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It has been shown that isolated magnetic domains in thin platelets (∼2 mils thick) of orthoferrites can be manipulated to perform memory, logic, and transmission functions. The purpose of this paper is to discuss the properties of orthoferrites that make them suitable for magnetic device applications and consider magnetostatic problems relevant to domain structures found to be useful. Included is a brief indication of how memory, logic, and transmission can be accomplished; however, the details will be reserved for a later paper. The stability conditions of a cylindrical domain are discussed in detail and data is reported to support the conclusions. Of particular interest are the sizes of cylindrical domains available in the various orthoferrites. Such data has been taken on five of the fourteen possible orthoferrites and it is found that the thulium orthoferrite, TmFeO3, gives the smallest stable domain diameter (2.3 mils) and LuFeO3 the largest. The stability results lead to a direct method for obtaining s̀w, the domain wall energy density. For TmFeO3, as an example, s̀w = 2.8 ergs/cm2. It is concluded that the orthoferrites are well suited indeed for device applications. Experimentally, 3 mil diameter domains have been manipulated and there is every reason to believe that operation of sub‐mil domains will soon be realized.

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In this paper we compute the change in the energy of a uniformly magnetized uniaxial platelet produced by the introduction of a cylindrical domain. Differentiation of the energy expression yields the translational force produced by gradients in plate thickness, material composition, or temperature. The force expressions provide a means for estimating the effect of gradients in these parameters on the margins of domain devices. Equating the sum of the gradient produced forces to the drag force yields a general domain velocity expression. The various results are presented in both graphical and tabular form.

We describe a numerical model that is capable of predicting important laser characteristics such as the threshold gain and the gain margin between the main and side modes for a distributed feedback (DFB) semiconductor laser of arbitrary complexity. The method consists of solving the coupled-mode equations with axially-varying parameters iteratively until the boundary conditions at the two facets are satisfied. We apply the numerical model to discuss two DFB laser structures. In the case of a multiple-phase-shift DFB laser our results show that such devices can have a more uniform axial distribution than that of a conventional quarter-wave-shifted DFB laser while maintaining sufficient gain margin between the main and side modes. In the case of a dual-pitch DFB laser we show that the incorporation of a slightly different grating period ( -0.1 percent) over a small section can provide a gain margin that is comparable to that achieved in quarter-waveshifted DFB lasers.