Magnetic Properties
Magnetic Properties
Magnetic properties of materials are a result of the magnetic moments of the atoms or ions of these materials. The magnetic moment of an atom comes from two sources: the spin of the electrons and the orbital motion of electrons around the nucleus. The behavior of a material in the presence of an external magnetic field is determined by its magnetic properties.
Types of Magnetic Materials
Magnetic materials are classified into several types based on their magnetic behavior:
- Diamagnetic Materials
- Paramagnetic Materials
- Ferromagnetic Materials
- Antiferromagnetic Materials
- Ferrimagnetic Materials
Diamagnetic Materials
Diamagnetic materials are those which are repelled by a magnetic field. They do not have any unpaired electrons, so their net magnetic moment is zero. When placed in a magnetic field, they induce a small and negative magnetic moment in the opposite direction.
Example: Copper (Cu), Gold (Au), Silicon (Si)
Paramagnetic Materials
Paramagnetic materials are attracted by a magnetic field. They have unpaired electrons and hence have a net magnetic moment. However, the individual magnetic moments do not align spontaneously in the absence of an external magnetic field.
Example: Aluminum (Al), Oxygen (O2), Platinum (Pt)
Ferromagnetic Materials
Ferromagnetic materials have a large and positive susceptibility to an external magnetic field. They have unpaired electrons, and their atomic magnetic moments can align themselves in a parallel fashion, resulting in a strong magnetic moment. This alignment can be retained even after the external magnetic field is removed, giving these materials permanent magnetism.
Example: Iron (Fe), Nickel (Ni), Cobalt (Co)
Antiferromagnetic Materials
Antiferromagnetic materials have a net magnetic moment of zero, even though they have unpaired electrons. This is because the magnetic moments of the atoms or ions are aligned in a regular pattern with neighboring spins pointing in opposite directions, canceling each other out.
Example: Manganese oxide (MnO), Iron oxide (FeO)
Ferrimagnetic Materials
Ferrimagnetic materials are similar to ferromagnetic materials, where the magnetic moments are aligned in parallel and antiparallel directions in a way that results in a net magnetic moment. However, the magnitudes of the magnetic moments in opposite directions are not equal, so there is a net magnetization.
Example: Magnetite (Fe3O4), Ferrites
Magnetic Susceptibility and Permeability
Magnetic susceptibility ((\chi)) is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field. Magnetic permeability ((\mu)) is a measure of how easily a magnetic field can penetrate a material.
The relationship between magnetic susceptibility and permeability is given by:
[ \mu = \mu_0 (1 + \chi) ]
where (\mu_0) is the permeability of free space.
Curie's Law
Curie's Law describes the magnetic susceptibility ((\chi)) of paramagnetic materials as a function of temperature (T):
[ \chi = \frac{C}{T} ]
where (C) is the Curie constant.
Hysteresis Loop
A hysteresis loop shows the relationship between the induced magnetic field (B) and the magnetizing field (H) for ferromagnetic materials. The area of the loop represents the energy loss due to the domain wall motion and magnetic ordering.
Table of Magnetic Properties
| Property | Diamagnetic | Paramagnetic | Ferromagnetic | Antiferromagnetic | Ferrimagnetic |
|---|---|---|---|---|---|
| Magnetic Susceptibility | Negative | Positive | Large and Positive | Small, Positive or Negative | Large and Positive |
| Retain Magnetism | No | No | Yes | No | Yes |
| Magnetic Ordering | None | Random | Parallel | Antiparallel | Mixed |
| Example | Bismuth (Bi) | Aluminum (Al) | Iron (Fe) | Manganese oxide (MnO) | Magnetite (Fe3O4) |
Examples
Diamagnetism
A piece of bismuth placed between the poles of a magnet will be repelled. This is because it is diamagnetic and induces a magnetic field in the opposite direction to the applied field.
Paramagnetism
Liquid oxygen, when placed in a magnetic field, will be attracted and move towards the stronger part of the field. This is because oxygen is paramagnetic and has unpaired electrons that align with the field.
Ferromagnetism
A bar of iron can be magnetized by placing it in a magnetic field. Even after the field is removed, the iron retains its magnetism because it is ferromagnetic.
Antiferromagnetism
Manganese oxide shows antiferromagnetic behavior below its Néel temperature. Above this temperature, it becomes paramagnetic.
Ferrimagnetism
Magnetite is a ferrimagnetic material that is used in magnetic recording media. It has a net magnetic moment due to the unequal alignment of its magnetic moments.
Understanding the magnetic properties of materials is crucial for applications in electronics, data storage, and medical imaging, among others. These properties are determined by the electronic structure and the arrangement of atoms within a material.