Magnetism
A sample of copper is magnetically drawn to the low field area to the right in the drawing, regardless of the orientation of the magnetic field. Diamagnetism is the name given to this type of behaviour.
A piece of aluminium, on the other hand, is drawn to the high field area by a phenomenon known as paramagnetism. Due to magnetization effects in matter, a dipole moment is created when the matter is subjected to an external field. Hence the degree of induced magnetization effects in matter is given by the magnetic susceptibility of the material χm, which is commonly defined by the equation
M = XmH
The magnetic field H is called the magnetic intensity, like M, is measured in units of amperes per metre and Xm is denoted as the degree of induced magnetization.
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For copper, the created dipole is opposite to the direction of the external field. Magnetic permeability is often used for ferromagnetic materials such as iron that have the largest magnetic susceptibility dependent on the magnetic field and the previous magnetic state of the sample. The magnetic permeability is defined by the equation,
B = μH.
The terms which are based on magnetization effects in matter are discussed in detail below.
Magnetic Field
A magnetic field is a vector field in the part of a magnetic material, electric current, or changing electric field, in which magnetic force is observable. Moving electric charges and intrinsic magnetic moments of elementary particles linked with a fundamental quantum property known as the spin create a magnetic field. The magnetic fields and electric fields are directly connected and are elements of the electromagnetic force, one of nature has four fundamental forces. A moving charge in a magnetic field has experienced a force perpendicular to its velocity and the magnetic field. The magnetic field of a permanent magnet draws or repels other magnets, as well as ferromagnetic materials such as iron.
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A magnetic field surrounded by magnetized materials and is created by electric currents such as those used in electromagnetic fields, and by electric fields varying in time.
A sample of copper is magnetically drawn to the low field area to the right in the drawing, regardless of the direction of the magnetic field. Hence is termed diamagnetism. A sample of aluminium is attracted toward the high field region is called paramagnetism.
A magnetic dipole is created when the matter is subjected to an external field.
Magnetic Dipole
A dipole of an object generates a magnetic field in which the field is considered to emerge from two opposite poles, one is the north pole and the second is the south pole of a magnet, much as an electric field emerge from a positive charge and a negative charge in an electric dipole.
The energy of a magnetic dipole is called the magnetic dipole moment. The amplitude of a uniform magnetic field is equal to the maximum amount of torque on the magnetic dipole, which happens while the dipole is at right angles to the field.
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The magnetic dipole has a measurement of current times or energy divided by magnetic flux density. The magnetization M of a small volume of matter is the addition of the magnetic dipole in the small volume divided by that volume.
Magnetic Flux
In physics, specifically magnetism, the magnetic flux is defined as the number of magnetic field lines passing through a given surface and magnetic field B over that surface. Hence, the area under consideration of any size and any orientation concerns the direction of the magnetic field. Magnetic flux is usually denoted by Φ or ΦB. The magnetic flux symbol is Φ or ΦB.
Magnetic flux formula is given by:
ϕB = B.A = BAcosθ
Where,
ΦB is the magnetic flux.
B is the magnetic field
A is the area
θ is the angle at which field lines cross the surface area
Magnetic flux is generally calculators with a flux meter. The SI unit and CGS unit of magnetic flux is given below:
The SI unit is Weber (Wb).
The CGS unit is Maxwell.
Magnetic Intensity
The magnetic field to magnetization ratio of a material medium is called its magnetic intensity (H). Magnetic intensity of magnitude is calculated by the number of ampere-turns that flows around the unit length of a solenoid, required to produce that magnetic field.
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Therefore, the magnetic intensity, due to a solenoid of n turns per meter length be H = ni,
Where
i is the current
n = N/l, N is the total number of turns and l the size of the solenoid.
Hence, the magnetic intensity does not depend upon the nature of the medium.
The SI unit of magnetic intensity (H) is ampere-turns per meter (Am⁻¹).
Magnetic Permeability
Magnetic permeability is described as the property of the material to accept the magnetic line of force to pass through it. In other words, the magnetic material can support the occurrence of the magnetic field. In (H) magnetic permeability of the magnetic line of force is directly proportional to the conductivity of the material. Magnetic permeability is the proportion of a material to respond to how much electromagnetic flux it can support to pass through itself within an applied electromagnetic field. In addition, the magnetic permeability of a material is the degree of magnetization capability.
