Definition of Coercivity

Coercivity is a fundamental magnetic property of a material that measures the strength of the magnetic field required to demagnetize it. It is the measure of the magnetic field needed to reduce the magnetism to zero after it has been magnetized along a particular direction. In simple terms, coercivity is the resistance of a magnetic material to lose its magnetism. It is an important property that determines the stability of the magnetization of a material.

Importance in Magnetic Materials

Coercivity is an essential property of magnetic materials, especially in the field of magnetic data storage. Magnetic data storage technology relies on the ability of magnetic materials to retain their magnetism for long periods without losing their stored data. Coercivity ensures that the data stored in magnetic media such as hard disks, credit card stripes, and magnetic tapes are not easily erased or corrupted by external magnetic fields.

Coercivity also plays a significant role in the design of magnetic materials for power generation and motors. The higher the coercivity, the more stable the magnetic material, and the less likely it is to lose its magnetism under high temperatures, stress, or external magnetic fields. This property is particularly important in the production of permanent magnets that are used in motors, generators, and other electrical equipment.

Measurement and Units of Coercivity

Coercivity is measured in units of oersteds (Oe) in the cgs (centimeter-gram-second) system or amperes per meter (A/m) in the SI (International System of Units) system. The measurement of coercivity is done by applying an increasingly strong opposing magnetic field to a sample until the magnetization is reduced to zero. The value of the magnetic field at which this occurs is the coercive field (Hc), which is used to calculate the coercivity of the material.

Example of Coercivity in Practical Applications

One practical application of coercivity is in the production of credit card stripes. Credit card stripes contain magnetic materials that are magnetized with the customer’s account information. The stripe needs to have a high coercivity to prevent accidental erasure or corruption of the data during use. If the coercivity of the stripe is too low, the stripe can be damaged by everyday magnetic sources such as phones, speakers, and other magnetic devices.

Another example is in the design of permanent magnets used in electric motors. Permanent magnets require a high coercivity to maintain their magnetic properties under operating conditions like high temperatures, vibrations, and strong magnetic fields. The coercivity of the magnet determines the efficiency and reliability of the motor, and thus, it is essential to select the right magnetic material with the appropriate coercivity to achieve optimal performance.