Magnetic Hysteresis

Definition

Magnetic hysteresis is the phenomenon where the magnetic flux density (B) of a ferromagnetic material does not linearly follow the applied magnetic field strength (H), but instead exhibits a lagging or hysteresis effect. This results in the material retaining a residual magnetism even after the external magnetic field is removed.

5 Must Know Facts For Your Next Test

1. Magnetic hysteresis is a fundamental property of ferromagnetic materials, which are used in the construction of electromagnets and permanent magnets.
2. The hysteresis loop, which is a graphical representation of the relationship between the applied magnetic field (H) and the resulting magnetic flux density (B), is a key characteristic of magnetic hysteresis.
3. The shape and size of the hysteresis loop are influenced by the material's composition, microstructure, and thermal history, which determine its magnetic properties.
4. Magnetic hysteresis is responsible for the energy dissipation that occurs during the magnetization and demagnetization of ferromagnetic materials, which can lead to heat generation and power losses in electrical devices.
5. The area enclosed by the hysteresis loop is a measure of the energy lost per cycle of magnetization, which is an important consideration in the design of transformers, motors, and other electromagnetic devices.

Review Questions

• Explain how the concept of magnetic hysteresis relates to the behavior of ferromagnetic materials.
  • Magnetic hysteresis describes the lagging or delayed response of the magnetic flux density (B) in a ferromagnetic material to changes in the applied magnetic field strength (H). This nonlinear relationship between B and H is a result of the material's internal magnetic domains, which can become aligned and reoriented in the presence of an external magnetic field. The hysteresis effect causes the material to retain a residual magnetism even after the external field is removed, which is a key characteristic of ferromagnetic materials and is essential for the functioning of devices like electromagnets and permanent magnets.
• Discuss how the shape and size of the hysteresis loop can provide information about the magnetic properties of a ferromagnetic material.
  • The shape and size of the hysteresis loop are directly related to the magnetic properties of a ferromagnetic material. A wider, more rectangular loop indicates a material with high coercivity, meaning it can retain its magnetization well and is suitable for use in permanent magnets. A narrower, more elongated loop suggests a material with lower coercivity, which is better suited for applications where the material needs to be easily magnetized and demagnetized, such as in transformer cores. The area enclosed by the hysteresis loop also provides a measure of the energy lost per magnetization cycle, which is an important factor in the design of electromagnetic devices.
• Evaluate the significance of magnetic hysteresis in the context of electromagnets and permanent magnets, and explain how it influences their performance and applications.
  • Magnetic hysteresis is a crucial property in the design and operation of both electromagnets and permanent magnets. For electromagnets, the hysteresis effect allows the material to retain a residual magnetism, which can be used to create a strong, persistent magnetic field when an electric current is applied. This makes electromagnets useful in a wide range of applications, from electric motors to magnetic resonance imaging (MRI) machines. In the case of permanent magnets, the hysteresis effect enables the material to maintain a strong, stable magnetic field without the need for a continuous power source. The shape and size of the hysteresis loop determine the magnet's coercivity, remanence, and energy density, which are critical parameters in selecting the appropriate permanent magnet material for a given application, such as in electric motors, generators, and data storage devices.

Related terms

Ferromagnetism: The property of certain materials, such as iron, nickel, and cobalt, to become strongly magnetized in the presence of an external magnetic field and to retain their magnetization to some degree after the field is removed.

Magnetic Domains: Small regions within a ferromagnetic material where the magnetic moments of atoms are aligned, creating a localized magnetic field.

Coercivity: The measure of a ferromagnetic material's ability to resist demagnetization, or the strength of the magnetic field required to reduce the magnetization of the material to zero.