---
title: "Classification of magnetic materials by magnetization"
subject: "Electrical Engineering Material"
chapter: 4
key: "semester_3/electrical_engineering_material:classify-magnetic-materials"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/classify-magnetic-materials
site: BCT Engineering
---

# Classification of magnetic materials by magnetization

Electrical Engineering Material · Chapter 4: Magnetic Materials

- Asked in: 2081 Chaitra (new course), 5 marks; 2080 Baisakh, 6 marks; 2075 Chaitra, 8 marks; 2073 Shrawan, 6 marks; 2070 Asar, 4 marks; 2068 Baisakh, 10 marks (asked 6 times)
- Video: [Types of Magnetic Materials Explained | 10 Min Series by Rishabh Sir (A.E.) #rishabhsir](https://www.youtube.com/watch?v=OULm3phZ3wc) — Engineering Innovation
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/classify-magnetic-materials
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4

## Question

Classify the magnetic material based on magnetization and explain each of them briefly.

## Short answer

Magnetic materials are classified by magnetization: diamagnetic (χ<0, no permanent moment), paramagnetic (χ>0, random moments), ferromagnetic (large χ, parallel domains), antiferromagnetic (antiparallel equal moments), and ferrimagnetic (antiparallel unequal moments).

## Answer

Magnetic materials are classified by how they magnetize in an applied field $H$, i.e. by the magnetization $M = \chi H$ and the arrangement of atomic magnetic moments.

| Type | Susceptibility $\chi$ | Moments | Example |
|---|---|---|---|
| Diamagnetic | Small, negative ($\sim -10^{-5}$) | No permanent moment | Cu, Bi, Ag, water, graphite |
| Paramagnetic | Small, positive ($10^{-5}$–$10^{-3}$) | Random, weakly aligned | Al, Pt, O₂, Mn salts |
| Ferromagnetic | Very large, positive ($10^2$–$10^5$) | Parallel, in domains | Fe, Co, Ni, Gd |
| Antiferromagnetic | Small, positive | Antiparallel, equal | MnO, Cr, FeO, NiO |
| Ferrimagnetic | Large, positive | Antiparallel, unequal | Fe₃O₄, ferrites |

#### 1. Diamagnetism
- Atoms have no net permanent moment (all electrons paired).
- An applied field changes electron orbital motion (Lenz's law) and induces a small moment **opposing** the field, so $\chi < 0$ and $\mu_r$ slightly less than 1.
- Independent of temperature. Diamagnetic materials are repelled by a magnet. Superconductors are perfect diamagnets ($\chi = -1$).

#### 2. Paramagnetism
- Atoms have permanent moments (unpaired electrons) but they do not interact; thermal motion keeps them random.
- A field partly aligns them, giving a small positive $M$.
- Obeys **Curie's law**: $\chi = C/T$. Weakly attracted by a magnet.

#### 3. Ferromagnetism
- Strong **exchange interaction** aligns neighbouring moments parallel, forming **domains** with spontaneous magnetization.
- Very large $\chi$, hysteresis, saturation, retentivity.
- Above the **Curie temperature** $T_C$ it becomes paramagnetic: $\chi = \dfrac{C}{T - T_C}$. Fe: $T_C = 770$ °C.

#### 4. Antiferromagnetism
- Exchange interaction aligns neighbouring moments **antiparallel** and of equal size, so net $M \approx 0$.
- $\chi$ is small and rises with $T$ up to the **Néel temperature** $T_N$, then falls as paramagnetic: $\chi = \dfrac{C}{T + \theta}$.

#### 5. Ferrimagnetism
- Two sublattices with **antiparallel but unequal** moments, so a net spontaneous magnetization remains.
- Domains and hysteresis like ferromagnets, but with high electrical resistivity (they are ceramics), giving low eddy-current loss.
- Examples: magnetite Fe₃O₄, MnZn and NiZn ferrites; used in high-frequency transformer cores.

```text
 Para:   ^ / -> v \   random
 Ferro:  ^ ^ ^ ^ ^    parallel
 Anti:   ^ v ^ v ^    antiparallel equal
 Ferri:  ^ v ^ v ^    antiparallel unequal
         (big ^, small v)
```

## Check yourself

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

1. Diamagnetic materials have:
   A. Small negative χ, no permanent moment, moment opposing the field
   B. Small positive χ, permanent moments
   C. Large positive χ
   D. Zero χ
   Answer: A. Orbital changes by Lenz's law induce an opposing moment. (Key point: Diamagnetism)

2. Paramagnetic susceptibility follows:
   A. χ independent of T
   B. χ = C/T (Curie's law)
   C. χ = C(T - Tc)
   D. χ = C/(T+θ)
   Answer: B. Thermal agitation opposes alignment so χ falls as 1/T. (Key point: Paramagnetism)

3. What aligns moments parallel in a ferromagnet?
   A. Thermal agitation
   B. Dipole-dipole attraction only
   C. Strong exchange interaction forming domains
   D. Orbital Lenz effect
   Answer: C. Exchange interaction gives spontaneous magnetization within domains. (Key point: Ferromagnetism)

4. Antiferromagnets have net M approximately zero because:
   A. Neighbouring moments are antiparallel and equal
   B. Moments are random
   C. Moments are antiparallel and unequal
   D. There are no moments
   Answer: A. Equal and opposite moments cancel. (Key point: Antiferromagnetism)

## Related in Electrical Engineering Material

- [Applications of soft magnetic materials](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Asoft-magnetic-applications) — Electrical Engineering Material, chapter 4, asked 2×
- [Hard vs soft magnetic materials for relays](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Ahard-soft-relay) — Electrical Engineering Material, chapter 4
- [Properties and uses of soft magnetic materials](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Asoft-magnetic-properties-uses) — Electrical Engineering Material, chapter 4
- [Magnetic material for electromagnetic relays](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Arelay-magnetic-material) — Electrical Engineering Material, chapter 4
- [Magnetic moments; ferro vs ferrimagnetic materials](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adipole-moment-ferro-ferri) — Electrical Engineering Material, chapter 4
- [Hard vs soft magnetic materials by hysteresis](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Ahard-soft-hysteresis) — Electrical Engineering Material, chapter 4

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