Magnetic Properties of Materials

Basic concept of Magnetism

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on otherferromagnetic materials, such as iron, and attracts or repels other magnets.

Magnetic field:

A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any given point is specified by both a directionand a magnitude (or strength); as such it is a vector field. Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamentalquantum property, their spin.

Magnetic field intensity:-

The magnetic field intensity at a point defines as the force experienced by a unit North Pole at that point. The tangent, which is drawn on the line of forces, gives the direction of magnetic field intensity. It measures in Telsa(T) or Gauss.

 Magnetic pole strength:Magnetic pole strength (symbol: p) is a physical quantity used to measure the strength of the pole of a bar magnet (or a hypothetical magnetic monopole). If there is an infinitely long wire where the electric current is I, then the magnetic pole strength is defined as follows:

Magnetic moment:

The magnetic moment of a magnet is a quantity that determines the torque that experience in an external magnetic field. A loop of electric current, a bar magnet, an electron (revolving around, a molecule, all have magnetic moments.

The magnetic moment may be considered to be a vector having a magnitude and direction. The direction of the magnetic moment points from the south to North Pole of the magnet. The magnetic field produced by the magnet is proportional to its magnetic moment. More precisely,It normally refers to a system's magnetic dipole moment, which produces the first term in the multiple expansion of a general magnetic field. 

The elements of terrestrial magnetism:

The elements of terrestrial magnetism are

 Declination: The declination at palace is the angle between the magnetic meridian and the geographic meridian of the earth. This arises due to the earth magnetic axis not coinciding with its geographical axis.The magnetic meridian is a vertical plane at a place which passed through the axis of the freely suspended magnet .The geographic meridian is the vertical plane at a place that passes through the axis of rotation of the earth. The angle of declination varies from place to place in the earth and even at a place it shows the periodic variation also.

Dip or inclination: The angle between the direction of the total intensity of earth's magnetic field and a horizontal line in the magnetic meridian is called angle of dip at a place. The value of dip angle at the equator is zero and at the poles is 90°. Hence value of angle of dip increases from equator to poles.

 Horizontal components of earth magnetic field: The horizontal component of the earth magnetic field H is the component of the earth‘s magnetic field along the horizontal direction in the magnetic meridian at a place.

Let I bet the magnetic field intensity at a place, H and V be its horizontal and vertical components respectively. In the magnetic meridian, the horizontal component is

H = I cosδ

And the vertical component is V = Isinδ

In the right angled triangle

H2+ V2= I2cos2⁡δ + I2sin2⁡δ

H2+ V2= I2

Tanδ = V/H

Classification of magnetic material;

1. Diamagnetic,

2. Paramagnetic,

3. Ferromagnetic:

Diamagnetic	Paramagnetic	Ferromagnetic
The magnetic moment, intensity of magnetization and magnetic susceptibility are all negative while magnetic permeability has value less than1	The magnetic moment, intensity of magnetization and magnetic susceptibility are all positive while magnetic permeability has value slightly greater than1	The magnetic moment, intensity of magnetization and magnetic susceptibility are all positive and quite large and magnetic permeability is of the order of hundreds and thousands.
The magnetic susceptibility is independent of temperature	The magnetic susceptibility decrease with rise of temperature	The magnetic susceptibility decrease with rise of temperature
They are feeble repelled by the magnet and magnetic field	They are feeble attracted by the magnet and magnetic field	They are strongly attracted by the magnet and magnetic field
Eg Antimony Bismuth , copper	Egaluminum ,chromium magnesium	Eg .cobalt nickel  gadolinium
When the diamagnetic bar is suspended in a magnetic field it orient itself perpendicular to the applied field	When the paramagnetic bar is suspended in a magnetic field it orient itself in the direction to the applied field	When the ferromagnetic bar is suspended in a magnetic field it orient itself quickly direction to the applied field.

Magnetic domains:

A magnetic material consists of a very large number of magnetized regions called magnetic domains.

Declination

 The declination at palace is the angle between the magnetic meridian and the geographic meridian of the earth. This arises due to the earth magnetic axis not coinciding with its geographical axis .the magnetic meridian is a vertical plane at a place which passed through the axis of the freely suspended magnet .The geographic meridian is the vertical plane at a place that passes through the axis of rotation of the earth. The angle of declination varies from place to place in the earth and even at a place It shows the periodic variation also.

Horizontal component of the earth magnetic field

The horizontal component of the earth magnetic field is the component of the earth’s magnetic field along horizontal direction in the magnetic meridian at place 

Let us consider I be the earth’s magnetic field at a place, H and V be its horizontal and vertical components is

H = Icos δ

And the vertical components V = I cos δ

In the right angle triangle

H2+ V2= I2cos2⁡δ + I2sin2⁡δ

H2+ V2= I2

Tanδ = V/H