文档介绍：POLYCRYSTALLINE MATERIALS AND THE M VERSUS H BEHAVIOR
The majority of the ic materials used in engineering is polycrystalline and therefore have a microstructure that consists of many grains of various sizes and orientations depending on the preparation and thermal history of ponent.
In an ized polycrystalline sample, each crystal grain will possess domains, as depicted in Figure .
The domain structure in each grain will depend on the size and shape of the grain and, to some extent, on the izations in neighboring grains.
Although very small grains perhaps smaller than µm, may be single domains, in most cases the majority of the grains will have many domains.
Overall, the structure will possess ization, provided that it was not previously subjected to an applied ic field. We can assume that ponent was heated to a temperature above the Curie point and then allowed to cool to room temperature without an applied field.
Suppose that we start applying a very small external ic field (µ0H) along some direction, which we can arbitrarily label as +x.
The domain walls within various grains begin to move small distances, and favorably oriented domains (those with ponent of M along +x) grow a little larger at the expense of those pointing sway from the field, as indicated by point an in Figure . The domain walls that are pinned by imperfections tend to bow out.
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