---
title: "Soft magnetic materials and commercial applications"
subject: "Electric Machine Design"
chapter: 1
key: "semester_5/electric_machine_design:soft-magnetic-applications"
source: https://www.bctengineer.com/q/semester_5/electric_machine_design/soft-magnetic-applications
site: BCT Engineering
---

# Soft magnetic materials and commercial applications

Electric Machine Design · Chapter 1: Materials used in electrical equipment

- Asked in: 2071 Chaitra, 5 marks; 2070 Asar, 5 marks (asked 2 times)
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/electric_machine_design/soft-magnetic-applications
- Whole chapter: https://www.bctengineer.com/md/semester_5/electric_machine_design/chapter-1

## Question

What do you mean by soft magnetic materials? Give their application according to their commercial use.

## Short answer

Soft magnetic materials have high permeability, low coercivity, and narrow hysteresis loop for easy magnetization. Uses: silicon steel in motors/transformers, nickel-iron alloys for CTs and shielding, ferrites for high-frequency cores, and amorphous metals for efficient transformers.

## Answer

**Soft magnetic materials** are easily magnetised and demagnetised. They have a narrow hysteresis loop with low coercive force (usually below about 1 kA/m), high permeability and low hysteresis loss, so they are suited to alternating and rotating flux.

#### Properties
- High permeability and high saturation flux density
- Low coercivity and low remanence
- Small loop area, giving low hysteresis loss
- High resistivity (in alloys and ferrites), giving low eddy loss

```text
          B
          |    ___---
          |  /
   -------|-/-------> H     narrow loop:
         /|                 small Hc, high mu
   ---__/ |
          |
```

#### Applications according to commercial use

| Material | Main property | Commercial use |
|---|---|---|
| Pure (Armco) iron, low-carbon steel | High saturation, cheap | DC machine field poles and yokes, relay cores, electromagnets |
| Cast iron / cast steel | Cheap, strong | Yokes and frames of DC machines |
| Hot rolled silicon steel (0.5–4.5 % Si) | Low loss, no ageing | Cores of rotating machines (dynamo grade), small transformers |
| CRGO silicon steel (about 3 % Si) | Very low loss along rolling direction | Power and distribution transformer cores |
| Cold rolled non-oriented (CRNO) steel | Uniform properties in all directions | Stator and rotor cores of motors and generators |
| Nickel-iron alloys (permalloy, mumetal) | Very high initial permeability | Current transformers, magnetic shielding, audio and pulse transformers |
| Iron-cobalt (permendur) | Highest saturation (about 2.4 T) | Aircraft generators, pole tips, where weight must be low |
| Soft ferrites (Mn-Zn, Ni-Zn) | Very high resistivity | High-frequency transformers, SMPS cores, inductors, antennas |
| Amorphous metal (metallic glass) | Extremely low loss | Energy-efficient distribution transformers |

Machines and transformers cannot work without soft materials. They provide the low-reluctance path for the working flux and keep iron losses and magnetising current small.

## Check yourself

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

1. Which set describes soft magnetic materials?
   A. High coercivity, high remanence
   B. Low coercivity, high permeability, small loop area
   C. Low permeability, wide loop
   D. High energy product
   Answer: B. Narrow loop, low Hc and high mu make them suited to alternating flux. (Key point: Properties)

2. Which material is used for power transformer cores?
   A. CRGO silicon steel
   B. Cast iron
   C. Alnico
   D. Soft ferrite
   Answer: A. CRGO has very low loss along the rolling direction. (Key point: Transformer cores)

3. Which material suits high-frequency SMPS transformers and inductors?
   A. Soft ferrites, because of very high resistivity
   B. Cast steel
   C. Permendur
   D. Hot rolled steel
   Answer: A. Ferrites have very high resistivity so eddy loss is tiny at high frequency. (Key point: High frequency)

## Related in Electric Machine Design

- [Soft versus hard magnetic materials](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Asoft-hard-magnetic-materials) — Electric Machine Design, chapter 1, asked 5×

## Related in other subjects

- [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×
- [Hysteresis loop energy, hard and soft magnetic materials](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ahysteresis-area-energy-hard-soft) — Electrical Machines I, chapter 1
- [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