For any material magnetized to fullness, the force required to cancel its magnetism is called magnetic coercivity. Coercivity is always carved out on the BH curve of a magnetic substance, where B represents the remanence and H represents the field intensity.
What is Magnetic Coercivity?
Magnetic coercivity is attained when the net flux is zero on the BH curve, also known as the hysteresis curve. At this point, there’s a balance between the magnetic field acting on a material and the force of the field present in the material. If the external field is removed at this point, the material will return to a full magnetic state. However, if the material is taken below the knee, at which point the external field exceeds the force of the material’s magnetic field, the material must be re-magnetized.
Understanding Magnetic Coercivity
In magnetism, coercivity and permeability are related. Permeability is concerned with the response of a material to magnetic influence. Understanding how permeability affects different materials simplifies the process of studying magnetic coercivity.
Remanence is another phenomenon that affects magnetic materials. While coercivity is a measure of the neutralizing field needed to demagnetize a material, remanence is the measure of the magnetization left in the material when the acting field is removed.
Materials are classified as either soft or hard magnetic materials based on coercivity. Soft magnetic materials are easy to magnetize and demagnetize. Once the applied magnetic field is removed, soft materials begin to demagnetize.
Hard magnetic materials are resistant to changes in magnetization. A hard magnetic material retains magnetism when the magnetic field acting upon it is removed. Rare earth materials, for instance, have a high coercivity and are difficult to magnetize.
The distinguishing behavior of soft magnetic materials determines their application. Given that their coercivity is much lower than hard magnetic materials, they fit for processes that require fluctuating magnetism and polarity. They can easily switch in-between cycles of magnetization and demagnetization.
Measuring Magnetic Coercivity
The unit for measuring magnetic coercivity is the Oersteds, Oe, with 1 Oe equaling 79.57747 A/m. The main methods of measuring a material’s coercivity are:
- Using a digital permeameter. This device measures several magnetic properties of materials, including magnetic coercivity.
- Using a vibrating sample magnetometer records electromotive force generated when magnetism is passed through a sample material, and the data obtained from its numerical analysis.
- Plotting a hysteresis loop. A hysteresis loop is formed when an alternating magnetic field is brought near a magnetic material. This loop can be constructed by reading the changes in the neodymium magnet using an oscilloscope.
- Using a hysteresis graph. This device measures a material’s remanence and coercivity; it is suitable for soft magnetic materials such as steel nails and hard magnetic materials such as Neodymium magnets.