A magnetic material is a type of substance or material which gets attracted towards a magnet. The magnetic material also acquires magnetization when it is placed in the magnetic field of a magnet. Depending on the magnetization property, there are two types of magnetic materials namely,
Let's start with some basics of hard and soft magnetic materials.
Hard magnetic materials are those types of magnetic materials that maintain a constant magnetic property after magnetization at once. Therefore, the hard magnetic materials are sometimes also termed as permanent magnetic materials.
Hard magnetic materials have high coercivity and low permeability. For this reason, it is quite difficult to demagnetize the hard magnetic materials. The area of hysteresis loop for hard magnetic materials is large, consequently these materials have large hysteresis loss. Although, the hard magnetic materials can store relatively high energy in the magnetic field. In practice, the hard magnetic materials are widely used for making permanent magnets. Some common examples of permanent magnetic materials are AlNiCo alloy, FeCrCO alloy, permanent magnet ferrites, etc
A type of magnetic material which can be easily magnetized and demagnetized is known as soft magnetic material. The soft magnetic materials have low value of coercivity and high value of permeability.
The area of hysteresis loop of the soft magnetic materials is small, as a result the hysteresis loss in case of soft magnetic materials is less. Generally, the soft magnetic materials have high resistivity. Consequently, the eddy current loss occurring in these materials is also low.
Soft magnetic materials store less energy in the magnetic field as compared to the hard magnetic materials. Since, the soft magnetic materials have high permeability, hence these are most suitable for making magnetic circuits for carrying flux in electrical machines. The most extensively used soft magnetic materials in electrical machines are silicon sheet steel and several soft ferrites. These materials are also used for making the electromagnets.
The major differences between the hard magnetic materials and the soft magnetic materials are listed in the following table −
| Basis of Difference | Hard Magnetic Materials | Soft Magnetic Materials |
|---|---|---|
| Definition | The magnetic materials that can retain their magnetism even after removal of external magnetic field, and are difficult to magnetized and demagnetized are known as hard magnetic materials. | The magnetic materials that can be easily magnetized and demagnetized are known as soft magnetic materials. |
| Magnetism | The magnetism of hard magnetic materials is constant. | The magnetism of soft magnetic materials is temporary. |
| Area of hysteresis loop | For the hard magnetic materials, the area of the hysteresis loop is large. | For the soft magnetic materials, the area of the hysteresis loop is small. |
| Ease of magnetization | Hard magnetic materials cannot be magnetized easily. | Soft magnetic materials can be easily magnetized. |
| Coercivity | The coercivity of hard magnetic materials is high. | Soft magnetic materials have relatively low coercivity. |
| Retentivity | Hard magnetic materials have large value of retentivity. | Soft magnetic materials have small value of retentivity. |
| Movement of domain walls | The domain walls of the hard magnetic materials do not move easily. | The domain walls of soft magnetic materials can move easily. |
| Value of H for magnetization | Hard magnetic materials require very large value of magnetizing force (H) for magnetization. It is because, they need comparatively more energy for the movement of domain walls. | Soft magnetic materials require comparatively low value of magnetizing force (H) for magnetization. |
| Hysteresis loss | Due to large area of hysteresis loop, the hysteresis loss in case of hard magnetic materials is high. | Soft magnetic materials have low hysteresis loss. |
| Permeability | The permeability of hard magnetic materials is low. | The permeability of soft magnetic materials is high. |
| Susceptibility | Hard magnetic materials are less susceptible as a result these are less influenced by the external magnetic field. | The susceptibility of soft magnetic materials is high. Consequently, the external magnetic field can easily influence them. |
| Eddy current loss | Hard magnetic materials have low electrical resistance. As a result, the eddy current loss in these materials is high. | Due to low value of electrical resistance of soft magnetic materials. These materials have less eddy current loss. |
| Energy stored | Hard magnetic materials can store high energy in the magnetic field. | Soft magnetic materials store less energy in the magnetic field. |
| Applications | Hard magnetic materials are used in a wide range of applications like in, making permanent magnets, microphones, loudspeakers, motor drives, injection pumps, printers, clocks, measuring instruments, lifting apparatus, robotics, MRI machine and many other medical instruments, etc. | Soft magnetic materials are extensively used in electrical engineering such as for making core the electromagnetics, core of electrical machines like transformer, motor, generator, parts of measuring devices, etc. |
| Examples | The examples of hard magnetic materials are alnico, ferrites, rare earth cobalt, cobalt platinum, etc. | Some popular examples of soft magnetic materials are pure iron with small carbon content, siliconiron alloy, nickel-iron alloy, etc. |
From the above discussion, we can conclude that hard magnetic materials have permanent and constant magnetism, while soft magnetic materials have temporary magnetism. Both hard and soft magnetic materials are widely used in different aspects of electrical engineering such as electrical machines, measuring devices, etc.