Ferromagnetic materials exhibit strong magnetism in the presence of an external magnetic field.
This is due to the alignment of magnetic domains within the material.
When the external magnetic field is removed, some ferromagnetic materials retain their magnetization, while others lose it.
- **Soft ferromagnetic materials:** These materials are easily magnetized and demagnetized.
They have a narrow hysteresis loop, indicating low retentivity (the ability to retain magnetization after the removal of the external field) and low coercivity (the magnetic field required to demagnetize the material).
Their magnetization largely disappears upon the removal of the external magnetic field.
Examples include soft iron.
- **Hard ferromagnetic materials:** These materials are difficult to magnetize and demagnetize.
They have a broad hysteresis loop, indicating high retentivity and high coercivity.
They retain a significant amount of magnetization even after the external magnetic field is removed, making them suitable for permanent magnets.
Examples include steel and alnico alloys.
- **Antiferromagnetic materials:** In these materials, the magnetic moments of adjacent atoms or ions are aligned antiparallel to each other, resulting in a net magnetic moment of zero.
They do not exhibit strong ferromagnetism.
- **Semiconductors:** These are materials with electrical conductivity between that of a conductor and an insulator.
They are primarily classified based on their electrical properties, not their magnetic behavior.
Based on the description in the question, materials whose magnetization disappears on the removal of the external magnetic field are **soft ferromagnetic materials**.