J. Watson

Hysteretic properties of permalloy I‐bars

Bitter solution observations and small‐spot Kerr effect measurements have been used to study the response of 100×12×0.3 μm permalloy bars to applied fields that exceed the range of linear response. Bitter patterns showed that a uniform applied field of sufficient strength saturates the center part of the bar by displacing a domain wall to the side of the bar. After reducing the field below its saturation value, remanent magnetization is maintained by a ’’zig‐zag’’ domain structure. The original domain pattern returns only at a certain lower value of applied field. An interpretation of the zig‐zag pattern is given. The polar effect was used to detect the annihilation and reappearance of Bloch walls in two sets of specimens, in response to similar sequences of applied fields. Differences in the measured renucleation field are attributed to edge effects. As a matter of further interest, the positive or negative polarity of a Bloch wall was found to be correlated with the CW or CCW orientation of the domain s...

Magnetostatic effects of I-bars: A unifying overview of domain and continuum results

Measured and calculated responses of Permalloy I-bar elements are compared on the basis of a proposed new classification. Small-spot Kerr effect measurements on 100 × 12 × 0.3-μm bars have permitted a detailed mapping of domain wall configurations for comparison with continuum calculations. The measured and calculated profiles of average magnetization show qualitative agreement but the local distribution of magnetization shows considerable discrepancy. Measured and calculated results of various investigators have been examined and may be conveniently classified as either of an average-magnetization type or of a pole-equivalent type. Finally, estimates of energy components in type I and type II wall configurations indicate that magnetostatic energy is dominant for the size and shape of Permalloy bars considered.

Small region magneto‐optic measurements of Permalloy I bars

We have developed a Kerr magneto‐optic probe capable of examining regions of ∼3 μm diameter and have used it to measure the magnetization distributions within Permalloy I bars. The measurements were made so as to bring into evidence the location and movement of domain walls. By suitable adjustment of the polarizing elements, signals can be observed either from the longitudinal Kerr effect from domains or from the polar Kerr effect of the out‐of‐plane magnetization of the Bloch wall. This paper reports the use of the polar effect to make precise determinations of Bloch wall locations in Permalloy I bars of 100×12×0.3 μm. Two different domain configurations were studied and wall locations were mapped as a function of applied field for each. Wall curvature is evident from the results. Local saturation and wall nucleation fields were also observed. Both types of domain configuration were found to respond qualitatively as predicted by a series‐based continuum calculation but with some notable differences.

Using parallel complex permeability for ferrite characterization

The authors address topics related to the characterization of linear ferrite materials using real and imaginary components of parallel permeability. Significant advantages are found in using the parallel rather than the usual series form of complex permeability to represent the performance of high-permeability ferrite cores. The findings include independence of the number of turns, a new equation for core loss density, a more direct examination of ferrite properties, and a reinterpretation of Snoeks limit. It is concluded that the parallel components of complex permeability provide direct measures of the inherent ferrite material properties. >

A simplified Fourier series method for the calculation of magnetostatic interactions in bubble circuits

A procedure is being developed for analyzing bubble circuits, based on periodic arrays of I‐bars as building blocks for more complex elements. This paper describes a method for solving the basic I‐bar magnetostatic problem, based on the simultaneous solution of Poisson’s equation and an equation of magnetic equilibrium. The solution uses a Fourier series approach which lends itself to spatially nonuniform applid fields, as caused by bubbles. The mathematical formulation of the bar geometry is in 3‐dimensions, with magnetization modelled along one axis, the major axis dominating. A numerical simplification results from analytically averaging the demagnetizing fields across the transverse axis, an 80‐harmonic calculation of an I‐bar array requires 5 seconds of computer time. Results compare well with others for I‐bars in uniform fields and for the potential well of a bubble on an I‐bar. In a new result with implications for analysis of logic gates, energy minima are found for two bubbles on opposite ends of...

Proximity and interaction effects in arrays of I-bars

Calculations have been made of interactions and fields in two-dimensional periodic arrays of I-bars. The results of the study shed light on several questions of interactions among bubble propagation elements. We have calculated interaction effects in arrays of I-bars as a function of both longitudinal and transverse spacing between bars. Three different geometries of I-bar show similar effects; the transverse and longitudinal interactions have opposing signs and are stronger in the transverse direction. We also have calculated local and average fields for an array of I-bars of geometries chosen to facilitate comparison with recent measurements. The local field in the gap between elements is found to be highly nonuniform but with an average value that obeys a simple relationship as the gap length is varied. The field profile is also nonuniform in the transverse direction, and exhibits a proximity enhancement that depends upon gap dimension. These results support the interpretation that bar-bar interactions can influence the magnetization in propagation arrays.

Effect of magnetic film switching of crystallite interactions

Relationships among dispersion, switching thresholds, ripple theory, the switching astroid, and the Landau-Lifshitz equation are indicated. It is conjectured that film dispersion should be less than a critical value of about 2 degrees if the influence of the switching astroid is to be prominent.

Eddy-current-free switching of permalloy thin films

Results are presented from an experimental investigation of large-angle flux reversal of magnetic films. The reported measurements were made with an unconventional instrument whose design features are briefly outlined. Switching characteristics for a selected film are shown; coefficients are compared with results of others in region II at 2° transverse bias. The 6 Oe .ns is a magnitude faster than others although the switching field rise time is an order of magnitude slower. On a 2 dimensional field plot, loci which define thresholds of incoherent rotation are found to have two prominent features : a disperse switching astroid for H_{s}\lsim H_{k} , and an extension described by H_{s}H_{\perp}/H_{k} = \Delta for H_{s} > H_{k} . The width of region II, the lower threshold for region II, and the independently-measured dispersion field are all approximately 0.1 Oe for the subject film. Thus \Delta \approx 2H_{k} \sin \alpha_{90} .

A two‐dimensional surface pole model for permalloy patterns

A method has been developed for modeling permalloy patterns for field access magnetic bubble devices, based on the distribution of poles rather than of magnetization. The present method has the advantage that the two dimensional distributions are of a single scalar quantity rather than two components of a vector quantity, which leads to numerical simplifications. The pole method also avoids the domain‐continuum question and the question of uniqueness of magnetization distributions. The numerical simplification, reducing the size of the matrix that must be solved, leads to a shorter program implementation that makes it possible to address more complicated problems. The method takes into account permalloy‐permalloy interactions between the nearby permalloy patterns of a periodic structure. The calculated potential profiles of a 3×15×0.4 μm3 rectangular bar are compared with the results of previous investigators. The versatility of this model is demonstrated by computing the potential profiles of a single ch...

Fundamentals of modeling I-bars and bubbles using fourier series

A Fourier series method is described for the calculation of the response of periodic arrays of I-bars to applied fields and bubbles. The underlying assumptions are emphasized for the exact solution of Poissons equation with an approximate constitutive equation. A general formulation is given for bubble-bar magnetostatic energy, the components of which are tabulated systematically. Results are given as comparisons with other investigators for calculated and measured potential wells and the variation of well with spacing, with applied field, and with bubble radius. Bubble-bubble interaction is treated.