What is magnetic hysteresis?

Magnetic hysteresis is a phenomenon that occurs in ferromagnetic materials, such as iron, nickel, and cobalt, when they are subjected to varying magnetic fields. It describes the lag or delay in the magnetization of a material in response to changes in the applied magnetic field strength. This lag results in a loop-shaped curve on a graph of magnetic flux density (B) against magnetic field strength (H), which is known as a hysteresis loop.

Here are the key points to understand about magnetic hysteresis:

Ferromagnetic Materials: Magnetic hysteresis is most pronounced in ferromagnetic materials, which have regions called domains that can be aligned with an external magnetic field. These materials exhibit strong and permanent magnetization when exposed to a magnetic field.

Hysteresis Loop: When you plot the relationship between the magnetic field strength (H) and the magnetic flux density (B) of a ferromagnetic material, you'll see a closed-loop curve. This curve is known as a hysteresis loop, and it illustrates how the magnetic properties of the material change as the applied magnetic field is varied.

Saturation: Initially, as the magnetic field strength (H) increases, the magnetic flux density (B) also increases. However, the curve eventually levels off, indicating that the material has become saturated, meaning it can no longer be magnetized further by increasing the applied field.

Remanence: After the magnetic field is reduced to zero, the material retains some residual magnetization. This retained magnetization is called remanence and is represented on the hysteresis loop as a point on the B-axis.

Coercivity: To completely demagnetize the material and bring it back to a zero magnetic state, you need to apply a reverse magnetic field. The strength of this reverse field required to reduce the magnetization to zero is called coercivity, and it is also represented on the hysteresis loop.

Hysteresis Loss: The area enclosed by the hysteresis loop represents the energy lost as heat when the magnetic material goes through a cycle of magnetization and demagnetization. This energy loss is known as hysteresis loss and is a key factor in the efficiency of magnetic devices like transformers and electric motors.

Magnetic hysteresis is an important concept in the design and operation of magnetic devices and materials, as it helps engineers and scientists understand how these materials respond to changing magnetic fields and how to minimize energy losses in magnetic circuits.