Class 12 > Unit # 21:Physics of Solids > Hysteresis Loss & Hysteresis Loop

Hysteresis Loss, Hysteresis Loop, Coercivity, Remanence, and Magnetic Materials Applications

Detailed Video Lecture

(Saturation, Remanence, and Coercivity)

Hysteresis Loss: When a material is not magnetized, the axes of different domains point in various directions, resulting in a zero magnetic effect. Upon the application of an external magnetic force, the axes align with the force, creating a strong magnetic field. Repeated cycles of magnetization and demagnetization disturb domain alignment, leading to hysteresis loss. Energy is stored during field establishment and returned during collapse, but hysteresis causes incomplete energy recovery, resulting in heat.

Hysteresis Loop: The hysteresis loop is a graphical representation that shows the relationship between the magnetic field strength (B) and the magnetization (H) of a material. The loop is particularly useful under a changing magnetic field, formed by plotting the material's magnetization against magnetizing force, illustrating a material's magnetic behavior.

When the magnetizing current increases, the material gets magnetized, and the magnetic field strength goes up, shown on the right side of the hysteresis loop. When the magnetizing current decreases, the material may not fully demagnetize, and the magnetic field strength remains at a certain level, shown on the descending left side of the loop.

The width of the hysteresis loop indicates energy loss (hysteresis loss) during magnetization and demagnetization cycles. The shape of the loop provides information about the material's magnetic properties, such as coercivity and remanence.

Coercivity: The resistance of a magnetic material to changes in magnetization, equivalent to the field intensity necessary to demagnetize the fully magnetized material.

Remanence (Retentivity): Retentivity, also known as remanence, is the ability of a ferromagnetic material to retain a certain amount of residual magnetization when the external magnetic field is removed.

Practical Examples and Material Selection

• 1. For Hard Steel: Due to its high retentivity power and large coercive force, this material is well-suited for permanent magnets. Since the area of the hysteresis loop for hard steel is large, hard steel is not suitable for rapid reversals of magnetization.
• 2. For Wrought Iron and Cast Steel: These rise steeply. Hence, these materials have high magnetic permeability and good retentivity; therefore, these materials are suitable for cores of electromagnets.
• 3. For Iron, Low Carbon Steel, Silicon Alloys, Perm-alloy (Nickel-Iron Alloy), or Mu-metal (Nickel-Iron Soft Ferromagnetic Material): Since the permeability of these materials is very high and hysteresis losses are very low, these materials are most suitable for transformer cores and armatures, which are subjected to rapid reversals of magnetization.

(Hard Steel, Cast Steel and Iron)