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Chapter 20: Problem 15

Briefly explain why the magnitude of the saturation magnetization decreases with increasing temperature for ferromagnetic materials, and why ferromagnetic behavior ceases above the Curie temperature.

Short Answer

Expert verified
In ferromagnetic materials, the magnetic moments of atoms are aligned within small regions called magnetic domains. As the temperature increases, the thermal energy causes fluctuations in the alignment of magnetic moments, leading to weaker exchange interactions within the domains. Consequently, the saturation magnetization, or maximum magnetization under an external field, decreases with increasing temperature. At the Curie temperature, the exchange interactions become too weak to maintain magnetic order, causing the material to exhibit paramagnetic behavior and lose its ferromagnetic characteristics.

Step by step solution

01

Understanding magnetic domains in ferromagnetic materials

Ferromagnetic materials consist of small regions called magnetic domains. Within each domain, the magnetic moments of the atoms are aligned in the same direction due to strong exchange interactions. In the absence of an external magnetic field, the material exhibits no net magnetization, as the magnetic moments of different domains are randomly oriented and cancel each other out.
02

Temperature dependence of magnetic domains

As the temperature of a ferromagnetic material increases, the thermal energy of the atoms also increases. This added thermal energy causes fluctuations in the alignment of the magnetic moments within the domains, leading to a weaker exchange interaction between neighboring atoms. As a result, the magnetic moment alignment within each domain becomes less parallel.
03

Saturation magnetization and temperature

Saturation magnetization is the maximum magnetization that a material can achieve when fully aligned by an external magnetic field. It is determined by the degree of alignment within the magnetic domains. As the temperature increases, the disorder in the alignment also increases, thus reducing the material's ability to achieve full alignment under an external field. This results in a decrease in the magnitude of saturation magnetization with increasing temperature.
04

The Curie temperature

The Curie temperature is the temperature at which the exchange interactions in a ferromagnetic material become too weak to maintain any magnetic order, and the material becomes paramagnetic. Paramagnetic materials have no net magnetization in the absence of an external magnetic field; their magnetic moments are randomly oriented and do not interact with each other to form domains.
05

Ferromagnetic behavior ceasing above the Curie temperature

Above the Curie temperature, the ferromagnetic material loses its characteristic magnetic order and exhibits paramagnetic behavior. This is because the thermal energy becomes too high for the exchange interactions to maintain the alignment of magnetic moments within the domains, and the material loses its ability to exhibit net magnetization without an external magnetic field. Thus, the ferromagnetic behavior ceases above the Curie temperature.

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