--- title: "Hard vs soft magnetic materials by hysteresis" subject: "Electrical Engineering Material" chapter: 4 key: "semester_3/electrical_engineering_material:hard-soft-hysteresis" source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/hard-soft-hysteresis site: BCT Engineering --- # Hard vs soft magnetic materials by hysteresis Electrical Engineering Material · Chapter 4: Magnetic Materials - Asked in: 2069 Chaitra, 6 marks - Video: [Coercivity & retentivity (Permanent & electromagnets) | Magnetism & matter | Physics | Khan Academy](https://www.youtube.com/watch?v=rGgKK3-wep4) — Khan Academy India - English - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/hard-soft-hysteresis - Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4 ## Question Differentiate soft and hard magnetic material taking help of hysteresis loop. ## Short answer Soft materials have a narrow, steep loop with low Hc and Br, easy magnetization and demagnetization, used in AC cores. Hard materials have a wide, nearly rectangular loop with high Hc and Br, retaining magnetism, used for permanent magnets. ## Answer Magnetic materials are divided into **soft** and **hard** according to the shape of their hysteresis loop. ```text B soft B hard ^ ___ ^ _______ | / Bs | / / Br |-/ / Br |-/ / -----+/--/----> H -------+/------/----> H /| / Hc small -Hc /| / Hc large / | / / | / /__|/ /__|___/ narrow, tall loop wide, fat loop ``` | Point | Soft magnetic material | Hard magnetic material | |---|---|---| | Loop shape | Narrow and steep | Wide and nearly rectangular | | Loop area (hysteresis loss) | Small | Large | | Coercivity $H_c$ | Low (< $10^3$ A/m) | High (> $10^4$ A/m) | | Retentivity $B_r$ | Low (remanence is easily removed) | High and stable | | Permeability | High | Low | | Saturation | Reached at small H | Needs large H | | $(BH)_{max}$ | Very small | Large | | Domain wall movement | Easy (pure, annealed, large grains) | Difficult (walls pinned by defects, fine particles) | | Magnetization / demagnetization | Easy | Difficult | | Eddy loss | Kept low by laminations / ferrites | Not important | | Examples | Soft iron, Si-steel, permalloy, soft ferrite | Alnico, NdFeB, SmCo, hard ferrite, carbon steel | | Applications | Transformer, motor and generator cores, relays, electromagnets | Permanent magnets, loudspeakers, meters, PMDC motors, magnetic storage | **Summary**: a soft material follows the field with little loss, so it suits alternating fields; a hard material holds its magnetism, so it suits permanent magnets. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How do the hysteresis loops of soft and hard materials compare? A. Soft: narrow and steep; hard: wide and fat B. Soft: wide; hard: narrow C. Both identical D. Soft: no loop Answer: A. Loop area gives hysteresis loss. (Key point: Loop shape) 2. Typical coercivity values: A. Soft: above 10^4; hard: below 10^3 B. Soft: below about 10^3 A/m; hard: above about 10^4 A/m C. Both about 10^3 D. Both zero Answer: B. Hard materials need strong reverse fields. (Key point: Coercivity) 3. Why is it hard to demagnetize hard materials? A. Their walls move freely B. They have no domains C. Domain walls are pinned by defects and fine particles D. Low remanence Answer: C. Pinned walls resist movement. (Key point: Domain walls) 4. Which pairing is right? A. Soft: permanent magnets B. Hard: transformer cores C. Hard: relays D. Soft: transformer cores and relays; hard: permanent magnets and loudspeakers Answer: D. Soft follows the field with little loss; hard holds its magnetism. 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