Introduction to Magnetism
Magnetic forces mediate a subset of a physical phenomenon known as magnetism. The magnetism of matter is the force exerted by magnets when they attract or repulse each other. Magnetic moments and the electric currents of basic particles give rise to a magnetic field, which acts on other magnetic and currents moments. The magnetic state of a material based on pressure, temperature, and the applied magnetic field. As these variables shift, a substance can exhibit several forms of magnetism. Magnetic properties of matter can be found in various Earth materials that act as insulators and conductors of varying degrees and shapes.
Michael Faraday is the first statistician who was discovered classifying substances according to their magnetic properties in the 19th century. The strength of a magnetic field always decreases with distance, though the required mathematical relationship between strength and distance varies.
Magnetic dipoles have been recognized, although some theories predict the existence of magnetic monopoles.
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Everyone Knows These Four Basic Facts About How Magnets Behave:
A magnet has two endpoints called poles, one is called a north pole or also called a north-seeking pole, and the other is called a south pole or also called a south-seeking pole.
The north pole of the first magnet attracts the south pole of a second magnet, while the north pole of the first magnet repels the second magnet's pole.
A magnet creates a magnetic field and is an intangible sphere of magnetism all over it.
The north pole of a magnet is roughly towards the Earth's north pole and vice-versa. That's because the Earth itself involves magnetic materials and behaves like a gigantic magnet.
Source of Magnetism
Magnetism is Derived from Two Sources:
Electric current.
Spin magnetic moments of elementary particles.
The magnetic properties of matter are mainly due to the magnetic moments of their atoms orbiting electrons. The magnetic moments of the nuclei of atoms are very small than the “electrons' magnetic” moments, so they are negligible in the condition of the magnetization of materials.
In addition, even when the electron configuration is such that there are unpaired electrons and also non-filled subshells, it occurs frequently. In that case, the various electrons in the solid state will give the magnetic moments of that point in different, random directions so that the material will not be magnetic. Hence, the magnetic behaviour of a material is based on its structure, particularly its electron configuration, and also on the temperature. Depending on whether there is an attraction or repulsion between the north pole and south pole of a magnet, the matter is classified as being either paramagnetic or diamagnetic, respectively.
Magnetic Properties of Matter
There are several magnetism properties of matters including Magnetization, Diamagnetism, Paramagnetism respectively.
Magnetization
In this section, we will learn about magnetization and the concept of magnetic intensity.
In electromagnetism, magnetization, also called magnetic polarization, is a vector field that contributes to the measure of the density of induced or permanent magnetic dipole moment in a given magnetic material. Magnetization is the magnetism of matter which was discovered by William Gilbert. The variation within this branch is described by direction and is either Axial or Diametric. As we know, magnetization results from magnetism, which results from the motion of electrons in the atoms or the spin of electrons in the atom or the nuclei.
The theory of magnetization helps us in classifying the materials based on their magnetic properties. Net magnetization is the result of the response material to an external magnetic field. The magnetization of a sample material M is called the net magnetic moment for that material per unit volume. The mathematical formula of magnetization field or M-field is,
M = \[\frac{m_{net}}{V}\]
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In a magnetic field, paramagnetic materials have a weak induced magnetism, which disappears when the magnetic field is eliminated and Ferromagnetic and ferrimagnetic materials have strong magnetization. That can be magnetised to retain its magnetism in the absence of an external field, resulting in the creation of a permanent magnet.
Diamagnetism
Michael Faraday discovered diamagnetism in September 1845. This is the weak form of magnetism that is arranged in the presence of an external magnetic field. This generates a magnetic moment that is very small and in a direction opposite to that of the applied field. Diamagnetic is a magnetism of matter in which materials are opposed by a magnetic field, an applied magnetic field creates an induced magnetic field in them that is usually in the opposite direction, causing a repulsive force. In addition, paramagnetic and ferromagnetic materials are attracted by a magnetic field.
When placed inside the strong diamagnetic and electromagnetic materials are attracted toward regions where the magnetic field is weak. In ferromagnetic and paramagnetic material, the weak diamagnetic force is controlled by the attractive force of magnetic dipoles in the material.
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Diamagnetism was first discovered by Michael Faraday in the year of 1845. In addition, when Anton Brugmans observed in 1778 that bismuth was opposed by magnetic fields. A simple rule of thumb is used in chemistry to determine whether a particle or atom or iron is paramagnetic or diamagnetic materials. In diamagnetic material, all electrons in the atom are paired, and the substance made from this atom. A paramagnetic material has an unpaired electron.
Paramagnetism
Paramagnetism has an unpaired electron in the material, so most atoms are incompletely filled with atomic orbitals. Hence this atom is called paramagnetism. Paramagnetism is a form of magnetism whereby several materials are weakly attracted by a strong magnetic field. In addition, paramagnetism creates a magnetic field in the direction of the applied magnetic field. Paramagnetism was discovered by the British scientist Michael Faraday in 1845. The materials that are arranged in paramagnetism are called paramagnetic. Therefore, true paramagnets are arranged in magnetic susceptibility conforming to the Curie-Weiss laws and exhibit paramagnetism over a wide temperature range.
This type of magnetization depends on Curie’s law. According to Curie’s law, paramagnetic materials, magnetic susceptibility χ are inversely proportional to their temperature. It is represented as;
M = χH = C/T x H
Where,
M = magnetization,
χ = magnetic susceptibility,
C = material-specific Curie constant,
T = absolute (Kelvin) temperature,
H = auxiliary magnetic field.
