Electromagnetic hysteresis is a phenomenon observed in ferromagnetic materials, which are materials that exhibit a strong response to magnetic fields. It refers to the lag or delay in the magnetization of a material as the magnetic field applied to it is changed. This lag results in a loop-shaped relationship between the magnetic field strength (H) and the magnetic flux density (B), which is known as the hysteresis loop.
Here's a breakdown of the concept:
Magnetization Process: When a ferromagnetic material is exposed to an external magnetic field, its magnetic domains (microscopic regions with aligned atomic magnetic moments) tend to align themselves with the applied field. As the strength of the external field increases, more and more domains align, and the material becomes increasingly magnetized.
Saturation: At a certain point, as the external magnetic field becomes stronger, most of the magnetic domains are fully aligned. The material reaches a state of magnetic saturation, where further increases in the external field have little effect on increasing the magnetization.
Changing the Magnetic Field: Now, if the external magnetic field is reduced to zero from the saturated state, the magnetization of the material doesn't immediately drop to zero. This lag in demagnetization is due to the residual alignment of some domains.
Coercivity: If the external magnetic field is reversed (i.e., its direction is reversed), the material doesn't immediately magnetize in the opposite direction. It requires a certain level of reverse magnetic field strength, known as the coercive force, to start demagnetizing the material. The higher the coercive force, the more resistant the material is to changes in its magnetization.
Hysteresis Loop: When you plot the relationship between the external magnetic field strength (H) and the resulting magnetic flux density (B) of the material, you get a loop-shaped curve called the hysteresis loop. As you change the external field strength back and forth, the magnetization follows this loop due to the lag in the material's response during both magnetization and demagnetization processes.
Energy Loss: The area enclosed by the hysteresis loop represents the energy loss in the material as it goes through repeated cycles of magnetization and demagnetization. This energy loss is usually converted into heat, making hysteresis an important consideration in applications where ferromagnetic materials are used, such as transformers, electric motors, and magnetic memory devices.
In summary, electromagnetic hysteresis is a result of the lag in the magnetization and demagnetization processes of ferromagnetic materials when subjected to changing magnetic fields. The hysteresis loop illustrates this behavior and has practical implications for various technological applications.