Magnetic Domains and the Process of Magnetization
Magnetic Domains and the Process of Magnetization
In this chapter we introduce the relevant energy terms to determine the formation of domains. The regions of transition separating one domain from the next are classified as Bloch, Néel, or cross-tie domain walls. We then analyze domain structures based on energy considerations and demonstrate their utility for simple structures such as particle and films. However, every domain configuration is one of many possible metastable states and which one is realized in practice depends on the magnetization history. The Stoner–Wohlfarth (S–W) coherent rotation model describes the magnetization reversal and hysteresis of an ensemble of small particles. This model, which shows that their coercive field is ideally equal to the anisotropy field, has great practical utility and is discussed further in §9 and §11. Two effective approaches to understanding the process of magnetization and its reversal are coherent rotation and alternatively, a simple potential energy approximation involving the movement, pinning, and de-pinning of domain walls. Finally, the magnetization behavior as a function of the magnetic field, has a simple functional form at both low and high field values. Broadly, domains are expected in the size range 1 nm−10 μm. Techniques for observing and modeling them are discussed in the next chapter.
Keywords: domains, domain energy, Bloch, Néel, cross-tie walls, Stoner–Wohlfarth, coherent rotation model, domain wall processes, pinning, fine particles, thin films
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