Origin of Magnetism
The origin of magnetism is explained by taking into consideration the circular motion of electrons. The electrons present inside the atoms move in circular orbits around the nucleus; this is similar to a circular coil carrying current. The electron's orbital motion gives rise to the orbital magnetic moment.
The electrons tend to spin around in their own axis, thus creating a spin magnetic moment. The magnetic moment of an atom is the result of the vector sum of the orbital and spin magnetic moment. Based upon the magnetic properties, the magnetic substances are classified into three groups, namely diamagnetic, ferromagnetic, and paramagnetic.
Short Brief on Diamagnetic Substances
Diamagnetic Definition
Diamagnetic substances are magnetized weakly when placed in an external magnetic field in a direction that is opposite to the applied field. The type of magnetism that is exhibited by these substances is known as diamagnetism. Examples of diamagnetic substances are copper, gold, antimony, bismuth, silver, lead, silicon, mercury, etc.
The electron's orbital motion gives rise to an orbital magnetic moment. In addition to this, the electrons tend to spin around their own axis, creating a spin magnetic moment. Electrons in an atom can have a clockwise or anticlockwise spin. In a similar way, the electrons can revolve around the nucleus in a clockwise or anticlockwise direction.
In the case of diamagnetic substances, the magnetic moments of atoms and the orbital magnetic moments have been oriented in such a manner that the vector sum of an atom’s magnetic moment becomes zero.
Characteristics
In a diamagnetic substance, the magnetic moment of every atom is calculated to be zero.
An external magnetic field can repel them weakly.
If diamagnetic substances are placed in a non-uniform magnetic field, then the substances move towards the weaker side of the field from the stronger side.
When these substances are placed in an external magnetic field, they get weakly magnetized in the direction that is opposite to the direction of the field.
Magnetic susceptibility turns out to be negative in diamagnetic substances.
Ferromagnetic Substance
Substances that get magnetized strongly in an external magnetic field in a direction which is the same as the direction of the externally applied field are known as ferromagnetic substances. These types of substances retain their magnetic moment even after the removal of the magnetic field. Ferromagnetic substances tend to move from weaker to stronger parts of the external field. Some examples of ferromagnetic substances are iron, cobalt, and nickel.
In the ferromagnetic substances spin, magnetic moments have a large contribution. These substances consist of a large number of small units that are known as domains. These domains experience torque when a ferromagnetic substance is exposed to an external magnetic field. Due to this, the domains rotate and remain parallel to the direction of the field.
Characteristics
A large number of small domains make ferromagnetic substances.
These substances do not lose their magnetism when the external magnetic field is removed.
These substances become paramagnetic when they are heated above the curie point.
The external magnetic field strongly attracts ferromagnetic substances.
These ferromagnetic materials tend to move from the weaker to the stronger part of the field when the magnetic field is non-uniform.
If a rod of ferromagnetic substance is placed in a uniform magnetic field, the rod comes to rest with its length being parallel to the direction of the field.
Paramagnetic Substances
Substances that get magnetized weakly when placed in an external magnetic field in the same direction as the direction of the externally applied field are known as paramagnetic substances. These substances are different from ferromagnetic and diamagnetic substances. They have a tendency to move from the weaker to the stronger part of the magnetic field. Some examples of paramagnetic substances are calcium, lithium, tungsten, aluminum, platinum, etc.
In a paramagnetic substance, each atom has a permanent magnetic dipole moment because of the way they spin, the magnetic moments are oriented. However, the direction of magnetic moments can have random orientations when there is thermal motion. Due to which the net magnetic moment of this substance is zero.
Characteristics
Every atom in this substance is considered as a magnetic dipole that has a resultant magnetic moment.
The external magnetic field creates a weak attraction to these substances.
They move from weaker to the stronger part of the field when placed in a non-uniform field.
These substances lose their magnetism when the external magnetic field is removed.
Types of Magnets
The 3 types of magnets are-
Permanent Magnet- Permanent Magnets are magnets that never lose their magnetic property once they're magnetized.
Temporary Magnet- Temporary Magnets are magnets that lose their complete magnetic property when the magnetic field is removed.
Electromagnets- Electromagnets are material that behaves like a magnet when electricity is passed through them.
Cause of Magnetic Field on Earth
The flow of liquid iron at the center of the Earth generates an electric current that produces magnetic fields. Earth’s magnetic field is produced very deep down in the core of the planet.
The cycle continues because the Charged metals passing through these fields produce their electric currents. This type of self-sustaining loop is called the geodynamo. The collective effect of magnetic fields produces 1 vast magnetic field going to the planet. This is the reason behind the magnetic fields on Earth.
Properties of a Magnet
Magnetic poles always occur in pairs.
The like poles of any magnet will repel each other while the unlike poles will always attract each other.
The smaller the distance between 2 magnets, the greater magnetic force there exists between the 2 magnets.
Whenever a magnet is left suspended freely in the air, it always eventually rests in a north-south direction.
The pole that points towards the geographic north is called the North Pole of the magnet. The pole that points towards the geographic South is called the South Pole of the magnet.
Magnets always attract ferromagnetic substances.
It is noticeable that, when any magnet is submerged in some iron filings, the iron filings stick only to the end of that magnet. This happens because the magnetic attraction is maximum at the ends of any magnet. These ends are also called the magnet poles.
Conclusion
This article presents you with a clear picture of Diamagnetism, Ferromagnetism and Paramagnetism. You can check out Vedantu for more information.
