Problem 1984 - JEE Physics

Question

The magnetic susceptibility is negative for (a) Paramagnetic materials (b) Diamagnetic materials (c) Ferromagnetic materials (d) Paramagnetic and ferromagnetic materials

Step-by-Step Solution

Answer

The magnetic susceptibility is negative (\(\chi < 0\)) for (b) Diamagnetic materials.

Step 1: Magnetic Susceptibility Definition and Relation to Magnetic Materials

Magnetic susceptibility (\(\chi\)) is a dimensionless quantity that indicates the degree of magnetization of a material in response to an applied magnetic field. The magnetic susceptibilities of different materials are: 1. \(\chi > 0\) for paramagnetic materials 2. \(\chi < 0\) for diamagnetic materials 3. \(\chi >> 0\) for ferromagnetic materials

Step 2: Identifying the Correct Answer

Based on the information about the magnetic susceptibilities of different materials above, the magnetic susceptibility is negative (\(\chi < 0\)) for diamagnetic materials. Thus, the correct answer is: (b) Diamagnetic materials

Key Concepts

Paramagnetic Materials

Paramagnetic materials are substances that demonstrate weak attraction toward external magnetic fields. This happens because they have unpaired electrons that act as tiny magnets themselves. When these materials are placed in a magnetic field, the electrons align partially with the field, strengthening it slightly. A key property of these materials is their positive magnetic susceptibility, usually represented by \( \chi > 0 \).
However, this effect is quite weak, and when the external magnetic field is removed, the materials do not retain any magnetization. Hence, they are not permanent magnets.
Common examples of paramagnetic materials include:

• Aluminum
• Titanium
• Platinum
• Manganese

These materials are usually used in applications involving temporary magnetic effects, such as in medical imaging techniques like MRI.

Diamagnetic Materials

Diamagnetic materials are unique because they exhibit a negative magnetic susceptibility, \( \chi < 0 \). This means they create an opposing magnetic field when exposed to an external one, leading to weak repulsion. All materials have some diamagnetic properties, but in certain materials, it is the dominant magnetic behavior.
The cause of this repulsion is the paired electrons in the atoms of diamagnetic materials, which create tiny loops that generate individual magnetic fields in the opposite direction to the external field. The result is a very weak and temporary effect.
Diamagnetic materials do not retain magnetic properties once the external magnetic field is removed. Some examples include:

• Copper
• Lead
• Gold
• Bismuth

Due to their property of opposing magnetic fields, these materials are often used in applications that require stabilization in magnetic environments, like magnetic levitation experiments.

Ferromagnetic Materials

Ferromagnetic materials are perhaps the most well-known type of magnetic materials. They have a large positive magnetic susceptibility, \( \chi >> 0 \), which implies a strong attraction to magnetic fields. In these materials, the atomic magnetic moments, particularly those of unpaired electrons, are aligned parallel to each other over large regions known as domains.
What makes ferromagnetic materials interesting is their ability to maintain magnetization even after the external magnetic field is removed. This property is known as remanence, making these materials perfect for creating permanent magnets.
Common examples of ferromagnetic materials include:

• Iron
• Cobalt
• Nickel

These materials are prominently used in various everyday applications such as motors, transformers, and magnetic storage devices.