Domains and Hysteresis

Photomicrograph showing the domain structure of an iron single crystal (arrows indicate directions of magnetization). 

Concept Check 20.4 Schematically sketch on a single plot the B- ersus-H behavior for a ferromagnetic material (a) at 0 K, (b) at a temperature just below its Curie temperature, and (c) at a temperature just above its Curie temperature. Briefly explain why these curves have different shapes. 

Concept Check 20.5 Schematically sketch the hysteresis behavior for a ferromagnet that is gradnally demagnetized by cycling in an // field that alternates direction and decreases in magnitude. 

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Figure 15.7 Relationship between domains and hysteresis, a) Typical hysteresis loop for a ferromagnet. h) For a virgin sample, // = 0 and M = 0 due to closure domains, (c) With increasing H, the shaded domain which was favorably oriented to H grows by the irreversible movement of domain walls up to point X. (d) Beyond point X, magnetization occurs only by the rotation of the moments, (e) Upon removal of the field, the irreversibility of the domain wall movement results in a remnant magnetization i.e., the solid is now a pennanent magnet.

The origin of the nonlinearity and hysteresis in the films is most likely due to displacement of domain walls [4], If domain walls move in a medium with a random distribution of pinning center, the response of the material can be described, in the first approximation by Rayleigh relations. We next demostrate how optical interferometry can be sued to verify whether this particular model applies to the investigated pzt thin film. In the case of the converse piezoelectric effect, when the driving field E is varied between — Eo and Eo, the piezoelectric strain x is hysteretic and can be expressed by the following Rayleigh relations ... 

Fig. 4.41. Magnetisation curve OAB, and hysteresis loop BCDEB as combinations of domain wall bowing, unpinning and displacement (Globus, 1977).

Ratajczak and Labedzka (1977) and Ratajczak and Goscienska (1979,1980) studied the anomalous Hall hysteresis loops in the vicinity of Tcomp for flash-evaporated films. They showed the relation between magnetic domain structures and hysteresis loops at Tcomp- They explained the anomalous configurations in terms of film homogeneity and the magnetization reversal process. They propose a model of change in film composition and reject the one of magnetic... 

The selectivity of an LDH firameworic in relation to the nature of anions, can be studied if the exchange reactions are carried out in solutions containing well-defined ratios of competitive anions. For some systems, the two kinds of anions are mutually exclusive, and a narrow domain of hysteresis is observed between the exchange and the reverse exchange. Such results are reported (Schollhom and... 

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