Hysteresis

Definition

Hysteresis is the phenomenon in which the state of a system depends on its history, particularly when an external force is applied and then removed, leading to a lag between the input and output. This effect is commonly observed in magnetic materials, where the magnetization does not immediately follow the changes in the applied magnetic field, resulting in a looped graph known as a hysteresis loop. This behavior is crucial in understanding how materials respond to external magnetic influences, particularly in ferromagnetic substances.

5 Must Know Facts For Your Next Test

1. Hysteresis loops graphically represent the relationship between the applied magnetic field and the resulting magnetization, showing that the path of magnetization differs when increasing or decreasing the field.
2. The area within the hysteresis loop is indicative of energy loss during magnetization and demagnetization processes, often seen as heat in practical applications.
3. Materials with high coercivity exhibit significant hysteresis, making them useful in permanent magnets, while materials with low coercivity show less hysteresis and are more suitable for temporary magnets.
4. Temperature changes can affect hysteresis behavior; for instance, heating a ferromagnetic material can reduce its coercivity and alter its hysteresis loop.
5. Hysteresis is not limited to magnetism; it also appears in other physical systems like mechanical systems (such as rubber bands) and thermal systems (like heating elements), demonstrating that it is a broad phenomenon across different fields.

Review Questions

• How does hysteresis illustrate the difference between ferromagnetic materials and paramagnetic materials in terms of magnetization?
  • Hysteresis demonstrates a key difference between ferromagnetic and paramagnetic materials by showing that ferromagnetic materials have a significant lag in their magnetization response to an external magnetic field, resulting in pronounced hysteresis loops. In contrast, paramagnetic materials do not exhibit hysteresis because their magnetization aligns quickly with an applied magnetic field and returns to zero once the field is removed. This lag and memory effect in ferromagnets are critical for applications like data storage and permanent magnets.
• Discuss how the area within a hysteresis loop correlates with energy loss in magnetic systems during cyclic loading.
  • The area enclosed within a hysteresis loop directly correlates with energy loss during cyclic loading of magnetic systems. As a magnetic material undergoes magnetization and demagnetization cycles, energy is expended to overcome internal friction and other resistance factors. This energy loss manifests as heat, which can affect efficiency in applications like transformers and inductors. Understanding this relationship helps engineers design more efficient magnetic devices by minimizing hysteresis losses.
• Evaluate how temperature influences the hysteresis characteristics of ferromagnetic materials and its implications for practical applications.
  • Temperature significantly influences the hysteresis characteristics of ferromagnetic materials, as heating generally reduces coercivity and alters the shape of the hysteresis loop. As temperature increases, thermal agitation can disrupt magnetic domain alignment, leading to reduced remanent magnetization and changes in energy loss per cycle. This behavior has practical implications; for instance, at elevated temperatures, permanent magnets may lose their effectiveness, making it critical to select materials suited for specific temperature ranges in applications such as electric motors or sensors.

Related terms

Magnetic Saturation: The point at which an increase in an applied magnetic field does not increase the magnetization of a material because all magnetic domains are aligned.

Coercivity: The measure of a material's resistance to becoming demagnetized; it is the strength of the external magnetic field that must be applied to bring the magnetization of a material back to zero.

Remanence: The magnetization left in a ferromagnetic material after an external magnetic field is removed; it represents the residual magnetism.