---
title: "Ferro, ferri and antiferromagnetism"
subject: "Electrical Engineering Material"
chapter: 4
key: "semester_3/electrical_engineering_material:ferro-ferri-antiferro"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/ferro-ferri-antiferro
site: BCT Engineering
---

# Ferro, ferri and antiferromagnetism

Electrical Engineering Material · Chapter 4: Magnetic Materials

- Asked in: 2074 Chaitra, 4+2 marks
- Video: [Ferromagnetic, Ferrimagnetic,Antiferromagnetic ,Permagnetic ,Diamagnetic](https://www.youtube.com/watch?v=8qZxJi0Rx1o) — MSP Edupark 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/ferro-ferri-antiferro
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4

## Question

On the basis of magnetic vector, explain the ferromagnetism, ferrimagnetism and antiferromagnetism.

## Short answer

Ferromagnetism: parallel spins give large net magnetization and hysteresis. Antiferromagnetism: equal antiparallel spins cancel, zero net moment. Ferrimagnetism: antiparallel unequal spins from two sublattices yield net magnetization, with hysteresis and high resistivity; example Fe₃O₄.

## Answer

These three types all have atoms with permanent magnetic moments that interact strongly through the **exchange interaction**. They differ in how the magnetic moment vectors of neighbouring atoms line up.

```text
 Ferromagnetic       ^  ^  ^  ^  ^   all parallel
 Antiferromagnetic   ^  v  ^  v  ^   antiparallel, equal
 Ferrimagnetic       ^  v  ^  v  ^   antiparallel, unequal
                    (long ^, short v)
```

#### Ferromagnetism
- Positive exchange interaction makes all neighbouring moment vectors **parallel**.
- Their sum gives a large **spontaneous magnetization** inside each domain; susceptibility $\chi \approx 10^2$–$10^5$.
- Shows hysteresis and saturation. Above the Curie temperature it becomes paramagnetic: $\chi = C/(T - T_C)$.
- Examples: Fe, Co, Ni.

#### Antiferromagnetism
- Negative exchange interaction makes neighbouring moment vectors **antiparallel and equal in size**.
- The two sublattice magnetizations cancel, so net magnetization is zero and $\chi$ is small and positive.
- $\chi$ increases with temperature up to the **Néel temperature** $T_N$, then decreases: $\chi = C/(T + \theta)$.
- Examples: MnO, FeO, NiO, Cr.

#### Ferrimagnetism
- Two sublattices A and B with moment vectors **antiparallel but unequal** ($M_A > M_B$).
- Net magnetization $M = M_A - M_B \ne 0$, so a spontaneous magnetization, domains and hysteresis exist, as in ferromagnets but smaller.
- They are ceramic oxides with very high resistivity, so eddy-current loss is low.
- Example: magnetite Fe₃O₄ (Fe³⁺ on A and B sites cancel; the Fe²⁺ moments remain), MnZn and NiZn ferrites; used in high-frequency cores.

## Check yourself

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

1. What do ferro, ferri and antiferromagnets have in common?
   A. Atoms with permanent moments coupled by the exchange interaction
   B. No permanent atomic moments
   C. Zero net magnetization in all
   D. Identical moment arrangement
   Answer: A. They differ only in how neighbouring moment vectors line up. (Key point: Common basis)

2. Why is the net magnetization of an antiferromagnet zero?
   A. All moments are parallel
   B. Equal and antiparallel sublattice moments cancel
   C. The moments are random
   D. Negative exchange removes the moments
   Answer: B. Equal opposite moments sum to zero. (Key point: Antiferro net M)

3. Why does a ferrimagnet have spontaneous magnetization?
   A. The sublattices are parallel
   B. The sublattices are equal and cancel
   C. The antiparallel sublattice moments are unequal, so M = MA - MB is not zero
   D. It has no sublattices
   Answer: C. Unequal antiparallel moments leave a net difference. (Key point: Ferri net M)

4. In magnetite Fe3O4, which ions produce the net magnetization?
   A. Fe3+ ions only
   B. O2- ions
   C. All ions add up equally
   D. Fe2+ ions, since Fe3+ moments on A and B sites cancel
   Answer: D. Fe3+ on A and B sites cancel, leaving the Fe2+ moments. (Key point: Magnetite)

## Related in Electrical Engineering Material

- [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×
- [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
- [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

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