" treatments of alloys, where significant gains in remanence may be obtained without appreciable increases in coercive force.  相似文献   

11.
First-order perturbation of the one-dimensional structure for the wall surrounding a bubble domain, lead to a set of linear differential equations, which should determine the wall twist for any magnetic material with a large quality factor Q provided the wall is stationary. A first-order solution of these equations is given in terms of two linear integrals whose numerical evaluation is much simpler than the evaluation of wall structure by minimizing numerically the wall energy, as has been done so far. Examples are given for the wall twist thus computed for several film thicknesses, which should give an idea of what the twist is when Q is large enough. For medium Q, however, the accuracy of the method turns out to be inadequate.  相似文献   

12.
A three-dimensional hybrid lattice Boltzmann method was used to simulate the progress of a single bubble’s growth and departure from a horizontal superheated wall. The evolutionary process of the bubble shapes and also the temperature fields during pool nucleate boiling were obtained and the influence of the gravitational acceleration on the bubble departure diameter (BDD), the bubble release frequency (BRF) and the heat flux on the superheated wall was analyzed. The simulation results obtained by the present three-dimensional numerical studies demonstrate that the BDD is proportional to \(g^{\mathrm {-0.301}}\), the BRF is proportional to \(g^{\mathrm {-0.58}}\), and the averaged wall heat flux is proportional to \(g^{\mathrm {0.201}}\), where g is the gravitational acceleration. These results are in good agreement with the common-used experimental correlations, indicating the rationality of the present numerical model and results.  相似文献   

13.
In an all-magnetic resistance-type shift register, a PRIME current pulsei_{p}(t), of amplitude Ip, is applied to Npand Nbturns through the minor and major apertures, respectively. For given operation frequencyf, the ratioR = I_{p}^{max}/I_{p}^{min}, whereI_{p}^{min} < I_{p} < I_{p}^{max}is the PRIME range of bistable operation, is maximized by matchingN_{p}/N_{b}so thatI_{p}^{max}values determined by spurious ZERO buildup and ONE dropout are the same. For a rectangular (or dc)i_{p}(t), the matchedN_{p}/N_{b}is fixed by the core properties, and Rmaxis limited (e.g., <7). However, ifi_{p}(t)rises gradually, the matchedN_{p}/N_{b}depends also on the rise time Trofi_{p}(t). The lowerfis, with corresponding larger Tr, the smaller is the matchedN_{p}/N_{b}, and the larger is Rmax. Calculation ofRis carried for ramp and half-sinusoidali_{p}(t)waveforms. The latter, for instance, atT = 25degC yields Rmaxvalues of 14.0 and 22.0 forfof 1.0 and 0.5 kc/s respectively. Such wide PRIME ranges permit reliable register operation in a wide temperature range without resorting to temperature compensation of Ip. Experimental results are in agreement with the calculation.  相似文献   

14.
Wall anisotropy causes bubble domains to be elliptical. A formula relating the eccentricity of an elliptical bubble to the anisotropic wall energy is derived, and an experimental technique for measuring the wall anisotropy is described. In Sm0.55Tb0.45FeO3a measured anisotropy energy of 1.7 percent of the wall-energy density at room temperature is responsible for eccentricities as large as 0.4 at average bubble radii equal to 85 percent of the bubble strip-domain transition radius. The relationship between material parameters and wall-energy anisotropy is briefly discussed.  相似文献   

15.
Under the assumption that in a double-layer film both layers are equally deformed, the following formula for the magnetostriction energyE = K_{c} sin^{2} alphahas been derived whereK_{c} = (9/40)(2U'U"/U'_{0} + U_{0}")is the coupling constant and α is the angle between the magnetization vectors. This formula is valid if we can neglect interaction with the substrate. The sign of the coupling constant is discussed. It turns out that where the composition of the two layers are different, the value of Kccan be, in some special cases, negative.  相似文献   

