For permanent (hard) magnetic materials used in machines and devices, which property combination is most desirable to ensure strong, stable magnetization and resistance to demagnetizing influences?

Introduction / Context:
Permanent magnets must retain magnetization in service and resist demagnetizing fields, temperature excursions, and mechanical shocks. The magnetic hysteresis loop provides a direct visual of the required properties: significant remanence and coercivity, and typically a large loop area.

Given Data / Assumptions:

• Application demands stable, long-term magnetization (hard magnetic material).
• Demagnetizing forces may be present (e.g., leakage fields, temperature variations).
• Losses from cyclic magnetization are secondary to retention for permanent magnets.

Concept / Approach:
Hard magnets are characterized by high coercive field H_c and high remanent induction B_r. The product (B H)_max reflects energy density available from the magnet and correlates with a “fat” loop. In contrast, soft magnetic materials (transformer steels) need low coercivity and narrow loops to minimize hysteresis loss.

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