Magnetic Domains, Classification of Magnetic Materials, Curie Point, and Curie’s Law
Detailed Video Lecture
(Randomly oriented vs. externally aligned magnetic domains)
Magnetic Domains: The magnetic domain theory was proposed by Weiss in 1907. According to this theory, a magnetic material contains a large number of tiny regions, and each region (magnetic domain) consists of atomic magnetic moments that are aligned in a specific direction. Initially, these magnetic domains are randomly oriented, resulting in a weak magnetization where the magnetic moments cancel each other out in the absence of an external magnetic field.
In the presence of a strong external magnetic field, these magnetic domains align in the direction of the field, resulting in strong magnetization. This alignment occurs because the magnetic moments within each domain are parallel due to the influence of the external magnetic field.
Classification of Magnetic Materials: There are three main types of magnetic materials:
- 1. Ferromagnetic Materials: Ferromagnetic materials have magnetic moments (tiny magnetic domains) that tend to align parallel to each other. When exposed to an external magnetic field, these materials can become strongly magnetized.
- 2. Paramagnetic Materials: Paramagnetic materials have individual magnetic moments that are randomly oriented, and they become weakly magnetized when exposed to an external magnetic field.
- 3. Diamagnetic Materials: Diamagnetic materials have no intrinsic magnetic moment. When exposed to an external magnetic field, they develop a weak, negative magnetization that opposes the applied field.
(The transition of ferromagnetic to paramagnetic behavior above the Curie Point Tc)
Curie Point: The Curie point, or Curie temperature, is the temperature at which certain materials lose their permanent magnetic properties. At the Curie point, thermal energy causes the atoms in a material to jiggle, disturbing their magnetic alignment. When the vibrations become too great, the atomic magnets can't line up as well, and the material loses its magnetism.
Curie’s Law: Curie's law states that in a paramagnetic material, the material's magnetization is directly proportional to an applied magnetic field. But when it is heated, the relation is reversed, i.e., the magnetization becomes inversely proportional to temperature.
Curie’s Law Equation:
Where:
- χ (Chi) = Magnetic Susceptibility
- C = Curie’s Constant
- T = Absolute Temperature (Kelvin)
Explanation: Consider an example of iron atoms with a temperature of 770°C (1043 K). Each iron atom acts like a tiny magnet at this temperature spontaneously. Each of them will align themselves as some kind of magnetic material. For pure iron, the atomic magnets are distributed within each microscopic domain. Pure iron is a kind of ferromagnetic material. The directions of the magnetic fields are the same so that their magnetic fields strengthen each other. The graph depicts the rise of temperature above the Curie point Tc, which can lead to the production of roughly similar patterns of decreasing magnetic property.
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