Which property describes a material's memory of magnetism after magnetization is removed?

• A. Retentivity
• B. Permeability
• C. Reactance
• D. Saturation

Answer: (A)

Retentivity describes how much magnetization remains in a material after the external magnetic field is removed. When a material is magnetized, its magnetic domains align; once you take away the magnetizing force, some alignment stays due to domain interactions, producing residual magnetization. This leftover magnetization is what we call retentivity, often linked to the remanent flux density. A material with higher retentivity holds onto more of that magnetization, while a material with low retentivity loses it quickly.

Permeability is about how easily the material becomes magnetized in the first place, not how much magnetization sticks around after removal. Reactance is an AC circuit concept about opposition to current, unrelated to magnetic memory. Saturation is the maximum magnetization attainable under a strong field, not the residual magnetization after the field is removed.

Understanding retentivity helps in selecting materials for components where residual magnetism matters, such as decisions about how long a magnetized state should persist.