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Here are some examples of paramagnetic materials, aluminium, oxygen, titanium, and iron oxide (FeO). In addition, a simple rule of thumb is used in chemistry to determine whether a particle or atom or molecule is paramagnetic or diamagnetic. This rule depends on the paired or unpaired electron.
FAQs on Magnetic Properties of Matter
1. What are the key terms used to describe the magnetic properties of matter?
To understand how materials behave in a magnetic field, we use several key terms as per the CBSE Class 12 syllabus for the academic year 2025-26:
- Magnetic Intensity (H): The degree to which a magnetic field can magnetise a material.
- Magnetisation (M): The net magnetic dipole moment developed per unit volume of a material when placed in a magnetic field.
- Magnetic Susceptibility (χ): A dimensionless quantity that measures how easily a material can be magnetised. It is the ratio of Magnetisation (M) to Magnetic Intensity (H).
- Magnetic Permeability (μ): The measure of a material's ability to support the formation of a magnetic field within itself.
2. How are materials classified based on their magnetic properties?
Materials are primarily classified into three main categories based on their response to an external magnetic field:
- Diamagnetic Materials: These are weakly repelled by magnetic fields. They develop a feeble magnetisation in the direction opposite to the applied field.
- Paramagnetic Materials: These are weakly attracted by magnetic fields. They develop a feeble magnetisation in the same direction as the applied field.
- Ferromagnetic Materials: These are strongly attracted by magnetic fields and can be permanently magnetised. They show strong magnetisation in the same direction as the applied field.
3. What is the fundamental difference between diamagnetic, paramagnetic, and ferromagnetic materials?
The primary difference lies in their atomic structure and response to an external magnetic field:
- Diamagnetism arises from the orbital motion of electrons and occurs in all materials. In diamagnetic substances, atoms have no net magnetic moment, but an external field induces a weak opposing moment. Example: Bismuth, Copper.
- Paramagnetism is due to the presence of atoms with unpaired electrons, which have a permanent magnetic dipole moment. These dipoles align weakly with an external field. Example: Aluminium, Oxygen.
- Ferromagnetism occurs in materials where atomic moments align spontaneously in large regions called domains. An external field causes these domains to align, resulting in very strong magnetisation. Example: Iron, Cobalt, Nickel.
4. Why do some materials exhibit paramagnetism while others show diamagnetism?
The magnetic behaviour of a material is determined by its electron configuration. Diamagnetism is a property of all atoms, caused by the change in orbital motion of electrons when a magnetic field is applied. However, it is a very weak effect. In materials with atoms that have only paired electrons, the magnetic moments cancel out, and only the weak diamagnetic repulsion is observable. In contrast, paramagnetic materials have atoms with one or more unpaired electrons. Each unpaired electron acts like a tiny magnet, giving the atom a net magnetic moment. These moments align with an external field, causing attraction that overpowers the underlying diamagnetism.
5. What is Curie's Law in magnetism?
Curie's Law describes the behaviour of paramagnetic materials. It states that the magnetisation (M) or magnetic susceptibility (χ) of a paramagnetic material is inversely proportional to the absolute temperature (T). This means that as the temperature increases, the random thermal motion of atoms disrupts the alignment of magnetic dipoles with the external field, causing the material's magnetism to decrease. The law is mathematically expressed as χ = C/T, where C is the Curie constant.
6. What is a hysteresis loop, and what does it tell us about a ferromagnetic material?
A hysteresis loop is a graph that shows the relationship between the magnetic flux density (B) and the applied magnetic field strength (H) for a ferromagnetic material. It reveals crucial properties:
- Retentivity: The amount of magnetism remaining in the material after the external magnetising field is removed. A high retentivity is desired for permanent magnets.
- Coercivity: The amount of reverse magnetic field required to demagnetise the material completely. A high coercivity indicates a 'hard' magnetic material suitable for permanent magnets.
- Energy Loss: The area enclosed by the hysteresis loop represents the energy lost as heat per unit volume during one cycle of magnetisation and demagnetisation. Materials with a narrow loop (soft iron) are used in transformers to minimise energy loss.
7. How do the magnetic properties of a material influence its use in making permanent magnets versus electromagnets?
The choice of material depends entirely on its position on the hysteresis curve:
- Permanent Magnets: These require materials that can retain their magnetism strongly once magnetised. Therefore, we choose 'hard' ferromagnetic materials with high retentivity and high coercivity. A wide hysteresis loop is characteristic of these materials, like Alnico and steel.
- Electromagnets: These need to be magnetised and demagnetised easily and quickly. We choose 'soft' ferromagnetic materials with low retentivity, low coercivity, and high permeability. A narrow hysteresis loop is ideal to minimise energy loss, making soft iron the perfect core material.
8. How does temperature affect the magnetic properties of a ferromagnetic material?
Temperature has a profound effect on ferromagnetism. As the temperature of a ferromagnetic material increases, the thermal energy causes the highly ordered magnetic domains to become more agitated and disordered. At a specific critical temperature, known as the Curie temperature (or Curie point), the thermal agitation becomes strong enough to completely overcome the domain alignment. Above this temperature, the material loses its ferromagnetic properties and behaves like a paramagnetic material.
