Magnetic Properties of Solids: Types of Magnets, Magnetic Field & Solved Examples

Magnetic properties or magnetism exist in every single object that surrounds us. Each material exhibits different properties in the presence of a magnetic field. The magnetic property originates from the magnetic dipole moment in magnetic materials. The magnetic dipole arises from the subatomic particle, in particular the electrons present in the atom or molecule. Thus, we can conclude that every single electron behaves like an individual magnet. Electrons are also referred to as small loops of current that retain their magnetic moment. Magnetic Properties of an object are observed due to the magnetic dipole and the electric currents.

Read Also: Physical Significance of Electric Field

Key terms: Magnetism, electrons, magnetic dipole, magnetic field, paramagnetic, diamagnetic, ferromagnetic, anti-ferromagnetic, ferrimagnetic

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Properties of Magnets

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Magnetic Properties of an object depends upon the two types of motion of the electron

• The orbital movement of an electron around the nucleus in an atom
• The electron spin on its own axis

Magnetic Properties also change with a change in the temperature for each type of substance.

Magnets exhibit distinctive properties. Some of them are as follows:

1. Attractive property- Magnets will always attract ferromagnetic substances. Like poles of the magnet attract each other.
2. Repulsive property- Unlike poles in a magnet are always repulsive towards each other.
3. Directive property- When a magnet is suspended it always comes to rest along the north-south direction.
4. Pair property- The poles of the magnet can never be isolated. It always comes in pairs.

The video below explains this:

Magnetic Properties of Substances value Detailed Video Explanation:

Check Also: Close packing in one, two and three dimensions

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Types of Magnets

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Magnets are of two types. They are:

1. Natural magnets that occur in nature and have inherent permanent magnetic fields. Example- lodestone.
2. Artificial magnets are magnets that are formed due to electromagnetism. They work based on the molecular theory which states that every molecule has a magnetic substance despite the fact of whether it is magnetized or not.

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Magnetic Field

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Magnetic field is defined as a vector field that determines the magnetic impact on electrical charges and currents and other magnetic materials. Since it is a vector field, it has direction and magnitude. The magnetic field is obtained by passing electric current and is directly proportional to the magnetic movement. Magnetic field is denoted by the letter ‘B’.

Magnetic Field

Intensity of Magnetic Field

The intensity of the magnetic field is an evaluation of how strong or weak the magnetic field of a solid is. It is denoted by ‘H’ and refers to the amount of force induced by the unit’s north pole at any given specific point in the magnetic field. The direction of the magnetic field is derived by drawing a tangent on the line of forces that are experienced at a given point.

Read More: Tetrahedral and Octahedral Voids

Due to our understanding of the concept of magnetic field other concepts such as Magnetic pole strength and Magnetic Movement were derived.

Intensity of Magnetic Field

Magnetic Dipole Moment

The magnetic moment is defined as the magnetic strength and orientation of a magnet or other object that produces a magnetic field

The magnetic dipole is given by the formula, 

τ = m × B

where,

τ is the torque acting on the dipole

m is the magnetic moment

B is the external magnetic field 

Bohr magneton (µB) is the smallest unit of the magnetic dipole moment of a solid. The value of Bohr magneton is equal to 9.27×10-27 Am2.

Check More: Electron hole and electron valency

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Classification of solids based on their magnetic property

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Solids of different types are classified into different groups based on their magnetic properties. They are

1. Diamagnetic
2. Paramagnetic
3. Ferromagnetic
4. Antiferromagnetic
5. Ferrimagnetic

Diamagnetic 

Solids that are weakly repelled by magnets are called diamagnetic substances. The solids which are diamagnetic possess paired electrons, hence the magnetic dipole is cancelled. These objects have a small magnetic dipole that is opposite to the magnetic field. These behave as an insulator and are used in electrical appliances.

Examples of diamagnetic substances include H2O, TiO2, NaCl, Benzene, and V2O5.

Paramagnetic

Solids that are weakly attracted by a magnetic field are called paramagnetic substances. These solids are magnetized in the same direction as the magnetic field but these are not permanent magnets. Paramagnetism is a result of one or more unpaired electrons being attracted to the magnetic field, hence they are temporary magnets. These are also used in electronic appliances. With the increase in temperature, the magnetization of the solid decreases. This is known as Curie’s law.

Examples of paramagnetic substances include O2, Cu2+, VO, VO2, CuO, and TiO.

Ferromagnetic

Solids that are strongly attracted by a magnetic field are known as ferromagnetic substances. In these solids, the ions group together in small regions called domains. These domains act as a miniature magnet. When these solids are subjected to a magnetic field, the domains get oriented in the same direction as the magnetic field. The domains, even after the removal of the magnetic field remain oriented in the same direction. Thus, they form permanent magnets. These are used to make cassette recorders.

Examples of ferromagnetic substances include Ferrous, Cobalt, and Nickle.

Antiferromagnetic 

These substances possess a net zero magnetic moment. Although they do possess domains just like ferromagnetic substances, these domains are oriented in the opposite direction which results in the cancellation of the magnetic moment. This results in zero magnetic moment.

Examples of antiferromagnetic substances include MnO and V2O.

Ferrimagnetic 

These substances possess little magnetic moment where all the magnetic moment domains of the substance are aligned in parallel and antiparallel directions in unequal numbers.

Examples include magnetite and Ferrites.

Electrical and magnetic properties of solids

Electrical and magnetic properties are two sides of the same phenomenon called electromagnetism. It is one among the four fundamental forces and exhibits electromagnetic fields such as magnetic fields, electric fields, and light. Solids possess different electrical conductivities, which is defined as the ability of a solid to conduct electricity. Alongside with conductivity, solids also possess other electrical properties that include resistivity, capacitance and impedance. 

The video below explains this:

Imperfections in Electrical and Magnetic properties of Solids Detailed Video Explanation:

Read Further: Notes on Electricity

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Things to remember

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• Every electron in an atom behaves like a small magnet.
• The magnetic moment produced is due to the angular momentum of the spinning motion of the electron.
• Magnetic movement depends upon the orbital movement and the electron spin.
• Magnetic properties also change with temperature.
• Diamagnetic, Paramagnetic, Ferromagnetic, Antiferromagnetic, and Ferrimagnetic are the classifications of the solids based on their magnetic properties.

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