Ferromagnetism

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Electromagnetic dynamic magnetic domain motion of grain oriented electrical silicon steel

Weiss-Bezirke1

Moving magnetic domains by Zureks

Ferromagnetism is a physical phenomenon in which a material exhibits spontaneous magnetization in the absence of an external magnetic field. This property is due to the alignment of magnetic moments of atoms or molecules in the material. Ferromagnetic materials are essential in various applications, including electromagnets, electric motors, hard disks, and other storage devices.

Overview

Ferromagnetism is a form of magnetism that can be observed in materials such as iron, cobalt, nickel, and some of their alloys. These materials can retain their magnetic properties even after an external magnetic field is removed, which distinguishes them from other types of magnetic materials, such as paramagnetic and diamagnetic materials, which do not retain magnetization in the absence of an external magnetic field.

Origin of Ferromagnetism

The origin of ferromagnetism lies in the electronic structure and the exchange interactions among atoms in the material. The exchange interaction is a quantum mechanical phenomenon responsible for the alignment of magnetic moments in the same direction, leading to spontaneous magnetization. This interaction is particularly strong in ferromagnetic materials, allowing them to exhibit permanent magnetism.

Domains and Domain Walls

In ferromagnetic materials, the alignment of magnetic moments occurs in small regions known as magnetic domains. Within each domain, the magnetic moments are aligned uniformly. However, the direction of magnetization can vary from one domain to another. The boundaries between these domains are known as domain walls. The process of magnetization involves the movement of these domain walls, leading to the growth of domains with a uniform direction of magnetization.

Curie Temperature

Each ferromagnetic material has a characteristic temperature known as the Curie temperature, above which it loses its ferromagnetic properties and becomes paramagnetic. At the Curie temperature, the thermal energy becomes sufficient to disrupt the alignment of magnetic moments, causing the material to lose its spontaneous magnetization.

Applications

Ferromagnetic materials are widely used in various applications due to their ability to retain magnetization. Some common applications include:

• Electromagnets: Utilizing ferromagnetic materials to enhance the magnetic field produced by a coil of wire.
• Electric motors and generators: Exploiting the interaction between ferromagnetic materials and electromagnetic fields to convert electrical energy into mechanical energy, and vice versa.
• Data storage: Using ferromagnetic materials in hard disks and magnetic tapes for storing data through magnetic domains.

See Also

• Magnetism
• Paramagnetism
• Diamagnetism
• Antiferromagnetism

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