Difference Between Hard Iron and Soft Iron

Main Difference – Hard Iron vs Soft Iron

A ferromagnetic material is a substance that can possess magnetization in the absence of an external magnetic field. There are two groups of magnetic materials as soft magnetic materials and hard magnetic materials. Iron is a good example of a ferromagnetic material. Iron also can be found in two types as hard iron and soft iron. This classification is done based on the magnetic properties of iron. The main difference between hard iron and soft iron is that hard iron cannot be demagnetized once it is magnetized whereas soft iron can be demagnetized once it is magnetized.

Key Areas Covered

1. What is Hard Iron
      – Definition, Magnetic Properties
2. What is Soft Iron
      – Definition, Magnetic Properties
3. What is the Difference Between Hard Iron and Soft Iron
      – Comparison of Key Differences

Key Terms: Demagnetize, Ferromagnetic Material, Hard Iron, Iron, Magnetic Domain, Magnetize, Soft Iron

What is Hard Iron

Hard iron can be made a permanent magnet by magnetization, but this magnetization cannot be removed easily once it is magnetized. In other words, demagnetization is either difficult or impossible once hard iron is magnetized.

The magnetic properties of iron come from the motion of electrons in the atoms. Each and every electron has a spin. A spin is an intrinsic form of angular momentum carried by an electron. Atoms are composed of orbitals where electrons are located in. One orbital can hold a maximum of two electrons. These two electrons have an opposite spin.

In iron, the neighboring atoms have spins that are aligned with each other. This results in what we call “domains.” A domain or a magnetic domain is a region within a magnetic material where magnetization is in a uniform direction. This uniform direction is caused by the aligning of the atoms.

When a bar of non-magnetized iron is placed in a magnetic field, the direction of magnetization of the magnetic domains tends to move towards the direction of the field. This makes the domains aligned with the direction of the magnetic field. This also expands the area of domains. This is what we call magnetizing a piece of iron.

Figure 1: A Permanent Magnet

In hard iron, the shifting of these magnetic domains is irreversible. In other words, the magnetic domains of hard iron do not return to the starting point when the magnetic field is removed. Therefore hard iron is commonly used as permanent magnets.

What is Soft Iron

Soft iron is iron that is easily magnetized and demagnetized with a small change of magnetic field. Soft iron does not refer to the soft nature of the metal; in fact, soft iron is also a hard, metallic iron.

But unlike in hard iron, the magnetic domains shifted towards the direction of a magnetic field can be shifted back to the initial state. In other words, it is reversible. But the returned magnetic domains will align in a random manner.

Figure 2: An Electromagnet

Soft iron is used in the production of electromagnets. Therefore, the field can be turned on and off. An electromagnet can be made by coiling a wire around a piece of soft iron and connecting the two ends of the wire to a battery. When the current is running through the wire, this system acts as a magnet. Then the domains of the soft iron bar align with the direction of the applied field and, the intensity of the magnetic field is increased by several magnifications.

Difference Between Hard Iron and Soft Iron

Definition

Hard Iron: Hard iron is iron that is difficult to demagnetize once magnetized.

Soft Iron: Soft iron is iron that is easily magnetized and demagnetized with a small change of magnetic field.

Material

Hard Iron: Hard iron is a hard magnetic material.

Soft Iron: Soft iron is a soft magnetic material.

Magnetization

Hard Iron: Magnetized hard iron cannot be easily demagnetized.

Soft Iron: Magnetized soft iron can be demagnetized.

Applications

Hard Iron: Hard iron is used as permanent magnets.

Soft Iron: Soft iron is used as electromagnets.

Conclusion

Iron can be found in two groups as hard iron and soft iron: classified based on the magnetic properties. The main difference between hard iron and soft iron is that hard iron cannot be demagnetized once it is magnetized whereas soft iron can be demagnetized once it is magnetized.

References:

1. Magnetic materials. BU Physics, Available here.
2. “MAGNETIC MATERIALS (HARD AND SOFT).” Whatwhenhow RSS, Available here.

Image Courtesy:

1. “Horseshoe magnet by Zureks” By Zureks – Own work, CC0) via Commons Wikimedia
2. “Electromagnet” By Anynobody – Own work by uploaderThis file was created with Blender (CC BY-SA 3.0) via Commons Wikimedia