---
title: "Ferromagnetism, paramagnetism and diamagnetism"
subject: "Electrical Engineering Material"
chapter: 4
key: "semester_3/electrical_engineering_material:define-ferro-para-dia"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/define-ferro-para-dia
site: BCT Engineering
---

# Ferromagnetism, paramagnetism and diamagnetism

Electrical Engineering Material · Chapter 4: Magnetic Materials

- Asked in: 2080 Bhadra, 6 marks
- Video: [Paramagnetic Materials, Diamagnetic Materials, Ferromagnetic Materials](https://www.youtube.com/watch?v=HIN3fWrGf_A) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/define-ferro-para-dia
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4

## Question

Define ferromagnetism, para-magnetism and diamagnetism with examples.

## Short answer

Ferromagnetism is strong spontaneous alignment of atomic moments within domains, giving large positive susceptibility (Fe, Co, Ni). Paramagnetism is weak field-induced partial alignment of permanent atomic moments, with small positive χ (Al, Pt). Diamagnetism is a weak induced moment opposing the field due to altered electron orbits, with small negative χ (Cu, Bi).

## Answer

#### Ferromagnetism
The property of some materials to show **strong, spontaneous magnetization** even without an external field, because the strong exchange interaction aligns atomic magnetic moments **parallel** within domains. They have very large positive susceptibility ($\chi \approx 10^2$–$10^5$), show hysteresis and saturation, and become paramagnetic above the Curie temperature, $\chi = C/(T - T_C)$.
**Examples**: iron, cobalt, nickel, gadolinium, Alnico.

#### Paramagnetism
The property of materials whose atoms have permanent magnetic moments (unpaired electrons) that are **randomly oriented** and do not interact. An applied field partly aligns them, giving a weak magnetization in the field direction. Susceptibility is small and positive ($10^{-5}$–$10^{-3}$) and follows Curie's law $\chi = C/T$. They are weakly attracted by a magnet and lose magnetization when the field is removed.
**Examples**: aluminium, platinum, manganese, oxygen, CuSO₄.

#### Diamagnetism
The property of materials whose atoms have **no permanent magnetic moment** (all electrons paired). An applied field changes the orbital motion of electrons and, by Lenz's law, induces a small moment **opposing** the field. Susceptibility is small and negative ($\approx -10^{-5}$), independent of temperature, and $\mu_r$ is slightly less than 1. They are weakly repelled by a magnet.
**Examples**: copper, bismuth, silver, gold, water, graphite; superconductors are perfect diamagnets ($\chi = -1$).

| Property | Dia | Para | Ferro |
|---|---|---|---|
| $\chi$ | Small, negative | Small, positive | Very large, positive |
| $\mu_r$ | < 1 | > 1 (slightly) | ≫ 1 |
| In a magnet's field | Repelled | Weakly attracted | Strongly attracted |
| Temperature effect | None | $\chi = C/T$ | $\chi = C/(T - T_C)$ |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Ferromagnetism has:
   A. Random moments
   B. Spontaneous magnetization, parallel moments in domains
   C. Small negative χ
   D. Temperature-independent χ
   Answer: B. Exchange alignment. (Key point: Ferromagnetism)

2. Paramagnetic atoms have:
   A. Permanent moments randomly oriented, non-interacting
   B. No moments
   C. Parallel moments
   D. Opposing induced moments only
   Answer: A. Field partly aligns. (Key point: Paramagnetism)

3. Diamagnetism arises from:
   A. Exchange
   B. Domains
   C. Orbital change opposing the field (Lenz)
   D. Unpaired spins
   Answer: C. All electrons paired. (Key point: Diamagnetism)

4. Relative permeability of diamagnets:
   A. Slightly less than 1
   B. Slightly above 1
   C. Much greater than 1
   D. Zero always
   Answer: A. χ negative. (Key point: μr)

## Related in Electrical Engineering Material

- [Diamagnetism, ferromagnetism and ferrimagnetism](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adia-ferro-ferri-magnetization) — Electrical Engineering Material, chapter 4
- [Hard magnets; dia, para and ferromagnetism](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Ahard-magnet-dia-para-ferro) — Electrical Engineering Material, chapter 4
- [Para, ferro, antiferro and ferrimagnetism](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Apara-ferro-antiferro-ferri) — Electrical Engineering Material, chapter 4, asked 2×