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Magnetic permeability is denoted by μ which is a Greek Letter. In 1885, Mathematician scientist Oliver Heaviside had termed magnetization effects as μ.
The SI unit is Henry per meter or newton per ampere-square.
FAQs on Magnetization Effects in Matter
1. What is meant by the magnetization of matter?
Magnetization of matter (symbolised as M) is a measure of the density of magnetic dipole moments induced in a material when it is placed in an external magnetic field. It is defined as the net magnetic dipole moment per unit volume. Magnetization explains how a material responds to and modifies a magnetic field. Its SI unit is amperes per metre (A/m).
2. What are the main types of magnetic materials based on their magnetization effects?
Based on their response to an external magnetic field, materials are broadly classified into three types:
- Diamagnetic Materials: These are weakly repelled by magnetic fields. They develop a weak magnetization in the direction opposite to the applied field. Examples include copper, gold, and water.
- Paramagnetic Materials: These are weakly attracted to magnetic fields. They develop a weak magnetization in the same direction as the applied field. Examples include aluminium, platinum, and oxygen.
- Ferromagnetic Materials: These are strongly attracted to magnetic fields and can be permanently magnetized. They develop a strong magnetization in the same direction as the applied field. Examples include iron, cobalt, and nickel.
3. What is the fundamental difference between Magnetic Field (B) and Magnetic Intensity (H)?
The key difference lies in what they represent. Magnetic Intensity (H) is the strength of the external magnetic field applied to a material, independent of the material's response. In contrast, the Magnetic Field (B), or magnetic induction, is the total magnetic field inside the material. It is the sum of the external field (H) and the field created by the material's own magnetization (M). The relationship is given by the formula B = μ₀(H + M), where μ₀ is the permeability of free space.
4. What is the physical significance of magnetic susceptibility and magnetic permeability?
Both terms describe a material's magnetic properties, but in different ways:
- Magnetic Susceptibility (χm): This dimensionless quantity indicates how easily a material can be magnetized. A negative value signifies diamagnetism, a small positive value signifies paramagnetism, and a large positive value signifies ferromagnetism. It connects magnetization to the applied field via the formula M = χmH.
- Magnetic Permeability (μ): This indicates a material's ability to support the formation of a magnetic field within itself. It is the ratio of the total magnetic field (B) to the magnetic intensity (H), i.e., μ = B/H. It shows the factor by which the magnetic field is increased or decreased inside the material.
5. What is the microscopic origin of magnetism in materials?
The magnetic properties of matter arise from the electrons within its atoms. There are two primary electronic origins:
- Electron's orbital motion: An electron revolving around the nucleus acts like a tiny current loop, which generates a magnetic dipole moment.
- Electron's spin: Electrons possess an intrinsic quantum mechanical property called spin, which gives them a spin magnetic dipole moment.
In most materials, these tiny magnetic moments are randomly oriented and cancel each other out. However, when an external magnetic field is applied, they tend to align, resulting in a net magnetization.
6. How does temperature affect the magnetic properties of different materials?
Temperature significantly influences a material's magnetic behaviour by affecting the thermal agitation of its atoms. For paramagnetic materials, increasing temperature makes it harder for atomic dipoles to align with an external field, thus decreasing their susceptibility. For ferromagnetic materials, there is a critical temperature known as the Curie temperature. Above this temperature, the thermal energy overcomes the forces holding the dipoles aligned, and the material loses its ferromagnetic properties, behaving like a paramagnetic material.
7. Why don't magnetic monopoles (isolated north or south poles) exist?
Magnetic monopoles do not exist because magnetic field lines always form closed loops. They always originate from a north pole and terminate on a south pole. If you cut a bar magnet in half, you do not get a separate north and south pole; you get two smaller magnets, each with its own north and south pole. This empirical fact is a fundamental principle of electromagnetism, mathematically expressed by Gauss's law for magnetism (∇⋅B = 0), which states that the net magnetic flux through any closed surface is always zero.
