The Ferromagnetic Domain

Ferromagnetism, in contrast to paramagnetism, is a cooperative phenomenon. A substance does not become ferromagnetic until the grain size exceeds a certain critical size, sometimes referred to as the 

A problem closely related to this is the ferromagnetic properties of thin films. 

These and related topics are discussed in a series of papers. (See Refs. 37-42.)  

In this section there will be shown several examples of how the intensity of magnetization, I, varies with changing field strength, and also how I varies with temperature for different fields. (The relation between I and ff is r = //d where d is the density.) 

The relations indicated in Figs. 36 and 36 hold for many substances. They lead to the conclusion that accurate comparison of specific magnetizations is best done at high fields and that accurate determination of Curie points is perhaps best done at low fields. The former is of most interest in the quantitative determination of catalyst components such 

---

Technical Magnetic Behavior. When a magnetic-field strength H is appHed to a ferromagnetic or ferrimagnetic material, the latter develops a flux density or iaduction as a result of orientation of the magnetic domains. The relation between B and H is... 

The crystal stmcture of the intermediate is not well understood. The final iron phase is termed superparamagnetic because the particle size is too small to support ferromagnetic domains. At low rates, the discharge occurs in two steps separated by a small voltage difference. At high rates, however, the two steps become one, indicating that the first step is rate limiting, ie, the second step (eq. 34) occurs immediately after formation of the intermediate (eq. 33). 

Let us now have a closer look at a ferromagnetic material before it is magnetized. In that case a number of areas exist in the material which are called domains. Within these domains a certain orientation of magnetic moments is present, which can vary in the individual domains (see figure 11.5.2). 

The profile Bz(x, y) is determined by the ratio of two length scales thickness of a ferromagnetic film D and distance between the domain walls w (hereafter we consider the width of the domain wall to be much less than ). Provided the ferromagnetic film is rather thick (D w), the magnetic... 

Ferromagnetic domains are regions in which unbalanced electron spins are aligned. Parts of three domains are indicated. The dashed lines are 180° and 90° domain walls. From W. F. Hosford, Physical Metallurgy (Boca Raton, FL CRC Press, 2005), p. 445, figure 26.4. 

---