The present state of understanding of the dynamics of magnetic domain walls and magnetic bubbles is reviewed. The theory of domain wall motion for the linear and non-linear regions is outlined. Experimental techniques for straight walls and magnetic bubbles are discussed. An extensive comparison between theory and experiment is made. Topics included are peak and saturation velocities, mobility, inertial effects and overshoot, hard bubbles, wall states and state transformations in magnetic bubbles. Origins of wall damping are also discussed.

The behavior of a helical spin configuration of a hexagonal crystal in an applied field is discussed for the case where the axis of the helix is identical with the hexagonal c axis and the magnetization vector in each layer is parallel to the basal plane. In a small field applied parallel to the basal plane, a slight deformation of the helix occurs resulting in a small increase in over-all magnetization. If the field surpasses a certain critical value, the helix changes abruptly into a state with high resulting magnetization. In this state the spin directions are oscillating about the direction of the applied field, the magnetization being about 85% of the saturation value. In still higher fields, saturation is reached completely. A helical spin configuration has been found in MnAu2 by Herpin,Mériel, and Villain. We have investigated the properties of the hexagonal oxide (Ba,Sr)2Zn2Fe12O22 which is of the Y-type. The Ba-rich composition is ferrimagnetic and has a preferential plane for the magnetization at all temperatures. The Sr-rich composition has no spontaneous magnetization, but a magnetization equal to the one in the Ba case can easily be induced by an applied field. This behavior can be explained by the assumption of a helical spin configuration. As an other example, we show that the magnetic properties of dysprosium as investigated by Behrendt,Legvold, and Spedding can be explained by assuming a helical spin configuration between 85°K and 178°K. The angle between two neighboring layers is equal to zero at 85°K, the ferromagneticCurie temperature, and increases at higher temperatures. The magnetization process mentioned above is modified slightly in dysprosium by the presence of a strong magnetic anisotropy in the plane. In the presence of this anisotropy the transition between the ferromagnetic state and the helical state turns out to be a first-order transition, which explains the observed specific heat.

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