---
title: "Diamagnetism, ferromagnetism and ferrimagnetism"
subject: "Electrical Engineering Material"
chapter: 4
key: "semester_3/electrical_engineering_material:dia-ferro-ferri-magnetization"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/dia-ferro-ferri-magnetization
site: BCT Engineering
---

# Diamagnetism, ferromagnetism and ferrimagnetism

Electrical Engineering Material · Chapter 4: Magnetic Materials

- Asked in: 2072 Chaitra, 8 marks
- Video: [Diamagnetic, Paramagnetic and Ferromagnetic Materials](https://www.youtube.com/watch?v=AwCTDtknYWU) — Najam Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/dia-ferro-ferri-magnetization
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4

## Question

Based on magnetization vector, explain the diamagnetism, ferromagnetism and ferrimagnetisms.

## Short answer

Diamagnetism: atoms have no permanent moment; an applied field induces opposing magnetization, yielding negative small susceptibility (e.g., Cu). Ferromagnetism: parallel alignment of permanent moments gives large spontaneous magnetization and hysteresis (e.g., Fe). Ferrimagnetism: antiparallel unequal sublattice moments produce net magnetization, high resistivity (e.g., Fe₃O₄).

## Answer

Magnetic behaviour depends on whether atoms carry a permanent magnetic moment and on how the magnetization vectors of neighbouring atoms are arranged. Magnetization $M = \chi H$ is the net moment per unit volume.

```text
 Diamagnetic:   no moments; induced m opposes H
                H ->    m <-  m <-  m <-
 Ferromagnetic: ^  ^  ^  ^   parallel
 Ferrimagnetic: ^  v  ^  v   antiparallel, unequal
               (long ^, short v)
```

#### Diamagnetism
- Atoms have **no permanent magnetic moment** (all electron orbits and spins paired).
- An applied field changes the orbital motion of electrons; by Lenz's law, the induced magnetization vector points **opposite** to $H$.
- $\chi$ is small and negative ($\approx -10^{-5}$), $\mu_r$ slightly below 1, and independent of temperature.
- Field lines are pushed out; the material is repelled from strong-field regions.
- Examples: Cu, Bi, Ag, Au, water, graphite. A superconductor is a perfect diamagnet, $\chi = -1$ (Meissner effect).

#### Ferromagnetism
- Atoms have permanent moments (unpaired 3d electrons in Fe, Co, Ni).
- Strong positive exchange interaction aligns neighbouring magnetization vectors **parallel**, giving spontaneous magnetization in **domains**.
- A small $H$ grows favourable domains and rotates others, so $M$ becomes very large: $\chi \approx 10^2$–$10^5$.
- Shows hysteresis, saturation, remanence. Above the Curie temperature $T_C$ (Fe 770 °C) it becomes paramagnetic: $\chi = C/(T - T_C)$.
- Examples: Fe, Co, Ni, Gd and their alloys.

#### Ferrimagnetism
- The crystal has two sublattices (A and B sites) whose magnetization vectors are **antiparallel but unequal**.
- Net spontaneous magnetization $M = M_B - M_A \ne 0$; domains and hysteresis exist, but saturation is lower than in ferromagnets.
- In magnetite Fe₃O₄, Fe³⁺ ions on A and B sites cancel and the Fe²⁺ moments give the net magnetization.
- Ferrites are ceramic oxides with very high resistivity, so eddy-current loss is small; ideal at high frequency.
- Above the Curie (Néel) temperature they become paramagnetic.
- Examples: Fe₃O₄, MnZn and NiZn ferrites, barium ferrite, YIG.

| Property | Dia | Ferro | Ferri |
|---|---|---|---|
| Permanent moments | No | Yes | Yes |
| Alignment | Induced, opposite to H | Parallel | Antiparallel, unequal |
| $\chi$ | ≈ $-10^{-5}$ | $10^2$–$10^5$ | Large (10–$10^4$) |
| Resistivity | Any | Low (metals) | High (ceramics) |
| Hysteresis | No | Yes | Yes |

## Check yourself

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

1. Why does a diamagnetic material show negative magnetization?
   A. An applied field changes orbital motion, and by Lenz's law the induced moment opposes H
   B. Atoms have permanent moments aligned against H
   C. Exchange interaction is negative
   D. Domains rotate against H
   Answer: A. Diamagnetic atoms have no permanent moment; the induced one opposes the field. (Key point: Diamagnetic origin)

2. Which describes diamagnetic susceptibility?
   A. Small, positive and falls as 1/T
   B. Small, negative (about -10^-5) and independent of temperature
   C. Large and positive
   D. Negative and proportional to T
   Answer: B. μr is slightly below 1. (Key point: Diamagnetic chi)

3. What causes the very large χ (10^2 to 10^5) of ferromagnets?
   A. Induced orbital currents
   B. Equal antiparallel sublattices
   C. Positive exchange aligns moments in domains and a small H grows and rotates them
   D. Absence of permanent moments
   Answer: C. Domains are already spontaneously magnetized. (Key point: Ferro chi)

4. In a ferrimagnet, net magnetization arises because:
   A. They are parallel
   B. They are antiparallel and equal
   C. No sublattices exist
   D. Two sublattice vectors are antiparallel but unequal
   Answer: D. The unequal antiparallel moments leave a net M. (Key point: Ferri net M)

## Related in Electrical Engineering Material

- [Ferromagnetism, paramagnetism and diamagnetism](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adefine-ferro-para-dia) — 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×
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