Question

Give a difference between hard and soft magnetic materials.

Short answer

Hard magnetic materials retain their magnetism and have high coercivity; soft magnetic materials are easily magnetized and demagnetized with low coercivity.

Step-by-step solution

Define Hard Magnetic Materials

Hard magnetic materials are materials that retain their magnetism after an external magnetic field is removed. These materials have high coercivity and remanence, which means they require a significant amount of energy to become demagnetized and maintain a strong magnetic field even without an external source.

Define Soft Magnetic Materials

Soft magnetic materials are materials that easily become magnetized and demagnetized. These materials have low coercivity and remanence, which means they require less energy to achieve magnetization and quickly lose their magnetism once the external magnetic field is removed.

Compare and Contrast

The key difference between hard and soft magnetic materials lies in their coercivity and remanence. Hard magnetic materials have high coercivity and remanence, making them difficult to demagnetize and maintaining a strong magnetic field without an external source. In contrast, soft magnetic materials have low coercivity and remanence, making them easy to magnetize and demagnetize but losing their magnetism quickly when the external field is removed.

Key concepts

Coercivity

Coercivity is a crucial property in understanding magnetic materials. It is the measure of a material's resistance to becoming demagnetized. In simpler terms, coercivity indicates how much external magnetic field intensity is required to reduce the magnetization of a material to zero after it has been magnetized.

High coercivity means the material resists demagnetization. This is a characteristic of hard magnetic materials like permanent magnets. They require a strong external magnetic field to lose their magnetism and hence are ideal for long-term magnetic storage and applications that need a stable magnetic field.

Low coercivity means the material easily becomes demagnetized. This is typical of soft magnetic materials, which can be magnetized and demagnetized with minimal energy. These materials are used in applications that require rapid and frequent changes in magnetization, like transformers and inductors.

Remanence

Remanence, or retentivity, is another vital aspect of magnetic materials. It is the measure of the residual magnetism that remains in a material after an external magnetic field is removed. Essentially, it's the strength of the magnetic field retained by the material without an external influence.

Materials with high remanence, such as hard magnetic materials, retain a significant level of magnetization once the external magnetizing field is removed. This is beneficial for making permanent magnets, which must hold their magnetic properties over long periods.

In contrast, soft magnetic materials exhibit low remanence. They do not retain much magnetism once the external field is removed, which is advantageous in applications requiring temporary magnetization, allowing them to switch on and off efficiently.

Magnetization

Magnetization is a fundamental concept describing the degree to which a material can be magnetized. It represents the density of magnetic dipoles in a material and is a crucial factor in both hard and soft magnetic materials.

Hard magnetic materials have high magnetization, meaning they can hold strong magnetic fields and maintain their magnetism over time. This high magnetization is why they are pivotal in constructing permanent magnets used in various technological applications.

Soft magnetic materials, however, achieve high magnetization quickly but cannot retain it once the external field is removed. Their low remanence and low coercivity allow them to be highly efficient in applications requiring frequent magnetization and demagnetization cycles. Examples include electromagnetic devices, where rapid switching is essential.