Electromagnetic hysteresis, also known as magnetic hysteresis, is a phenomenon observed in ferromagnetic materials when they are subjected to a changing magnetic field. It describes the lagging of the magnetic induction (B) with respect to the applied magnetic field strength (H) during the process of magnetization and demagnetization.
Ferromagnetic materials, such as iron, nickel, and cobalt, have unique properties that make them highly susceptible to magnetic influences. When a ferromagnetic material is exposed to an external magnetic field, the atomic magnetic dipoles within the material tend to align themselves with the applied field. This alignment contributes to the overall magnetic behavior of the material.
The relationship between the magnetic field strength (H) and the magnetic induction (B) in a ferromagnetic material is not linear. Instead, it exhibits a nonlinear behavior, resulting in a hysteresis loop when the magnetic field strength is varied from positive to negative and vice versa. This loop is a graphical representation of the magnetic properties of the material during the magnetization and demagnetization processes.
The hysteresis loop is typically shown on a graph with the magnetic field strength (H) on the x-axis and the magnetic induction (B) on the y-axis. The loop has two main branches: the magnetization curve when the field is increasing (B-H curve) and the demagnetization curve when the field is decreasing (B-H curve).
When the external magnetic field is applied to the initially unmagnetized material, the B-H curve moves upward along the increasing magnetization branch, showing how the magnetic induction (B) increases with the magnetic field strength (H). As the field strength is reduced to zero, the B-H curve does not follow the same path during demagnetization, resulting in a remnant magnetization (also called residual magnetization) remaining in the material. This remnant magnetization indicates that the material retains some magnetic properties even when the external field is removed.
To completely demagnetize the material, a magnetic field in the opposite direction must be applied, reaching a point called the coercive field strength. This causes the B-H curve to follow a different path during demagnetization, and the magnetic induction eventually reaches zero.
The width of the hysteresis loop represents the energy loss as the material undergoes the process of magnetization and demagnetization. Materials with narrow loops are more efficient and experience less energy loss, making them suitable for applications like transformers and electric motors.
Electromagnetic hysteresis is a crucial phenomenon in various engineering applications and plays a significant role in understanding the behavior of magnetic materials used in electrical devices and other magnetic components.