Short Answer

Magnetic susceptibility is a property of a material that shows how much it can be magnetized when placed in a magnetic field. It tells us how strongly a material responds to an external magnetic field. If the susceptibility is positive, the material is attracted to the field; if it is negative, the material is slightly repelled.

Different materials have different magnetic susceptibilities. Ferromagnetic materials have very high susceptibility, paramagnetic materials have small positive susceptibility, and diamagnetic materials have small negative susceptibility. This property is useful in classifying materials and understanding their magnetic behaviour.

Detailed Explanation

Magnetic susceptibility

Magnetic susceptibility is an important property in magnetism that describes how easily a material becomes magnetized when placed in an external magnetic field. It reflects the degree to which a material’s internal magnetic moments align with the applied field. Magnetic susceptibility is represented by the symbol χ (chi) and is a dimensionless quantity, meaning it has no unit.

In simple terms, magnetic susceptibility tells us whether a material will be attracted to or repelled by a magnetic field, and how strong that response will be. It is one of the most commonly used measures in classifying materials based on their magnetic behaviour.

Meaning of magnetic susceptibility

Magnetic susceptibility indicates:

• How much magnetization occurs in a material
• How strongly a material reacts to an external magnetic field
• Whether the material will be attracted or repelled

It is defined mathematically as:

χ = M / H

Where:

• χ = magnetic susceptibility
• M = magnetization of the material
• H = applied magnetic field strength

A high value of χ means the material is easily magnetized.

Types of magnetic susceptibility based on material behaviour

Different materials respond differently to magnetic fields. Based on magnetic susceptibility, materials are classified into three main groups:

1. Diamagnetic materials

• Susceptibility is negative (χ < 0)
• They are slightly repelled by a magnetic field
• Weak magnetic response
• Examples: copper, gold, water

Diamagnetism is caused by induced magnetic moments that oppose the applied field.

2. Paramagnetic materials

• Susceptibility is small and positive (χ > 0)
• They are weakly attracted by a magnetic field
• Examples: aluminium, magnesium, oxygen

In paramagnetic materials, atomic magnetic moments align slightly with the applied magnetic field.

3. Ferromagnetic materials

• Susceptibility is very large and positive
• Strongly attracted to a magnetic field
• Examples: iron, cobalt, nickel

Ferromagnetic materials have magnetic domains that align strongly with the field, producing a very high magnetization.

Factors affecting magnetic susceptibility

Magnetic susceptibility depends on several factors:

1. Temperature

• For paramagnetic materials, susceptibility decreases with rising temperature.
• For ferromagnetic materials, susceptibility changes drastically near the Curie temperature.
• For diamagnetic materials, temperature has little effect.

2. Material composition

The internal structure and arrangement of atoms play a major role.

3. Strength of the magnetic field

In weak fields, susceptibility remains constant.
In strong fields, some materials saturate and susceptibility changes.

Importance of magnetic susceptibility

Magnetic susceptibility plays a key role in:

1. Understanding magnetic behaviour

It helps classify materials as diamagnetic, paramagnetic, or ferromagnetic.

2. Designing magnetic materials

Engineers use susceptibility data to choose materials for electromagnets, transformers, and magnetic sensors.

3. Geophysics and Earth science

Magnetic susceptibility helps study rocks and minerals to understand the Earth’s magnetic history.

4. Medical imaging

MRI machines rely on magnetic properties of tissues, influenced by susceptibility.

5. Material science

Susceptibility measurements help understand purity, composition, and atomic structure of materials.

Difference between magnetic susceptibility and permeability

Although both relate to magnetic behaviour, they are different:

• Magnetic susceptibility (χ) tells how much a material gets magnetized.
• Magnetic permeability (μ) tells how easily magnetic field lines pass through a material.

They are related by the formula:

μ = μ₀ (1 + χ) for most materials.

Relation with magnetization

Magnetic susceptibility connects magnetization (M) and magnetic field (H):

M = χH

This means:

• If χ is large, a small magnetic field produces a large magnetization.
• If χ is small, the magnetization is very low even in a strong field.

Practical examples

1. MRI machines
   Different tissues have different susceptibilities, which helps produce clearer images.
2. Transformer cores
   High-susceptibility materials like iron increase magnetic efficiency.
3. Magnetic sensors
   Devices detect changes in magnetization due to susceptibility differences.
4. Chemistry
   Susceptibility helps identify chemical compounds and molecular structures.
5. Earth science
   Rocks with high susceptibility indicate the presence of iron minerals.

Conclusion

Magnetic susceptibility is a measure of how much a material becomes magnetized when placed in an external magnetic field. It helps classify materials into diamagnetic, paramagnetic, and ferromagnetic groups. Susceptibility depends on temperature, material structure, and field strength. This property is essential for understanding magnetic behaviour and is widely used in electromagnets, transformers, MRI technology, and scientific research. Knowing susceptibility helps us properly choose and design materials for magnetic applications.