Magnetic properties metrics: after the magnetizing force is removed, the ratio of the remaining magnetic flux (remanent flux) to the saturated magnetic flux is termed what property of the material?

Introduction / Context:
Hysteresis loops capture several key magnetic properties: saturation, remanence, retentivity, and coercivity. The question asks for the term describing how much magnetization remains as a fraction of saturation once the external magnetizing force is removed.

Given Data / Assumptions:

• The material has been driven to magnetic saturation.
• The external field is then reduced to zero.
• The remaining magnetization (remanence) is observed and compared to saturation.

Concept / Approach:
When the magnetizing field H is removed after saturation, the flux density B does not drop to zero for ferromagnets; it falls to a residual value called remanent flux density (or remanence). A material’s tendency to retain this magnetization is called retentivity. Coercivity, by contrast, is the reverse field required to reduce B to zero. Saturation is the maximum B level; hysteresis refers to the looped relationship between B and H over a magnetization cycle, not a specific ratio.

Step-by-Step Solution:

Verification / Alternative check:
Typical permanent-magnet materials exhibit high remanence and high coercivity, indicating high retentivity; soft magnetic materials (e.g., transformer steels) show low coercivity/retentivity to minimize hysteresis losses.

Why Other Options Are Wrong:
Saturation: indicates the maximum B, not the retained portion.

Hysteresis: the loop behavior overall, not the specific retention measure.

Coercivity: the required reverse field to demagnetize, not the retained fraction.

Common Pitfalls:
Mixing up remanence (a value) with retentivity (a property describing how well the material holds that value); confusing coercivity and retentivity.

Final Answer:
retentivity