Substances which are magnetic but having less magnetic moment than theoretically calculated value are called

Options

A. Ferromagnetic
B. Ferrimagnetic
C. Antiferromagnetic
D. Diamagnetic

Answer

To solve the question, we need to identify the type of magnetic substances that exhibit a magnetic moment but have a lower magnetic moment than what is theoretically expected.

### Step-by-Step Solution:

1. **Understanding Magnetic Substances**:
- There are different types of magnetic materials: ferromagnetic, ferrimagnetic, antiferromagnetic, and diamagnetic. Each type behaves differently in the presence of a magnetic field.

2. **Ferromagnetic Substances**:
- Ferromagnetic materials have a strong magnetic moment and align with the magnetic field, which increases their magnetic moment. Therefore, they do not fit the criteria of having a lower magnetic moment than expected.

3. **Ferrimagnetic Substances**:
- Ferrimagnetic materials have unequal magnetic moments due to the opposing spins of electrons in different sublattices. This results in a net magnetic moment that is less than the sum of the individual moments, which means they can have a magnetic moment lower than the theoretical value.

4. **Antiferromagnetic Substances**:
- In antiferromagnetic materials, the magnetic moments of adjacent atoms or ions align in opposite directions, effectively canceling each other out. This leads to a very low or zero net magnetic moment, which also does not match the criteria.

5. **Diamagnetic Substances**:
- Diamagnetic materials are characterized by their weak repulsion from a magnetic field and do not have a permanent magnetic moment. Therefore, they cannot be considered as having a magnetic moment less than the theoretical value.

6. **Conclusion**:
- The only type of magnetic substance that can have a magnetic moment but is less than the theoretically calculated value is **ferrimagnetic** materials.

### Final Answer:
Substances which are magnetic but having less magnetic moment than theoretically calculated value are called **ferrimagnetic**.