Physics
Study Material

# Magnetic Properties of Materials

Diamagnetic substances are those which have tendency to move from stronger to the weaker part of the external magnetic field. These materials are repelled by a magnetic field. Read about all the magnetic properties in detail below.

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Posted by Mahak Jain, 24/11/2021

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Magnetic properties of a substance refers to the response of substance to an applied magnetic field. Based on the behavior of materials in the magnetic field Magnetic materials are classified into three categories.

• Diamagnetic
• Paramagnetic
• Ferromagnetic

## Intensity of Magnetization

The intensity of magnetization is the per unit volume magnetic dipole moment, that develops when we place a magnetic material in the magnetizing field.

Intensity of magnetization (l) = magnetic dipole moment (M) / Volume (V)

Intensity of magnetization represents the extent to which a specimen is magnetized when placed in a magnetizing field.

As I = M / V

I = m × l / A× l     ( Here A is area )

I = m / A. So, it is the pole strength that developes per unit area of cross section.

It is a vector quantity whose direction is along the direction of magnetic field.

### Different formulas/relations between magnetic properties

• Volume intensity of magnetization

I = M / V

• Mass intensity of magnetization = Imass = 1/ρ (M/V)
• Molecular intensity of magnetization

• Molar intensity of magnetization = Imolar = W/ρ (M/V) = (W/ρ)I

Here W : atomic weight of substance

## Magnetic Field Intensity

Magnetic field intensity is measure of strength of magnetic field. It is the force that is experienced by the pole of magnet in magnetic field. The SI unit and dimension of magnetic field intensity is  Ampere/meter (A/m) and [ MT‾²A‾¹] respectively.

H = B/μ0 – M

B = µ0 (H + M)

Here H : Magnetic field intensity

B : magnetic field magnitude

µ0 : Permeability of free space

## Magnetic Susceptibility

The magnetic susceptibility is the ratio of

magnetization to magnetizing field intensity. It is a dimensionless quantity.

χ = M / H

Here χ: magnetic susceptibility (magnetic moment per unit volume)

M: magnetization

H: field intensity

Magnetic Susceptibility is the measures of how much a material will be magnetized in an applied magnetic field.

• If χ is negative a material is diamagnetic
• When χ is positive and small the material is Paramagnetic
• And, if χ is large and positive, then the material is Ferromagnetic

Thus, it is the degree to which an external magnetic field can magnetize a material.

### Relation between Magnetic Properties χ, I and H

Magnetic susceptibility (χ) = I / H

Here I : the intensity of magnetization

H : the intensity of the magnetizing field

## Hysteresis

Hysteresis is a loop representing the relationship between the magnetizing force (H) and the magnetic flux density (B) of a ferromagnetic material. It is a lag of magnetic flux density (B) behind the magnetic field strength (H).

We plot the hysteresis loop by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

The magnetic substance is magnetized first in one direction and then magnetized in opposite direction. This demagnetize previously magnetized substance. Thus, completing one cycle of magnetization. In this process the flux density B lags behind the applied magnetization force H.

The magnetic hysteresis loop,

In loop, point b is retentivity and c is coercivity of substance.

### Retentivity

Retentivity is the amount of magnetization retained when the external magnetizing field is removed after saturation is known as retentivity. It is the ability of substance to retain magnetization after removal of external magnetic field.

### Coercivity

Coercivity is the amount of reverse external magnetic field intensity which is required to completely demagnetize the substance to ground state.

## Diamagnetism

Diamagnetic substances are those which have tendency to move from stronger to the weaker part of the external magnetic field. These materials are repelled by a magnetic field.

The field lines in diamagnetic substance are repelled or expelled and the field inside the material is reduced.

Examples : Mercury, water, copper, bismuth, and gold etc.

## Paramagnetism

Paramagnetic substances are those which gets weakly magnetised when

placed in an external magnetic field. Paramagnetic substances have  tendency to move from a weak magnetic field region to a strong magnetic field region. Paramagnetic substances gets strongly attracted to a magnet. These consists permanent magnetic dipole of their own.

Field lines in paramagnetic substances,

Examples : Sodium, aluminum, calcium, oxygen (at STP) and copper chloride etc. the magnetization of a paramagnetic material is inversely proportional to the absolute temperature T,

M = C B0/T

χ = C μ0/T

Thus for a paramagnetic material both χ and µr depend on both the material and  on the sample temperature.

## Ferromagnetism

Ferromagnetic substances gets strongly magnetized when placed in an external magnetic field. They have strong tendency to move from a weak magnetic field region to strong magnetic field region. Simply ferromagnetic substances get strongly attracted to a magnet. The individual atoms in a ferromagnetic material having a dipole moment of their own.

The ferromagnetic property depends on temperature as,

χ = C/(T-Tc), [T>Tc]

Examples : Iron, nickel, cobalt,gadolinium etc.

Diamagnetic, Paramagnetic and ferromagnetic ;

Diamagnetism, para-magnetism and ferromagnetism are most important magnetic properties.