Koercitivitu

Koercitivita, often referred to as coercivity, is a fundamental property of ferromagnetic materials. It quantifies the resistance of a magnetic material to changes in its magnetization. More specifically, it is the value of the reverse magnetic field (H) that must be applied to a ferromagnetic material to demagnetize it, reducing its magnetic flux density (B) to zero after it has been magnetized to saturation.

In simpler terms, coercivity measures how strong a magnetic field needs to be to completely erase the magnetic memory of a material. Materials with high coercivity are difficult to demagnetize and are thus considered magnetically hard. These materials retain their magnetization even when subjected to significant opposing magnetic fields. Conversely, materials with low coercivity are easily demagnetized and are classified as magnetically soft. They lose their magnetization readily when the external magnetic field is removed or reversed.

The coercivity of a material is an important factor in its applications. For instance, permanent magnets, which are designed to maintain their magnetic field over long periods, are made from materials with high coercivity. Examples include neodymium magnets and alnico magnets. On the other hand, materials with low coercivity are preferred for applications where rapid and easy magnetization and demagnetization are required, such as in transformer cores, inductors, and magnetic recording media like hard drives. The coercivity is influenced by factors such as the material's composition, crystal structure, and the presence of defects.