Dynamic Properties of Magnetic Bubbles
In the previous chapter we saw that the energy of a magnetic bubble is a function of the applied bias field HB, the film thickness h, the magnetic parameters of the film, e.g., 4πM and K, and the presence of permalloy overlays. We would therefore expect that any gradient in the magnitude of one of these parameters across the film would be reflected in a force tending to move a bubble toward lower energy. Indeed, a bubble will move into a region of lower bias, a thicker portion of the film, or under a spot of permalloy overlay. The usual method of propelling bubbles is to create an effective bias field gradient and in this chapter we concentrate on understanding the motion of a bubble due to a simple bias field gradient. That motion is controlled by the gyromagnetic behavior of magnetic moments in a magnetic field and can be very complicated when driven by high field gradients. To understand the basic principles we shall first consider the motion of a planar wall segment both without and then with Bloch lines. Following that we apply the same considerations to circular bubbles to gain an understanding of such concepts as bubble mobility, coercive force, dynamic deflection, velocity saturation, overshoot and creep.
KeywordsAnisotropy Torque Sine Nism HAas
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