Design and development of single-layer, ion-implantable small bubble materials for magnetic bubble devices

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Abstract
The general magnetic and physical requirements that a material must meet in order to be useful in magnetic bubble devices are reviewed. An approximate expression relating stripe width and film thickness to the material length parameter (l) is presented. The well‐known equations relating anisotropy, moment, Q factor and exchange constant are rearranged, and, combined with the approximate expression for l, result in a convenient set of equations which are useful for materials design and for evaluating magnetic property measurements. The exchange constant (A) of epitaxial bubble garnet films is presented as a function of Curie temperature. Nominal compositions are given in the (YLuSmCa)3(FeGe)5O12 system which will support bubble diameters from 3.0–1.7μm. The range of λ111 values which are needed to implement Ion Implanted Propagation Patterns (I2P2) is presented. An approach is presented for increasing the uniaxial anisotropy in the 〈111〉 crystallographic direction without significantly changing the damping factor of the material. This approach utilizes the ’’Lanthanum Effect’’, where La exhibits a zero B value in the phenomenological anisotropy expression. Nominal compositions are presented in the (LaLuSmCa)3(FeGe)5O12 and (LaLuSm)3(FeGa)5O12 systems which will support bubbles ranging from 1.7–1.1 μm. Bias margin and longevity data taken on I2P2 type circuits of 8 μm period and bias margin data on 6 μm and 4 μm period circuits are shown. Phase equilibria data in the system Flux‐ΣLn2O3‐Fe2O3 are presented.