---
title: "Magnetic material for electromagnetic relays"
subject: "Electrical Engineering Material"
chapter: 4
key: "semester_3/electrical_engineering_material:relay-magnetic-material"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/relay-magnetic-material
site: BCT Engineering
---

# Magnetic material for electromagnetic relays

Electrical Engineering Material · Chapter 4: Magnetic Materials

- Asked in: 2073 Shrawan, 6 marks
- Video: [Magnetic Materials Used in Electrical Machines, Instruments and Relays](https://www.youtube.com/watch?v=ZK5q2tE6VfA) — EEE - E Learning
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/relay-magnetic-material
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-4

## Question

What type of magnetic material would you chose for electromagnetic relays? Justify.

## Short answer

For an electromagnetic relay, a soft magnetic material (e.g., soft iron) is chosen because high permeability gives strong pull with low coil current, and low coercivity and remanence ensure the armature releases instantly when current is off, preventing sticking.

## Answer

For the core, yoke and armature of an electromagnetic relay a **soft magnetic material** is chosen, such as soft iron, low-carbon steel, silicon steel, or Ni-Fe alloys (permalloy) for sensitive relays.

#### How a relay works
```text
       spring
   +----/\/\--+
   |    armature (soft iron)
   |  ====*===========  contacts
   |  |   ^ pulled when coil on
   |  |  +--+
   |  |  |##| coil on soft-iron core
   +--+--+--+--- yoke
```
When current flows in the coil, the core is magnetized and pulls the armature, closing (or opening) the contacts. When the current stops, the core must lose its magnetism immediately so the spring can pull the armature back.

#### Justification
1. **High permeability**: a small coil current (low power) produces enough flux to pull the armature; fast pick-up.
2. **Low coercivity and low retentivity**: on switching off, almost no residual magnetism remains, so the armature releases at once and does not stick. A hard material would keep the armature held.
3. **Narrow hysteresis loop / low hysteresis loss**: suitable for frequent operation and for AC relays; less heating.
4. **High saturation flux density**: strong pull from a small core.
5. **Good mechanical workability and low cost**: soft iron is easy to shape into cores and armatures.

A small non-magnetic shim (residual pin) is often fixed on the armature to keep a tiny air gap, further preventing sticking due to any residual magnetism.

| Requirement of relay | Soft material | Hard material |
|---|---|---|
| Quick release | Yes (low $B_r$) | No (high $B_r$) |
| Low coil power | Yes (high $\mu$) | No |
| Low loss | Yes | No |

## Check yourself

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

1. What type of magnetic material is chosen for a relay core and armature?
   A. Soft magnetic material such as soft iron or silicon steel
   B. Hard magnetic material such as Alnico
   C. Diamagnetic material
   D. Square-loop ferrite
   Answer: A. A relay needs to magnetize and demagnetize quickly. (Key point: Material choice)

2. Why are low coercivity and low retentivity needed?
   A. To increase the pull force
   B. So almost no residual magnetism remains after switching off and the armature releases
   C. To raise the saturation flux density
   D. To make the loop wide
   Answer: B. A hard material would keep the armature held. (Key point: Release)

3. Why is high permeability desirable?
   A. It increases hysteresis loss
   B. It stops eddy currents
   C. A small coil current produces enough flux to pull the armature
   D. It raises the Curie temperature
   Answer: C. High μ gives low power and fast pick-up. (Key point: Permeability)

4. What is the purpose of a small non-magnetic shim on the armature?
   A. It increases the flux
   B. It reduces coil resistance
   C. It raises the coercivity
   D. It keeps a tiny air gap to prevent sticking from residual magnetism
   Answer: D. The gap reduces the residual pull so the spring can release the armature. (Key point: Residual pin)

## Related in Electrical Engineering Material

- [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
- [Demagnetizing via B-H curve; data storage material](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Ademagnetize-bh-curve-storage) — Electrical Engineering Material, chapter 4
- [Domains, domain walls and magnetic losses](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adomain-walls-magnetic-losses) — Electrical Engineering Material, chapter 4
- [Classification of magnetic materials by magnetization](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Aclassify-magnetic-materials) — Electrical Engineering Material, chapter 4, asked 6×
- [Strong magnetic field and critical current](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Acritical-current-strong-field) — Electrical Engineering Material, chapter 5, asked 5×
- [Magnetic domains in an external field](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adomains-in-external-field) — Electrical Engineering Material, chapter 4, asked 3×

## Related in other subjects

- [Static vs electromagnetic relays; components](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Astatic-vs-electromagnetic-relays) — Switchgear and Protection, chapter 8, asked 4×
- [Types of electromagnetic relays and applications](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Aelectromagnetic-relay-types) — Switchgear and Protection, chapter 7, asked 2×
- [Soft magnetic material, Faraday's laws](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Asoft-magnetic-faraday-laws) — Electrical Machines, chapter 1
- [Why CRGO is a superior magnetic material](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Acrgo-superior-material) — Electric Machine Design, chapter 1