FAQs on Diamagnetism,Ferromagnetism,and Paramagnetism
1. What are diamagnetic, paramagnetic, and ferromagnetic substances?
These terms classify materials based on their response to an external magnetic field:
- Diamagnetic substances are those that get weakly magnetised in the direction opposite to the applied magnetic field. They are repelled by magnets.
- Paramagnetic substances are those that get weakly magnetised in the same direction as the applied magnetic field. They are feebly attracted by magnets.
- Ferromagnetic substances are those that get strongly magnetised in the same direction as the applied magnetic field. They are strongly attracted by magnets and can be permanently magnetised.
2. What are the main differences between diamagnetism, paramagnetism, and ferromagnetism?
The key differences lie in their atomic structure and behaviour in a magnetic field:
- Cause of Magnetism: Diamagnetism arises from the orbital motion of electrons. Paramagnetism and ferromagnetism are due to electron spin and the resulting permanent atomic magnetic moments.
- Response to Field: Diamagnetic materials are weakly repelled, paramagnetic materials are weakly attracted, and ferromagnetic materials are strongly attracted.
- Magnetic Susceptibility (χ): For diamagnetic materials, χ is small and negative. For paramagnetic materials, χ is small and positive. For ferromagnetic materials, χ is very large and positive.
- Effect of Temperature: Diamagnetism is largely independent of temperature. Paramagnetism decreases as temperature increases (Curie's Law). Ferromagnetism disappears above a certain point called the Curie temperature, above which the material behaves like a paramagnetic substance.
3. Can you provide some common examples of diamagnetic, paramagnetic, and ferromagnetic materials?
Certainly. Here are some common examples for each category as per the CBSE syllabus:
- Diamagnetic Examples: Copper (Cu), Gold (Au), Silver (Ag), Water (H₂O), Mercury (Hg), and Bismuth (Bi).
- Paramagnetic Examples: Aluminium (Al), Calcium (Ca), Lithium (Li), Platinum (Pt), and Oxygen (O₂).
- Ferromagnetic Examples: Iron (Fe), Cobalt (Co), Nickel (Ni), and their alloys like Alnico.
4. Why do diamagnetic materials get weakly repelled by a magnetic field, while paramagnetic materials are weakly attracted?
The difference in behaviour is due to their atomic magnetic moments. Paramagnetic materials have atoms with permanent, randomly oriented magnetic moments. An external field aligns these moments slightly, causing a weak attraction. In contrast, diamagnetic materials have atoms with no net magnetic moment. When an external field is applied, it induces a small magnetic moment in the atoms that, according to Lenz's law, opposes the external field. This opposition results in a weak repulsive force.
5. How does temperature affect the magnetic properties of paramagnetic and ferromagnetic substances?
Temperature significantly impacts magnetism by affecting the alignment of atomic dipoles.
- For paramagnetic substances, as temperature increases, the thermal energy causes the atomic dipoles to become more randomly oriented. This counteracts the aligning effect of an external magnetic field, thus reducing the magnetic susceptibility. This relationship is described by Curie's Law.
- For ferromagnetic substances, increasing temperature also increases thermal agitation. At a critical temperature known as the Curie Temperature (Tc), the thermal energy becomes strong enough to break down the ordered alignment of magnetic domains. Above this temperature, the material loses its ferromagnetic properties and behaves as a paramagnetic substance.
6. What are magnetic domains, and why are they crucial for explaining ferromagnetism?
A magnetic domain is a microscopic region within a ferromagnetic material where the magnetic moments of all atoms are aligned in the same direction, making it strongly magnetised. In an unmagnetised ferromagnetic material, these domains are randomly oriented, so their net magnetic effect is zero. When an external magnetic field is applied, the domains aligned with the field grow in size, and other domains rotate to align with the field. This collective alignment of a vast number of atoms within domains is what produces the strong magnetic effect characteristic of ferromagnetism, which is absent in paramagnetic and diamagnetic materials.
7. How do magnetic susceptibility (χ) and relative permeability (μᵣ) help in classifying these three types of magnetic materials?
Magnetic susceptibility (χ) and relative permeability (μᵣ) are key quantitative measures used to classify magnetic materials:
- Diamagnetic Materials: Have a small, negative susceptibility (χ < 0) and a relative permeability slightly less than 1 (μᵣ < 1). This indicates they oppose an external magnetic field.
- Paramagnetic Materials: Have a small, positive susceptibility (χ > 0) and a relative permeability slightly greater than 1 (μᵣ > 1). This shows they are weakly attracted to a magnetic field.
- Ferromagnetic Materials: Have a very large, positive susceptibility (χ >> 1) and a relative permeability much greater than 1 (μᵣ >> 1). This signifies their ability to become strongly magnetised.
8. Why are ferromagnetic materials essential for making permanent magnets and electromagnets?
Ferromagnetic materials are ideal for these applications due to two specific properties derived from their strong magnetic nature:
- For Permanent Magnets: Materials like Alnico are chosen because they have high retentivity (ability to retain magnetism after the external field is removed) and high coercivity (resistance to demagnetisation).
- For Electromagnets: Materials like soft iron are used as cores because they have high magnetic permeability, which means they can concentrate magnetic field lines and create a much stronger magnet when current flows, but they also have low retentivity, allowing them to lose their magnetism quickly when the current is turned off.