16.
The operation of a bubble-domain straight-line propagation circuit has been simulated successfully. This simulation has been achieved by our approximating the motion of an s = 0 frozen-azimuth bubble placed under a drive fieldH_{Z}(X, Y, T)= -H_{p} cdot cos [2pi(X/R_{X} - n(T)/4)] cdot exp [-(Y/R_{Y})^{2}]. The simulation has been generated from a previously developed numerical scheme to simulate the motion of a bubble, whose domain shape and magnetization structure along its domain wall were variable. The drive field has been modeled after a dual conductor-sheet, current-access propagation structure, which has a bit period RXand a transverse width on the order of2R_{Y}. The entire field contour has been advanced stepwise in the positiveXdirection by an increase of the integern(T), which represents the drive-phase number. The bubble motion has been observed during the first six drive phases to produce operating margin diagrams for drive frequencies of 250 KHz, 796 KHz and 1 MHz. The method of calculation and the results of the simulation are given.  相似文献   

17.
A new kind of bubble having two stable states for a bias field HBhas been found in thin garnet films. The bubble becomes smaller with increasing HBand disappears abruptly at some critical fieldH_{C1}. However, it does not collapse atH_{C1}. When HBis lowered, it comes into sight suddenly at another critical fieldH_{C2}. This means that for HBbetweenH_{C1}andH_{C2}the bubble has two stable states, one for a large bubble and the other for an unobservably small bubble. This has been well explained in terms of the stability of bubbles containing a definite number of Bloch lines.  相似文献   

18.
Scaling of magnetic bubble devices to smaller bubble sizes and higher density is considered. Drive field requirements, materials requirements, fabrication requirements, current requirements, and detector signal-to-noise ratio are all calculated as a function of bubble size and related to practical limits imposed by bubble materials, fabrication techniques, and electromigration limits. It is concluded that "conventional" bubble devices using Permalloy bars can be made practical with 1-μm bubble domains (storage densitysim6 times 10^{6}bits/cm2). Although it may be possible to extend these Permalloy bar devices to even smaller bubbles, it seems more likely that other bubble devices such as contiguous disk devices or bubble lattice devices will in fact be used for densities greater than 6 × 106bits/cm2.  相似文献   

19.
In the present paper, the bubble growth and departure at the tip of capillary tubes with different wall wettabilities in a stagnant fluid is experimentally investigated by using a high-speed visual system. The visual experiments show that the bubble growth experienced three typical stages: the initial growth, the speed-up growth, and the speed-down growth, with distinct varying behaviors of tip contact angle and size of bubble. The formation mechanism of each growth stage is discussed individually. It can be deduced from the experimental results that the bubble breakthrough point for a hydrophilic capillary tube is resulting from the triple contact line rapidly advancing from the inner wall slightly beneath tube tip to the inside surface edge of the tube tip when the contact angle of the bubble on the inner wall approaches the receding contact angle. The wall wettability has a significant effect on bubble growth and departure. The departure size and growth cycle period of bubble for a Teflon tube with hydrophobic wall is obviously smaller than these for glass tube with hydrophilic wall. Furthermore, the triple contact line of the bubble locates at the inside surface edge of the tube tip for glass tube, while one locates at the outside surface edge for Teflon tube before bubble departure. The liquid incursion into the tube tip for glass tube has never arisen for the Teflon tube after bubble departing from the tube tip.  相似文献   

20.
The dependence ot the in-plane drive field at which bubble domains spontaneously nucleate in field-accessed bubble devices has been investigated as a function ofH_{k} - 4piM_{s}and of spacer thickness between the bubble film and permalloy propagation elements. The experiments were carried out on amorphous GdCoMo bubble films with T-bar and Y-bar structures. For a given structure and spacer thickness the nucleation field increases linearly withH_{k} - 4piM. Larger spacer thicknesses also lead to increased nucleation fields. A model based on the Stoner-Wohlfarth astroid is compared to these data and found to be useful in explaining the qualitative trends, but to be in poor quantitative agreement. It is concluded that since the drive field required in a device is proportional to4piM_{s}, Q - 1 = (H_{k} - 4piM_{s})/4piM_{s}must be greater than some minimum value for a given device structure and spacer thickness to permit reliable device operation.  相似文献   

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